US3892970A

US3892970A - Relativistic electron beam device

Info

Publication number: US3892970A
Application number: US478199A
Authority: US
Inventors: John R Freeman; James W Poukey; Steven L Shope; Gerold Yonas
Original assignee: US Department of Energy
Current assignee: US Department of Energy; Energy Research and Development Administration ERDA
Priority date: 1974-06-11
Filing date: 1974-06-11
Publication date: 1975-07-01
Anticipated expiration: 1992-07-01
Also published as: AU8204475A; JPS5129864A; FR2275112A1; FR2275112B3; DE2526123A1

Abstract

An electron beam device for irradiating spherical hydrogen isotope bearing targets may include hollow cathodes facing each other, means for injecting an anode plasma at a plane between the cathodes, and means for producing an approximately 10 nanosecond, megajoule pulse between the anode plasma and the cathodes. Targets may be repetitively positioned within the anode plasma between the cathodes, and the accelerator diode structure arrangement permits adjacent materials to survive repetitive operation as required in a fusion power source.

Description

United States Patent Freeman et al.

l l RELATIVISTIC ELECTRON BEAM DEVICE [75] Inventors: John R. Freeman; James W.

Poukey; Steven L. Shope; Gerold Yonas, all of Albuquerque, N. Mex.

[73] Assignee: The United States of America as represented by the United States Energy Research and Development Administration, Washington, DC.

22 Filed: June 11, 1974 211 Appl. No.:478,199

[52] US. Cl. 250/396; 250/398; 250/492; 250/493 [51] Int. Cl. G21G 5/00; GOlK 1/08 [58] Field of Search 250/398, 399, 400, 492, 250/493, 396, 311

[56] References Cited UNITED STATES PATENTS 3,094,474 6/1963 Gale 250/396 ENERGY STORAGE SECTION l l 42 5 34 3O 38 vAcuuu PUMP July 1,1975

3,720,828 3/1973 Nablo U 250/3ll Primary Examiner1ames W. Lawrence Assistant Examiner-T. N. Grigsby Attorney, Agent, or FirmDean E. Carlson; Dudley W. King; Richard E. Constant [57] ABSTRACT An electron beam device for irradiating spherical hydrogen isotope bearing targets may include hollow cathodes facing each other, means for injecting an anode plasma at a plane between the cathodes, and means for producing an approximately 10 nanosecond, megajoule pulse between the anode plasma and the cathodes. Targets may be repetitively positioned within the anode plasma between the cathodes, and the accelerator diode structure arrangement permits adjacent materials to survive repetitive operation as required in a fusion power source.

13 Claims, 5 Drawing Figures SHEET 1 GENERATQR (2| (-22 24 20 CHARGNG CONTROL TARGET SUPPLY cmcurr SOURCE HEAT l EXCHANGER FIG. 2

ENERGY STORAGE SECTION VACUUM PUMP 1 RELATIVISTIC ELECTRON BEAM DEVICE BACKGROUND OF INVENTION Many new methods are being investigated in order to produce high energy density plasmas which may result in thermonuclear fusion, or may be used for material studies, testing of deposition of high energy in materials or for similar purposes. One such technique or device is a high intensity relativistic electron beam (REB) accelerator which is used to irradiate a small, generally spherical pellet or target. Such accelerators have been built or are being developed which are capable of producing electron beams with currents of from about 100,000 to greater than 1,000,000 amperes at voltages of from about 100,000 volts to greater than 10,000,000 volts and depositing this energy in time periods of 100 nanoseconds or less.

In order to produce the desired interactions and reactions of the materials, and particularly compression and heating of the thermonuclear fuel pellet to achieve fusion conditions, the electron beam device should focus the electron beam to a few millimeters or less in a spherically symmetrical and uniform manner. It has been found to be difficult to produce high energy electron beams having suitable pulse durations and which may be focused to a desired size to produce sufficiently dense and high temperature plasmas to achieve fusion.

For example, these high temperature and high den sity plasmas may be produced by irradiating a millimeter size target with roughly one megajoule of energy with a relativistic electron beam (REB). The irradiation of the target should be symmetric about its outer surface and the beam energy should be deposited in time periods of about nanoseconds. In order to achieve useful energy outputs from fusion of such targets, targets must be irradiated by the electron beam device in a sequential, repetitive manner. Since the fusion reaction of even a small target will produce signifcant neutron, x-ray and debris flux, provision must be made to protect the electron beam device from the products of the fusion reaction so that the irradiation of another target may take place in a relatively short period of time, such as in the neighborhood of once every 0.1 to 1 second.

SUM MARY OF INVENTION In view of the above, it is an object of this invention to provide an electron beam device which is capable of repetitive irradiation of small, thermonuclear fuel targets with acceptably small damage to adjacent electrode materials resulting from each REB induced thermonuclear microexplosion.

It is a further object of this invention to provide an electron beam device which may uniformly irradiate such a target to produce significantly high temperatures and densities within the target.

It is a further object of this invention to provide an electron beam device for efficient irradiation of a thermonuclear target so as to produce electrical energy from the buming" of the target resulting from its irradiation.

It is a still further object of this invention to provide such an electron beam device which is capable of simultaneously focusing two intense electron beams onto the target from opposite sides thereof.

Various other objects and advantages will appear from the following description of the invention, and the most novel features will be particularly pointed out hereinafter in connection with the appended claims. It will be understood that various changes in the details, materials and arrangements of the parts, which are herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art.

The invention relates to an electron beam device which utilizes annular or hollow cathodes separated from each other by a generally planar anode plasma, and means for simultaneously accelerating intense REBs between the cathodes and the single plasma anode so as to irradiate a target disposed within the anode plasma.

DESCRIPTION OF DRAWING The invention is illustrated in the accompanying drawing wherein:

FIG. 1 is a perspective and somewhat schematic view of an electron beam device to produce two beam irradiation of a spherical target in a repetitive manner;

FIG. 2 is a somewhat simplified cutaway view of a portion of the device shown in FIG. 1;

FIG. 3 is a more detailed, cutaway view of a portion of the electron beam device diodes and the transmission line which feeds electrical energy thereto;

FIG. 3a is an expanded view of the discharge region of the diodes shown in FIG. 3; and

FIG. 4 is a cutaway view of an anode plasma producing apparatus for use in device of FIGS. l-3.

DETAILED DESCRIPTION A relativistic electron beam device or REB driven fusion reactor incorporating features of this invention is illustrated in FIG. 1 in a somewhat schematic and simplified form to illustrate the overall arrangement in which this invention is utilized, As shown, the device 10 includes a generally spherical reaction chamber housing 12 in which electron beams irradiate a target to induce a fusion reaction, an energy storage and discharge section 14 generally encompassing and uniformly spaced from housing 12, a pulse forming line 16 interconnecting the energy storage section 14 and the electron beam accelerating apparatus or diodes (described below) in housing 12. The energy stored in energy storage 14, is simultaneously transferred to the pulse forming line 16 for subsequent circumferential application thereof to the electron beam diodes in housing 12. The pulse forming line 16 also acts to shape the electrical pulse to have a desired rise time and pulse provide effective energy deposition into the target.

When the target is irradiated and imploded by the electron beams in housing 12, as will be described more fully below, the thermonuclear fuel in the target may be ignited by achieving the required density and temperature so as to release high levels of radiation energy. The housing 12 may be provided with a suitable material within its outer walls which is capable of absorbing this energy and converting the same to a high temperature fluid, such as by using a lithium blanket, which may be circulated through a suitable heat exchanger 18 to extract the thermal energy. This thermal energy, may then be utilized to operate a turbine or other electrical power generating equipment 20 in a manner well known in the art. A portion of the electrical energy produced by generator 20 may be distributed to a power grid, or the like, with another portion fed back through a charging supply 21 to the energy storage section 14. Control circuit 22 may be utilized to trigger the energy storage 14 into the pulse forming line 16 and sequentially release or inject a new target from target source 24 into housing 12 for irradiation thereof. and to provide other control functions.

Energy storage l4 may include one or more high voltage converters. such as a plurality of Marx-type generators. or the like. which convert the electrical energy input from charging supply 21 into a high voltage at a sufficient power level for purposes of this invention. The high voltage converters. in turn, may supply this high voltage and high energy electrical power to intermediate storage capacitors arranged symmetrically about the circumference of the pulse forming line 16 if needed to further intensify the electrical power. By way of example. in order to achieve the levels of target irradiation desired by this invention. the combined Marx generators or other converters and storage capacitors may have a total storage capability of about 2 megajoules of electrical energy and be capable of generating pulses of l megavolt or higher. In addition. the voltage converters and storage capacitors of energy storage 14 should be provided with switching and conductor arrangements which are capable of discharging a significant portion of the entire stored energy in the generator and capacitors into pulse forming line 16 at a rate of about 0.l to [.0 pulse per second. In order to achieve such operation. the energy storage 14 might include from about to separate Marx generators evenly spaced in the generally circular arrangement shown and connected in parallel with sufficient capacitance to store about 2 megajoules. and appropriate triggered switching (not shown) to deliver this energy with small jitter.

The pulse forming line 16, as shown in greater detail in FIG. 2, may include a generally disk-like. central conductor 30 which is placed between and uniformly spaced from a pair of disk-like

outer lines

32 and 34, such as in the general form of Blumlein lines (shown schematically only). The

conductors

32 and 34 may be separated from the central conductor 30 by

suitable gaps

36 and 38 which are filled with an appropriate dielectric. such as transformer oil or high purity water. so as to provide sufficient electrical holdoff for the electri- :al pulses carried by the pulse forming line 16. The dizlectric between the pulse forming line conductors may ielp support the central conductor and may be sealed vithin the gaps by appropriate

annular insulators

40, 12. 44. and 46 at inner and outer locations of line 16. The spacing between conductors must be sufficient to vithstand or holdofl the voltage applied across these nsulators by the energy storage 14 and carried by the Julse forming line 16. The energy in the storage capaciors in energy storage 14 may be switched by the trig- :ered switches. so as to inject a pulse of about 1 megaolt in amplitude and 1 megajoule in energy into the auter periphery of the pulse forming line 16, such as )

CIWCCII conductors

30 and 32 and between conducors 30 and 34 with conductor 30 biased positive with espect to

conductors

32 and 34. As the electrical pulse njected into the pulse forming line 16 from energy torage 14 travels along line 16, the pulse is shaped by he pulse forming line 16 characteristics so that when he pulse reaches the inner position adjacent housing 2. the pulse will be in a desired pulse shape. For examle. in the present application. this pulse should have a pulse length of from about It) to 20 nanoseconds and a pulse rise time of about 5 to l0 nanoseconds. The pulses thus produced between the respective conductor pairs. that is

conductors

30 and 32 and

conductors

30 and 34, at the inner circumference of pulse forming line 16 are then applied simultaneously to the appropriately configured

annular diodes

48 and 50 described more fully below.

The housing 12 may include an inner spherical wall 52 spaced from an outer hollow spherical wall 54 so as to enclose a medium for absorption of thermonuclear energy and conversion of the same into heat. such as a suitable lithium blanket 56, which can also be used to breed the required tritium fuel. The lithium in lithium blanket 56 may be dispersed throughout the hollow spherical chamber formed by

walls

52 and 54 or may be carried by appropriate tubing or directed by appropriate baffling and other flow control means so as to flow through the housing 12 chamber and heat exchanger 18 through inlet tubing 58 and outlet tubing 60. The blanket could also be cooled via gas forced through tubes within the blanket. The interior 6] of housing 12 must be evacuated and reaction products removed therefrom by an appropriate vacuum pump or evacuation system 62 through tubing 63 so as to have the discharge area around

diodes

48 and 50 at a pressure of from about l0 to 10 Torr at the beginning of each discharge pulse. Inner wall 52 should preferably be made ofa material which has high strength, specific heat, sublimation energy and ablation resistance and preferably though not necessarily producing only short lived induced radioactive decay products.

As mentioned above. the target to be irradiated may be supplied by target source 24 when signaled by control circuit 22 through an appropriate inlet port 64 through the walls of housing 12. The targets may be injected so as to be positioned at a central location within housing 12 and with respect to the

diodes

48 and 50 when a pulse from energy storage 14 and pulse forming line 16 reaches the diodes, such as in the location indicated by target 66.

In a typical electron beam driven fusion reactor 10 arrangement in which it is desirable to produce commercial quantities of electrical energy. the overall device may have a diameter of about 30 meters with a few megajoules of energy storage capacity. The pulse forming line 16 may be less than I meter in width and connect to a housing 12 having an outer diameter of 5 to 10 meters. The hollow or

annular diodes

48 and 50, in turn, may have an inside diameter of from about 0.5 to 1 meter and a gap width between cathode discharge surface and anode plane of from a few to about 50 millimeters with the insulators 44 and 46 (and consequently the inner diameter of pulse forming line 16) having a diameter of from about 3 to 4 meters. With about I megajoule delivered to the target in the diode arrangement described below. and with an appropriate target, about 20 megajoules of neutrons may be generated; with a 40% conversion of blanket thermal energy to electricity, about 8 megajoules of electricity may be produced. With 2 megajoules of energy being fed back through charging supply 21 to energy storage section 14, there may be about 6 megajoules of electrical energy remaining to be fed to the power grid. With l0 pulses per second and an array of 10 such units as shown in FIG. 1, an output power of 600 megawatts could be generated.

FIG. 3 illustrates additional details of the diodes 48 and S0 and the arrangement of their elements and components. With the arrangement to be described, a pair of electron beams may be generated and focused to a spherically symmetric irradiation pattern on the target 66. The diode elements themselves are positioned at a sufficient distance from target 66 and with a relatively low radial cross section therefrom so as to be subjected to minimal damage from reaction products caused by the irradiation of the target. The target 66 is preferably of spherical shape and made of hydrogen isotope bearing materials which will effectively absorb electrons.

As illustrated in FlGS. 3 and 3a, the target 66 is appropriately positioned or located along the longitudinal axis and on a plane halfway between

hollow diodes

48 and 50 which is at the midpoint between a pair of hollow

annular cathodes

70 and 72 of

diodes

48 and 50 and perpendicular to the longitudinal axis. Each of the

cathodes

70 and 72 includes an annular

planar discharge surface

74 and 76 of sufficient width to extract the current levels needed (typically about 0.] meter) which are disposed about the entire circumference of the cathodes and facing each other and separated by a distance which is approximately twice the desired discharge gap width. The

cathodes

70 and 72 include

intermediate sections

78 and 80 which connect the inner terminal portion of the

outer members

32 and 34 of pulse forming line 16 adjacent to the location of

insulators

44 and 46 to the cathode discharge surfaces 74 and 76. The

portions

78 and 80 converge uniformly towards the discharge surfaces 74 and 76 and terminate at inner locations or

walls

82 and 84.

Portions

78 and 80 preferably converge on a line or lines which meet at target 66 with the

ends

82 and 84 having as small a width as possible so as to minimize the dimensions of the

cathodes

70 and 72 which are in radial alignment with target 66 and the reaction products which may emanate therefrom when the target is irradiated and disintegrated by the electron beams. For example, it is preferred that the outer surfaces of

portions

78 and 80 be aligned with target 66 in order to minimize the solid angle subtended by the

cathode structure

70 and 72 and to reduce the flux of radiation and debris on the electrode surfaces. The smaller the angle, the greater will be the area of lithium blanket 56 subjected to the energy produced by the microexplosion of target 66. The length and changing cross section of

portions

78 and 80 should be selected so as to provide an efficient electrical impedance coupling between the pulse forming line 16 and

cathodes

70 and 72 to minimize electrical losses and to aid in shaping the pulse reaching the diodes to the desired pulse width and rise time. Discharge surfaces 74 and 76 may be positioned at an angle, as shown, so as to be masked by

walls

82 and 84 from target 66 and debris emanating therefrom. It may be desirable to recoat or otherwise refinish

surfaces

74 and 76 after each discharge. This may be done with cathodes in place by forcing an appropriate gas or liquid through pores in the discharge surfaces of porous cathodes or by otherwise recoating the discharge surfaces by a suitable spray.

An appropriate plasma source 86, an example to be described below, may be positioned within a hollowed out inner portion 86 of the central conductor 30 of pulse forming line 16 with a channel 88 communicating between plasma source 86 and the discharge regions or gaps of

diodes

48 and 50. Portion 87 may reduce the overall weight of the pulse forming line 16 and result in a more readily supported system and divide the center conductor 30 into two layers or

walls

30a and 30b which are maintained at the same electrical bias. The plasma source 86 should be capable of generating and expelling through channel 88 sufficient plasma to provide a generally planar plasma anode 90 distributed throughout a generally planar shaped region which is midway between cathodes and 72 to the center point of the hollow diodes and encompassing target 66. Because of the electrical characteristics of the plasma, the plasma 90 so produced may act as an anode to the discharge produced from

cathodes

70 and 72 and as a return path of low resistance for the electrons deposited in the target. After the target 16 is irradiated by the electron beams from the diode discharges, the plasma anode 90 will be dissipated and will have to be regener ated for each pulsing of the diodes.

The inner conductor 30 of pulse forming line 16 may be made hollow or with recessed portions to accommodate the plasma source 86 and with exterior walls 91a and 91b which converge in the same manner as

portions

78 and 80 of

cathodes

70 and 72 with their terminal edges and channel 88 being at a location near to a line with the

end walls

82 and 84 of the cathodes about the circumference thereof. The converging walls 91a and 91b of center conductor 30 thus pass near or between the discharge surfaces 74 and 76 of the cathodes and inject the anode plasma into the region internal to or radially inward of

annular cathodes

70 and 72.

An example of a plasma source 86 which may be utilized in device 10 is illustrated in FIG. 4. A chamber 92 may be formed within the converging walls 91a and 91b of center conductor 30 of the pulse forming line 16 by an insulative wall 94. The inner surfaces of walls 91a and 9lshould be shaped so as to maximize radial velocities of ions in plasma 90. When it is desired to form the plasma for injection as plasma anode 90, a suitable inert gas may be injected into chamber 92 from a gas source 96 via a plurality of tubes 98 and an appropriate control valve (not shown). After the chamber 92 is filled or partially filled with this gas to a pressure of such as about 100 millitorr, an appropriate power supply or source of energy, such as the capacitor bank 100 shown, may be switched into the chamber 92 through a plurality of spark-gap type of switches 102 to initiate a discharge along wall 94 between walls 91a and 91b which in turn produces an ionized gas in chamber 92. As the current rises from the discharge of capacitor bank 100, a magnetic pressure may be produced behind the current sheet produced by the discharge and drive the plasma which is produced in the discharge toward the channel or nozzle 88 ionizing and sweeping up the gas as it passes. The plasma may then be driven so as to flow from channel 88 towards the longitudinal axis of the

diodes

48 and 50 along the anode plane to the target 66. The plasma will have a maximum density on the diode axis due to the geometric convergence of the plasma and may produce electron densities of the order of 10 to l0 per cubic centimeter at the center point of the diodes and around target 66. It is understood that the gas injection into chamber 92 and the discharge is occurring from substantially throughout the circumference of the annular plasma source 86 so as to simultaneously inject the plasma throughout the discharge region of the

cathodes

70 and 72. It is also understood that the energy required to produce the discharge and generation of the plasma anode 90 may be achieved by a prepulse of energy from energy storage 14 produced between

conductor walls

300 and 30b just prior to the main diode discharge pulse. All of these respective operations may also be controlled and timed by the control circuit 22.

In order to achieve the desired discharge over the en tire circumference of

diodes

48 and 50 and the entire volume of the chamber 92, for example a volume of about 30 liters, a total energy of about 85 kilojoules may be required to produce about 15 kilojoules of anode plasma 90 energy. As the plasma is injected into the discharge region of the cathodes towards the center point or target 66, the beam may diverge slightly, as shown, completely immersing target 66 therein and in a radius of about 0.5 meter may typically reach a thickness of about 100 to 200 millimeters. When the target 66 is irradiated by the electron beam, this plasma about the target 66 may function as a space charge neutralizing plasma near the diode axis and to provide a relatively low resistance path for return current.

Electron beam pinching may be further enhanced if necessary by injecting or producing a resistive-type of plasma around target 66 in an appropriate manner such as by prepulsing the target with a high energy laser pulse to ablate a portion of target 66. Such a plasma should also aid in space charge neutralization of the diode electrons and should not current neutralize diode electrons or impede their flow. Under these conditions, the diode electrons may see" the full pinching force of their own magnetic field and the longitudinal diode electric field.

After the injection of the anode plasma into the discharge region of the

diodes

48 and 50, control circuit 22 may initiate the main pulse along pulse forming line 16. When the main discharge pulse energy reaches the discharge surfaces 74 and 76 of

diodes

48 and 50, electron beams may be initiated simultaneously throughout the circumference of the discharge surfaces 74 and 76 towards anode plasma 90 and the converging walls 91a and 91b of center conductor 30, as indicated by electron flows 102a and 102i). The electron beams will radially drift toward the center or longitudinal axis of the diodes and produce electric and magnetic fields which will effect a self-pinching of the beams so that the beams converge from opposite sides of target 66 through the plasma anode 90. The self-pinching of the electron beams results in a large spread in angles of the beam electrons incident on target 66 causing the electron beams to behave like a high temperature electron gas thus permitting spherically symmetric irradiation. The outer surface and portions of target 66 will ablate and vaporize under the influence of the electron beams aroducing a resistive plasma about the target and driv- .ng the target to implode. The implosion may heat and :ompress the fuel and cause it to be ignited and to prolide a thermonuclear reaction. The resulting neutron autput will serve to heat the lithium blanket which may hen be utilized, as described above in the heat ex- :hanger 18 and power generator 20. After the appro- )riate vacuum is reached via the pump 62, another target may then be injected into the interior of housing 12 mm target source 24 by control circuit 22. A new mode plasma 90 may then be produced by plasma ource 86 and the

diodes

48 and 50 again energized. lecause of the arrangement of the diodes and their repective elements, the discharging of the diodes may be continued at a repetitive rate which is commensurate with desired device 10 outputs.

With the above described electron beam device, two electron beams may be focused to the diameter needed to ignite the thermonuclear fuel target or pellet in an efficient manner using a hollow diode arrangement in which the diode elements, cathode and anode, consist of radiation resistant materials and are located far enough away from the exploding pellet to escape dam age. The overall arrangement of the diode also provides an electron beam environment in which the electron act as a gas or are gas-like in nature so as to evenly bathe all surfaces of the target.

What is claimed is:

1. An electron beam device comprising first and sec ond cathodes separated from each other by a gap on a common longitudinal axis; means for providing and injecting an anode plasma intermediate said cathodes at said gap along a plane perpendicular to said axis; and means for producing electron beams between said anode plasma and said cathodes.

2. A device as claimed in claim 1 wherein said cathodes are of annular configuration and said anode plasma injecting means is intermediate the cathodes.

3. A device as claimed in claim 2 wherein said cathodes each include a discharge surface generally facing each other and said plasma injecting means and said discharge is produced simultaneously from throughout the circumference of said cathode discharge surfaces.

4. A device as claimed in claim 3 wherein said annular configuration cathodes include inwardly converging wall portions tenninating in said discharge surfaces and in circular end walls.

5. A device as claimed in claim 4 wherein said converging wall portions are in a line with the center point between said cathodes.

6. A device as claimed in claim 4 wherein a housing encloses said tapering wall portions, and means is provided for evacuating gases and products therefrom.

7. A device as claimed in claim 6 wherein said housing includes spherical shaped inner and outer walls enclosing blanket means for converting neutron output to electrical energy.

8. A device as claimed in claim 7 wherein means is provided for supplying targets to said housing within the confines of said cathodes.

9. A device as claimed in claim 4 wherein said anode plasma injecting means is substantially concomitant with said circular end walls.

to. A device as claimed in claim 9 wherein said anode plasma injecting means includes inwardly tapering wall portions terminating with a nozzle coextensive with said circular end walls.

1 1. A device as claimed in claim 4 wherein said electron beam producing means includes a pulse forming line coupled to said wall portions of said cathodes and to said anode plasma injecting means throughout the circumference thereof.

12. A device as claimed in claim 11 wherein said electron beam producing means includes means for injecting electrical energy into the outer periphery of said pulse forming line for simultaneous application of an electrical discharge pulse to said cathodes and anode plasma throughout their circumference.

13. A device as claimed in claim 1 including means for repetitively injecting hydrogen isotope bearing targets to a central location between said cathodes and then actuating said anode plasma providing means and said electron beam producing means to sequentially irradiate said targets one at a time with electron beams from both of said cathodes.

Claims

1. An electron beam device comprising first and second cathodes separated from each other by a gap on a common longitudinal axis; means for providing and injecting an anode plasma intermediate said cathodes at said gap along a plane perpendicular to said axis; and means for producing electron beams between said anode plasma and said cathodes.

4. A device as claimed in claim 3 wherein said annular configuration cathodes include inwardly converging wall portions terminating in said discharge surfaces and in circular end walls.

10. A device as claimed in claim 9 wherein said anode plasma injecting means includes inwardly tapering wall portions terminating with a nozzle coextensive with said circular end walls.

11. A device as claimed in claim 4 wherein said electron beam producing means includes a pulse forming line coupled to said wall portions of said cathodes and to said anode plasma injecting means throughout the circumference thereof.