US3617909A - Electrostatic lens and feed-through - Google Patents

Abstract

Apparatus for focusing and passing a charged particle beam from a region of low pressure to a higher pressure region. The apparatus is a unitary structure including both the feed-through means and the means for electrostatically focusing the beam as it passes to the higher pressure region.

Description

1l-'O2-7l XR 396179909 72] Inventors Thomas E. Horton, Jr. [56] References Cited Oxford, -1 UNITED STATES PATENTS Charles 3,042,832 7/1962 Owren 313/83 x 2.5 3 2 3,193,712 7/1965 Harris 307/147 1 71, 4 101955 N d 3137474 45 Patented Nov. 2, 1971 2 95 [73] Assignce The United States of America as 'y 514mm" y F Hossfeld re e t d b th secretary of h Army A!torneys- Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and William P. Murphy [54] ELECTROSTATIC LENS AND FEED-THROUGH 4 Claims, 4 Drawing Figs. [52] U.S.Cl 328/228, ABSTRACT: Apparatus for focusing and passing a charged 1 219/121 EB, 313/83, 313/85 particle beam from a region of low pressure to a higher pres- [51] lnt.Cl. HOlj 29/58 sure region. The apparatus is a unitary structure including [50] Field of Searchm. 174/28, both the feed-through means and the means for electrostati- 102; 219/121 EB; 307/147; 313/83, 85, 63, 74; cally focusing the beam as it passes to the higher pressure re- 328/228,229,233,237,227 gion.

VO LTAG E VACUUM SOURCE SOURCE PATENTEU NUVZ I971 SHEET 1 OF 2 Thomas E. Horton, Jr. Charles M. Coson,111

INVENTORS.

PATENTEDnuvz 19?: 3,617,909

sum 2 OF 2 VACUUM SOURCE V 4 VOLTAGE SOURCE FIG. 3

Thomas E. Hortomdr. Charles M. Coson III INVENTORS.

FIG. 2 BY Z' W ELECTROSTATIC LENS AND FEED-THROUGH BACKGROUND'OF THE INVENTION v I This invention relates generally to generators of charged particle beams, and further to the means included therein for focusing the beam and that for passing the beam from the lowpressure area inside the generator to the'outside higher pressure area.

Prior art generators of charged particle beams utilize a focusing means to converge a charged particle beam emitted from a source and accelerated through a field into one end of a capillary feed-through which passes the beam from the lowpressure in which the source operates to the higher pressure area outside the generator. The desired result'is an intense and highly directional output beam containing as many of the charged particles emitted from the source as possible.

A problem in conserving particles between the source and the output beam lies in the necessity of achieving a very precise alignment between the focusing means and the capillary feed-through. The inner diameter of the feed-through must be small to preserve the low pressure of the chamber in which the source must operate; however, the smaller the inner diameter of the feed-through is made, the greater is the problem of aligning the focusing means sufficiently to assure that a sizeable fraction of the particles enter the end of the feed-through. In applications of generators where the pressure difierence is great so that the inner diameter of the feedthrough must be very small, such as in electron guns used for welding under atmospheric pressure, the alignment problem has been severe.

SUMMARY OF THE INVENTION This invention eliminates the problem of alignment between the focusing means and the feed-through by combining both elements into an integral compact device. The capillary feedthrough is provided by a conducting tube separated by an insulator from a surrounding coextensive conductor having tubular end sections disposed coaxially with the tube. A voltage is applied between the inner tube and the outer conductor at points between the end sections to produce an electrostatic lens effect at each end of the device. When the device is aligned coaxially with respect to the beam emitted from the source, the beam is automatically focused so as to pass through the inner tube of the device. The device may be constructed so that the beam will be focused again upon leaving the inventive device. Hence the problem of alignment between a focusing element and a separate feed-through element present in the prior art is eliminated.

For further explanation of the invention, the following drawings and description disclose the preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Refer first to FIGS. 1, 2, and 3. A circular tube 2 is made of a rigid conducting material, preferably oxygen-free copper,

generator using the device and has inner diameter d outer diameter d,,, and length L. A conductor 3 is a circular tube expanded at one end, is also preferably copper, and has inner diameter D, at one end and D, at the other end and length L. Tubes 2 and 3 are separated by a solid insulator 4, preferably epoxy. A conducting wire lead 5 to the tube 2 is located away from the ends of the device 1. A voltage source 6 applies a voltage V between wire 5 and tube 3 to produce an electrostatic lens effect at each end of device 1.

Refer now to FIG. 4. Device l is mounted in a hole in a generator wall 11 so as to be aligned along the axis of a charged particle beam 12 being emitted from a source 13 located a distance S from wall 11. A pumping means 14 maintains a low pressure inside the generator. A voltage source 15 applies a voltage between wall 11 and source 13 to accelerate beam 12. As the diverging beam 12 approaches the end of device 1, it is automatically focused to pass through the inner tube of device 1, and is focused again at the other end of device 1 to emerge as an intense, highly directional beam 16.

Length L and diameter d, will be determined to the first order solely by the leakage that can be afforded across the pressure differential, which in turn will be determined by the efficiency of the vacuum pumps maintaining the low-pressure inside the generator. The separation Drd, and the voltage difference V will. govern the strength of the electrostatic field focusing the charged particle beam into the inner tube, and for a given value of V the separation D -d will be determined by the distance S, the average energy and directional qualities of the charged particle beam, the diameter d and the fraction of the beam desired to be focused into the inner tube. Likewise, the separation D,d, will be determined by the amount of focusing of the beam desired at the output end. The exact dimensions of a device made according to the invention can be determined by the person skilled in the art according to his particular application.

The claimed invention is:

1. Apparatus for generating charge particle beams and for passage thereof from a low-pressure area to a higher pressure area, comprising: a wall forming a chamber; a source for emitting said beam carried in said chamber; pumping means for maintaining low-pressure inside said chamber; means for applying a voltage between said source and said wall to accelerate saidbeam; feed through means secured in said wall in alignment with said charged particle beam, said feed through means including an open-ended passage communicating therethrough for directing said beam out of said chamber and electrostatic focusing means for electrostatically focusing said beam at the ends of said through said feedthrough means.

2. Apparatus as in claim 1 wherein said feed-through means includes:

a. a conducting circular tube;

b. a conducting means disposed around and coextensive with said tube and having two circularly tubular end sections disposed coaxially with said tube;

c. an insulator disposed between said tube and said conducting means; and

d. said electrostatic focusing means including means for applying a voltage between said tube and said conducting means at points between said end sections.

3. The apparatus as in claim 1 said tube, said end sections,

and said insulator being rigid.

4. The apparatus 3 as in claim 3 said tube and said end sections having appropriate dimensions for producing at each end thereof an electrostatic lens effect.

It l l i t

Claims (4)

1. Apparatus for generating charge particle beams and for passage thereof from a low-pressure area to a higher pressure area, comprising: a wall forming a chamber; a source for emitting said beam carried in said chamber; pumping means for maintaining low-pressure inside said chamber; means for applying a voltage between said source and said wall to accelerate said beam; feed through means secured in said wall in alignment with said charged particle beam, said feed through means including an open-ended passage communicating therethrough for directing said beam out of said chamber and electrostatic focusing means for electrostatically focusing said beam at the ends of said through said feedthrough means.

2. Apparatus as in claim 1 wherein said feed-through means includes: a. a conducting circular tube; b. a conducting means disposed around and coextensive with said tube and having two circularly tubular end sections disposed coaxially with said tube; c. an insulator disposed between said tube and said conducting means; and d. said electrostatic focusing means including means for applying a voltage between said tube and said conducting means at points between said end sections.

3. The apparatus as in claim 1 said tube, said end sections, and said insulator being rigid.

4. The apparatus 3 as in claim 3 said tube and said end sections having appropriate dimensions for producing at each end thereof an electrostatic lens effect.

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