US2555850A - Ion trap - Google Patents

Description

June 5, 1951 I GLYPT|$ 2,555,850

ION TRAP Filed Jan. 28, 1948 I hwnim- M66 014233.

iatented June 1951 UNITED STATES ?ATENT OFFICE ION TRAP Nicholas D. Glyptis, Chicago, Ill.

Application' January 28, 1948, Serial No. 4,757

11 Claims.

, The present invention relates to the control of ions and electrons in electron discharge tubes.

Electrons are negatively charged minute particles which are planetary to nucleus to form atoms. Whenever an atom loses or gains one or more electrons it is called an ion. A positive ion lacks one or more electrons while a negative ion possesses one or more extra electrons.

In cathode ray tubes, whether they be gas filled orhigh vacuum, a stream of electrons are emitted from a cathode and directed to impinge upon a target such as an electrode, a fluorescent screen or a photographic plate. Generally, the cathode is indirectly heated and surrounded by a grid structure comprising a disc having an aperture through which the stream of electrons are emitted.v The emitted stream is conducted through accelerating and focusing elements including masking apertures to provide a beam of reasonably small section when it strikes the target.

However, it has been found that negative ions which are very deleterious to a high potential target ,such as a fluorescent screen, are present in large quantities in the beam. These negative ions emanate from positive ion bombardment of the cathode surface which, when thereby bombarded, surrenders negative ions. A further source of negative ions arises wherever positive ions strike other electrodes or atoms are hit by electrons. V

Negative ions reaching the target give up their extra electrons by low 'velocity transition, become sluggish atoms manifested by deposits on the target sometimes referred to as black coat, ion spot or ion cross. This impairs operation, deteriorates the target, and shortens tube life.

Efforts have been made heretofore to remove the negative ions from the cathode ray but they have been less than 50% effective in most cases,

and those which are the best distort the beam from its highly desirable round-pencil form. Moreover, ion traps heretofore used do not remove negative ions developed by ionization taking place within the lens system of cathode ray tubes. Not only this, but the adjustment and operation of existing traps are delicate and easily unbalanced.

A principal object of the present invention is to trap and harmlessly disperse practically all of the negative ions in devices employing electron guns before the target is impinged by the beam, particularly those where a stream of electrons is beamed to strike fluorescent screens. I

A further object is to provide a cathode ray tube in which a magnetic flux causes different trajectories to exist between the paths of electrons and the negative ions to eliminate the latter without need for extra or additional prongs or external equipment on the tube. 7 3

Another object of the invention is to accelerate a columnated cathode ray sufiiciently that negative ions therein have an. inertia which carries them through a magnetic field with little if any deflection.

A further object of the invention resides in de-' focusing negative ions along a collision trajectory while simultaneously focusing a stream of electrons to a round beam form to clear a barrier.

The invention is further characterized by separating ions from an electron beam at the last limiting aperture of the electron gunbefore it is put into use with a screen or target.

These being among the objects of the inven-' tion, other and further objects, including simplicity of construction and of operation, will appear from the drawing, the description relating thereto, and the appended claims.

Referring to the drawing:

Fig. l is a plan view, partly diagrammatical, showing a cathode ray television tube 'embod'y ing the invention; and

Fig. 2 is an enlarged longitudinal section through the gun portion of the tube illustrating the structural characteristics of the embodiment of the invention.

Although the invention may find embodiment with external ring-like electromagnets if a uni potential lens is split, it is preferred to employ an internal axial permanent magnet, sometimes referred to as a ring magnet, located between two axially spaced windows or apertures of the focusing electrode or just ahead of the last aperture through which an electron beam is confined to flow. The inner margin of the ring magnet is located slightly outside the path of direct flow between the two windows, and the downstream or exit window is made smaller than the upstream orentrance window.

With this arrangement the electron flow diverges slightly as it passes beyond the entrance window. Then when it reaches the concentrated restricted field of the magnet, the field of flux which is generally parallel to the tube axis at this point will sharply deflect the flow of electrons to initiate convergence as the flow approaches the exit window. However, the negative ions, being heavier, do not respond appreciably to the magnetic field deflection as rapidly as the lighter electrons, and their inertia due to accelerated speed persists sufiiciently that they continue along a diiferent trajectory and strike the marginal wall around the last window where their effect is dissipated as heat, or as a deposit, or bounce back as harmless atoms. The electrons in the flow are converged suiiiciently to pass as a circular beam through the last window substantially free of harmful negative ions for use beyond the window without appreciable loss of electrons.

Tests have revealed that 90% of the negative ions can thereby be eliminated and the remaining 10% disperse themselves without reaching the target to which the electron beam is directed, thus reducing fouling, improving longevity, and eliminating the need for other elements to inhibit or remedy damage done by negative ions. Moreover, given a predetermined emissivity more electrons will be conserved and concentrated for use in the resulting beam than heretofore possible with conventional ion traps.

The invention is illustrated in connection with a cathode ray tube such as a television tube in. The electron emitter comprising a filament (not shown) surrounded by a cup is indicated at H as located inside the usual control grid [2 which has a window l3 through which electron-ion generation is emitted along the axis 40 of the cylindrical portion M of the tube. The electron component of the emission is represented in broken lines 38 while the ion component is represented in dotted lines 4|.

From the grid the emission passes through an accelerating anode l5 into the focusing device or electrode l6 which constitutes the structure shown in Fig. 2. Acceleration is desirable be cause it increases the velocity and therefore the inertia of the negative ions to carry them along a predetermined trajectory.

The focusing device preferably comprises a metal plate member l1 having an entrance window or aperture 3 therethrough at the narrow end of an outwardly extending frusto-conical wall 20. The plate member -il covers a metal cup-member 2l having cylindrical sides upon which inward protuberances 22 are preferably provided halfway down its sides. The bottom wall 23 of the cup member is symmetrical sectionally with respect to the plate ll except that a radial flange 24 is provided on the narrow end of the frusto-conical portion 20a, which flange 24 has an exit opening 25 of a size smaller than the entrance opening H3. The inner face of the flange around the opening 25 will be referred to generically as an interception or collision wall 25.

An axial or ring magnet at having an inside diameter approximately the same as the wide portion of the frusto-conical walls 29 and 29a is mounted coaxially with and preferably midway between openings [8 and 25 by glass heads 3! fusedto the protuberances 22, the magnet being mounted in the cup 2| before the plate 1! is secured in place in any suitable way establishin electrical connection. If not electrically connected to provide the same potential, the focusing action may be controlled by varying the potential between the two Walls 29 and 26a as desired. in which case it is preferred to have the second window at higher potential to take further advantage of a divergence of the negative ion trajectory ahead of the window 25. which would accompany same. Moreover, although the magnet may be connected to the same potential, it is preferred to connect it to a diiferent potential than the walls 20 or 28a to give it static as well as magnetic properties.

Beyond the focusing device, a second or high potential anode 35 may be provided, and either the usual static deflection pairs of plates 36 shown or magnetic deflecting coils can be used which deflect the focused beam to strike the screen 3'! in a calculated way.

In the embodiment shown, the windows I8 and 25 of the focusing electrode are statically charged positive preferably at the maximum voltage on the anode 35 and the resulting action is to accelerate and focus the emissions from the oathode axially through the windows, the rays of emissions converging as they leave the focusing electrode to meet at a pencil point upon the screen.

However, having a calculated field of magnetic force and a calculated distance or difference in potential between the openings l8 and 25, the ions in their flight 4| are not deflected enough to pass through the smaller opening 25. They strike against the interception barrier 26 where they give up their negative charge and they rebound they leavev as harmless atoms which ultimately travel back to the grid or cathode.

Thus a diverging electron optical action of an immersion lens or a unipotential lens even when one electrode is lower in potential than eitheror both of the other two, can be balanced for electrons by calculating a collision electron trajectory therethrough, contracting electron trajectory by a restricted axial magnetic field so that the electron beam goes through a limiting aperture while the ion stream is defocused along the calculated collision trajectory with little deflection due to the magnetic component, or otherwise diffused to a tolerable ion concentration.

What is claimed is:

1. In a cathode ray tube the combination of an electron discharge cathode and a control electrode aligned with said cathode for. generating a cathode ray, and an aligned focusing electrode including a barrier disposed around the center line of the ray, said barrier forming an element in a lens system, and magnet means disposed in front of said barrier and surrounding the ray for subjecting the cathode ray to magnetic flux at a predetermined point of concentration spaced from the barrier.

2. In a cathode ray tube the combination of an electron discharge cathode and control electrode for generating a cathode ray, a barrier having an opening at the center line of the ray, said barrier forming an element in a lenssystem, means disposed in front of said barrier and, surrounding the ray for subjecting the cathode ray to magnetic lines of flux parallel to said ray at a predetermined point of concentration spaced from the barrier to converge the electron stream at the opening in the barrier.

3. An ion trap for electron discharge tube comprising a unipotential lens having an entrance aperture and an exit aperture, said aper-- tures being axially spacedand. aligned and the exit aperture being smaller as defined by a surrounding collision barrier, and a ring magnet disposed between said apertures defining an opening larger than the entrance aperture.

4. An ion trap for electron discharge tubes comprising a lens having'an entrance; aperture and an exit aperture, said apertures. being axially spaced and aligned and the exit aperture being smaller as defined by a surrounding: collision barrier, and a ring magnet disposed between said apertures having an opening coaxial'with. the exit aperture.

5. In a cathode ray device the combination of a barrier having an opening therethrough, means for directing a stream of electrons and negative ions towards the barrier, and a magnet spaced from the barrier ahead of it for converging the stream of electrons at the opening in the barrier.

6. In a cathode ray device the combination of a plurality of spaced barriers having openings therethrough, means for directing an electron beam through two of the openings and a portion thereof against the last barrier, and a magnet spaced from the last barrier ahead of it for deflecting the flow of said electrons to converge the beam through the opening in the last barrier, leaving the flow of the heavier negative ions to collide with the last barrier.

7. A unipotential lens for cathode ray tubes including two spaced barriers having aligned windows, one barrier of which has a smaller window in it than the other, and magnet means disposed between said barriers and defining an opening aligned with said windows of a size larger than the larger window.

8. A unipotential lens for cathode ray tubes including two spaced walls having aligned windows, one window of which is smaller than the other, and a magnet disposed between said walls and defining an opening aligned with said windows of a size larger than the larger window.

9. A unipotential lens for cathode ray tubes comprising two spaced walls having aligned windows, one an exit window which is smaller than the other, and ring magnet means disposed between said walls and defining an opening aligned with said windows of a size larger than said other window.

10. A combination beam focusing and ion trap device for electron discharge tubes comprising a lens having entrance and exit electrodes defining an entrance aperture and an exit aperture respectively, said electrodes being charged electrostatically, and said apertures being axially spaced and disposed in aligned relationship on the tube axis, said exit aperture being smaller than the entrance aperture, a ring magnet disposed between said apertures and coaxial therewith, and means for varying the electrostatic potential of said magnet.

11. An ion trap for electron discharge tubes comprising a lens system coaxial with the tube axis and adapted to focus a cathode ray, said lens system containing a barrier having an opening, means producing an effective magnetic field in advance of said barrier and surrounding said cathode ray whereby the electrons of said ray are focused through the barrier opening and the ions of said ray are intercepted by said barrier.

NICHOLAS D. GLYPTI'S.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,942,572 Rogowski et al Jan. 6, 1934 2,149,101 Ploke Feb. 28, 1939 2,181,850 Nicoll Nov. 28, 1939 2,138,579 Schlesinger Jan. 30, 1940 2,211,613 Bowie Aug. 13, 1940 2,212,206 Holst Aug. 20, 1940 2,274,586 Branson Feb. 24, 1942 2,454,345 Rudenberg Nov. 23, 1948 2,455,474 Wainwright Dec. 14, 1948 2,455,977 Bocciarelli Dec. 31, 1948 2,460,609 Torsch Feb. 1, 1949 2,472,766 Woodbridge June 7, 1949 2,496,127 Kelar Jan. 31, 1950 2,498,354 Bocciarelli Feb. 21, 1950 2,499,065 Heppner Feb. 28, 1950 2,500,455 Fisher Mar. 14, 1950 2,503,173 Reisner Apr. 4, 1950 FOREIGN PATENTS Number Country Date 440,560 Great Britain Dec. 30, 1935 464,637 Great Britain Apr. 21, 1937 498,491

Great Britain Jan. 9, 1939

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