CA2079910C - Ion processing: storage, cooling and spectrometry - Google Patents

Abstract

An ion processing unit (10), including a series of M perforated electrode sheets (12), driving electronics (14, 16) and a central processing unit (18), allows formation, shaping and translation of multiple effective potential wells (42). Ions, trapped within a given effective potential well (42), can be isolated, transferred. cooled or heated, separated, and combined. Measurement of induced image currents allows measurement and typing of ion species by their respective charge-to-mass ratios. The combination of many electrode sheets (12), each having N multiple perforations (22), creates a plurality of parallel ion processing channels (26).
The ion processing unit (10) provides an N by massively parallel ion processing system, furnishing means for processing large numbers of ions in parallel in the same manner, but with different ion processes deployed at different sections of each ion processing channel (26). In addition, the space-filling parallel structure of the present invention provides an efficient means for temporary storage of large numbers of ions, including charged antimatter.

Description

WO 92/14259 PCr/US92/01096 2~79910 ION PROCESSING: STORAGE. COOLING AND SPECTROMETRY
Field of the Invention The present invention relates to ion pr~cescing systems and, more particularly, to radio-frequency mass ~f~uL~ .. and ion storage ~.y~.lf l~.. A major objective of the 5 present invention is to provide flexible app~tus for the plùcessulg~ storage, and analysis of large numbers of ions in parallel.
Background of the Invention Mass ~ecL~Luf Lly, or more generally the techniques and a~ u~Lus for control andanalysis of charged particles or ions, has provided ihll~c,l L~lt tools for sçi~ ntifi~
1 0 exploration. Traditionally definf~, a mass ~.~ecL~u~ ,L~l is an in .LIulllell~ which produces ions from one or more subst~nces, sorts these ions into a ,.~e~Llulll according to their mass-to-charge ratios and records the relative abnn~n~e of each species of ion present.
From its beginnings in the early 1900's, mass spe~;L,ulll~,tly has becollle a necessary and integral com~ollf llt of n~ern science and co.. -~e. Many areas of current research 1 5 depend upon mass specl,~LueLlic techniquec to ~,lrulm crucial e~ ntc For example, mass ~e~;LIumf;Lly has found use in the analysis of upper atmospheric gases, detecting and studying ozone depletion p~ucesses. Medical l~Sf ~u~;h and practice routinely use mass analysis in~.LI.~ f ..t~tion for the ~let~ile~ analysis of protein structures and the genetic coding in DNA. These analytical ...~ Iho~l~ require the precise separation and identification 2 0 of the mass and 4uanLily of each ion extracted from an initial particle mixture. In many e~ f l,L~l regimes, new la'o~ c,ly ~ xesses rapidly create a large range of molecular species in great quantities, placing ever increasing flPm~n~1c on the rate and fidelity with which mass analysis must occur. Current mass spec~lu"l~t~ ~ technology faces difficult challenges in meeting these f;~ needs.
2 5 The domain of ion processillg encomp~cses more, however, than just theanalytical Luf asul~ lent of distributions of ion mass. Other technologies involve the preparative separation and storage of different ion species. One example would be the separation of isolûpes, which vary in atomic mass. The accurate isolation of radioactive isotopes finds use in medicine, nuclear energy and pure physics research. Another use for 3 0 ion processing techniques involves the separation, burr~ g and long-term storage of charged ~ Uillr.~ . Most large particle accell~lor facilities produce ~ r~ in the form of anti-protons (posillul~ l) and anti-electrons (positrons). Since the ~nnihil~tion of matter with ~ el results in the most efficient conversion of matter into energy,extensive efforts are being made, as discussed in report AF~PLTR-85-034, from the 3 5 University of Dayton Research Tn~titl]te, toward the trapping, storing and ~nnihil~ting of posil,uniulll. New generations of spacecraft capable of harnessing the energy released in controlled matter-~ntim~tter ~nnihi1~tion could achieve e~LIGIllely high velocities.
is highly reactive, however, and must be stored in perfect isolation until finaluse. The current inability to reliably and effectively cool and store significant quantities of WO 92/14259 PCr/US92/0109~

cLal~ed ~A~ lA~; . in po~table ~y~t~ s is a key factor p~ g practical use of 'All~ el propulsion. The storage moth~ used to Ill;~ in such S~ ;lnA~ ions compri~e another eY~mple of potential ion y~ccscil~g techniques.
The explosive growth of mass ~e~,~u~hic applications throughout science and 5 industry rests on the ability of eYt~n~Al and easily controlled ele~ slu~ic~ m~A~n~t~ aLic and electrodynamic fields to precisely and ~ tely ...~1.;l- .1~ ~ charged matter, abilities un.oq~lAlF~ by other neutral manipulation leclmi~luGs. However, all such charged-particle devices suffer from the effects of space charge, that is, mutual conlomhic repulsion remA-ins a r~.n~;..nF .,l~l physical limit. Yet today, i~ l . ;Al and s~;;enl;rc demAn-ls for 1 0 greater c..nol-..l~ of ;nr.~ AI;.~e and yl~alati~re outputs from smaller samples of matter, and in shoqter periods of time, have well e~cee~F~ the limits illlyosed by space charge on device throughput.
All mass ~yec~olllet~ operate as flow ~y~t~,llls. Ions, either caylul~d or created by joni7~tion~ are guided through or co~-r~led within a volume prior to and during their 1 5 detectiQn The mutual coulombic rep~ n of like charges, ~ , mAkes difficult the yludu~;Lion or capture of dense ion fluYes. The .. ~.x;.. output (either in analytical ll~ion or in yl~a~ali~/e ion rod~1ction) remains direcdy yroyullional to dhe average number of ions (the ion current) passing through the ...Ackinf per unit time. The coulombic repulsion from space charge limits this average flow per unit volume.
2 0 UltimAtely, dhe volume governable by precise ion control limits the throughput of a given device.
Various mass ~;lr~. . .et~, ~, or more generally, tools for the processing, control and analysis ~f ions, remain ~ nlly available. Each device cc,-nhines unique operation attributes together widh particular l;lll;li~l;ons~ suffering more or less from space charge 2 5 restrictions. Early mass ~y~l~t~ were what are now termed mi~gneti~ (or mi~gnetic and ele;llu~ic) sector illsllu~.ll~. These devices generally use static mAgnetic, or mQgnPtic and electri~ fields to carefully disperse focused beams of moving ch~edparticles. Depen-ling on dhe charge-to-mass ratio, the particles' paths bend in dirr~,l.,llt ~u~ . A mass spectrum for a particle group (dhat is, a m1merici~1 analysis of the mass 3 0 distribution) con~rrices lllea~ul~ taken of dhe numbers of particles at each focus point.
One form of sector syecllullle~ disperses the mass ~yecllulll onto a strip of photûgraphic film, forming a mass spectrograph. Photographic means can detect minute comyollellls of a subst~n~e being analyzed, thus roviding a means for ac~ le mass 3 5 de,te- ".;~ t;on Photographic techniques, however, are less well suited for relative mass Ab m-l~nce mea~ul., ll~,llt~. As an alternative m~thofl, then, sector illSII u~ llS scan their m~gn~tir and/or electric fields such that various masses scan across a narrow st~tion~
slit. Ions passing through this slit can then be d~te~te~ electronically. The ~imlllt~neous photographic approach yields the greatest device throughput; relative ablln-l~n~e wo 92/14259 PCr/US92/01096 "._ mea~,u~ lcnb through sector sc~nning are gained at the cost of inru~ ion through-put.
Time-averaging techniques can increase the amount of illr~ ,. collected, but only during relatively short periods due to inherent inctabiliti~,c in the magnetic and electric C~ lF~ fields.
While the sector-type mass s~ )lllc~r was one of the earliest instruments in widespread use, it has certain inherent pr~)bl_l~s. The magnsti~ fields used to focus the char~e~ particles in one direction tend to defocus ions in the ~l~n li~;ular direction, lc luuing fur~er focusing cl~ ..- 1-l~ The large magnetic fields required to focus ions often require bulky, heavy and yet precisely machined m~nstc As l~;se~-;h moves toward1 0 larger particle masses (as in b;oc~ l analysis of proteins), the mass ranges of sector ins~ en~ must be in~as~l. Yet it is difficult to ...~ ;.. a highly fo~;used beam over a very wide mass range, thus ~uiling greater çn~ . ;ng expenditures. A principal dl~back of convention~1 sector mass ,~eclr~mete.s is their e~n~e, in both engineering and fa~icati~n costs.
1 5 The changing dem~n~l~ of applied chemistry, physics and medicine have led to radical and innovative changes in all mass ~,~ec~l~ll~cLlic in~ ;on. The diversity of available co~ .;ial in~lu~l,L~, d~mon~trates that no single il~ ull~nl can meet the wide d~man-l~ of co.. ~- .. ;ial and sç~çntifi~ applic~*~n~ Sector i~ ull~n~s have in many in~tan~e~ been supplanted by Time-Of-Flight (TOF) mass spe~;l,.,~e~ , Fourier 2 0 Tl~sr~ Ion Cyclotron Resonat~ce (FT-ICR) devices, Quadrupole specllull~lel~7 triple Quadrupole (Quadrupole-Octupole-Quadrupole), and Ion Trap ins~ These classes of mass spec~loll~ , differ in thwr ap~acl, toward controlling and measuring ionsamples (i.e., they have different ion op*cs), and have particular advantages and disadvantages. The at~ibutes of dirrw~nt devices, including mass range, mass (or2 5 energy) resolution, flexibility to detect both positive and nega*ve ions, ion storage, throughput (in~ ing sc~nning rate), dynarnic range, ionization mf tho 1~, simplicity in opera*on and ~ 1f n~n~e, and cost, allow co.~.p, ;~Ol S to be made among them. When other characteris*cs such as the methods of signal detection, portability, and ease of co~-1-f~!;Qn with other e~ -f .t are also eY~mine~, no single current mass specllù,net~
3 0 device can be best used across a Majoflly of applications.
Time-of-flight (TOF) imsll u~llLS rely on the fact that ions with equal kinetic energies but with dirr~len~ masses travel with different velocities. Thus, a burst of similarly-el~ elic ions at one end of a time-of-flight device reach the other end separated in time in a mannerrelated to theirrespective masses. Time-of-flight mass specl,ullletel~
3 5 provide excellent resolutions of mass with a very high recording speed, allowing study of fast re~ction~ such as explosions. In addition, the insLIulll~.lt~lion is simple and does not n~cess~rily involve complicated magnetic focusing elements.

4 PCr/US92/0109f~
2 0 7 9 9 10 Problems exist with time-of-flight in~u~ n~ as well. The total l~ulllbc;l of ions per initial pulse must usually be limited to prevent a spread in energies by Coulomb repulsion, resulting in a loss of rnass resolution for the device. In addition, as with the sector devices, the time-of-flight mass Sp~;~ ,t~,l provides no means for storage or 5 ~urr~ g of ions.
One type of device that does provide for ion storage and analysis is an ion cyclotron resonance (ICR) ~ e.. This device (also known as a Fourier Transform ICR (FT-ICR)), uses the principle of a cyclotron. In a cyclotron, a particle can be excited by a high-frequency voltage to ~ve in a spiral, while held within a magnetic field. The 1 0 angular frequency of motion for the charged particle (the cyclotron frequency) depends upon the m~gneti~ field strength and the mass of the particle. A typical ICR instrument uses an RF voltage to excite ions trapped in a conductive box i.~ed in the field of a ~U~lcon~uc~ing m~n-ot ~jThe RF voltage is applied to opposing electrode walls of the box. The RF voltage translationally excites the charged particle which, constrained by the 1 5 magnetic field, moves in a spiral. The ions then orbit on the same radial path, but with dirr~ fi~u~l cies depçn(ling upon their mass. The cohcl~nt, orbiting ions induce an image current in another set of detector electrodes. The image current has an amplitude plupolLional to the nu~l~l of ions and a frequency ~Iv~lLional to mass, ~ ....;lling measurement of the relative ab.m~i~n~e of ions in a mixture.
2 0 Since an ICR device relies on the analogue technique of indll~ti~n of image Cu~ lt~ for mea~ul~ of mass, it lell~ains limited in dynamic range. Further, while the in~ ll~nt exhibits high mass resolution, long acquisition times (due to space charge limit~tion~) and limited inf~ ti~n through-put often precludes its use in detection of short-lived ion species, or for events exhibiting rapid real-time fll1ctn~tions. Hence, the 2 5 storage capabilities of the ICR are typically elcpendçd for analysis, not for the ion burr~fillg required for large, or high-speed, bursts of ions.
Perhaps the most widely used mass ~I~ec~ today rely upon radio-frequency quadrupole techniques. Quadrupole mass Sp~;llu~ i were first explored by Wolfgang Paul and others in the 1950's, and were the subject of a United States Patent No.
3 0 2,939,952. The patent presented two ~Jfil-Ci~ types of quadrupole devices. The first device, a quadrupole mass filter, generally comprises four electrode surfaces extending lon~inl-lin~lly in space. The longitu~1in~1 &~lion foqms the path for ion travel. The device can be seen in Figure 1 of the Paul patent. Ideally, these electrode surfaces cut hyperbolic arcs through a plane perpçn~1ic~ r to the ion motion and have equal and 3 5 opposite initial voltages applied to neighboring electrode pairs. Thus, the electrostatic potential around the central ion path is quadratic in form. By multiplying the applied electrode potentials with a periodic function of time, the electric fields at a given point can be made to periodically switch directions. The ch~a~;t~listic motions of ions traveling through the mass filter exist in one of two exclusive states. In the first, stable state, ions WO 92/142~9 PCI/US92/01096 ~,,_,..
pclr~lm osc ~ ti- n~ about the center of Syll~ ,t~y of fields with amplitudes that are smaller than some critical value. In the second, nn~t~h1e state, the amplitude of oscillation increases rapidly so that, within a short time, the ions imrin~ upon the field-generating electrodes and remove, or neutrali~, thlom~elves. Given an applied potential and a 5 particular periodic function, ions with certain ch,ll~-to-mass ratios travel along a stable path, while ions with other charge-to-mass ratios follow unstable trajectories and are lost.
Thus, by varying the amplitude, L~ue.~;y and DC offset of the voltages that dcte ~lh~e the periodic function, certain masses of ions are allowed to pass through the mass filter while others are neutrali~d.
1 0 The equations of motion for a quadrupole mass filter device in the x-y plane pGl~n~licular to the ion llaje~;lul~ path z are given by:
x + (q/mro2) ~ x = O, (1) y - (q/mro2) ~ y = 0, (2) where x and y l~ sel t the position of the particle in the plane, q is the charge of the 1 5 ion, m is the ion's mass, rO is the closest ~;tcl~nce ~t~. ~n the center of the device and a hyperbolic electrode and ~ is the applied potential function. On injecting ions into the mass filter with a certain velocity in the z &~;~ll, Equations (1) and (2) provide the ion motion in the xz and yz planes. If ~ were merely a constant, all ions would obey paths of simple h~ o,~i~ motion in the xz plane and ion L,ajec~ul;es would all be 2 0 "stable", i.e., remain fixed in amplitude. Yet, in the yz plane, the ions would diverge from the z axis (called defocu~ g) and eventually escape, crlli-ling with the filter electrodes. If, on the other hand, ~ were a periodic function in time, the trajectories in both planes are ~lt~ ]y deflected toward and away from the central zero point.
Stability exists in both planes if the peri~licity of the potential function ~ is short 2 5 enough and the ion is heavy enough that it cannot respond sl1ffi-iently during the defocussing portion of the cycle to escape the device.
In a further mo~lific~ion, if the ~lcn~al function ~ combines a direct (or constant) colll~nelll and a periodic ~ co,ll~nel-t, light ions are more affected by the ~lt~ ."AI;ng c~nenl. LTI the x direction, the light ions would tend to have 3 0 lm~t?~ble ~ s whenever the ~1t~ g co,ll~onent is larger than the directcomponent. Ions following nn~t~b1e l~ajecl~,ics would exhibit oscillations of ever-increasing ~mplitu~l.o The x dil~;~n would thc.~,f~ provide the equivalent of a high-pass mass filter. Only high masses would be 1l~l l~l l l;l l~ to the other end of the quadrupole without striking the x electrodes. Sim-llt~neously, in the y direction, heavy 3 5 ions are lln~t~ble because of the dero~ sing effect of the direct co,~ olle.ll, but some Iighter ions are st~nli7~?d by the ~ I;ng cc,llJ~onent if its m~gnit~1de and frequency coqrect the llajCClOI ~' when the ~mplit 1de tends to increase. The y direction is ~lel~Ço~
a low-pass mass filter. 'Ille two directions together provide a mass filter with a certain pass-band.

6 PCI/US92/0109~

2 0 7 9 9 1 ~ When using a mass filter, an ion sample is formed and introduced at one end of the device. Then, while carefully varying the filter's electrical pal~t~ , the quantity of ions ~ u g at the other end is measured. As t~ se~ when the function multiplying the applied voltages has both a fixed (time-invariant) co.,l~ne.l~ and a periodic c~ onenl, the device allows only ions within a certain mass range, or pass-band, to have stable paths and emerge for ",easu,~ at the output end. The RF
amplitude defines the mass stability range for a given DC offset, and ramping the RF
amplitude sweeps through a given mass stability range.
The ~ ;r~l L~ 1 of ion motion in a quadrupole device, as discussed 1 0 above, relates the in~ eous motion of an ion with the it.~ ,-eous elecLn~ Lic field.
Another more intuitive vi~n~li7~tion of stability in a quadrupole device analogizes a charged ion confined on an ia~ -t~4u~ potential surface to that of a ball rolling on a saddle. As the ball begin~to roll down the lower slopes of the saddle, the saddle's surface inverts: what~vas sloping downhill is now sloping uphill. If the frequency of the 1 5 inversion is well-chosén, the ball ,~,~ins trapped inflef1nitely in the saddle. If trapped in the x-y saddle, a particle traveling through a 4u~11u~ole mass filter along the z-axis remains confined within the electrodes and reaches the other end of the device.
Yet another useful con.~l;c n of quadrupole operation creates a time-average of the i~ eous l~ot~ ulr~ces experienc~ by a given ion to construct an effective 2 0 potential sn fare Because the ions moving through a quadrupole device move much slower than the quadrupole oseill~ting fields, the ions experience a time-averaged force that, depe~nrling on their cha~-to-mass ratios, either keeps them bound or gives them an unstable orbit. A time-averaged potential map for a paT ticle would then show a dep,~,ssion or effective potential well, whose height in energy may either keep a 2 5 particle bound or allow it an ~m~t~b1e Llaiec~()ly. The time-aver~aged effective potential (for a given oscillating field) seen by an ion varies with both its charge and its mass.
An ion trap is the second form of the quzd. upole mass ~ u~ L.,l . The ion trap follows the same general principles as the quadrupole mass filter, but instead of having ions ¢avel along an axis through the device, an ion trap .. ~ il-s ions at the 3 0 center of the device cavity. Accordingly, the ion trap takes the hy-perboloid form of the electrodes of the mass filter and revolves them about a Syllll~Lly axis, forminghyperboloid sulraces of revolution enclosing an inner volume (Figures 11 and 12 of the Paul et al patent). Dirr~.ellLial voltages applied to neighboring elecl,.)de surfaces create a thre,e~limPn~ion~l quadrupole field, ~yll~ hiC about the rotation axis. Again, 3 5 when a peri~i~ function mocl~ es the applied voltage, the electric fields at a given point within the volume perio~lic~lly ~wiLclles directions. Ions caught within the fields are attracted one direction and then the next. As with the mass filter, ~"~fiateselection of the applied m~nl~ting function ensures that a field with a pass-band of only a certain range of charge-to-mass ions forms stable oscillations within the ion ~vo 92/14259 Pcr/Us92/01096 _ 7 2079910 trap. All other co~ ;n-l;on~ follow ~ln~tAbl~ paths eventually colliding with the electrode cavity walls.
Both the 4ua~11ul)ole mass filter and ion trap have found eno~nous co~ ;ial uses in a variety of SC;f .-~;r;c and ind~ls~i~l fields. The devices co~ ine sensitivity 5 with adequate reso1nhon in a c~nlra~t simple and light-weight a~U~lus. F.~ 11yim~~ l.,fils are the l~laçe~cnt of ~;u,~ e and eA~nsi~re magnets with high-speed electronic sc.~nning and linear mass scaling. Still, quadrupole devices entail unique problems. To l~luduce quadratic fields within the active device volume, the electrodes must have precise h~lbolic sl.. r~es Yet it is eAIl~,ll,ely difficult to 1 0 macl~ille such surfaces. As a result, mass filter mATlufA(;~ often substitute easily r~tnred s~,helical snrfaces, which unfollullately inLIaduce errors into the fields and reduce device resolution and precision. In addition, fringing fields from imperfect devices introduce further ~ ;..h .~ errors into ion IYlCa:iUl~ i. RF devices arealso known to suffer mass di~c . ;...;.-~I;on, where the l,~ ll efficiency of 1 5 particles varies with mass.
As a partial answer to ~lifficlllt fabrication problems of quadrupole mass Spe~llull~el~ ltemS~tive llh .1~ for ~lllrli~ating the quadrupole fields have been developed. Arnold, in United States Patent No. 3,501,631, describes methods of replicating quadratic fields by sub~ ;ng a collection of electrodes held at precisely 2 0 varied potentials for the single hylJ~,lbolic electrodes of a st~ndard quadrupole device.
In effect, the second type of quadrupole device ;~..;l~les the first type. The second type applies potentials to a c~ tic n of electrodes in a manner cu~ ~nding to the potentials of a 4ua~1,upole field. Despite simpler fabrication of electrode snrf~ces, the long-term stability of the applied ~te~ lc (l~UUCd to ~l.,plir~le quadrupole action) 2 5 may offset any econolllic adv~nt~gec.
The quadrupole a~luaches, both the first standard type and the second em~ t~-A type, do not completely address the problem of ion separation and control.
In quadrupole devices, ions outside the pass-band, those not selecteA to pass through or stay collrlned, collide with the outer electrodes, el;lll;~lA~;~Ig them from further 3 0 analysis. In addition, l~;~a~d collicinn.c of de-sel~teA ions with the electrodes can create further problems when these adsorbed ions desorb under vacuum, Cull U~lillg later samples. While the ion trap allows for storage of ions, it is pulsed, must use a neutral buffer gas, and only a fraction of the stored ions are eventually analyzed, and collisions with buffer gases result in further ion excitation and fra~ lt~lion, often 3 5 changing the observed mass S~;I~U111 in unpredictable ways.
While each mass S~l1U11~el1;C approach provides its own ben~rl~ and involves its own difficl~lties, certain general problems persist for all cull~nlly-used mass-analytical techniques. The fields used for conru~ing and directing charged particles, wh~,tl~r magnetic as in sector-type and ICR devices, ele. LIu~tic as in TOF, WO 92/14259 PCI'/US92/0109 2 0 7 9 9 1 ~ or electrodynamic as in 4uadl u~ole in~Ll ulllenLs, all provide generally conservative field en~u~lllnf ~l~ for the manipulation and analysis of ions. Conservative fields usually are desired, since the total energy of the system, in-~ln-ling both the ions and the conr.~ g fields, remains consL~t during the analysis process. The energy co~ y provides a high degree of predictability in the ~A~l~nt~l process and its resulting spectra. But the con~L,~in~ that an ion's total energy, both kinetic and )otenLial, lell~linS C41l~ )OSf.,S consLl~lL ~ on the r,...~1~nh nl~l designs ofCOllL~ Oldl~ mass S~llvll~
Because their total energy must usually remain fixed at precise and reproducible1 0 levels, the total llum~l of ions that may be pnxessed concull~lltly is much smaller than the llulll~l available in any given sample. To InA;n~;.;n the precise energy levels, the ions must follow spatial paths of small toleran~e, in a limited volume. This has two adverse effects. First, the fields that hold ions to the exact paths must beextraol~inalily precise, i~uiling complex, highly-eng;nP~.~d and e~ si.le ion 1 5 optics. Second, and perhaps more fun(l~n~nt~l, space charge effects limit the ql~ntiti~os of ions that may be pl~cesseA at a given time.
The mutual repulsion of like charges limits the num~r of same-charge ions that can exist in a given volume of space. The co.-r.n.~ fields counter the space charge repulsion to some extent. But, at greater ion den~itiçs ion mutual repulsion o~ el.;~llles 2 0 the precise rOcusil g of the ion optics and degrades in~L, ulll~n~ resolution. To avoid degradation, the IIUm~ of ions introduced into an illsll Wll~ nt must remain below critical limits. But, reduçing total ion current reduces the illr~lllla~ion dlroughput of the device. For many routine applir~ti-:>n~, these limits are not signifi~nt Yet, in rnany other uses, the limitAtions becomc severe, especially when ~le ..p~ g Illca iul~m~,n~ of 2 5 very low ab~1n~Ance ions, and large a~ounts of the sample must be ~ccnml~lAted before gaining an adequate or m~o~nin~ful result.
In other Appli~l;olls, it is not the amount of sample available but the time window available for analysis that strains analytic methods. Real-time analysis of atmospheric cc.~ A~ may require very rapid mass spectra rea~lin~s. Mass 3 0 spe;~ m. t~lS ~tta~h~ to gas c}.lu lla~ugraphy a~pa~a~us must analyze ion species from sep~ua~ed peaks as they elute from the chr~llla~o~a~h co111mn When such peaks follow in rapid succession, analysis time for a given peak may be only a few seconds.
If space charge repulsion limits the total number of ions for sampling, reducingthrough-put and ~ leÇûle length~ning data sampling time, such high-speed uses may 3 5 be beyond current mass S~;llùn~elliC techn~1ogies.
An inability to cool ion particles ~ S~,ntS a further problem for current mass specllullle~cr devices. Most ~ ~tel devices depend upon an initial sample of ions introduced to the device at a sc,llle~l-at unirc~ level of energy. However,c,lc,ge~ic ion samples often arrive with vastly dirr~"~ent en~ ies. Most mass WO 92/14259 PCI'/US92/01096 s~e~lwl~,~ handle these particles by simply scl~n~lg out wrong-energy ions.
Odler uses for ion ~loce;,~ g a~ us, such as storing cha~ged ~ , depend upon some medhod for ~ ;"li~i"i"g the kinetic energy of particles widlin critical limits.
Methods of making urlirOllll a collection of ion energies are known as cooling 5 techniques. The conservative fields of current mass ~CI~ Ct~ usually cannot direcdy cool ions while ~n~;r~ ;n~ their uaje~ " since the ion's total energy ~mains precisely fixed or at worst increases. Thus, l~,se~cl.el~ deploy other techniques to sep~ately cool ions for ~ubse luent storage or analysis.
One cooling ~chnhlue i~ ,a luces a cool neutral gas into the path of the ions.
1 0 Collisions bel~n the gas and the ions absorbs and makes more ullirulm the energies of the ion sample. Another cooling technique relies on having each ion induce animage current in an outer c~n~ur,tive wall. The image current can transfer energy from the ion to an eYtP,rn~ nce and ~lissip~te it as heat. Application of carefully tuned laser ~rli~tion can cool ions, through Doppler-shifting and re-emission effects.1 5 However, dhe l~Uil~ high-power lasers are not yet practical for routine applications such as mass analysis. Another technique involves ~ bi~ti~, expansion by slowly d~l~iasing the ll~ping potential, and eA~ rling the trapping volume for the confined particles. The n~,tht d is equivalent to convention~1 adiabatic expansion of gases. Any attempt to restore dhe trapping ~,ot~nlial to dle original value reheats the confined ions to 2 0 at least their origini~1 energy, if not higher. Stochastic cooling is a variant of image cu-rrent te~hniques In ~xh~l;c cooling, ele~llonic feeAb~rk ~loni~l~ the time-coh~l~nt motion of ions in storage rings and Penning traps through image currentinrluce~ at a pick-up electrode. From knowledge of the ion motion, a transient potential applied to a kicker electrode can apply a retarding force for cooling of the 2 5 coh~ ,nt collection of ions. The latter method is only useful for cohel~nt groupings of ions, found only in highly spe~ r~ applir~tion~ None of these cooling techniquesallow direct use of the ion conr..~ fields to cool incoh~,nt groups of ions, while il~lA;nil~ their lla~
None of the l.w Iho~s ~iscus~e~ for mass ~ r or for ion storage and 3 0 manipulation provides a complete and flexible system for ion processing. What is needed is an improved m~thod and system for the ~r~ces~;,-g, control and analysis of ions. An improved ion pr~cessh-g system should routinely handle very large samples of ions that, due to space charge limitAtio~, are beyond the capacity of current ion optics. In addition, the method and system should be able to store It~ ly7 or buffer, high-volume bursts 3 5 of ions for later processing The method should provide for non-destructive spatial sep~,on of ion species to allow complete analysis of an ion sample, and ~im-lltAn~ously provide an em~ient tool for ion/isotope separation. Further, the method should provide cooling for stored ions without the use of neutral gases, laser radiation or any means other than the conl;nil-g fields themselves. Ideally, the method should allow insll.-.-.. .,1~1 2 0 7 9 9 10 access to trapped charged particles, providing fe~b~r~ to ~nitOl operational status in real time. The method should provide a simple and cost-effective technology for trAns1~ting, storing, cooling and analyzing ion particles.
Sullllll~y of the Invention In accol~ance with the present invention, an ion procçssing system co---h;l-es an electrode means for est~b1i~hing an electric po~,llial field in space, driver means for applying electric ~t~ ;Al~; to the electrode means, and a control means for changing the electric potential field. The varying electric potential field creates one or more wells of an effective potential. Each effective polclltial well can confine one or more charged par~cles 1 0 to specific regions in space. By gradually ~djllstin~ the el~ir~l potential field, the control means can change the position or center of each effective ~ten~ial well. By allowing elaborate control over the local shape of the effective potential field, charged particles may be tr~n~l~teA,;cooled, stored, ~o~ u~d, and se~led in large qu~ntities in an e~ ely flexible manner.
1 5 The effective potential wells of the present invention can follow each other successively along a lon itu~lin~1 path. Thereby, each effective potential well can provide either transverse confinement of a charged particle (generally pe~ rul~r to the path), or lon~ (linAl cor.rii-f ~~ -1 of a charged particle (c~.ril-f -.h nl from well-to-well along the path), or both. Thus, when the control means gradually adjusts the electric potential field 2 0 and the positions of each effective potential well, the position of a charged particle trapped -in a well can be changed either transverse to the dil~iUII of the lon~it l~lin~l path, or longihl-lin~lly along the path, or in some combined direction. As an alternativearr~ngr~ mrnt, the effective potential wells can provide isût upic col.ri-~ t of a charged particle and can be arranged indepen-l~ntly at various points in space. Even so, the control 2 5 means can adjust the position in space of these effective potential wells and the positions of the trapped particles. The invention provides both storage, or trapping, of charged particles and spatial translation.
In one embodiment of the present invention, the electrode means corn~i~es a series of M ~,rulaled e1f~ctrir~lly c~ ndllctive sheets, spaced and e~Yten~ling along a 3 0 longihl~lin~l path. The ~ÇolaLions can be hf Y~n~l for effi~ent packing and aligned to provide a plurality of N ~ Cf s~ g ch~nnrlc for ion travel and COI-l;~ nl A driver means applies a series of oscillating clf~ 1 potentials to each of these electrode sheets, creating osrill~ting electric fields within each pluces~;ng channel. The time-averaged potential of the electnc fields, as disc~lc~A, creates an effective potential field. By 3 5 employing co..-~ t~ ~ control over the applied pot~nt~ , a variety of effective po~ellLial maps can be deployed to trap charged particles within effective potential wells within the ch~nnel~. Varying the applied potentials ch~nges a given potential map and allows the ion processor to translate either transversely or longinldin~lly the position of trapped charged 11 2~79910 particles. In addition, a single ~tential well may be smoothly broken into two or more s~ale wells, allowing for separation of an ion sample into smaller groups.
To handle the rapidly oscil1sting ~ll~ials applied to each grid, voltage ~mplifi~rs are ~ h~ to the electrode sheets. The radio rl~ue,ncies of the applied potentials are typically ~t~ ,en 0.5 and 5 MHz, and the applied voltages typically range ~lwet;n +500 volts. A central com~Jul~l controls the waveform output of each amplifier, changing its ! potential amplitude and Ll~uency at proper times to change the effective potential map.
The grids are thin, with little volume taken by the ele.,LIode wires, leaving mostly free space broken into a plurality of parallel ~ ces~ g ch~nn~l~. Each pn)ces~il g channel, as 1 0 described, forms a virtual cavity for applying a variety of potential maps for controlling and prc!ces~ing ch~,ed particles. The availability of high-speed COml)U~ i and high-voltage amplifiers enables the present invention to execute the rapid and precise changes in potential required during O~la~ll.
The parallel deployment of many l~luces~ ch~nl~els within the electrode sheet 1 5 structure r.. ;~h~s the means for pl~ces~;.. g large numbers of ions in parallel in the same ma~ er. While the l~ ulL path th~ough each ~locessing çh~nnel is subject to space charge limit~tiQnc, the device comr~es many such ch~nn~l~ shiel~ling each group of ions from the mutual charge effects of ~dj~ent groups of ions. Pa~llel pr~ces~ing of ions o el-;o,lles previous space charge diffi~lllti~s~ allowing rapid analysis of sizable null,bel~, 2 0 of charged particles cimlll~ ,usly. In addition, the parallel structure of the present invention provides an efflfient means for the storage of large nul~ of ions. Thepresent invention prwides an ideal system for long-term co..lA;-....f --~t of charged particles.
In ~flflition~ the present invention furnishes a~alus and methods for cooling 2 5 charged particles confined within an effective potential well. Previous mass ~;llullleters for the most part provide cons~ re fields for the control and separation of charged particles. Ions int~r~fcting with such fields undergo elastic collisions in which the total energy and .~ .- of the system (both the ions and the field) is conserved.
Conservative fields do not couple the t~n.cl~tional energy of the cont~ine~ charged 3 0 particles to the exterior en~/u~.",..- -,l, since kinetic energy merely converts into potential energy and vice versa Net cooling l~Uil-_S a controllably non-conservative field, one that provides an extra degree of freedom by which ion energy can be coupled to and fli ccipated in the ~u~ uuding en~/i,unment. The present invention, by filrniching means for rapidly and accurately changing the local charartç~ictics of the effective potential field, provides a 3 5 controllably non-conservative field that allows controlled dire~tif~n~l transfer of energy from or to a trapped charged particle, without signifif~nt1y changing the volume of the trapping well. A particle-field system will be said to be "non-conservative" herein if the total system energy is less than or greater than the initial total system energy of particle and 9 ~ ~
~~ 12 70622-50 field. The invention can simultaneously confine a particle and lower or raise translational energy by a cooling or heating process, using only the confinement fields themselves.
- The present invention supplies means for mass separation as well. The virtual cavities of each processing channel can emulate an ion trap at an arbitrary position along their length.
The same mathematical treatment presented above for ion containment and separation in conventional ion traps applies to charged particles trapped in virtual ion traps. A representative ion processing routine could include the following steps:
introduction of an ion sample into each virtual cavity processing channel, possibly from a high-volume ion production source, buffering and cooling each sample somewhere along the processing channel for later analysis, separating and translating a portion of the sample to another section of the processing channel for monitoring the ions, further translation of the ion sample to a virtual ion trap for extraction and measurement of relative amounts of each mass present, and then acceleration and ejection of the ion samples from the apparatus, either for disposal or for ; 20 further processing.
The present invention provides apparatus and techniques for handling orders-of-magnitude more charged particles, and for higher through-put in experimental measurements, than are available from conventional ion processing technologies. Also, the increased ion volume and through-put do not require highly engineered and bulky ion optics. The present invention allows buffering of high volume bursts of incoming ions (that is, for temporarily storing streams of charged particles for subsequent Q 7 ~Q ~ a .
12a 70622-50 processing) without risking interactions between the charged particles and large containment surface areas or requiring expensive, complex ion optics. In addition, the invention provides for the storage and cooling of highly energetic ion particles without using outside agents such as neutral gases or laser radiation. The present invention furnishes apparatus and techniques for the spatial separation and translation of charged particles in a controlled, non-destructive manner, by charge-to-mass ratio. Additionally, ~he present invention provides apparatus for executing all of the above-described features in a compact, readily manufactured and flexible system.
In accordance with the present invention, there is provided charged particle processor apparatus for manipulating charged particles that have an energy and a mass, the apparatus comprising: an electrode array, said electrode array including a plurality of transversely extending, substantially planar electrode sheets, each of said electrode sheets having at least one perforation therein; a plurality of spacer means, each of said electrode sheets being separated from adjacent electrode sheets by said spacer means, said electrode sheets being aligned relative to one another such that respective perforations of each of said electrode sheets align to form at least one charged particle channel; a vacuum enclosure enclosing said plurality of electrode sheets; a plurality of electric potential drivers, each of said drivers being coupled to a respective electrode sheet; digital-to-analog converter means coupled to said plurality of drivers; a data bus, said data bus being coupled to said digital-to-analog converter means; and a computer coupled to said digital-to-analog ~'a7~g ~0 '- 12b 70622-50 converter means through said data bus, whereby data from said computer is converted by said digital-to-analog converter means to analog data and causes at least one of said drivers to apply an electric potential to at least one of said electrode sheets.
In accordance with another aspect of the invention, there is provided a method for processing charged particles having particle energy ancl particle mass, the method comprising the steps of:
(a) applying electric potentials to an electrode array to create an electric potential field (600A) within a selected volume of space through which said charged particles can propagate;
(b) introducing said charged particles into said selected volume of space;
(c) controlling said applied electric potentials to establish an effective potential field (400A) within said selected volume of space for said charged particles, said effective potential field including a plurality of first effective potential wells, each well being capable of confining said charged particles within a portion of said selected volume; and (d) varying said applied electric potentials to combine at least two of said first effective potential wells into a single new effective potential well that allows a transfer of charged particles confined to said combined first effective potential wells to said new effective potential well.
In accordance with another aspect of the invention, there is provided charged particle processor apparatus for controlling the motion of charged particles having particle energy and particle mass, the apparatus comprising: a plurality of J

~7~9 ~C

'~ 12c 70622-50 electrodes with J >3, numbered consecutively j=1,2,...,J and spaced apart from each other by electrically insulating means in a selected longitudinal direction, for creating substantially ~ independent electrical potentials (600A) in the volume between and defined by any two consecutive electrodes, each electrode having a plurality of perforations therein that are arranged so that a sequence comprising one such perforation from each electrode forms a channel through which the charged particles can propagate; a vacuum enclosure enclosing the plurality of electrodes; a plurality of electrical potential drivers, one such driver being electrically connected to each electrode, to apply an independent electrical potential to each electrode; and computer control means for controlling and varying with time the electrical potential applied by each driver to the corresponding electrode to establish an effective potential, including a potential well with a well center, in the volume between any two consecutive electrodes, where a potential well is capable of confining a charged particle within the well, the computer control means varying the electrical potentials applied to the electrodes with time so that the potential well center is translated with time from the volume between electrodes number m and m+l to the volume between electrodes m+l and m+2(1< m <J-2) so that a charged particle confined in this potential well is also translated in the selected longitudinal direction with time.
In accordance with another aspect of the invention, there is provided a method for processing a stream of charged particles that have particle energy and particle mass, the method comprising the steps of: providing a plurality of J electrodes ,~
,.

~ 12d 70622-50 with J >3, numbered consecut.ively j=1,2,...,J and spaced apart from each other by electrically insulating means in a selected longitudinal direction~ for creating substantially independent electrical potentials (600A~ in the volume between and defined by any two consecutive electrodes; providing each electrode with a plurality of perforations therein that are arranged so that a sequence comprising one such perforation from each electrode forms a channel through which the charged particles can propagate;
providing a plurality of electrical potential drivers, one such driver being electrically connected to each electrode, to apply an independent electrical potential to each electrode; and controlling and varying with time the electrical potential applied by each driver to the corresponding electrode to establish an effective potential, including a potential well with a well center, in the volume between any two consecutive electrodes, where a potential well is capable of confining a charged particle within the well, the applied electrical potentials being varied with time so that the potential well center is translated with time from the volume between electrodes number m and m+1 to the volume between electrodes m+1 and m+2(1< m <J-2) so that a charged particle confined in this potential well is also translated in the selected longitudinal direction with time.
These and other features and advantages of the present invention are apparent from the description below with reference to the following drawings.
Brief Description of the Drawings Figure 1 shows an exploded view of an Ion Processing Unit in accordance with the present invention.

12e 70622-50 Figure 2 shows an assembled view of an Ion Processing Unit corlfigured as a high-volume mass spectrometer in accordance with the present invention including ion generation and detection.
Figure 3 illustrates a wire-frame model of a portion of an ion processing c.hannel comprising a series of hexagonal electrode elements.

,~
..

WOg2/14259 13 P~'~7Y~
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Figure 4 shows a series of effective ~tel-lial wells formed within a field inside an ion ~lvce-si~;ng ch~nn~l Figure S shows a two--lin Pn~i~ nql topographical plot of the electric field inside an ion processing ~h~nn~.l Figure 6 shows a three~lin~n~ic)n~l plot of the ir~ nrous electric potential formed inside an ion plucess;llg channel at one point of the RF cycle.
Figure 7 shows a three~ n~:on~l plot of the inc~ f~us electric potential formed inside an ion pl~ce-s~ g ch~nn~l at the oppo~ilc period of the RF cycle as that in Figure 6.
1 0 Figure 8 shows a three~l;llh n~: .. 1~1 plot of the in~ ~us electric potential formed inside an ion ~luce~.~;ng ch~nnçl with a particular configuration of electrode ~et~,ls, dirr~ t from those in Figures. 6 and 7.
Figure 9 shows a three-rlimen~il n~l plot of the err~ve potential formed inside an ion proces~ing channel with the particular c~nfigllration of ele~llode ~ -t~. ~ used in Figure 8.
Figure 10 shows a three--lim~ncional plot of the in~ nti~n~us electric potentialformed inside an ion ~luc~-s~;ng ch~nnçl with a particular configuration of electrode p~all~ls, ~ nt from those in Figures 6, 7 and 8.
Figure 11 shows a three~imencional plot of the effective potential formed inside2 0 an ion prûces~ing ch~nn~l with the particular confignr~ion of electrode p~u~ull~,t~ used in Figure 10.
Figures 12A through 12J show three-~1;l l ~~ n ~;onal plots of a contiguous series of potential wells undergoing ~ucct~sive translations inside an ion processing ~.h~nnçl Figure 13A illustrates a two~lim~n~ion~l mapping of slices through the series of2 5 potential wells shown in Figures 12A through 12J, and the pa~ el~ characteri7ing each slice.
Figures 13B and 13C show two-~im~n~ional timing diagrams for t~n~l~ting and stationary potential wells inside an ion ploceS~; ~-g ch~nnçl .
Figure 14A shows a time-lapsed trajectory of a cl~ed particle trapped within a 3 0 tr~n~l~ting effective potential well, colllpli~illg injection and capture, translation, storage, tr~n~l~tion and ejection.
Figure 14B shows a portion of the trajectory shown in Figure 14A when the trapping effective potential remains stationary, during the storage phase.
Figures lSA through 15E illustrate the creation of in~ ce~ electrostatic and 3 5 electrodyna_ic cuul~ S in cle~,l.udes by the motion of ions in the present invention and by which ion cooling is controllably achieved.
Figures 16A through 160 illustrate sçh ~ ;c diagrams of the inl~lacLion of a moving ion and an effective potential barrier, showing the difr~ ;nce between pointwise cons~lt vs. poirllwise lirr~ Lial barrier motion.

WO 92/14259 14 PCI'/US92/01096 2 0 7 9 910 Figures 17A through 17D show three--limon~irn~l plots of an ion ~ r~-n;~,ll employing a moving ~t~--lial well bc~ n st~tion~ry trapping ch~lbe inside an ion l. ucess;l~g channel, ill~ g the operations of merging, splitting,direction~l ion llallsr~. and mass-selective, direction~l ion transfer.
Figures 18A through 18I shows a series of topographical mappings, illustrating acomplete ~ausr~,~ cycle, as excerpted in Figures 17A through 17D.
Figures 19 shows a two-~imPnsinn~l marpin~ of slices through the series of potential wells shown in Figures 17A through 17D, and the l~a~t~ col~ onding to each slice.
1 0 Figure 20 illus~at~,s an ele~;~ical circuit that may be used for driving an electrode and for 111~ ;,.g inrl~lcer~;ull~nls in the electrode, in accc,~ce with the invention.
Figure 21 illu~llatés a block diagram of the present invention as an N x M
massively parallel ion ~ cessol.
Description of the E~ef~ l Elllbo~
1 5 In acco~ ce with the present invention, FIG.1 shows a~alatus for the pl.~cessillg, control and analysis of ions. Thr~ughout the present description, "ion"
and "charged parlicle" are used in~lcl-~l-g~bly to refer any form of electrir~lly charged matter. A series of M planar electrodes 12a, 12b, 12c, etc. are arranged longiblrlin~lly along the x-axis, s~a~ed by spacers 24. Each electrode sheet 12 conne~ls to a high 2 0 voltage ~mrlifier 14a, 14b, etc., which form an array 14 of in~epen-1~ntly operable amplifiers. A pl~l~ll.l..~hl~ digital-to-analog converter (orDAC) array 16 governs the operation of the ~mrlifiers 14 and receives program signals from a central proces~ing unit 18 along a data bus 20. The central ~loces~ g unit 18 thereby has cc.ll~lete cont~ol over the applied ~l~"llials at each electrode plane, çnqhling rapid and accurate 2 5 changes in the effective potential fields expçriçnreA by charged particles travelling through the invention.
Each electrode can be f~q-~riratçd by pholoch. .~;rqlly mq~l~ing and etching an electrirqlly con-luçtive sheet, preferably from a high-tensile strength con~ ctive metal.
In the ~nerell~d e llh~l;llh~n~, each electrode cc.lll~.. ;~s a mesh of thin metal, arranged 3 0 in an array of N h-oYqgon~lly shaped holes 22. ~rYq~n~ are self-paç~ing polygons having the greatest area-t~ ;~h t~,~ ratio; the hexagonally shaped holes allow the greatestchqnn~ol areatocle~;l,.de~- ;11~ t~ ratio. Inthe~ ,f~ dembo~limrnt,each hexagonal hole 22 in the electrode sheet 12 measures a~l(,~ lat~ly 2 ce.~ e~
across, the system corlPin~ M z 100 ~lrolaled electrode sheets and N ~ 400 3 5 hexagonal holes. Each ~lÇ~la~,d electrode sheet 12 essentiq-lly comprises a series of N hexagonal electr~de rings co~ d elect~ically and moçhqnirqlly together. Those skilled in the art will l~o~ e that Lrr~ nt ~1;",. ..~;ons and llulll~l~ of electrodes can be chosen to implement the present invention.

Wo 92/14259 PCr/US92/01096 The thin ele~llude sheet 12 can be fixed taut in a ~u~ g frame 23, while each electrode sheet can be stacked on the next sheet, se~alaled by small ceramic spacers 24. The electrodes are stacked such that ~ucces~ e holes in each sheet align with each other to form hexagonal IJloces~ g channels 26 in the x direction through 5 the device. One such ch~nnçl 26 is shown by the hiphli~hte~ l~cLi.~e hexagonalholes 26a, etc. In normal operation a vacuum enrlos-lre surrounds and protects the entire array of ele~ udes. Each ele~,~ude aTray cle n~l co..ne~ to an edge comleclol, that in turn con n ecls in vacuo to an amplifier array 14, that in the ~ f~ ,d embc~ nt, applies rapid and relatively high voltage changes to each electrode 23.
1 0 The base of the vacuum housing 17 (shown in FIG.21) serves as a heat sink for the array, while ~mplifier power and control signals enter the vacuum area via standard high-vacuum fee~ lc ugh devices. As ~lçs~ibe~d, the control signals for the amplifiers 14a, 14b, etc. travel through a shielde~ bus 28 dnven by the DAC alray 16, which in turn is driven from signals carried by de.l;~~tl~ bus 20 and ge. ~ ed by the central 1 5 processing unit 18.
FIG.2 illustrates a typical application of an N by M ion ~ ~xes~ g unit (N x M
IPU) 10 for high-volume mass analysis. Ions formed in a sepal~e, difrt;le.l~ially pumped ion cl-z. . .ly . 30 are gendy accelel~t~d into an injection vestibule 32surrounded by one or more ion plocess;..g units 10. Only ions of a certain energy 2 0 range and direction are ~uccçs~rully C~lul~d by dhe effective potential supp~lled by a given cl-~nn~l 26 in an ion ploces~ unit 10; ions outside dlis direction and energy window (such as ion 33) deflect back into the injection vestibule 32 to be swept out by diffusion pump 34. In a ~ref~l~,d embodilllcnl, ions pass dlrough distinct processing regions of the IPU 10: first, an injection region 36a, then a bulk cooling and 2 5 t~,lll~l~ y storage region 36b; second, a mass selection region 36c, an acceleration region 36d and finally a collision of the ion species onto a large-area photocc.u~led ion detector sheet 38. All collisions can then be recorded by a CCD alray 40, or a phû~ll~ultiplier tube, a reticon array, or a similar device for tabulation. In the ~lcÇcll~d embodiment, CPU 18 (FIG. 1) controls and l~lon;~ the ion processes in the ion 3 0 a~ay 10, and stores final analysis results from CCD array 40.
FIG.3 illustrates a wire-frame model of a single ~ cec~;ng channel 26 colllposed of an array of hexagonally-shaped electrode rings 22, labeled 1, 2, 3, etc.
Charged paTticles travel through the center of l,~vces~,ing channel 26, which has a characteristic radius Ro. As mentioned, the pierell~ embo~ nt uses hexagonally-3 5 shaped areas for tne electrodes, a~ f ly 2 cm in ~ tions madefor the preferred embo~liment assume an electrode-to-electrode sp~cing of Ro/13 (i.e., a~ u,llately 13 electrodes per cm). As the spacing b~ ,w~ electrodes decreases, each electrode requires less applied power to reproduce the same field, and this allows use of more finely constructed field shapes. The fields ~up~lled by the present WO 92/14259 PCr/US92/0109f~

7 9 9 10 invention can be created and ,~ ru~ ed without using elaborately constructed, fixed 2 0 electrode shapes, as in the prior art. The following analysis and examples show how the present invention can control barrier hPightc, translate charged particles, and achieve ejection, cooling and heating of ion groups. The metho~1c refer to a multi-variable e luaLiOIl of co~ letely general form to desr~fibe these ~)lVCeSSeS. Various pl~cesses can be colllbined to create multiple concull~nl effects. For example, the tr~nC1~tion of trapping wells along the longinl-lin~l path of a ~l~ces~ g ch~nnpl can be combined with the selective cooling of a particular packet of ions within one potential well. Any nu,~ of field configurations can be s.,i~ ;...l.osed.
1 0 As intlic~te~l, the present invention co.~ s both tr~ncl~tion control and energy control over ions and groups of ions. Translational control and energy control need not be linked together, for simrli~ity~ the two topics are fli~cncsed sepalaL~ly.
However, the present invention allows the two processes to co~bine to provide pv~.rul and cffiri~Pnt tccl-l-h~J~es for controlling, analyzing and mass-selectively 1 5 sep~aLillg ions. ~;
Net translation of trapped ions in the present invention adds energy to these ions. If the cooling (or energy-altering) aspects of the present invention are not employed, either in the~retical ~ lcc-ion or in actual practice, some other method should be used to d~ this added energy. As in some prior art ion trap 2 0 appli~ationc, a neutral collision gas (such as helium, He) can be introduced in the invention; ion collisions with this bacl,~,ul d gas can unifc~ ly remove energy from groups of trapped ions. Th~refol~;, when the tr~ncl~tion~l aspects of the invention are first discussed, it may be ~csnmPA that a snffisie.nt pn,s~ , of He buffer gas is present in the IPU region 10 of the invention to provide collicion~l damping. The buffer gas 2 5 can later be replaced by the active cooling fim~tionc that the fields of the present invention provide, as ~liccussed below.
Several widely used and understood t~P~hniq~le,c can establish the o~l~Lillg char~ctP-fictics of radio-frequency devices, and the behavior of charged particles in these devices. The most co-....-ol-ly used de~- ;p!;on refers to the exact solutions of the 3 0 class of Mathieu difr~,ential equations. Solutionc to these equations describe ion stability and instability in quadrupole devices, ion traps and other similar in~LIul~ L~.
Early descriptions of the theory and operation of traditional quadrupole devices, in~l~le~d by Mathieu eq~l~tinns~ were given by Paul et al in U.S. Patent No.
2,939,952 and have been repe~t-P~ with variations by others (such as U.S. Patents 3 5 Nos. 3,501,631, 4,755,670), see Ouadrupole Mass SpecLI~ and Its Applications. ed. P.H. Dawson, Elsevier, Alll~t~,l.lam, 1976, Ouadrupole StorageMass Specl ~lllell~ R.E. March and R.J. Hughes, eds., John Wiley, New York, 1989, and the references therein. These sources may be consulted for analytical methods and results.

Wo 92/14259 pcr/us92/o1o96 17 2079~10 Another, ~l,p~ e technique, con~l,u.;ls a time-averaged effective (or pseudo-) potential. Ions which would have stable Ll~jeel~!~ ;es ~l~iclcd by exact sol~1ti- n~ to Mathieu equ~tion~, would be conrl,led within ~ulr~ces defined by the effective ~lclllial. Dehmelt and others cited in Advances in Atomic and Molecular Physics. Ac~ mic, New York (1967) Vol. 3, p. 53, and discussions in Mechanics~
3rd Ed., L.D. T ~n~ and E.M. I ifshit~, Oxford, New York, 1976, have used an analytical a~ ;u~h~ n of the effective ~te.llial for systems of quadratic ~ymlllelly.
For a hy~ olic multipole, one can write:
Ueff(r) = (n2q2V2t 4m~2ro2) (r / r0)2n-2 + U
1 0 where n is the l'IUI11~1 of sets of poles (which in quadrupole devices is two), rO is the closest d;~ e ~l~,.~n the center of the effective potential and the electrode surface, r is the ion ~ e from potential center, q is the ion charge, m is the ion mass, V is the ul-- applied voltage to the elecll3des, cl) the frequency of the applied field and Us is the DC offset. The equation is valid for ~o >> l/~, where ~ is the transit time across 1 5 the d;~ -ee sp~nn~ by an effective potential well for an ion species of a given kinetic energy in the nhsen~e of the RF field. nec~llse this analytical equation applies only to devices of quadratic ~y~h,l~y, it is too restrictive for use in the present invention.
However, it provides an illl~l~t intuitive picture of the behavior of charged particles in radio-frequency fields which can be applied to the present invention. Namely, the 2 0 shape of the time-averaged fields which confine, trap or guide ions in radio-frequency fields is ~ ional to the ~mp1ihl~1ç of the oscil1~tin~ voltage at that point divided by the frequency of osr~ tion, squared. The ion mass scales the effective ~ol~.l~ial, dct,~....;.~;l-~ the intensity, but not the shape, of the effective potential. Hence, various values of L~uellcy and voltage can generate a similar trapping effective potential for a 2 5 given charge-to-mass ratio.
The operation of the present invention can be explained by reference to a broader, more general des~ lion of the effective ~t~nlial. Rather than being colls~ d to the quadratic rullclions l~uh~,d by conve-ntion~1 RF mass ~ t~"~, the local electric potential for the present invention arises from the 3 0 interaction of the potentials applied to a large lwlll~l of parallel electrodes. The elllials applied to each electrode can be changed dlbill~uily and in~epen-l~ntly in time and amplitude. Thus, to adequately encompass the variability of the fields gellcl~t~d by the present invention, the local electric ~t~nlial can e~l~,ssed as a n~1m~rit~1, three-dim~n~ion~1 electrostatic array ~(x(i),y(i),z(i) ) coml)osed of n points. The effective 3 5 potential arises from a set of potentials P(j,t) applied to the M electrodes in the electrode array 12. Using nllm~ri~l Lechl~iques to c~ tç and express local fieldquantities has two adv~nt~ges. First, as ~esçribe~l, the present invention is capable of creating an infinite variety of effective ~ot~,llLial maps, through the s~u~nlial application of distinct sets of potentials to the electrode array 12. The fields created 2 0 7 9 910 would defy closed-form analytical solution~ but are c~ hl~. to any speçifi~1 degree of precision by digital nllm~ri~ ~l meth~l~ Second, a high-speed colllpulel 18 applies c~l~-l~t~ pot~nti~l~ to the electrode array 12 in rapid succ~ss;- n, and a nnm~ic ~l~co.~posiLi~n of the potentials ideally suits a digital control means.
Techni4ues for nnm~rir~l analysis of RF fields and charged particle behavior is broadandwell-understood. Themlm~ Y~lion~ andc~ ,yul~l~imlll~tion lechni~lues used by the ylGr~l~;d e .~ to d~ t~ ;"r. the local electric potential from the potentials applied to the elA;Llus~tic array are found in the Simion PC/PS2 User's Manual, Version 4, by D.A. Dahl and J.E. Delmore, Idaho National Engineering 1 0 Labol~loly, Idaho Falls, ID, 1988. See also Oua~u~le Storage Mass Spe ;Ll~ e~
R.E. March and R.J. Hughes, John Wiley, New York (1989), generally and at pages 67-69, and G. Leclerc and L. Sanche, C~l~utel~ in Physics. Vol. 4, p. 617, (1990). The SIMION PC/PS2 V. 4 ele iLl~sl~tic field methofls and l)lOg~a.l1S, as one approach among many, model a set of electrodes and the resl.lt~nt RF field as a two~ u~ n~l numerical 1 5 array. A subset of array points are de~igrl~d as d~~ 1cs while the lG.II~ g points sent the electric field points. A three~;~ n~l electrode array and fields can beindirectly modeled using ~y lle~, by rotating the two~lim~nsional alray about a collllllon axis.
Col,l~ul4~ sim~lAtio~ Pl~~sl~s such as SIMION PC/PS2 V. 4 can provide several 2 0 illl~l ~t calegulies of infc . ~ ;Qn, to preA~ ed levels of precision. First, they can predict the static electric field arising from a s~e~-; r.~A el~llude ~ll U~;lUlG. Second, ~im~llAtions can predict the spatial and l~ je~;lu. ;es of p~,clPs of given mass and charge injected into the predicted static field. Thus, the focusing, or ion-optic, ~lu~ ies of the electrode ~lluclule can be des~iheA Third, ~u~.~o~ilions of the c~lcnlAte~l fields 2 5 can be made, yielding complex and sophi~tir~at~d el~1ludyllamic fields which can change through time. In other words, ~,~ter maps can be col.;.llu~txl SIIIIIIIIA~ ;7ing field shapes and e1P~ . ;~,?1 ch-. ~.,. t~ s And fourth, the complex ll~jec~. ;es of ions injected into these complex, time-d.,~endenl fields can also be evaluated. Thus, for a given ion, the p~l~t~,l maps of Step Three can be evaluated for regions of mass stability and mass 3 0 inctAbility These c~ tions provide a method of the present invention for evaluating ion-specific l~ç~c. lies of a particular electrode confi~ .. lion, of sto~ing sets of evaluation results as p&ld~t~_~ maps, and of real-time control of the inventive 2~p2ll~luS by both real-time calculation and look-up tables.
The el~;LIu~Lic field in the present invention is . . .~eled as a l~und~u ~-value 3 5 solution to T ~rl~e s equation. In general, to c~lc.l~At~ the potential at a given point (x,y,z), one forms a weighted sum of the potçntiAls applied to the electrode sllrf~es, where the weights are c~ llr~l by ~1AYAt;~-n m~th~ (see the Leclerc et al. article cited above). In a three-llim~o-nsional space colll~osed of cubic cells ûf l~ f l~C '~n ~3 (where is a small interval), T ~rlA~e's e4uaLion can take the foqm WO 92/1425919 PCr/US92/01096 ,.,~
~(i,j,k) = [f(i+l,j,k) + f(i-1,j,k) + f(i,j+l,k) + f(i,j-l,k) + f(i,j,k+1) +
f(i,j,k-1)] / 6, (4) where (ij,k) = (xn/~, Yn/~ Zn/~) is the cocldi,lale, in ~ units, of the grid point ch 3r~rt~n~ng cell n.
The co.. ~ 3~;0nal process occurs in two steps. First, the field contributions of each el~l-ude in a panicular aTTay of el~l.des 12 are c~l~ul~t~l~ A lef~ voltage is applied to those array points c(,ll~,;,~nling to the ith electrode 12i lit~"àlul~ relaxation of array points around ele~ odc 12i, accc,l.ling to Equation (4) (or some similar manner), provides an ap~ solution to Laplace's equation. The greater the llUIll~l of1 0 iterations, the closer the solntion app~,~;n-~t~ s the actual result. The process continues until the dirr~ el ce ~e" calcnl~ticnc at each array point (i,j,k) is less than some threshold value. More sophicti~tçd iterative methods can be applied in practice to achieve the identir 31 result but in a shorter amount of time. For in~l~nce the SIMION PC/PS2 V.
4 system describes and imrl~ .lc a dyn 3mic~11y self-adjusting over-r~l~Y 3ti~n method 1 5 thatcansavecol~ uli-:;Qn~l time. Theresultoftheco---~ l;onisamapofweights.
These weights Pnc 3r.~ te the contrihution a po~ ial on electrode 12i makes to each auy array point, scaled to the initial reference voltage.
For each clecllude, there is a similarly c~31~ t~ weighting map, scaled in the ~l~r~ d embodimcnt to the same reference voltage. Solutions to Laplace's equation are 2 0 additive; to c~ t~ the voltage at an ~I~ ~y point, the w~ighting maps for each electrode, mllltirlied by the applied potential at that cle~ l ~de, can simply be added at the aubill~uy point. If ~j(x(i),y(i),z(i)) l~yleserl~ the weighting map for adding a time-variant pvt~ n lial P(j,t) from the jth electrode surface to an ~bi~aly ith point in space (x(i),y(i),z(i)), then the time-depen-lrnt n11mçric~1 potential at an ~L~ill~y point (from an 2 5 array of M electrodes) can be writte~as ~(x(i),y(i),z(i))= ~ (x(i),y(i),z(i) )P(j,t), (5) Thus, the time-variant field created by the array of ele~ odes 12 can be modeled to any degree of precision using r~1~Y~tion n~thlxls and Equation (5).
The analytical solution of the effective pol.,nlial for the prior art quadrupole and ion 3 0 trap devices ~ui-~s that the fields in the devices obey an ideal quadratic equation such as ~ (x,y,z) = f(t) (aX2 + ~y2 _~yz2)~ (6) shown as Equation l in the Paul et al Patent, where a + ~ = ~. The present invention uses a more general and flexible eA~ ssion for the fields it may gell~.ale (Equation (5) ).
The force exerted on a test charge q ins~L~d in such a n11m~ir~11y calculated field can be 3 5 t;Apl~ssed as:
F(x,y,z,t) = qEn(x,y,z,t), (7) where the electric field En is found by ~ g a nllm~rir~lly-evaluated gradient of the pot~lllial field En(x,y,z,t) = VnUm ~(x,y,z,t). (8) WO 92/14259 20 PCr/US92/01096 2 0 7 9 910 It has been shown that the effective potential e~ sed in terms of the position-pçndent force can then be written as Ueff(x,y,z) = I FmaX(x,y,z) 12/ 4m~2 + Us ~ (9 or more generally as Ueff(x.y.z) ~ IFmax(x~y~z)l2~ (10) where all variables except the n~ .. force at a given point are co~ See the Landau and ~.if~hit7 l~f~nce, the Dehmelt reference, both cited above.
Equations (7) through (9) provide a method for nnm~nc~11y c~ *ng an effective potential map for a given set of applied time-depçndent ~t~ll~ials P(j,t) applied to each 1 0 electrode. The pl~e~ nl of a test charge at various 1~ti~n~ in space allows one to map the shape of the effective pot.onti~1 These maps illustrate fo. . n~l ;. n of effective potential trapping wells when the conditi-)n~ of osei11~til)n fi~u~ cy, voltage amplitude and ion energy c~ ,spond to a stable, confined ~je~tory. In other words, the maps provide the shape of the trapping effective potential well when the ion is bound. The maps described 1 5 and shown in the present invention we're calculated using this method.
To find the stability and trajectory of a given ion of particular mass and initial kinetic energy, a further n.. ~ . ;c~1 ~iml11~til~n of its motion through the calculated time-dependent fields can be made, through convention~l l.ajeclOI.y calcn1~til-ns Operation of the present invention can be thought of as r~,sn1ting from the action of the time-averaged 2 0 effective polell~ al on a given ion at a given point. Thus, for a given frequency and voltage ~qmr1itude the relative shape of the effective pol~ntial is c~1c'u1?teA with respect to a given charge. The abso1ute depth of that effective potential is de~e.mil~ed by the mass of the ion, ill~,;,~i~e of the stable ion's energy. The ion's energy can either be sufficiently low to trap the ion, or s11ffirient1y high to allow the ion to escape over a particular effective 2 5 potential barrier.
The mass-dependent stability of an ion trapped in a particular effective potential well is governed by the local DC offset, L~qu.,rlcy and voltage ~mrlitllde If an ion is unstable in a well (as o~osed to a stable ion being sl1fficient1y en~ ,~ic to o~l.;ome a local effective potential baTrier), then the ion il~ el~ibly gains energy from the trapping 3 0 field until it either: a) pen~t~a~s a COI~Iillg effective ~s~ nti~1 barrier and strLkes an electrode, or b) escapes over a local barrier into a new region where it is stable (i.e., does not irreversibly gain energy from the field).
The c-.nr~ t of a charged particle can be with respect to one or more ~1imrn.cions. The position of confin~on~nt refers to the total volume of conrn~---f .lt, 3 5 including both its shape and location. For convenience in ~liccucsing tr~n~l~tionC of wells, the midpoint of similarly shaped wells can be used as the trapping center position. Thus, tr~nCl~tion (as used th~oughout this ~liscllccion) includes both the enl~E,~ ,nt and shrink~ge of a trapping well (while keeping the trapping center stationaIy), as well as the movement of a well's trapping center in space.

~lVO 92~14259 21 ~ O ~ gS9 1 0 To ~..... ~. ;7.~ thus far, the present invention co,llbines a series of electrodes 12 wit'n a central ~lUC~s~;..g unit 18, ~L.,l~,by potential amplitudes are applied to each electrode. As with the prior art, each applied potential can be mod~ tecl in time by an amplitude function V(t). In ~1flitinn, CPU 18 can rapidly change each applied potential, 5 altering the shape of the effective potential in space, and allowing for a much greater variety of trapping potentials than available in the prior art. These changes in shape of the effective pOtelllial barrier allow co~ ...f .~l, translation and energy removal from charged particles moving within the present invention. These changes can also be used to locally govern a given ion's mass~epen~lent stability or in~tability.
1 0 Nl................. ~ . ;ç~ for ç~ tinE the fields of the elec~ode array in accordance with the present invention do not involve any analytic field formlllatisns, as do the Mathieu equations o r effective potelllial e lualiOllS of the prior ar~ Ion motion through the çalclllat~A field maps can be mlm~ric~lly evaluated from initial co~ ns (ion position, velocity, initial potentials on the elecll~des) and the subsequent timing seqllf nce of 1 5 potentials applied to each el~ll~,de.
Each sequence of applied ~t~ ials can create different effects for the same ions, and the same se lu~,nce can cause dirr~ l~n~ results for different ions. To effectively use the infinite llulll~l of possible sequ~nces, one can exploit the ability to rapidly colll~ule nnm~ri~l maps of p&~ e~ space, i.e., pd~ el~l~ describing the timing of potentials in 2 0 the electrode array can be pl~l~,sji~rely changed and the results can be S~ ;7Yl, as is shown below. F~ g these maps pinpoinls regions in palal,lelcl space to pelro~
desired proces~ing ~peradons. The accumulAtisn of these palaQletl,l maps ~ .,senls an ~ achicv_~l.,nl of the present invention, allowing the con~illual discovery, storage and reuse of useful p~alll~,t~,l sequences.
2 5 Instead of an analytic c~ ssion for the electric field, the present invention SUb~l;lulrS a general c~ esjion conlA;,~ g relatively few variables. The gene~l c~ ssion can be slowly altercd to ~ n~lalc a timing diagram that describes the sequence of applied pot~ .~I;A1C~ The desc ;ln;ol~ of those po~ions of p~a~l~l space conlainillg useful o~lalions can then be ~u~ ;iLed in terms of these variables. In addition, the 3 0 algc,~ lls or program codes that control the a~llalalus of the present invention can also be ~""""~, ;7PA by the general eA~ ,ssion.
FIG.4 shows a COLUYUt ,1 simlll~tion of simple effective potential wells folmed along a path within a processing cll~nn~l 26 of the present invention FIG.4 provides two mappings. The upper mapping 400A, as in~ te~l reveals the height D in effective 3 5 potential units, of the effective potential barrier in the x-z plane. Since the procçs~ing channel 26 is rot~tion~lly syrnm~tric~ the same plot would apply in the y-z plane. As a particle moves from the center C of the c-h~nnel Oulwalds along a radius Ro, the effective potential batrier grows larger, trapping the particle within a given well, such as well 42.

WO 92/14259 PCI'/US92/0109 2 0 7 9 9 1 ~ The lower mapping 400B, provides a topographical lC- .-lf .; ng of the same effective potential barrier surface.
In the c~ulcr cimlll~ion creating these wells, the potentials applied to the array of electrodes 12 as shown in FIG.3 are given by the general ex~,ssion P(i,t) = p(j,t) V(t) = Sign[A(j,t)] IA(j,t)lS(i,t) V(t) (11) where A(j,t) = cos[f(j,t) 2~w(j,t) - k(j,t)] (12) and where s(i,t), f(j,t), w(j,t) and k(j,t) are electrode-specific, time-dependent potentials, V(t) = ~o sin(c~) is an ove~all applied m~ ting function as in the prior art, and the 1 0 Sign[A] function merely provides the sign of its a~ nl E(lua~iOl~S (1 1) and (12) lc~l~,~lll one of a nulll~ of possible lc~se~ ons for conveniently mapping the relative pot~ ials of succeccive electrodes. The particular functions used in Equations (11) and (12) are ~l~ / and place no limit~tion on the generality of the appliedpo~ellLialS and anay concf~L~ of the present invention.
1 5 A cosine function is used to straigLLrol~valdly map a cim~coid~lly-varying potential to electrodes along the x-axis, creating the series of wells 42 as shown in FIG.4. The cx~nell~ s(j,t) rh~n~es the slope of the cosine function, in~;lcasing the barrier slope from well-to-well. The electrode ~ nm~nt function f(j,t) also rh~n~es the slope of the cosine function and l~ lt~ the time~epen-lent application of the cosine function to each 2 0 surces~ive jth electrode. In the first ~imnl~tion shown in FIG.4, f(j,t) is given by f(j,t) = [e(j,t) - 1]/ 29, (13) where e(j,t)= 1,2,3,4,5,.. ,28,29,1,2,3,................ (14) for j = 1, 2, 3, 4, 5, ..., 28, 29, 30, 31, ...
2 5 w(j,t) is a pole multiplicity function which can stretch or COIlLla~;L the wavelength of the cosine fim~ion as applied to a ~ries of electrodes. The eY~mple in FIG.4 has w(j,t) as a con~t equal to 1, and an f(j,t) given by Equations (13) and (14) such that electrode 1 and electrode 30 both have an electrode ~signmPnt f(j,t)=(1-1)/29=0. Given that the shift-control ru..c!;oll k(j,t)=0 in the current example, and the barrier slope s(j,t)=1.5, the 3 0 pole,l~ial applied to these two electrodes is the same and equals Icos(0)11 5=1. The polen~ial applied to electrode j=15 (or 45, etc.) l~,l.,se~ the opposhe node of the cosine wave and therefore equals Sign[cos(7~)] x Icos(~)11 5 = -1. Given the notation of Equation (11), and the selected pal~llelel~ the applied potentials repeat (i.e., pass through a 360~ cycle) every 30 consecutive electrodes. With an overall barrier slope of 3 5 1.5, this ~.rO. .. lAlion can be s~ ~ as "360/30/1.5". The resulting in~l~nlAneous potential surface is shown in FIG.6 and a topo~;l~hic~ map of the potential is shown below the potential surface in FIG.6 and more explicitly in FIG.5. As ~ii~~lsse~l above, d~e electrodes are spaced Ro/13apart WO 92/14259 23 PCr/US92/01096 ~079910 The ...~ ... applied potential ~0 is 500 Volts and the charged particles are ~s--m~l to be singly charged so that q~0 = 500 eV for the ~im~ tion~. The applied ~inn~oi~l~l function sin(~t) uses an angular frequency ~27~ (~sec~l), where t ist;,.~r~ssed in micl~scco.~ Sin(~t) is a ~~ ;-------- when t=0.25, 1.25, etc., a Ill;
when t=0.75, 1.75, etc., and is zero when t=0.0, 0.5, 1.0, etc.
FIG.5 reveals the electric ~cst~ ~ial lines 500A within the ~,luces~ g çh~nnel 26 at a llJa~illlUlll point in the applied A-~pl;1.~de mt~ tion r~ ;nl~ V(t), while FIG.6 shows three-ll;.-- .~;ol-~lmap600Aofthe;~ lt;~ u~,electric~tc.,lial. R~l~,se,~ e electrodes 1, 15, 30, etc. are shown along the x-axis of the maps. The in~ e~,us1 0 electric ~t~"lial lines give rise to the i~ electric potential map. A charged particle could be l~ sellt~;l by a marble on the saddle 44 of the electric potential map 600A of FIG.6. As the marble rolled down the hill and into one of the low points 46a, the entire m~ap would switch dil~Lions. what was low at 46a would becollle a hill at 46b, what was a hill at 48a would beco,l,~ low at 48b. The resl~lting invened potential map 1 5 700A is shown in FIG.7, for t = 0.75. Thus, if timed coll~lly, a marble (i.e. the charged particle) could be trapped at the saddle point 44 of the in~O~ f~us potential. That trapping effect is ~ lt~d by each SUCC~S~ , well 42 in the time-averaged effective ~t~,n~ial map 400A shown in FIG.4. The time-averaged cycle of potential snrfaces 600A
and 700A as shown in FIGS.6 and 7 give rise to the effective potential barrier 400A
2 0 shown in FIG.4.
The effect of ch~nging several of the ~ . .. t~ . ~ of Equation can be seen in FIGS.8 through l l. FIGS.8 and 9 illustrate the effects of ch~nging the ba~ier slope function s(j,t). While s(j,t) = l.5 for the first examples shown in FIGS.4 through 7, the example in FIG.8 changes only pa.a,llete, s(j,t) to 0.25 (i.e., taking the fourth root of the 2 5 cosine function). FIG.8 ~~ ;sents the in~ ~us field voltage, and FIG.9 shows the time-averaged effective potential. While the overall depth D of the wells 42 l~,l,ains the same in FIG.9 as in FIG.4, the longit~lin~1 barriers 50a, 50b, 50c have risen to better sel~a,ut~ the individual ll~pping wells 42.
The height of 1~ l barriers 50 can also be ch~nged by altenng the relative 3 0 node spacing dete . . .i l-ed by w(j,t). The example shown in FIGS. lO and l l was created by ch~n ing only w(j,t), from 0.5 to 2.5. Again, FIG.lO ~ r~F,ellb the inct~nt~neous field voltage, while FIG. l l shows the time-averaged effective potential. There is now very little dirr~ ce in effective pole ,L,al ~l..~n the wells 42 and the longit~1in~1 barriers 50. The transverse barrier 51, cc.~.li.-;ng charged particles in a direction 3 5 p~l~ endicular to the axis of the ion ~ ces~;ng ch~nn~1, however, has become rather high.
Having illustrated how the present invention can be used to trap a particle in an effective potential well, the higher-order ru"c~l s of the invention can also be illustrated.
That is, both linear Ill~llh ~11lllll operations (in~h1tling both the ullpal~g of ...u.... ~-h---- and the ~nc1~tion of a trapping potential well) can be shown, and, also, functions capable of -~ 0 7 9 9 1 o cooling (or heating) e~ ~ic charged particles can be illustrated as well, in a ~liccllc~ n of cooling below.
A com~ut~ ~imlll~te l t;~le of the point-wise tr~n~l~ti~n of a series of potential wells 42 can be seen in FIGS.12A through 12J. The effective ~t~n~ial surfaces 1200A
5 (and two-~lim. n~ic n~l topographical mappings 1200B) were created using the same p~u~ctel~ for Equation as in the first çy~mple of FIG.4. However, for each successive FIG. 12A through 12J, the shift-control function k(j,t) i,~cleases by 15~ (or in certain steps by 30~) so that k(j,t) = 180~ for FIG. 12J. The result is a shifting of the center of each potential well 42 along the x-axis as one passes from one figure to the next 1 0 co,~ efigureinthe s~ n~e Figure 12A- 12J. Co.. Ipn~;ng insequenceeach effective ~:~nti~l surface 1200A, FIG.12A shows an effective ~otenlial well 42a st~rang near electrode r ulll~l 1. Electrode 1 is the closest el~l.vde to the eYt~rn~l en~Lu"~ ,n~, particularly the injection vestibùle 32 C~ult~ g a prel;-"in~ sample of ions. Effective potential well 42a SGt)~t~S its trapped charges from the eY~n~l en~/~or..llcnt with 1 5 effective potential barrier 50a By FIG.12D, ~nlial well 42a has been tr~n~l~tYl along the x-axis, while a new lc ngitudin~l barrier 50b has begun to rise near the opening to pr~cessi,lg channel 26. By FIG.12F, the new ]ongihldin~l ba~Tier 50b has risen so far as to create a new potential well 42b. FIG.12J shows the process having come full circle, such that new 2 0 potential well 42b and lnngitll~lin~l baITier 50b occupy the spatial positions of old potential well 42a and lnng~ 1 ba~Tier 50a in FIG.12A. The process ~im~ t~l in FIGS.12A through 12J allows a sample of ion particles to be swept into the processing channel 26, and then c~plul~d within a nascent potential well by a newly formed longiturlin~l barrier. The same process may be used at the end of the processing2 5 channel, during the accelelation and ejection cycles, to eject an analyzed sample from the array.
Translation of the pOkulLial well center may be seen in a dirr~,l. .~t manner byeY~mining slices along the axis of the tOl)ûgla~hic maps of FIGS.12A through 12J.
For example, FIG.12A has a line AA cut through the center of effective ~lel~Lial map 3 0 1200B. Similarly, FIG.12B has line BB and so on. FIG.13A ~ 5;l;7~S all such slices through the center of the topographical mappings for each value of the shift-control function k(j, t). The graph's x-axis provides the electrode number along the x-axis of ploces~i ng channel 26, while the y-axis gives the phase-shift of k(j,t) in degrees. The particular slices for A through J are also noted. The blank areas 54 3 5 ~ se"l the trapping wells 42, while the areas of dense lines 56 l~ ,senl steepening of the effective potential (i.e., the longit~-~lin~l barriers). As k(j,t) sweeps through the values in time, a hori7l)nt~1 line sweeps upward in the map of FIG.13A. The linerepresents a slice down the center of processing ch~nn~l 26. The ch~ng~s in effective polel~Lia~ ~senl~d by the shifting line, allow an opening 54 into the channel of WO 92/14259 PCr/US92/01096 2~79910 procçs~ing channel 26 which then closes off from a new longit~ in~l barrier 58. A
timing diagram of applied pot~ at each ele~,l,ude c~~ g to these process steps is shown in FIG.13B. The timing diagram of FIG.13B shows topographical collloul~ of cons~nl voltage, in 100 volt incl~..h ~ , where solid lines r~,pr~senl 5 positive voltage, and dashed lines r~plcsent ncg~ive voltage. FIG.13B illustrates how the applied voltages at each electrode change in time, providing a to~o~hical equhalent to the in~ n given in F.qu~tion (11). Thus, one can see that the sequence of applied ~t~n~ials repeats every 30 electrodes, and that the L~u~,ncy of the applied RF voltage is a cycle every 1 ~lsec, or 1 MHz. Also, the pattern of 1 0 l,o~elllials is shifting along the electrode array in time, in FIG. 13B, exactly as the effective potential wells shown in FIGS.12A through 12J. The rate of the shift k(j,t) can be ~1~ te- . .~ ~1 from the drawing as well. FIG. 13B can be cO~ ,d with the static case shown in FIG.13C. The timing diagram shown in FIG.13C su~ ~cs the applied pOtC~ lc that yield the potential field shown in FIGS.6 and 7, and the 1 5 ~ ;Ol-~. y effective potential wells shown in FIG.4.
The eY~mples of FIGS.4 and 12 illustrate operations on many local effective ~tenlial wells in unison along the entire lc-ngitndin~l path of a particular procescing ch~nnel 26. Compl~Y operations were e-se~uted by controlling the pa~l~t~l~7 of Equation . No coullt~ exists in the prior art for the flexible control of fields and 2 0 the res.llting effective ~.llials as provided by the present invention. Even more complex op~r~tion~ can be ~lr~llled upon individual groups of ions. These operations may be SU~I i.ll~osed upon the overall translation of groups through the processing çh~nnl~l FIGS.14A and 14B illustrate a combin~tion of the operations of the present 2 5 invention. F~G.14A shows a ti_e-lapsed trajectory 60 of a ch~g~d particle ofArgon+(39.94 AMU) being ca~lul~d, tr~n~l~ted, stored and ejected from a charged particle pr~cessi~-g ch~nn~l The trapping ~le..l ;~ used to perform these operations are the same as used above in the tr~n~l~tion of FIGS. 12A through 12J but where the prinr~iple electrûde pSl~,t~,.. , are 360/30/0.25, the .~ .. applied voltage is 500 3 0 volts at an applied RF frequency of 3 MHz. The ion had an initial kinetic energy of S
eV, with 45~ initial c.. ;~ l;oll to the çh~nnel axis. The capture and tr~n~l~tion rate of the effective potential wells, ~k(j,t)/~t = 7 (~lsec)~l. The overall mov~lenl of the particle from left to right, similar to the operations shown in FIG.12, l~ senls the particle trapped within a particular tr~n~l~ting well. The translation was halted for 50 3 5 llsec as shown in FIG.14B to illustrate the relationship l;.,l~.l the trajectory 62 of the trapped particle and the effective ~t~nlial 1400B. The total translation from beginning of the çh~nnel to ejection at the end took 180 ~lsec.

WO 92/14259 26 PCI'/US92/0109 Control over the shape, loc~tion and structure of the effective ~,IL al 2 o 7 9 9 10 balTier, as well as control over applied DC offsets to the electrode array 12, allow em~ tinn of ion trap co.-r;n~ Ion trap çmn1~tion can cause ion inct~hilities that select ions by their mass. The present invention does not require a net loss of ions from a particular processing rh~nn~1 undergoing mass selection operations. By p~ef~ Lially lowering one transverse ba~ier a mass-selective pall;L;ol-ing between two succescive wells can occur, where the ion group splits into two or more groups on the basis of their mass. If the altered trapping potential were the last potential well in the particular ~h~nnel, the process would yield a mass-selective ejection from the 1 0 ap~ us. Registration of the ejected ions on the single-ion ~letection device 38 provides accul~le accounLulg of the ion mass spectra in an effirient and rapid manner.
The a~u~Lus can be c~nfi~1red thereby as a very-high-volume throughput mass spe~;Llulll~. The device has the c~r~hil-ty of burr~ g groups of ions, to accû~ o~ts the high-volume ion bursts co~,on in gas c}hu,l~ glaphy mass 1 5 ~ecL umeh~ (GC-MS) app1ic~;onc~: tThe l urr.,~ g c~r~bility of the present invention c~ lds to the burst mode operation used in video and compul~ ;lhleclu.~,s.
The lengthwise buLr ling of ions groups within each pl~ ces~ing rh~nne] 26, combined with the replication of procescing çh~nn~lc 26 across the face of the present invention, allow a great in.,lease in the ion mass under analysis. The parallel p-.ces~ g and 2 0 burr~"i,lg rea~ s of the present invention allow the device to OV~;.J11l~ the space charge limit~tionc of conv~ ;ol-~l mass s~ecLlull~ ,. in~L,u-uenLs of a similar size.
Discussion of Ion Cooling The llic~lccir)n given above for the trapping, linear translation and mass selection operations of the present invention ~csnme~l the pl~sc.lce of a buffer gas to 2 5 cool ions heated by the action of the col;--i-~g fields. As ~lic~usse~l above, other mP.tho~s of cooling trapped ions exist (such as laser cooling). The present invention is distinct from previous energy transfer techniques in that the trapping fields themselves can remove or add energy to the conrlncd ion groups, without any internal ~.Lu~ba~ion or excitation of the ion, as occurs in collisional damping or laser eYcit~tion. In 3 0 collisional damping (as with a neutral gas), co11icinnC result in electronic, rotational and/or vibrational excitation. Internal excitati~n can cause structural rearrangement and even mole~ul~r fr~..L ~ ;on. Laser cooling l~Uu~S use of intense laser fields, and can also cause molecular frag, . .~ l ;on from multi-photon absorption. Processes involving Fourier transform techniques, as in FT-ICR ~ ,Llu---eL,y, and analogous 3 5 techniques applied to ion trap and quadrupole devices (see, for example, U.S. Patent No. 4,755,670, issued to Syka et al.), require substantial translational excitation to induce a coherent ion group. The coherent group passes sufficiently close to a conductive surface to induce image ~;ull~.lL~ that can be analyzed. The rlissip~tion of the image current through external resistance relaxes the ions to their initial state, but u~o 92/14259 27 PCr/US92/01096 2~79910 usually results in no net cooling. Fourier ~u~Srul~ detec~ on l~uil~s coherent motion of the ions, which in quadlupole or ion trap lll~lllods is norrn~lly chaotic.
One of the plill,iple cl-~ ~et~ - ;Cticc of the present i"~",tion, the physical method in which an cl~llode array ge~ la~s the RF field, allows novel control over 5 the energy of trapped particles, in Adllition to theirpositiûn and l.i.je~ . In general, the prior art ûften creates RF fields through large conductive electrode c4 .,~nl~, having a single con-luctive surface that runs either parallel to or bounds co~letely one or more trapping coc ldinàles. The in~lepenrlently controlled eleclludes of the present invention allow for greater control over ion energy, position and velocity.
1 0 The energy control of the present invention arises from the "pseudo-conservative" ~lv~lLes of the rapidly osc~ ting (and co,~lct~,ly cl~ngf ~'~lc) elecl,~...A~etir field which the cle~LIode array provides. As .];~c~.cs~ and illustrated above, the el~ u. I~ ti~ fields ~ d by these elect~des can create one or more trapping wells formed in an effective potential barrier. The c~mr'cx physical system 1 5 cc~ ;ng the el~;~lode array 12, the ;nject~A ions and the lab~la~l~/ frame conserves energy. However, energy partitions itself among various con~ e~lc of the system.The oper~tion of the present invention creates several ".~,. nicmc for le,ll~ ing energy controllably from trapped ions to the eYt~rnAl l~ o. ~r, allowing cooling of the ion groups.
2 0 The cooling mo~h~nicmc are best ~ -ctTnted in a succes~ion of FMS. 15Athrough l5E. The present invention involves a complicated interplay bc~ ,en the electrodyll~l,ic fields gen~ alcd by the clc~-des 12 (and their associated electronics 14, 16 and 18), the trapped ion groups, and second~ry fields ge.-c. ille~l by the moving ions. The first case to be e~h...;n~d is that of one or more ions trapped in a stationary 2 5 potential well. FIG.lSA illu~ tes the action of a single ion and a local electrode ring 22, being the portion of an elecllude 12 ~i~ to one pl~css~;i-g cll~nn~1 26. Thesch---.. I;csystem l~S ~lesany c~ n~lu~ c objectc~...~e.,l~linsome"~a"nertoa source of charge (or to ground). As the chal ~d ion 74 a~pl~ hes the conductive plane 22, image charge 76 is drawn to the local elect~de loop 22 to balance (and3 0 thereby n~utr~li7e) the app,~,~ck;..g ion's charge. As the ion recedes, the image charge 76, through its mutual repulsion, retreats to ground again. This ele~llu~la~ic flow of charge can create a small but finite current in the leads 15 to the ele~lludes. If dropped across a resi~t~nce 77, the current can dissipate energy in the form of heat. Since the image charge and the approaching ion charge form a cQnl-~t~d ele~L,us~c system, the 3 5 loss of energy of the image charge can f~ ip~e heat from the ion, slowing it down.
Sscf nf3~ry elsctr~ly"~l,ic effscts can occur as well. The moving trappsd ion charge 74 creates a supplem~nt~l elecllu...~netic field, which combines with the field creatsd by the electrodes them~elves, to form a reslllt~nt field shown as B in FIG.lSB.
This field rapidly oscill~tes, trapping the ion group in an effective potential well, but WO 92/14259 28 PCr/US92/0109 ~ 0 7 9 9 1 0 also causing image charge 76 brought into the local electrvde loop 22 by the trapped ion to ey~nrnr~e oscill~ting ele~;llvlllu~i.~e forces. These forces can cause circnl~tion 78 of the image charge arvund the local electrode loop.
While the image current and its ci~ulation can ~l;c~ e ion energy in the fo~n 5 of heat, the local nature of the ~i~s;~l;. n does not allow these cu~ lls to provide much useful illf ~ ;on about the trapped charges. A further cooling frh~ can allow e~ ;llh ~ access to the in-luced el~llvde ~;Ull~ i and to in~ .. s~l ;on about the trapped ions. FIG.15C illu~llates two neighboring electrode loops 22a and 22b ;el.-~;ng the resnlt~nt in~llre~l ma~Fnetir field B l~lvduced by the electrode alray and 1 0 ion ~tion. FIG.lSC also shows the resnlting cle~v~l~l;r~lly and electrvdyn~mic~lly ion-inr1uce~ . The two loops 22a and 22b are co~lne.~ d in the eYtrnn~
labu~ by a resistive load 82, which can also be an ~ t~ . or similar electri device. In general, both th~ion motion and the elecllu...~etir fields have coml)olle.lb peIpen-lienl~r to the x-axis of ~lvce~!.;.-g ch~nnel 26 (i.e. in the in the y-z 1 5 plane). These Cv~ vllen~ can ge.lelale an elc~v ~lvLi~e force arûund the loop compri~ing the local electrode loops ~, the leads to these loops 15, and resistive load 82. The in~uceA el~1lu~ e force thereby can cause circnl~tic-n current 80 to flow around the loop co..~r.. ;~;ng the ele~trir~l leads, and thrvugh device 82, allowing both resistive d~mping of ion energy and llJe,asul~nls of the in~luceA rl~mring Each ion 2 0 species reacts in difrc.~,l t ways to the trapping field, and induce different current ~ign~hlreS that can allow ion mass typing ûf the trapped ion grûups.
Both the elecllv~Lic image current 76 and the electrodynamic circulation currents 78 and 80 shown in FIGS. lSB and lSC can cool the trapped ion charge 74. The reslllting cvoling occurs for a single ion because the ion forms a nahurally cohe~.ll charge 2 5 bundle (compri~ing only one charge), and the cooling is analogous to the action of FT-ICR techniques described above. However, the effi~en~y of such cooling decreases as the IIUIll~ of trapped ions goes up. As the number of ions becomes large, there no longer is a ~leÇ~l~l ~ ioll for overall ion ~tion. The st~ti~ti~l ~v~ n~ of large nul~ of trapped iûns results in a mutual c~n~ell~ion of the elc,~u~ lly and 3 0 electrodyn~mi~lly ion-in~uced ~iUIll,lll~. FIG.15D shûws equal and opposite ion velociti~s v; (74a, 74b). Such a degellc.a.;y in the eYtern~lly Ill~uuable individual ion-in~uce l ~;ullcnls greatly reduces the efficiency of the cooling lllecl-~n;~
The present invention, however, provides techniques for tr~n~l~ting ion groups along each ~loces~ing channel 26. The net velocity applied to each ion splits the 3 5 degeneracy of ion motion as seen by the stationary electrodes. As illustrated in FIG. lSE, ions within a trapped group (centered about a "trapping center") moving with the overall translational motion 74a exhibit an increased velocity Vi + v relative to the electrode loops 22. Ions moving against the translational drift of the group 74b exhibit a decreased velocity v; - v relative to the electrode loops 22. The res~lhing velocity can induce the WO 92/14259 29 C~ O

cl~l~ amic image current 76 and the s~bs~uenl culrent cir~ulations 78 and 80 in order to cool the trapped ions. Hence, the second case, compri~ing a trapped ion charge group being tr~ncl~t~l along a pl~,ces~ g channel, allows for cooling of larger groups of ions.
The present invention provides a dlird, and ~re ~elih~te~ scenario for cooling groups of trapped ions. Motions of the effective p~tell~ial barrier walls can impart and remove energy from ions trapped within them. FIG.16A l~senl~ a one~imton~ional effective pot.,n~ial ba~ier where the x-direction ~ sell~ a single spatial tlin~n~ion (for an actual device, there would be three rlim~n~ions) and the vertical axis l~ ,S~ S the 1 0 energy or Ub of the effective potential ba~ier at each point x. A ch~,xl particle colliding with the ba~Tier Uo is stopped at that point xo where its total energy is equal to the potential energy of the barrier, Ub(xo).
In the case of a static effective potential ba~rier, as shown in FIG. 16A, and as ch~act~istic of con~en~ n~l RF ~ ole trapping devices, the shape of the field and 1 5 the ~ l RF amplitude l~ls col~lt. Referring to Equation (11), the potentials p(j,t) applied to each electrode are held con~ -t FIG.16A starts with a system where a bound ion travels from the center of the potential well Uo toward a col~ g wall. Since the wall does not move with respect to the electrodes, the total energy of ion/field system is conserved. To say it another way, the particle's motion is stopped and reversed at that 2 0 point xo where the effective potential Ub is equal to the particle's own energy. After colli~ion, the particle's dhe~ is lG~ and upon colliding with an o~po~ g wall l G~ S cOl l r; l l C~
As ~ lcseA the present invention, however, allows the potential barrier to move together in a locally conn~t~A f~chion, or "p;ecG..~se", with respect to the local electrode.
2 5 This motion is dia~ ed in FIG. 16B, where the barrier Uo(x) shifts parallel to itself along the x-axis to form barrier Ul(x). This motion of the barrier is one consequence of allowing the pot~ ial ~mrlitu~les applied to each electrode, p(j,t), to vary relative to one another in time. With point-wise movemenl, the field can possess linear 1lll~ so that during int~l_c~ion and turn-around, the particle loses energy EL equal to the kinetic 3 0 energy transfe~ed by the field. FIG.16B shows qualitatively the loss in energy from the a~plv~cl ing particle and the receAing particle, as a drop from energy level Eo to El. The rest of the energy has been absorbed by the traveling barrier. Lf the interaction is reversible, then closing the barrier back from Ul(x) to Uo(x) would impart kinetic energy to the ion and return the ion to its initial level Eo. The exr~n~ n and contraction of the 3 5 fields in a reversible way would provide an ~ ~tic eYr~n~iQn and contraction of the cu~ ..;..g potential well. The mo~el~lll of a l~n itll~lin~l barrier wall, while keeping the trapping center stationary, is similar to the second cooling sc~n~riQ described above, where the entire ion group moved relative to the elec~des. In the first and second cooling scen~rios~ represented by FIGS. 15A-lSB and FIG. lSC, respectively, the WO g2/14259 PCr/US92/01096 ~ o 7 9 910 cooling effects are made possible by dropping the ;...J.,ce~ . nls in the el~l-odes across a re~ict~nce. It is the ability of the present invention to add lc3;~ nces to the inrlucerl cuIrent flows that allows the present in~,~ n~ion to create a controllably non-conserv~ative trapping field. In such a controllably non-conservative field, trapped ions can be made to lose or gain energy as desired.
The in~ acLion of the field's linear .. O.. Ii~ and the particle's linear ~.. --.~ can also be i~ ible, where a CO/~ lOU5 linear accel~ion of the field during collision does work on the particle, adding additional kinetic energy into the syster~ After an ihl~ ible process, the kinetic energy of the particle would always be higher when the 1 0 barrier returned to its initial location Thus, using only linear n .. n~ attributes of the potential field, the particle's kinetic energy i".;l,.,ases with completion of an expansion and co~ ;on cycle. Th,_l~ru c, an elastic collicion ~l-.~11 a particle and a ~ ~ial well co~lning barrier cons~l~r~c s e4~rgy and does not provide a ".~ for removing energy fr~m the particle while ~nrlning it to a particular volume in space.
1 5 FIGS.16C and 16D show the effects of allowing the potential barrier to move inclG...to~ l~lly and ~iscon~ ollcly. In FIG.16C, the points ~çfining the local potential barrier move around the crrc.~i~,e potçn~ l well center R. As shown, the particle enters the collicion with an energy Eo and leaves the colli~i~n with a lower energy El.
Dirr~, nlial motion of the effective ~l~l~lial barrier filmi~h~s a method wh,, leb~ the 2 0 conl;.-;ng~ fields alone can cool and confine a trapped particle. This cooling ability is shown in FIG.16D. Certain ch~n~s of the effective potential barrier can make the relative velocity of the barrier at a higher energy (for example, Eo) greater than that at a lower energy (El). Th,_lcrc.,e, the energy ~ r, l would be greater for particle collisions at higher energy than at lower energy.
2 5 If the barrier is restored to its foqmer loc ~ti~n, creating the same confinçm~nt space as before the colli~ion in FIG. 16C, particle p colli~les with the barrier at its lower energy El. As the barrier moves back from Ul(x) to U2(x), the amount of energy conrcl,cd to the particle EG is c ~n~i~ç~hly less than the enagy that the particle origin~lly lost. The particle now l,ossess_s an energy E2 less than Eo, its original energy. The return of the 3 0 barrier should (and, with the present invention, can) be ~ he~l s~rr~:f ~.lly quickly that the trapped ions cannot recover their original energy. The dirr.,~nLial motions described by FIGS. 16C and 16D produce a particle that has less enagy but is confined to the same spatial volume. Providing energy non-conserving collisions with a potential well barrier, for example through use of a resistive elç., ~ ol as illu~ d in FIGS. l5A, l5B
3 5 and l5C, allows removal of t~ncl~tion~l energy from the particle. The present invention, through its comrl~ ~ control over the effective potential shape, provides for field cooling of trapped particles. Again, the ~l~l~ transfa is ~..~n the ion/IPU system and the outside world. Providing resict~nce across the flow of ~;ull._.lL~ in(l~lce~ by the motions of ~'VO 92/14259 PCI/US92/01096 trapped ions provides a critical method of the present invention to controllably transfer energy to or from ions within the appal~Lus.
The ~,c~A;ng ex~mrles and analysis show how the present invention can control barrier h~ightc, translation, injection, ejection, cooling and hf~ting, by employing an 5 Equation (11 ), which is of general foqm I~ ...f.~ l barrier disp~ .nfn~ can be comhine l to create mllltiple effects. As a simple ~ le, the translation of a sequence of wells 42a, 42b, etc. along a longitu(lin~l path Llllougll a yl~ces~ g ch~nnel 26, as shown in FIG. 17A, may be comhin~l with selective cooling of a particular packet of ions within one effective potential well. Any number of suy~,.yosiLions of fields can be achieved. An 1 0 example might be sul~. ;...po~-g a lon~;l..(l;..~l balTier 50 with a potential well 42, allowing ions to transfer out of a ~ li7~d group.
Comhin~tionc of succe~scive potential maps can provide the confinf mf nt and cooling effects ~escribe~l above, and also furnish other "building blocks" for basic ion process;ng Altering the applied potentials to each electrode in precise ways can alter ~e 1 5 basic corlGnillg potential well. As shown above, the pOIf;lllial well can be tr~n~l~tf~1 in space, either along the ~luces~ g channel longil l(lin~l x-axis or transverse to the x-axis, or in some combinf~ direction. Thus, parLicles trapped within the well can be relocated in a controlled ll~nel within the proces~ing ch~nn~l In addition, a single well can be made to split into multiple wells. This allows a 2 0 single group of ions to be split into several groups. FIGS.17A through 17D show the result of varying pal~t~.s to gradually split well 42a from a larger effective potential well (or ch~mher) A and transfer the split well 42a to another larger chamber C. FIGS.
18A through 18I ~ the two-~limen~ion~l lopo~hical mappings of the effective potentials and reveal the controlled transfer of an effective p~t~,..lial well 42a (and any ions 2 5 trapped within) along a line of ,l~lsr~r 85 ~lv~n one larger chamber and another. FIG.-19 ~.. ~. ;7PS the time-varying p~ t.. ~ used to COIISlluCl the illu~ ed effective potentials. As ~ c~lcse~ above, the two large ch~mhers, section A of the ion processing channel (co. . .~ g electrodes 1 through 90) and section C (cc..-~ i . .g electrodes 120 tnrough 200), employ the ~ ,tc.s 1080/30/1.5 (a 1080~ cycle for every 30 consecutive 3 0 electrodes with a slope s(j,t) =1.5). The central B region, where the ~ , potential well 42a is created and t~n~l~t~rl employs ~ tel~ 360/30/0.25. The shift function k(j,t) changes to effect the transfer as in~ tçd in FIG.19.
Because the processes described in FIGS. 17 through 19 can be reversed in time, the same pa~ ,t~.~ can be used to cause multiple in-lepçn~lent wells to coalesce into a 3 5 combined new effective ~t~. l,al well. In fact, the merging of a transfer effective potential well 42b with the second large cha.~ area C (which itself comprises an effectivepotential well) is shown in FIGS.17 and 18. Both the merging and separation shown in FIGS.17 through 19 represent only one possibility for similar operations of the present invention.

2 o 7 ~f~ 32 PCr/US92/01096 The ability to create both stz~tionSry and translating pot~ l wells within each processing chS~nn~ allows relatively large ~lc ~-~;I;es of ions to be stored in a relatively srnall space. The a~us is well-suited for storing cl,a~ d S~..t;."~lt~ l. As Alll;ll~ l iS
produced, groups of po~illu. iu,ll or other charged A~ll;llli.ll~.l can be introduced into each 5 proees~ing chS~nn~l 26 and held co~ ~ to an individual effective potential well. These wells can be trz~n~lS~ted as was shown in FIGS.12A through 12J. Large i~,ounls of ;n-;~lt~.. could thereby be "clocked" in just as a ele~,l.o~c buffer clocks in a digital signal. The adaptive fields of the present invention allow long-term storage of the Anl;n~ ~ in a kind of el~llode sponge. If the A~lt;~n~1h . were used for space propulsion, 1 0 the ion pr~ces~ing unit 10, filled with ~ ., could be stored as a fuel tan~ When needed, Slnl;...-lh.. could be released from each ~luces~;,-g chS~nnçl and guided to an annihilS~tion çh~."hf,l for craft propulsion. This example ~l~sellls just one use of the present invention for the handling of ~lirr~ forms of charged matter.
As ~lisc~lsseA above, a single trapping well can emlllSttç a conventionStl ion trap by 1 5 applying gr~duJted potentials as ~es~ibeA. in the Arnold patent. Thus, mass selection can be accomplished at any point along the longihl~linsal path of the elech~de array 12.
Conventi~nz~l pe~i~ic potentials could ~L~,l.,r(~l~ selectively destabili~ certain ions. By a~rv~fiately shifting the applied ~t~lllials along the electrode array, the ~locessillg of a particular packet of ions could ~luceed with a general tr-sm~ls~hir~n of the trapping potential 2 0 along the ~l~.ssi.-g chz~nnçl path.
An addi~nal method for analyzing dirr~lc.l~ ion species within the ~I- cessillg channel takes advantage of the fact that energy absorbed or given off by an ion during a heating or cooling process must enter or exit the system thrvugh the electrodynamic field The change in the field due to energy exchange with trapped ions induces elech ic current 2 5 in the nearby elechrodes~ This inrl~1c~A. current h~ ases the current required to drive the electrode array in the absence of any ions~ The in~ ce~ current carries implicitinrvllllalion on the number, mass and ~lluclulc of ions eYrh~nging energy with the field.
Because heating and cooling of ions occurs during nv~mal ion pl~ces~ within the array, ind~lced current iulr,....~, ;.,,- can be e~ ~ co~tin.lAlly.
3 0 FIG.20 lJlGSGII~ ~clitionAl ~ CuiLIy for ~ ;ng indllced current illfolllldlion from the electrode array. F~ c~l module 19 lG~JlGS~nls the driving and Il~A~lll ;ng ciruuilly for the electrodes, while digital-to-analog (DAC) 16 and analog-to-digital (ADC) 84 converters prvvide and ca~y away a~lv~liate signals. Bus lines 20 prvvide digital signals to DAC 16. DAC 16 drives the operational Amplifi~r 14 th~vugh low voltage RF
3 5 line 28. The high voltage output signal from the op amp 14 drives a coll~,s~ondi,lg electrode by sen~ling a potential voltage over a high voltage RF line 15 to an electrode frame 23. A switch 73 allows inrluced current to be sent through resistor 71, dissipating energy and increasing the cooling efficiency of the invention, or, ~lt~nAtively, through a conductive line, both attArheA to the output terminal of the operational amplifier 14. A

~40 92/14259 33 PCr/U~ 0 dirr~"~,.,L,al ~mplifiçr 66 s~mrles the low voltage and high voltage RF lines through a first line 68 conn~t~ ~~ the input t~ormin~l and a first input tçrmin~l of the amplifier and through a second line 70 co.~ t~ ~e~ n the output tçrmin~l of the operational ~mplifi~r 14 and a second input tçrmin~l of the ~mrlifi~r 66. This prvduces an output signal from the amplifier 66 that cl,a.;d t~ s the current in~lncç l in the electrode, which signal can be converted by an analog-to-digital converter 84. Typically, each ion spçcies induces dirr~l~,nt char~t~ri~tic L~uencies in the clecllvde array. A Fourier transform of the in~luce~ current Lc~lue~cles can prvvide a S~;l1 UL~ for cataloging trapped ions, using a metho~ analogous to ICR techniques. See for e~le the methods ~1isc~1sse~ in 1 0 Gaseous Ion Chemistry and Mass Spe~;llv,lle~ ~. Ed. J. H. Futrell, John Wiley & Sons, New York, 1986, and the references therein. Tn~uce~d current metho~c would often be s~lp~ri~r to ion trap çm~ tion, since no loss of ions would be required and the process would t},elcrvl~ be non-dc;,~ e.
The present invention provides meth~ of mass control and analysis that can be 1 5 massively parallel, similar to the o~tion of massively parallel C~LU~Ut~ eS.
Mass s~ gla~hs in ll,el.,selves provide a type of simple pa~llçli~m~ in that all masses are collected at once. The c~lclll~tions used during World War II for the separation of ul~ufium iso~es also eYploitef3 a simple p~rall-oli~m, whereby many mass spectrographic channels are operated side-by-side to çnh~nt~e the extraction process.
2 0 In addition, the Paul et al. U.S. Patent 2,939,952 illustrates in Figure 10 another m~tho~l of simple par~lleli~m for mass s~;~lul~ll~, using an array of rods defining a plu~lity of parallel ch~nnel~ Similar devices have been con~lluct~,d, including four-fold monopoles, but driving such large c~ra~tive devices with a single RF source greatly increases power f3em~nfl~, and they are not widely used. In addition, this simple parallel 2 5 a~l~ach provides only modest improvcm~ at the ~n~ of increased i~ un~
compleYity.
The present invention provides a much more SOP1~ I ;f ~t~ cl parallel mass spe~ ,t~,.. The present invention can be conceived as an N by M massively parallel ion processing unit (IPU) 10 as shown in FIG.21. Each electrode sheet 12 is an independent 3 0 site of ion control, including trapping, translation and cooling, and also of i,~ ion gathering, through inrlur,e~ cull~n~ as fl;~ucs~ above and as registered in the electrical module circuitry 19 shown in FIG.20. If N is the number of local hexagonal perforations 22 in an electrode 12, then the present invention has N ion proces~ing çh~nnel~ 26. Each electrode would therefore have N by 1 ~rocessing sites for conuull~l-t ion plocessil-g. If 3 5 there are M electrode grids 12 orthogonal to each ion ~,vces~;.-g ch~nn~l axis, the invention as a whole would have N by M ~ ces~;..g sites (each eleu~ de ring 22) and M
control and inÇo. - ~ ;on ~-~ c~ tion locations (each electrode 12). The massivepar~lleli~m of the present invention, where M and N are greater than one, allows for the sophi~tir~te~l and efficient control of ion species and the ability to simlllt~neously collect WO 92J14259 PCI/US92/OlO9~
34 w 9 9 1 0 vast ~-.. o~n~c of hlrc~ ;on In one emborlim-ont, the massively parallel ion pr()cesso 2 ~ 7 could include a host c~ -u~ - 18 that sends general plU~l~llll information to an array controller 86 which in turn governs the ~ eous operation of the IPU 10 through an array controller bus 20. The array controller m~n~es the overall goals of the M
indepen~.ont, self-cl nt~in~ colnl,ut~l~ or logic units 90. These s~alale logic units 90 subsllm~ the DAC 16 and ADC 84 functions for sending hlÇo....~I;on to and receiving hlro,ll~lion from the cil~;uill~/ for an de~llude module 19. The se~ e logic units 90 can be each similarly prClgl~ llRd, governed by a CO~Il clock. Each electrode module 19 can handle local signal l~ucec~;ng and ~cum~ tion for its portion of the electrode array 1 0 10. As effective pol~nlial wells are tr~n~l~te~ down the ploce~~ g unit 10, the data co,~ onding to a local ion packet (trapped within a well) ~.~,~r~ to the next logic unit 90. The system thereby provides a cc",.,s~,on-lenr~e of inr~,l"~Lion and control between the sepala~ electrode logic units 90, the electrode m~~ os 19, and the trapped charge packets. The host C~ Jul~. 18 rètrieves i,-r~"lllat,on as does a ~ t~ Digital Signal 1 5 Processor (DSP)88, to process inr~ ;Ol on a real-time basis. FeeAbaclf from inrcl~ ion Q~cllm~ te~l by the host c~----l-ut~ ~ 18 to the array controller 86 allows ;.""~liQ~e ~s~nses to sample ulÇo....~I;on, and the array controller can update or adjust the program se~u~ncing of the M logic units 90 to achieve more effirient operation or optimize pl~ces~;,-g p ~-,.-.-et~ . ~. The plocess;ng of ion groups in the present invention is 2 0 adaptive to h-~ ~us çhQnges in the analyzed sample and can flexibly react to many ylocessulg conditions.
The present invention provides a simple yet po~rul system for processing charged particles in a flexible manner. The present invention, by providing multiple ~lucessillg chQnnelc, allows for orders-of-magninlde higher CA~.illl~,nl~l through-put 2 5 than available by conventional means by cignifirQntly increasing the available ion volume.
The present invention furnishes methods and aW~alus for ~rul~ulg all re~uired ion processing maneuvers, inr,luAing buffering of high-volume, high-speed bursts of ion samples, sampling and splitting offportions of buffered samples, trQncl~ting trapped ion samples along the pluces~;llg path, cooling trapped particles to ullirOlll~ energy levels 3 0 through field interaction alone, mllltirle meth~lc of mass d~ t~ ;on (including ion trap emlllQtion and/or mea~ulc~ nl of in~luce~ image cullc-lb), and finally ion acceleration and detectic)n The present invention provides a relatively simple, readily mQn~lfQctured and flexible system for ion ~iùcess;ng, analysis and control.
Although the present invention has been des~ibe~ with l~cÇ~.~,nce to ~lcÇ~l~d 3 5 c~bo~ .t~, those skilled in the art will recognize that various mo lifi- Qtic-ns may be provided. For eYQmple, the particular honcycol~lb cavities combine to provide parallel ces~;ng channels can be replaced by other gWIll~ tliCS. In fact, only one cavity might be used, with dirr~ l elecllude ~illUClUlcs and plQ~ e...~ nlc Dirr~ mQteriQlc, including conductive plastics, can be used for electrodes. It should be understood that two electrode --'O g2/14259 PCr/US92/OlOg6 ~ 35 2~ 7991 0 snrf~es, c~ lly co~ ~ and hence given the same potenti~l~ at all times, can be conci(lered one de~ ode. Various equivalent electrical dnver devices exist for applying voltages to col~ o~ . Dirr~ form~ m~ for applying time-varying pot~,nlials to each electrode can be adopted, without altering the basic effect of allowing the time-averaged 5 effective po~ ial to be ch~nged While the ~lef~l~l elllbo~ nl uses a digital c~ u as a control means for controlling the applied electrode ~te .~ , other means inc~ 1ing analog comput~ or analog ~. a~follll m~"llul~/ devices, are available. The mlothorls and a~alalus of the present invention may be ~ 1 osed upon other ion ~xes~;.-g ~c~ues to achieve further novel results. For e~cample, a time-variant effective potential 1 0 may be ~ pose~l upon charges col.rn~ by ~ el;~ fields. The effective potential can then be used to cool ion groups conrlned by other mothrYl~ These and other v~ri~ticn~ upon and m~ifi~2tionc to the ~les~ibe~ e ..bo.l;..~ are provided for by the present invention, the scope of which is l~mited only by the following claims.

Claims (36)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Charged particle processor apparatus for manipulating charged particles that have an energy and a mass, the apparatus comprising:
an electrode array, said electrode array including a plurality of transversely extending, substantially planar electrode sheets, each of said electrode sheets having at least one perforation therein;
a plurality of spacer means, each of said electrode sheets being separated from adjacent electrode sheets by said spacer means, said electrode sheets being aligned relative to one another such that respective perforations of each of said electrode sheets align to form at least one charged particle processing channel;
a vacuum enclosure enclosing said plurality of electrode sheets;
a plurality of electrical potential drivers, each of said drivers being coupled to a respective electrode sheet;
digital-to-analog converter means coupled to said plurality of drivers;
a data bus, said data bus being coupled to said digital-to-analog converter means; and a computer coupled to said digital-to-analog converter means through said data bus, whereby data from said computer is converted by said digital-to-analog converter means to analog data and causes at least one of said drivers to apply an electric potential to at least one of said electrode sheets.

2. An apparatus as claimed in claim 1, further comprising a charged particle source that produces at least one charged particle, said charged particle source being located in relation to said plurality of electrode sheets such that said charged particle produced by said charged particle source can enter said one charged particle processing channel.

3. An apparatus as claimed in claim 1, further comprising a charged particle detector, said detector being located in relation to said electrode array such that said charged particle that exits from said one charged particle processing channel can be detected.

4. An apparatus as claimed in claim 1, wherein said electric potentials are applied to said electrode sheets by an array of amplifiers.

5. An apparatus as claimed in claim 1, wherein each of said perforations has a hexagonal shape and has a diameter of approximately 2R0, and any two consecutive electrode sheets are spaced apart by a distance of approximately R0/13, where R0 is a distance from the center of each hexagonal perforation to a vertex thereof.

37a

6. An apparatus as claimed in claim 1, wherein said electrode sheets are numbered consecutively J=1, 2,...,J(J~2) and said electric potential applied to said electrode sheet number j has the form P(j,t)=.PHI.0 Sign [A(j,t)] ~A(j,t)~ S(j,t) sin(.omega.t), where A(j,t)=cos[2.pi.f(j,t)w(j,t)-k(j,t)], where t is a time variable,.omega. is a selected angular frequency, .PHI.0 is a selected electric potential amplitude, and f(j,t), s(j,t), w(j,t) and k(j,t) are time-dependent functions selected for said electrode sheet number j.

7. An apparatus as claimed in claim 6, wherein said functions f(j,t), s(j,t), w(j,t) and k(j,t) for at least one of said integers j are chosen so that said charged particles lose net energy when said charged particles are adjacent to said electrode sheet number j.

8. An apparatus as claimed in claim 1, wherein at least one of said electrode sheets is electrically connected to a source of ground potential through a path that has a selected electrical resistance.

9. An apparatus as claimed in claim 1, wherein at least two adjacent electrode sheets are electrically connected to each other through a path that has a selected electrical resistance.

10. An apparatus as claimed in claim 1, further comprising a low pressure gas of neutral particles that surround said electrode sheets and undergo collisions with said charged particles, thereby reducing kinetic energy of said charged particles.

11. A method for processing charged particles having particle energy and particle mass, the method comprising the steps of:

(a) applying electric potentials to an electrode array to create an electric potential field (600A) within a selected volume of space through which said charged particles can propagate;
(b) introducing said charged particles into said selected volume of space;
(c) controlling said applied electric potentials to establish an effective potential field (400A) within said selected volume of space for said charged particles, said effective potential field including a plurality of first effective potential wells, each well being capable of confining said charged particles within a portion of said selected volume; and (d) varying said applied electric potentials to combine at least two of said first effective potential wells into a single new effective potential well that allows a transfer of charged particles confined to said combined first effective potential wells to said new effective potential well.

12. A method as recited in claim 11, further comprising the step of providing said electrode array as a plurality of electrode sheets that are spaced apart from one another along a selected longitudinal direction, with each electrode extending transversely relative to the selected longitudinal direction.

13. A method as recited in claim 11, further comprising the step of applying said electric potentials to said electrode array by an array of amplifiers.

14. A method as recited in claim 11, further comprising the step of providing a computer to control application of said electric potentials to said electrode array.

15. Charged particle processor apparatus for controlling the motion of charged particles having particle energy and particle mass, the apparatus comprising:
a plurality of J electrodes with J ~3, numbered consecutively j=1,2,...,J and spaced apart from each other by electrically insulating means in a selected longitudinal direction, for creating substantially independent electrical potentials (600A) in the volume between and defined by any two consecutive electrodes, each electrode having a plurality of perforations therein that are arranged so that a sequence comprising one such perforation from each electrode forms a channel through which the charged particles can propagate;
a vacuum enclosure enclosing the plurality of electrodes;
a plurality of electrical potential drivers, one such driver being electrically connected to each electrode, to apply an independent electrical potential to each electrode; and computer control means for controlling and varying with time the electrical potential applied by each driver to the corresponding electrode to establish an effective potential, including a potential well with a well center, in the volume between any two consecutive electrodes, where a potential well is capable of confining a charged particle within the well, the computer control means varying the electrical potentials applied to the electrodes with time so that the potential well center is translated with time from the volume between electrodes number m and m+1 to the volume between electrodes m+1 and m+2 (1~m~J-2) so that a charged particle confined in this potential well is also translated in the selected longitudinal direction with time.

16. The apparatus of claim 15, wherein said electric potentials are applied to said electrodes by an array of amplifiers.

17. The apparatus of claim 15, wherein each of said electrodes is a substantially planar sheet and extends transversely relative to said selected longitudinal direction and each electrode has a plurality of longitudinally oriented perforations therein.

18. The apparatus of claim 17, wherein said perforations have hexagonal shapes.

19. The apparatus of claim 17, wherein said electric potentials applied by said drivers to said electrodes are non-conservative to allow a transfer of energy between said charged particle confined within said potential well and an environment external to said electric potential.

20. The apparatus of claim 15, wherein each of said perforations is hexagonal and has a selected diameter of 41a approximately 2R0 and any two consecutive electrode sheets are spaced apart by a distance of approximately R0/13, where R0 is a distance from the center of each hexagonal perforation to a vertex thereof.

21. The apparatus of claim 15, wherein said electric potential applied to said electrode sheet number j has the form P(j,t)=.PHI.0 Sign[A(j,t)]~A(j,t)~S(j,t) sin(.omega.t), where A(j,t)=cos[2.pi.f(j,t) w(j,t)-k(j,t)], where t is a time variable, .omega.
is a selected angular frequency, .PHI.0 is a selected electric potential amplitude, and f(j,t), s(j,t), w(j,t) and k(j,t) are time-dependent functions selected for said electrode sheet number j.

22. The apparatus of claim 21, wherein said functions f(j,t), s(j,t), w(j,t) and k(j,t) are chosen so that, for at least one of said integers j, said charged particles lose net energy when said charged particles are adjacent to said electrode sheet number j.

23. The apparatus of claim 15, wherein at least one of said electrode sheets is electrically connected to a source of ground potential through a path that has a selected electrical resistance.

24. The apparatus of claim 15, wherein at least two adjacent electrode sheets are electrically connected to each other through a path that has a selected electrical resistance.

25. The apparatus of claim 15, further comprising a low pressure gas of neutral particles that surround said electrode sheets and undergo collisions with said charged particles, thereby reducing kinetic energy of said charged particles.

26. A method for processing a stream of charged particles that have particle energy and particle mass, the method comprising the steps of:
providing a plurality of J electrodes with J ~ 3, numbered consecutively j=1,2,...,J and spaced apart from each other by electrically insulating means in a selected longitudinal direction, for creating substantially independent electrical potentials (600A) in the volume between and defined by any two consecutive electrodes;
providing each electrode with a plurality of perforations therein that are arranged so that a sequence comprising one such perforation from each electrode forms a channel through which the charged particles can propagate;
providing a plurality of electrical potential drivers, one such driver being electrically connected to each electrode, to apply an independent electrical potential to each electrode; and controlling and varying with time the electrical potential applied by each driver to the corresponding electrode to establish an effective potential, including a potential well with a well center, in the volume between any two consecutive electrodes, where a potential well is capable of confining a charged particle within the well, the applied electrical potentials being varied with time so that the potential well center is translated with time from the volume between electrodes number m and m+1 to the volume between electrodes m+1 and m+2(1~ m ~J-2) so that a charged particle confined in this potential well is also translated in the selected longitudinal direction with time.

27. The method of claim 26, further comprising the step of providing said electric potentials applied to each of said electrodes by an array of amplifiers.

28. The method of claim 26, further comprising the step of choosing each of said electrodes to be substantially planar sheets and to extend transversely relative to said selected longitudinal direction.

29. The method of claim 28, further comprising the step of choosing said perforations to have hexagonal shapes.

30. The method of claim 28, further comprising the step of choosing said electric potentials (600A) applied by said drivers to said electrodes to be non-conservative to allow a transfer of energy between said charged particles confined within said potential well and an environment external to said electric potential.

31. The method of claim 26, further comprising the step of choosing each of said perforations to have a hexagonal shape of a selected diameter of approximately 2R0 and spacing any two consecutive electrode sheets apart by a distance of approximately R0/13, where R0 is a distance from the center of each hexagonal perforation to a vertex thereof.

44a

32. The method of claim 26, further comprising the step of choosing said electric potential (600A) applied to said electrode sheet number j to have the form P(j,t) =.PHI.0 Sign [A(j,t)]~ A(j,t)~

s(j,t) sin(.omega.t), where A(j,t)=cos[2.pi.f(j,t) w(j,t)-k(j,t)], where t is a time variable, .omega. is a selected angular frequency, .PHI.0 is a selected electrode potential amplitude, and f(j,t), s(j,t), w(j,t) and k(j,t) are time-dependent functions selected for said electrode sheet number j.

33. The method of claim 32, further comprising the step of choosing said functions f(j,t), s(j,t), w(j,t) and k(j,t) so that, for at least one of said integers j, said charged particles lose net energy when said charged particles are adjacent to said electrode sheet number j.

34. The method of claim 26, further comprising the step of connecting at least one of said electrode sheets to a source of ground potential through a path that has a selected electrical resistance.

35. The method of claim 26, further comprising the step of connecting at least two electrode sheets to each other through a path that has a selected electrical resistance.

36. The method of claim 26, further comprising the step of providing a low pressure gas of neutral particles surrounding said electrode sheets and allowing particles of this gas to undergo collisions with said charged particles, to thereby reduce kinetic energy of said charged particles.