US3693004A

US3693004A - Reflex type electron multiplier

Info

Publication number: US3693004A
Application number: US51476A
Authority: US
Inventors: Emil E Sanford
Original assignee: Monsanto Co
Current assignee: Monsanto Co
Priority date: 1970-07-01
Filing date: 1970-07-01
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19

Abstract

Described herein is an electron generating device comprising a tubular member whose inner walls are covered with a resistive, secondary-electron emissive coating. One section of the tubular member is curved and extends between electrical contacts provided on the secondary-electron emissive coating. Another section of the tubular member is substantially straight. It too, extends between the electrical contacts, and forms, together with the curved section, a continuous, reflex-type particle path around the tubular member. An electron exit aperture is provided near one of the contacts and a D.C. power supply is connected to the contacts. Electrons are multiplied or amplified along the curved section of the tubular member and resulting positive ions are fed back along the straight section to liberate further electrons for amplification. Electrons egress through the exit aperture in a defined path. For enhanced electron beam generation, a tubular, toroidal-shaped embodiment of the invention is also described.

Description

United States Patent Santord 1 Sept. 19,1972

1541 REFLEX TYPE ELECTRON MULTHPLIER [72] Inventor:

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: July 1, 1970 [21] Appl. No; 51,476

Yellin et al.; Ion Detection Using a Continuous Channel Electron Mutliplier, The Review of Scien- Emil E. Sanford, Montclair. NJ.

tific Instruments, volume 41, number 1, January 1970, page 18 cited.

Primary Examiner-Robert Sega] Att0rneyJohn D. Upham, William J. Bethurum and Harold R. Patton [5 7] ABSTRACT Described herein is an electron generating device comprising a tubular member whose inner walls are covered with a resistive, secondary-electron emissive coating. One section of the tubular member is curved and extends between electrical contacts provided on the secondary-electron emissive coating. Another section of the tubular member is substantially straight. It too, extends between the electrical contacts, and forms, together with the curved section, a continuous, reflex-type particle path around the tubular member. An electron exit aperture is provided near one of the contacts and a DC. power supply is connected to the contacts. Electrons are multiplied or amplified along the curved section of the tubular member and resulting positive ions are fed back along the straight section to liberate further electrons for amplification. Electrons egress through the exit aperture in a defined path. For enhanced electron beam generation, a tubular, toroidal-shaped embodiment of the invention is also described.

1 Claim, 3 Drawing Figures POWER SUPPLY REFLEX TYPE ELECTRON MULTIPLIER FIELD OF THE INVENTION BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART In the field dealing with the generation of electrons and electron beams, it has been the general practice to employ a directly or indirectly heated cathode electrode comprising, or coated with, a suitable electronemitting metal or metal oxide to obtain electron emission. In addition to requiring a filament (indirect heating) or a high cathode current (direct heating), such electron sources have a lifetime limited by the particular characteristics of the metal, metal alloy or oxide coated upon the cathode.

The general purpose of this invention is to provide an electron generating device which embraces advantages of similar electron sources, yet is nontherrnionic in nature and may have a substantially longer lifetime. That is, it does not require the generation of substantial heat, nor require substantial electrical power for its operation. To attain this purpose, the present invention utilizes a unique, reflex tubular member having a specially treated inner wall suitable for multiplying electrons and simultaneously providing positive ions which may be employed to stimulate the emission of additional electrons for further multiplication.

An object of the present invention is the provision of an electron emitting device which does not require or produce substantial heat dissipation.

Another object of the present invention is the provision of an electron generating device which sustains its own operation independent of an external, stimulating source.

Still another object of the present invention is the provision of a self-sustained, electron-emitting device which employs ions feedback to further stimulate the generation of an electron beam.

In the present invention these purposes (as well as others apparent herein) are achieved generally by enclosing a reflex, tubular member in an evacuated envelope. The tubular member has first and second tubular sections intermediate positive and negative electrical contacts, one section defining a curved, electron amplifying path and the other section defining a positive ion path. At least the first section has its inner wall covered with a resistive, secondary-electron emissive coating. The tubular member is further provided with an electron exit aperture located in close proximity to the positive electrical contact. A D.C. potential is applied to the electrical contacts, thereby to establish an electron-accelerating field along the curved section path, and an ion-accelerating field along the straight section.

Electrons within the tubular curved section are accelerated and bombard the secondary-electron emissive coating to produce a multiplicity of electrons. These are greatest in quantity at the end of the curved (circular) path, i.e. near the positive contact. The energetic electrons strike the emissive coating and the contact with the ability to ionize these materials. The resultant ions are vigorously attracted to the negative contact to create further ions and electrons. These electrical particles further populate the paths and in turn recreate more electrons, and provide for the excess electrons spraying out of the electron exit aperture.

BRIEF DESCRIPTION OF THE DRAWINGS Utilization of the present invention will become apparent to those skilled in the art from the disclosures made from the following description, as illustrated in the accompanying drawings; in which FIG. 1 is a perspective, schematic view (brokenaway in part) illustrating the principle of operation of an electron emitting device constructed in accordance with the present invention;

FIG. 2 is a cross-sectional view of a toroidial-shaped embodiment of the electron generating device of the present invention; and

FIG. '3 is a view of the device of FIG. 2 looking toward its electron exit aperture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring now to the drawing, wherein like reference characters designate like or corresponding parts .throughout the several views, there is illustrated in FIG.

1 a nonthermionic electron generating device, generally designated 10. The electron generating device 10 is shown positioned within an evacuated envelope 12, which for example, may take the form of a sealed glass tube such as that employed for cathode ray tubes, electronic vacuum tubes, and the like. It should be apparent to one skilled in the art, that the electron generating device may be supported in the envelope 12 by any suitable, conventional means such as glass rods, or the like, and therefore such support means are not shown in the drawing. Furthermore, it should be understood that the drawings are not necessarily to scale and that the device 10 may be extremely small in comparison to the envelope 12.

The electron generating device 10 of FIG. 1 may take the form of a reflex tubular member 14 formed from glass tubing, or the like, having a typical inside diameter of 0.01 inch. It is comprised of an electron-accelerating path section, designated 16, whose longitudinal axis is curved and an ion-accelerating path section, designated 18, which is substantially straight. The two

sections

16 and 18 are interconnected and together form a continuous, generally annular, elongated chamber.

Electrical contacts

20 and 22 are provided at spacedapart locations on the tubular member 14. One contact 20 is positioned at the intersection of the curved section 16 and the straight section 18, whereas the other contact 22 is positioned upon and extends away from a short projection positioned outward of the intersection of the other end of the curved section 16 and the straight section 18.

The innerwall surfaces of the tubular member 14 are coated with a resistive, secondary-electron emissive material, such as a lead bismuth glass, or similar material having a relatively high-resistance, secondary electron emission characteristic. This coating is best seen in FIG. 1 at the broken-away section and is generally designated by reference numeral 24. It should be apparent that the secondary-electron emissive coating 24 is electrically connected to the

contacts

20 and 22. More specifically, the electrical contact 22 may be deposited or affixed to the outer surface of the tubular member but an extension (not shown) is provided to extend through the tubular member 14 to contact the emissive coating 24. Similarly, the electrical contact 22 may be deposited or secured to the outer surface of the member 14 but formed so as to wrap around and extend into the inner chamber of the tubular member 14, thereby making electrical contact with the secondaryelectron emissive coating 24.

The

electrical contacts

20 and 22 are electrically connected, by means of a switch 30, to the negative and positive terminals, respectively, of a DC. power supply 26 preferably located externally to the evacuated envelope 12.

The tubular member 14 is further provided with an electron-exit aperture 28 at or near the electrical terminal 22. In this manner, the electron-exit aperture 28 of the electron generating device 10 defines an egress path for electrons which are generated and accelerated within the tubular member 14. It should be apparent to one skilled in the art that the beam of exiting,electrons can then be directed to a utilization device (not shown) by conventional accelerating and/r deflecting electrodes, and the like.

In describing the operation of the electron generating device 10 of FIG. 1, let it be assumed that the resistance of the secondary-electron emissive coating 24 is of the order of 500 megohms and that the DC. power supply provides a potential of approximately 1,500 volts. Upon the closing of switch 30, it follows that a very small current of approximately 5 microamps flows in the secondary-electron emissive coating 24, such current resulting in very little heat dissipation. However, the application of the high D.C. potential establishes a strong electrical field within the device between its

electrical contacts

22 and 24. Any stray or thermally excited electrons within the curved tubular section 16 are accelerated by this electric field and tend to move in a straight line toward the positive contact 22. In so doing the electrons bombard the emissive coating 24, as indicated by the arrows 32 in FIG. 1. The bombardment of each electron results in impact ionization which liberates secondary electrons from the coating 24. These released electrons move in the direction of the electrical field releasing or liberating further electrons. This multiplication of electrons continues throughout the curved section 16 of the electron generating device 10, until the accelerated electrons reach the exit aperture 28. There the electrons exit the electron generating device 10.

Thus, the curved section 16 of the tubular member 14 serves as an electron accelerating and multiplying path. Its curvature not only insures that electrons once liberated from the coating 24 will strike the coating to release further electrons, but further prevents positive ions, resulting from impact ionization from moving in the opposite direction through the curved section 16. This follows, in part, because the ions are of much greater mass than the electrons and the curvature of the curved section 16 prevents them from achieving high velocities before they impact the inner wall of the tubular member 14. Thus, the ions, so generated, tend to recombine.

However, positive ions which are generated at or in close proximity to the intersection of the straight section 18 and the curved section 16 of the tubular member 14 are accelerated by the strong electrical field established between the electrical terminal 22 and the electrical terminal 20. The straight section 18 does not impede the acceleration of these ions, as the curved section does, and they move at high velocities to the electrical terminal 20. The movement of the ions terminates when, they collide with and bombard the terminal 20 and the secondary-electron emissive coating 24. This bombardment releases further electrons which then begin the multiplication progression around the curved section 16 of the tubular member 14 in the manner aforedescribed.

Thus, it should be apparent that the electron generating device 10 employs a positive ion feedback technique which sustains the electron generation. In this manner, the electron generating device 10 provides a beam of electrons which may be utilized in the manner of that associated with other electron generators. However, in contrast, the electron generating device 10 does not employ a filament heater, or other thermionic emission mechanisms.

Referring now to FIGS. 2 and 3, there is shown an electron generating device 10, similar in operational principle to the electron generating device 10 of FIG. 1, but generally toroidal in overall shape. The toroidal, election generating device 10 has a configuration obtained by the rotational expansion of the device 10 of FIG. I. As such, the device 10 provides a multiplicity of electron and ion paths for generating a higher density beam.

The electron generating device 10' has an annular glass core 32 and an outer shell 34, being spaced-apart to define the electron and positive ion accelerating paths of the electron generating device 10'. The innerwall of the outer shell 34 and the core 32 are provided with a resistive, secondary-electron emissive coating 24', similar to that described with reference to the device 10 of FIG. 1.

Appropriate negative and positive electrical contacts 20' and 22' are deposited on the inner core 32 and the outer shell 34. These electrical contacts are generally annular in shape, as may be best seen with reference to FIG. 3, and correspond to the

electrical terminals

20 and 22 of FIG. 1. For purposes of clarifying the illustration of this embodiment of the electron generating device of the present invention, the external connections to an appropriate power supply are not shown. However, it should be obvious to one skilled in the art that these connections can be made to the power supply through the evacuated glass envelope 12'. In addition to contacts 20' and 22', another electrical contact 36 is provided. The contact 36 takes the form of a pointed electrode which extends through the outer shell 34 and terminates in the opening 37 defined by the core 32. This contact 36 is connected, as indicated, to a positive power supply terminal.

An electron exit aperture 28' is provided in the outer shell 34 opposite the pointed position of the contact 36.

The operation of the electron generating device is similar to that described with reference to the electron generating device 10 of FIG. 1. That is, electrons are accelerated by the electrical field within the curved section 16' and travel from the electrical contact 20' toward the positive contacts 22' and 36. These electrons bombard the walls of the secondary-electron emissive coating 24', thereby multiplying the number of electrons. The resulting accelerated electrons exit the electron generating device 10 by means of the exit aperture 28. Positive ions which are generated in the vicinity of the positive electrical contacts 22' are accelerated by the strong electrical field established between electrical contacts 20', 22' .and are accelerated along the positive ion path toward the negative electrical contact 20'. These accelerated positive ions bombard the emissive coating 24 within the curved section 16 and result in the self-sustain generation of further electrons.

In conclusion, it should be apparent that the present invention provides a -nonthermionic, electron emitting device which may be utilized in many different applications. The positive ion feedback feature of the invention results in a self-sustained saturated electron emitter.

Obviously, many modifications and variations are possible in view of the above teachings. Therefore, it is to be understood, that the invention may be practiced otherwise than as specifically described.

lclaim:

1. An electron generator device comprising:

a. an evacuated envelope,

b. a tubular member positioned within said evacuated envelope; said tubular member having an outer non-conducting wall and an inner wall which defines a substantially continuous particle reflex cavity; said tubular member having first and second tubular sections extending between first and second spaced apart electrical terminals, with said first tubular section defining a curved cavity section having openings at the ends thereof and having an inner wall including a resistive, secondary-electron emissive coating; said first and second electrical terminals electrically connected to said coating near the respective ends of said first tubular section, said second tubular section being substantially straight and connecting between one of said openings and a further opening in the wall of said first tubular section near the other of said openings and including a resistive, secondary-electron emissive coating on its inner wall, said other of said openings being an electron exit aperture in close proximity to said second terminal to receive electrons from said first tubular section and direct same into said envelope, and

. means electrically connected to said first and second terminals for accelerating electrons along said curved cavity section to electron exit aperture, and further for accelerating positive ions within said second tubular section, whereby ions resulting from secondary electron bombardment of said coating are fed back along said second tubular section to liberate additional electrons in the vicinity of said first terminal to sustain electron generation.

Claims

1. An electron generator device comprising: a. an evacuated envelope, b. a tubular member positioned within said evacuated envelope; said tubular member having an outer non-conducting wall and an inner wall which defines a substantially continuous particle reflex cavity; said tubular member having first and second tubular sections extending between first and second spaced apart electrical terminals, with said first tubular section defining a curved cavity section having openings at the ends thereof and having an inner wall including a resistive, secondary-electron emissive coating; said first and second electrical terminals electrically connected to said coating near the respective ends of said first tubular section, said second tubular section being substantially straight and connecting between one of said openings and a further opening in the wall of said first tubular section near the other of said openings and including a resistive, secondary-electron emissive coating on its inner wall, said other of said openings being an electron exit aperture in close proximity to said second terminal to receive electrons from said first tubular section and direct same into said envelope, and c. means electrically connected to said first and second terminals for accelerating electrons along said curved cavity section to electron exit aperture, and further for accelerating positive ions within said second tubular section, whereby ions resulting from secondary electron bombardment of said coating are fed back along said second tubular section to liberate additional electrons in the vicinity of said first terminal to sustain electron generation.