US3360663A

US3360663A - High-voltage generator

Info

Publication number: US3360663A
Application number: US456013A
Authority: US
Inventors: Albert V Crewe; Yokosawa Akihiko; Geeter Dale J De
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-05-14
Filing date: 1965-05-14
Publication date: 1967-12-26
Anticipated expiration: 1984-12-26

Description

Dec. 26, 1967 A. v. CREWE ET AL 3,360,663

HIGH'VOLTAGE GENERATOR Filed May 14, 1965 lectron Beam 29cc; 6 Z erator fiieutrajz Bea/f7? f/caelerator INVENTORS fllbert Zfi Creme Ikihiko Z/o/rosazua ,Date ,1. De Geeter /F--( 4 4m [Zia/.1283

United States Patent O 3,360,663 HIGH-VOLTAGE GENERATOR Albert V. Crewe, Palos Park, Akihiko Yokosawa, Naperville, and Dale J. De Geeter, Lemont, IllL, assignors to the United States of America as represented by the United States Atomic Energy Commission Filed May 14, 1965, Ser. No. 456,013 7 Claims. (Cl. 310-) This invention relates to high-voltage generators and more particularly to means for producing a high voltage between first andsecond members using an electron beam.

In the particle accelerator field, beam motion is often controlled bypassing the beam between two deflection electrodes mounted in a partial vacuum and having a high voltage established therebetween. Present systems use a conventional high-voltage source with the output therefrom cabled to one of the deflection electrodes. A hollow ceramic bushing is mounted between the deflection electrode and the chamber housing the deflection electrodes. The ceramic bushing is filled with oil and the cable from the source is passed therethrough and connected to the deflection electrode.

One problem encountered with the present high-voltage system is the termination of the cable and the bushing at the deflection electrode. At the termination and along the cable, electric fields develop to a value such that the oil and other insulation materials contained within the bushing deteriorate, causing electrical breakdown thereof. After the first electrical breakdown of the insulation, the insulating properties thereof rapidly deteriorate, so that subsequent electrical breakdowns occur more easily and the system has to be dismantled, cleaned, the cable repaired, and new oil inserted therein. Further, with an electrical breakdown discharge in the partial vacuum, the surface of the ceramic insulating bushing tends to accumulate a film coating of metal, thereby requiring removal and cleaning thereof. The present systems as described are limited to voltages up to 500 kv., continuous duty operation becoming increasingly diflicult as one approaches the 500 kv. value.

Accordingly, it is one object of the present invention to provide means for generating a high voltage between two electrodes spatially mounted with respect to each other in a partial vacuum.

It is another object of the present invention to provide means for generating a'voltage in excess of 500 kv. between two electrodes spatially mounted with respect to each other in a partial vacuum. I It i s still another object of the present invention to provide means using an electron beam for generating a voltage in excess of 500 kv. between two electrodes spatially mounted with respect to each other in a partial vacuum.

Otherobjects of the present invention will become more apparent as the detailed description proceeds.

In general, the present invention comprises a Faraday cupmounted in electrical connection with one of two electrodes spatially disposed with respect to each other in a partial vacuum. Means are provided for generating and directing an electron beam into the Faraday cup, whereby a negative charge accumulation occurs on the electrode having the Faraday cup attached thereto and a high voltage is developed between the two electrodes. Further understanding of the present invention may best be obtainedfrom consideration of the accompanying drawings wherein:

FIG. 1 is a representative schematic diagram of an apparatus for the practice of the present invention; and

FIG. 2 is a representative schematic diagram of the preferred apparatus for the practice of the present invention.

In FIG. 1 the

electrodes

10 and 12 are used to deflect a variable mass charged particle beam passing therebetween. The electrodes are rigidly mounted within an evacuable chamber 14. The electrode 10 is mounted to the walls of the chamber and electrically grounded therewith. A Faraday cup 16 is mounted in electrical contact with electrode 12 and connected via resistor 18 to the wall of the chamber 14. The electrode 12 and Faraday cup 16 are spatially mounted with respect to the walls of chamber 14 by a standoff insulator 20. The resistor 18 is sealed from the atmosphere of the chamber 14 by a ceramic bushing 22 filled with oil or a gas, such as sulfur hexafiuoride. An electron beam accelerator 24, such as a Van de Graafl, is connected via tube 26 to the chamber 14. The Faraday cup 16 is aligned so that the electron beam from the accelerator 24 is captured therein.

In operation, electrons from the electron beam are captured by the Faraday cup 16 to thereby produce a negative charge on electrode 12. The voltage between

electrodes

10 and 12 follows the formula where Q=the charge on the electrode 12, and C=the capacitance between the

electrodes

10 and 12. Electron loss from the cathode 12 will follow three paths, the first, 1;, through the standoif insulator 20, the second, I through the resistor 18, and the third, I between the

electrodes

10 and 12. The current I; is very small due to the high resistance of the standoff insulator 20. The current I varies according to the spacing between the

electrodes

10 and 12. The current I varies according to the value chosen for the resistor 18. For the purposes of the present invention, the resistor 18 is chosen so that it has a relatively low value, whereby the value of the current I therethrough far exceeds I and I and is determinative of the potential achieved by'the electrode 12. Thus, the potential developed on electrode 12 is the product of the current I times the resistance of resistor 18. Since I is far greater than I (the current flowing through the insulator 20) and I (the current flowing between the electrodes), the current I approaches in value the beam current of the accelerator 24. The potential on electrode 12 is thus varied in an approximately linear manner by varying the beam current of the accelerator '24. In operation, the potential of electrode 12 is maintained below that of the electron beam whereby the problem of beam defocusing, as hereinafter described, is avoided. For the embodiment of FIG. 1, a cylindrical chamber 14, five feet in diameter, and

electrodes

10 and 12, six feet long x 20 inches wide with a 5-15 cm. gap there between, were used. The Faraday cup 16 was 18 inches long with a cross section of 3.5 x 2.5 inches. Resistor 18 had a value of 5 l0 ohms. With an accelerator beam current of microamperes at a potential of 800 kv., a potential was established on electrode 12 of 600 kv. The foregoing values are merely illustrative for the practice of the present invention and the present invention is not to be limited thereto. With higher beam currents, one may obtain higher potentials on the electrodes with the parameters of the various elements being modified in accordance therewith.

With the embodiment of FIG. 1, potential regulation of electrode 12 is accomplished as hereinbefore described by regulation of the beam current of the accelerator 24. Close regulation of the beam current of an accelerator is more difiicult than regulation of the potential thereof. FIG. 2 illustrates the preferred embodiment for the practice of the present invention, wherein regulation of the potential of electrode 12 is accomplished via regulation of the potential of the beam current of accelerator 24.

As for the embodiment of FIG. 1, electrodes and 12 are symmetrically disposed in an evacuable chamber 14. Electrode 10 is mounted to the walls of the chamber and electrically grounded therewith. A Faraday cup 16 is mounted in electrical contact with electrode 12 and connected via a standofi insulator 20 to the wall of the chamber 14. An electron beam accelerator 24 is connected via tube 26 to the chamber 14. The Faraday cup 16 is aligned so that the electron beam from the accelerator 24 is captured therein.

In the embodiment of FIG. 2, the electrons from the electron beam of accelerator 24 are captured by the Faraday cup 16 and deposit their charge on electrode 12 to raise the potential thereof. The charge on the Faraday cup 16 will increase until it is equal to CV where C: the capacitance between

electrodes

10 and 12 plus the capacitance from electrode 12 to the walls of chamber 14 and V=the potential of the electron beam, at which time only sufficient additional electrons will be captured thereby to replace electrons lost through the standoff insulator 20 (I and between the electrodes 10 and 12 (I The upcaptured electrons in the beam from accelerator 24 are reflected back to the walls of the chamber 14. Thus, when the potential of electrode 12 equals that of the electron beam from accelerator 24, electron capture by the Faraday cup 16 is effected only to replace electrons lost through I and 1 As the load or current I between the

plates

10 and 12 increases (by varying the gap therebetween), then less electrons are reflected to the walls of the chamber 14. The embodiment of FIG. 2. is therefore self-regulating, since any change betwen the potential of electrode 12 and the energy of the electron beam is automatically adjusted by either fewer or more electrons being reflected to the walls of the chamber 14.

For operation of the present invention as described supra in the embodiment of FIG. 2, it is necessary that the Faraday cup 16 is designed so that any defocusing effect on the electron beam is minimized as the electrode 12 approaches and equals the energy of the electron beam. If this is not done, as the potential of electrode 12 equals that of the electron beam, the electron beam may be deflected so that it never strikes the Faraday cup 16 or the defocusing effect of the electric fields about the Faraday cup may become such that inefiicient electron capture by the Faraday cup results. To minimize any defocusing effect on the electron beam, it is necessary that the aperture of Faraday cup 16 have a minimum diameter of approximately two inches. With this aperture size, the equipotential lines of the electric fields existing between the cup. 16 and the walls of the chamber 14 penetrate to a depth within the cup 16 sufficient to permit eflicient trapping by the cup 16. Further improvement in operation may be achieved by insuring that the length to diameter ratio of the cup 16 has a minimum value of approximately 6:1, whereby secondary particle escape from the cup 16 will be prevented. For the purposes of the present invention with a Faraday cup having a rectangular cross section, the shortest side of the cross section is used in determining the length to diameter ratio.

With the embodiment of FIG. 2, it is thus seen that the voltage or the potential of electrode 12 is regulated by the energy of the electron beam from accelerator 24. To increase or decrease the value of the potential of electrode 12, it is only requisite that one increase the value of the energy of the electron beam from accelerator 24. Since the energy of an electron beam from an accelerator 24 may be closely regulated, the potential of electrode 12 is similarly able to be closely regulated. It is to be noted that the potential of electrode 12 is self-regulating with respect to the electron beam from accelerator 24. Using the same component values as for the embodiment of FIG. 1 (with the deletion of resistor 18 therefrom), a voltage of 600 kv. was obtained with a beam current of 300 microarnperes at a potential of 600 kv. from accelerator 24. The beam current of 300 microamperes was necessary to replace the leakage currents I load current I and provide sufiicient electrons to the wall of chamber 14 to maintain the self-regulating operation.

It is to be noted that the examples given for the embodiments of FIG. 1 and FIG. 2 are merely illustrative of voltages obtainable using the present invention and that the present invention is not to be limited to the values of the elements in each of the embodiments. It is to be further noted that for the practice of the present invention, neither electrode 10 nor chamber 14 has to be grounded but that they may be at some other electrical potential.

Persons skilled in the art will, of course, readily adapt the teachings of the invention to methods and embodiments far dilferent than the methods and embodiments herein described. Accordingly, the scope of the protection afforded the invention should not be limited to the particular embodiments and methods described and shown above but should be determined only in accordance with the appended claims.

What is claimed is:

1. A device for producing a high voltage between first and second electrodes mounted in a partial vacuum, comprising means for generating an electron beam, a Faraday cup mounted in electrical contact with said first electrode, means for directing said electron beam into said cup to cause a negative charge accumulation on said first electrode, whereby a high voltage is developed between said first and second electrodes.

2. The device according to claim 1, further including a resistor connected between said first electrode and electrical ground.

3. The device according to claim 2 wherein said resistor has a resistance value substantially lower than the resistance existing between said first electrode and electrical ground and the resistance between said first and second electrodes.

4. The device according to claim 1 wherein said Faraday cup has a minimum diameter of approximately two inches.

5. The device according to claim 1 wherein said Faraday1 cup has a minimum length to diameter ratio of 6 to 6. A device for producing a high voltage between first and second electrodes mounted approximately 10 cm. apart in a partial vacuum, comprising means for generating an electron beam having an energy of 800 kv. and a current of microamperes, a Faraday cup mounted in electrical contact with said first electrode, a 5 l0 -ohm resistor connected between said first electrode and electrical ground, means for electrically grounding said second electrode, means'for directing said electron beam into said Faraday cup to cause a negative charge accumulation on said first element, whereby a voltage of approximately 600 kv. is developed between said first and second electrodes.

7. A device for producing a high voltage between first and second electrodes mounted in a partial vacuum, comprising means for generating an electron beam having an energy of 600 kv. and a current of 300 microamperes, a Faraday cup 18 inches long x 3 inches wide x 2.5 inches high mounted in electrical contact with said first electrode, means for electrically grounding said second electrode and means for directing said electron beam into said cup to cause a negative charge accumulation on said first electrode, whereby a voltage of 600 kv. is developed between said first and second electrodes.

References Cited UNITED STATES PATENTS Coolidge 3105 XR Labin et al. 315-3 Snyder 315 XR Gale et al. 3105 XR 6 Gale 3106 XR Gale 315-3 Goldie 31363 Gale 310-6 XR Rose 25049.5 Goncz 313106 MILTON O. HIRSHFIELD, Primary Examiner. D. F. DUGGAN, Assistant Examiner.

Claims

7. A DEVICE FOR PRODUCING A HIGH VOLTAGE BETWEEN FIRST AND A SECOND ELECTRODES MOUNTED IN A PARTIAL VACUUM, COMPRISING MEANS FOR GENERATING AN ELECTRON BEAM HAVING AN ENERGY OF 600 KV. AND A CURRENT OF 300 MICROAMPERES, A FARADAY CUP 18 INCHES LONG X 3 INCHES WIDE X 2.5 INCHES HIGH MOUNTED IN ELECTRICAL CONTACT WITH SAID FIRST ELECTRODE, MEANS FOR ELECTRICALLY GROUNDING SAID SECOND ELECTRODE AND MEANS FOR DIRECTING SAID ELECTRON BEAM INTO SAID CUP TO CAUSE A NEGATIVE CHARGE ACCUMULATION ON SAID FIRST ELECTRODE, WHEREBY A VOLTAGE OF 600 KV. IS DEVELOPED BETWEEN SAID FIRST AND SECOND ELECTRODES.