US2932768A - Magnetic electron multiplier - Google Patents

Description

April 12, 1960 w. c. WILEY MAGNETIC ELECTRON MULTIPLIER 2 Sheets-Sheet 1 Filed 001,. 21. 1955 wumnom um Bm INVENTOR. WILLIAM C. WILEY BY ATTORNEY April 12, 1960 w. c. WILEY 2,932,768

MAGNETIC ELECTRON MULTIPLIER Filed Oct. 21, 1955 2 Sheets-Sheet 2 POTENTIAL DISTANCE ALONG PLATE 36 IN VEN TOR.

4 WILLIAM c. WILEY AT ORNEY United States Patent 2,932,768 MAGNETIC ELECTRON MULTIPLIER Application October 21, 1955, Serial No. 542,057 6 Claims. c1. SIS-39.63)

This invention relates to magnetic electron multipliers.

In copending application Serial No. 531,878 filed September 1, 1955, now Patent No. 2,841,279, by William C. Wiley there is disclosed a novel magnetic electron multiplier of continuous plate construction which includes a pair of plates disposed in substantially parallel relationship and having a conductive coating on the inner surface of each plate. When a current fiow is passed through each conductive coating an electric field is pro vided in the region between the plates to cause any electrons in the region to travel in cycloidal paths and to successively strike the conductive coating of one of the plates so as to produce a multiplication of the electrons.

This invention relates to the use of conductive strips on the conductive coatings of the above mentioned continuous plate multipliers. By applying different voltages to such strips, the electric field at dilierent positions in the multiplier may be varied to produce a desired action upon any electrons traveling in the multiplier. For eX- ample, the electrons may be subjected to a gating action in this manner.

-An object of this invention is to control the flow of electrons in magnetic electron multipliers of continuous plate construction.

Another object of this invention is to provide conductive strips on the surface of the plates of such multipliers and to apply different voltages to the strips to vary the electric field in the region between the plates.

A further object of this invention is to provide a gating action on electrons flowing in a magnetic electron multiplier.

Other objects and advantages will become apparent from the following detailed description and from the appended claims and drawings.

In the drawings:

Figure 1 is a perspective view, partly in block form, of a magnetic electron multiplier including a plurality of conductive strips which together constitute an embodiment of this invention.

Figure 2 is a plan view of the electron multiplier in Figure 1 showing the electron flow under certain conditions in the multiplier.

Figure 3 is a plan view of the electron multiplier in Figure 1 showing the electron flow under diiferent conditions in the multiplier.

Figure 4 is a graph of the potential along the conductive coating of the multiplier in Figure 1.

.In .one embodiment of the invention a source is adapted to emit particles. For example, the source 10 may be a mass spectrometer adapted to emit ions for travel towards a plate 12 having a secondary emissive surface. Positioned adjacent to the plate 12 is a magnetic electron multiplier of continuous plate construction generally indicated at 14. The multiplier 14 includes a pair of substantially parallel plates 16 and 18 which are spaced from each other a distance such as /8 of an inch. The

plates 16 and '18 are made of an insulating material such as glass or Bakelite.

The plate 16 is provided with a conductive coating 20 on its inner surface and a similar conductive coating 22 is provided on the inner surface of the plate 18. The conductive coating consists of a secondary electron emissive material having a relatively high resistance, such as a tin oxide or carbon compound.

Conductive strips 24, 26, 28, 30, 32 and 34 are provided on the surface of the conductive coating 20, The conductive strips extend transversely of the plate 16 and are made of a material having a very low resistance, such as silver which may be sprayed on the conductive coating or deposited in any other suitable manner. Similarly, conductive strips 36, 38, 40 and 42 are provided on the surface of the conductive coating 22 in substantial alignment with the strips 24, 30, 32 and 34 on the coating 20.

An anode plate 44 is disposed in substantially perpendicular relationship to the plates 16 and 18 to receive any electrons flowing through the region between the plates. The anode 44 is connected through a resistance 46 to a power supply 48 which applies a direct voltage such as zero volts to the anode.

The power supply 48 is also connected to the conductive strips 32 and 34 through a resistance 50 and may apply a direct voltage, such as zero volts to these strips. The strips 32 and 34 are also connected through a capacitance 52 to a pulse source 54. The pulse source is adapted to introduce to the conductive strips 32 and 34 a negative square wave voltage pulse, such as -130 volts. The pulse source may be set to apply this pulse at any desired time. For example, Model 902 of a Double Pulse Generator manufactured by the Berkeley Scientific Instrument Company of Richmond, California may be adapted to introduce such pulses to the strips 32 and 34. This model generator is fully disclosed in a publication entitled Instruction Manual, Berkeley Double Pulse Generator, Model 902 issued by the Berkeley Scientific Company in August 1950.

Direct voltages, such as l00, +100, 25, +25 are applied, respectively, to the conductive strips 24, 26, 28

and 30 from the power supply 48. The curve A in Figure 4 represents a plot of these voltages along the coating 20. Similarly, the power supply 48 applies direct voltages such as -600, and -l25 volts, respectively, to the conductive strips 36, 38 and the strips 40 and 42 which have a common connection. The curve B in Figure 4 represents a plot of these voltages along the coating 22. A direct voltage, such as 800 volts is also applied to the plate 12 from the power supply 48.

A pair of pole pieces 56 are disposed above and below the plates 16 and 18 to provide a magnetic field in the region between the plates in a vertical direction and substantially parallel to the face of the plates. For example, a magnetic field of 300 gauss may be provided by the pole pieces 56.

The application of different voltages to successive conductive strips on a coating causes a particular amount of current flow through the coating between the successive strips. This results in a uniform voltage drop or rise between successive strips as is illustrated by the curves A and B in Figure 4. Since the same voltage is applied to the strips 32 and 34 and to the strips 40 and 42, no current flow or voltage change occurs between these strips. The electric field produced in the region between the coatings 20 and 22 is determined by the dilference in potential between the coatings. Therefore, the magnitude of the electric field in the region varies in accordance with the difference between the curves A and B in Figure 4.

It will be noted that the magnitude of the field is great 3f est in the region defined between the strips, 24 and 26. In the region between the strips 26 and 28 the field is considerably reduced to a particular value at the strip 28 and in the region between 28 and 30 the field is moderately reduced to a particular value at the strip 30.

Thereafter the electric field is maintained at a constant magnitude in the regions between the strips 30 and '32 and between the strips 32 and 40. However, the potential of the coatings 20 and 22 is reduced between the strips 30, 32 and 38, 40, respectively, while the potential'rern-ains the same between the strips 32, 34 and 40, 42.

Particles from the source are emitted towards the plate 12. When these particles impinge upon the plate 12, the'plate emits a proportionate numberof electrons. Because of the combined action of the magnetic and electric fields in the region between the plates 16 and 18, the electrons emitted by the plate 12 travel in a cycloidal path 70 and impinge upon the conductive coating 22 which in turn emits a proportionately increased number of electrons which in turn travel in a cycloidalpath 72. In this way, successively emitted electrons travel across the surface of the coating 22 in successive cycloidal paths as shown in Figure 2 to multiply the number of electrons initially emitted by the plate 12. Although for convenience the electrons are shown traveling a path of a common cycloid, the electrons may also travel in the paths of curtate cycloids or prolate cycloids;

It will be noted that electrons travel in a larger cycloidal path in the region between the strips 24 and 26 since the electric field is greatest in this region. The cycloidal paths become progressively smaller in the region between the strips 26 and 30 because of the reduction of closed above, the gate is highly efficient because substantially all of the electrons in the multiplier are passed through the gate when it is opened. Other type electron multiplier gates are not as efiicient because they receive and pass only a portion of the electrons.

It will be recognized by persons skilled in the art that i the conductive strips may be of difierent types than that .disclosed. For example, the strips may actually be the magnitude of the electric field.- In the region between the strips 30 and 34, the electrons travel in cycloidal paths of the same size since the electric field remains the same. However, since the potential of the coatings 20 and 22 is reduced between the strips 30, 32 and strips 38, 40, respectively, the electrons in the region defined by these strips do not further strike the coating 22. Instead, the electrons rise from the coating 22 and travel through the region between the strips 30 and 34 along an equipotential line until they impinge upon the anode 44 as shown in Figure 2.

When a negative voltage pulse, such as -130 volts, is applied to the strips 32 and 34, the electric field in the region between the strips 30 and 32 is reduced and the electric field in the region between the strips 32 and 34 is actually reversed as shown by the dotted line in Figure 4. Because of this change in the electric, field the electrons emitted from the surface of the coating 22 are prevented from passing through the region between the strips 32 and 34 and instead are deflected towards the conductive coating 20 as shown in Figure 3 where the electrons impinge upon the coating and are absorbed.

in the manner disclosed above, the region between the strips 32 and 34 acts as a gate to pass or prevent the passage of electrons. During the period that no pulse is applied to the strips 32 and 34, the electric field in the region is in a direction to cause the electrons to move through the region as shown in Figure 2 so as to impinge upon the anode 44 for detection. However, when a negative voltage pulse is applied to the strips 32 and 34 from the pulse source 54, the electric field in the region is actually reversed and electron passage through the region is blocked.

The invention disclosed above has several important advantages. By using conductive strips at various positions on the conductive coating, the electric field in a multiplier can be changed to any desired value so as to produce a desired action on electrons. The provision of the conductive strips is very simple and inexpensive and their use makes possible a highly versatile multiplier which can be readily adapted for many purposes; in the use of the conductive strips for gating purposes as diswires which are attached to or imbedded in the conductive coating;

Furthermore, the strips may be placed on the coating in directions other than the transverse direction to obtain a desired movement of the electrons. For example, the strips may be placed on thecoating in a lengthwise direction to produce an electric field in a direction to cause electrons traveling in the lengthwise direction to be deflected in a transverse direction so as to be received by an anode which may be placed on the side of the electron multiplier plates. Also, the strips'may be of any desired configuration. For example, the strips may be curvilinear'in shape to provide a certain type electric field for special applications.

Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent topersons skilled in the art. 1 The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

What is claimed is:

l. A magnetic electron multiplier, including, a first plate, a second plate disposed a particular distance from the first plate to define a first region between the first and second plates, at least one of the plates having a secondary emissive surface facing the first region, means for producing a flow of current through the first and second plates to provide in the first region an electric field having a component in a direction substantially perpendicular to the plates, at least one strip of conductive material on the surface of the first plate, means for applying a voltage to the strip to produce a change in the current flow in the first plate and a corresponding change in the electric field in the first region, and means for providing a magnetic field in the first region in a direction substantially perpendicular to the electric field.

'2. A magnetic electron multiplier, including, a first plate, a second plate disposed a particular distance from the first plate in substantially parallel relationship to the plate to define a first region between the'first and second plates, at least one of the plates having a secondary einisv sive surface facing the first region, a first conductive coating of relatively high resistance on a surface of the first plate, a second conductive coating of relativelyhigh resistance on a surface of the second plate, means for producing a flow of current through the first and second coatings to provide in the first region a uniform electric field having a component in a direction substantially perpendicular to the plates, at least one conductive strip of relatively low resistance on the surface of the first conductive coating, means for applying a voltage to the strip to produce a change in the current flow in the first con ductive coating and a corresponding change in the electric field in the first region, and means for providing a mag netic field in the first region in a direction substantially face of the first plate facing the first region, a second;

conductive coating of relatively high resistance on a surface of the second plate facing the first region, at least one of the conductive coatings being secondarily emissive, a first plurality of conductive strips of relatively low resistance on the surface of the first conductive coating, the strips in the first plurality being spaced from one another and being disposed in substantially parallel relationship with respect to one another, means for applying idifierent voltages to the strips in the first plurality to produce different amounts of current flow in the first conductive coating between adjacent strips and to produce a variation in the potential along the surface of the first conductive coating, a second plurality of conductive strips of relatively low resistance on the surface of the second conductive coating, the strips in the second plurality being spaced from one another and being disposed in substantially parallel relationship with respect toone another, means for applying different voltages to the strips in the second plurality to produce difierent amounts of current flow in the second conductive coating between adjacent strips and to produce a variation in the potential along the surface of the second conductive coating for providing in the first region a variable electric field in accordance with the diiferencc in potentials along the first and second conductive coatings, and means for providing in the first region a magnetic field in a direction substantially perpendicular to the electric field and substantially parallel to the plate.

4. A magnetic electron multiplier, including, a first plate, a second plate disposed a particular distance from the first plate in substantially parallel relationship to the plate to define a first region between the first and second plates, a first conductive coating of relatively high resistance on a surface of the first plate contiguous to the first region, a second conductive coating of relatively high resistance on a surface of the second plate contiguous to the first region, at least one of the conductive coatings being secondarily emissive, a plurality of conductive strips of relatively low resistance on the first and second coatings extending in a transverse direction across the coatings and being spaced from one another at various intervals in a longitudinal direction on the coatings, means for applying various voltages to the strips to produce varying potentials along the first and second coatings and to provide in the first region an electric field variable in a longitudinal direction in accordance with the potential ditference of the coatings, means for providing in the first region a magnetic field in a direction substantially perpendicular to the electric field and parallel to the plates. 1

5. A magnetic electron multiplier, including, a first plate, a second plate disposed a particular distance from the first plate in substantially parallel relationship to the 1 facing the first region, a second coating of conductive material having a relatively high resistance on a surface of the second plate facing the second region, at least one of the coatings being secondarily emissive, a plurality of conductive strips of relatively low resistance on the first and second coatings, the strips being spaced apart in a longitudinal direction on the coatings and being disposed in substantially parallel relationship with respect to one another, means for applying various voltages to the strips to produce varying potentials along the first and second coatings in a longitudinal direction and to provide in the first region an electric field variable in accordance with the potential difference between the coatings, means for applying a voltage pulse to at least one of the conductive strips on the first coating to produce a change in the po-.

tential of the coating and a corresponding change in the electric field in the first region during the application of the voltage pulse, and means for providing in the first region a magnetic field in a direction substantially perpendicular to the electric field and parallel to the plates.

6. A magnetic electron multiplier, including, a first plate means, a second plate means disposed a particular distance from the first plate means to define a first region between the first and second plate means, at least one of the plate means having a secondary emissive surface facing the first region, means for producing a flow of 7 current through at least one of the plate means to provide in the first region an electric field having a component in a direction substantially perpendicular to the plate means, at least one strip of conductive material being on the surface of said first plate means, means for applying a voltage to the strip to produce a change in the electric field in the first region, and means for providing a magnetic field in the first region in a direction substantially perpendicular to the electric field.

References Cited in the file of this patent UNITED STATES PATENTS 2,141,322 Thompson Dec. 27, 1938 2,147,825 Zworykin Feb. 21, 1939 2,160,799 Teal May 30, 1939 2,779,811 Picciano et a1. Ian. 29, 1957

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