Magnetically shielded high voltage electron accelerator

• US 5,463,268 A
• Filed: 05/23/1994
• Issued: 10/31/1995
• Est. Priority Date: 05/23/1994
• Status: Expired due to Term

• Current Assignee: National Electrostatics Corporation
• Original Assignee: National Electrostatics Corporation
• Inventors: Schroeder, James B.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): DAY, MICHAEL HENRY
• Application Number:
  US08/247,261
• Time in Patent Office: 526 Days
• Field of Search: 313/293, 313/297, 313/313, 315/85, 174/35 MS
• US Class Current: 313/293
• CPC Class Codes: H01J 2237/0264 magnetic
• CPC Class Codes: H01J 37/09 Diaphragms; Shields associated with electron or ion-optical arrangements; Compensation of disturbing fields
• CPC Class Codes: H05H 5/02 Details targets for producing nuclear reactions H05H6/00

Abstract

The high voltage electrostatic accelerator of this invention has spark arrester rings which form magnetic shield elements around an acceleration tube and which together with mu-metal rings between accelerator segments shield the electrons being accelerated from stray static and dynamic magnetic fields. The spark arresters surround the accelerating electrodes. The rings between accelerator segments are formed of mu-metal, an alloy of nickel designed for its magnetic shielding properties and consisting of 77 percent nickel, 4.8 percent copper, 1.5 percent chrome and 14.9 percent iron. The mu-metal spark arresters together with the rings between accelerators segments provide an effective magnetic shield in a cost-effective manner. Because mu-metal has a high permeability, magnetic field lines tend to travel about the Mu-metal rings rather than pass through the acceleration tube, where they would influence electrons being accelerated. The discontinuous nature of the shield allows it to be super-positioned as an integral part of the spark arresters positioned about the accelerating electrodes.

Claims

1. A magnetically shielded high voltage electron accelerator comprising:

an electron source;

a high voltage vacuum tube for accelerating electrons, wherein the tube for accelerating electrons is composed of a plurality of segments, and wherein each segment has a plurality of axially spaced annular insulating elements and a plurality of annular voltage-carrying elements, and at least one segment attachment ring, and wherein a plurality of first magnetic shield elements formed of a high magnetic permeability material are connected to each vacuum tube segment, each magnetic shield element being connected to a voltage carrying element, the first magnetic shield elements being closely spaced along each segment, wherein the connected segments of the vacuum tube abut at connected segment attachment rings to form joints, and wherein the first magnetic shield elements are closely spaced along the vacuum tube and not continuous with each other, the first magnetic shield elements forming a magnetic shield along each vacuum tube segment; and

second magnetic shield element formed of a high magnetic permeability material which extends across each joint between connected vacuum tube segments.

2. The apparatus of claim 1 wherein the first and second magnetic shield elements are made from mu-metal.

3. The apparatus of claim 2 wherein the first and second magnetic shield elements are made from a metal comprised of between 20 and 25 percent iron.

4. The apparatus of claim 1 wherein the first and second magnetic shield elements are made from a metal comprised of between 75 and 80 percent nickel.

5. In a high voltage electrostatic accelerator having a pressure vessel filled with high pressure insulating gas, a support member within the pressure vessel, an insulated high voltage electrode spaced a substantial distance from said support, and an acceleration tube extending from the high voltage electrode to the support member, the tube being composed of it multiplicity of insulating segments and a multiplicity of voltage carrying plates, each plate being connected to a metal spark arrester ring surrounding the tube, the tube for accelerating electrons being composed of a plurality of segments having segment attachment rings which abut to form joints, the segments being composed of the insulating elements and the annular voltage-carrying elements;

wherein the improvement comprises;

forming the spark arrester metal tings of a material of high magnetic permeability, so shielding the acceleration tube from magnetic fields; and

a magnetic shield ring formed of the high magnetic permeability material, which extends across each joint formed by the segment attachment rings.

6. The apparatus of claim 5 wherein the material of high magnetic permeability is mu-metal.

7. The apparatus of claim 5 wherein the material of high magnetic permeability is a metal comprised of between 75 and 80 percent nickel.

8. The apparatus of claim 5 wherein the material of high magnetic permeability is a metal comprised of between 20 and 25 percent iron.

9. A magnetically shielded high voltage electron accelerator comprising:

a) a pressure vessel filled with high pressure insulating gas;

b) a support member within the pressure vessel;

c) an insulated high voltage electrode spaced a substantial distance from said support;

e) an electron source spaced within the electrode;

f) a high voltage vacuum tube for accelerating electrons which extends from the high voltage electrode to the support member and which is comprised of a plurality of segments, wherein each segment is comprised of a plurality of connected annular insulating elements and annular voltage-carrying elements, and each voltage-carrying element has a first means for magnetically shielding formed of a high magnetic permeability material, and wherein the voltage-carrying elements of each segment are closely spaced along the vacuum tube to form a low frequency magnetic shield;

g) at least one segment attachment ring on each vacuum tube segment, wherein the segment attachment rings of connected segments abut to form joints; and

h) a second means for extending a magnetic shield across the joints formed by the connected segments.

10. The apparatus of claim 9 wherein the first means for magnetically shielding and the second means for extending a magnetic shield are formed of mu-metal.

11. The apparatus of claim 9 wherein the first means for magnetically shielding and the second means for extending a magnetic shield are formed of a metal comprised of between 75 and 80 percent nickel.

12. The apparatus of claim 11 wherein the first means for magnetically shielding and the second means for extending a magnetic shield are formed of a metal comprised of between 20 and 25 percent iron.

13. In combination with a high voltage electron accelerator of the type having an electron source a high voltage vacuum tube for accelerating electrons composed of segments of connected axially spaced annular insulating elements and annular voltage-carrying elements each segment having a segment attachment ring, such that adjacent segments of the vacuum tube are connected at joints defined between adjacent segment attachment rings, and wherein each voltage-carrying element has a spark arrester attached thereto, the improvement comprising:

a) forming the spark arrester of a high magnetic permeability material; and

b) a ring of high magnetic permeability material positioned across the joints between the segment attachment rings to form a magnetic shield which extends along the vacuum tube.

14. The apparatus of claim 13 wherein the material of high magnetic permeability is mu-metal.

15. The apparatus of claim 13 wherein the material of high magnetic permeability is a metal comprised of between 75 and 80 percent nickel.

16. The apparatus of claim 15 wherein the material of high magnetic permeability is a metal comprised of between 20 and 25 percent iron.