US3667058A

US3667058A - Electrostatic accelerated-charged-particle deflector

Info

Publication number: US3667058A
Application number: US26576A
Authority: US
Inventors: Alfred W Maschke
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1970-04-08
Filing date: 1970-04-08
Publication date: 1972-05-30
Anticipated expiration: 1989-05-30

Abstract

An electrostatic accelerated-charged-particle deflector includes a first electrode and a plurality of wire second electrodes spatially mounted with respect to each other and the first electrode to permit the passage of the accelerated charged particles between the first electrode and the second electrodes. A power supply is connected to establish a voltage gradient between the first electrode and the wire electrodes normal to the direction of motion of the charged particles to interact therewith and deflect the charged particles. The potential gradient is established with the wire second electrodes being electrically positive in potential relative the first electrode.

Description

United States Patent Maschke 1 May 30, 1972' 54] ELECTROSTATIC ACCELERATED- 2,473,477 6/1949 Smith ..3l3/62 CHARGED-PARTICLE DEFLECTOR 2,567,406 9 1951 Skellett... 313/78 x 2,691,116 10/1954 Allwine ..'......3l3/78 [72] Imam: Maschke wheat, 3,5o4,222 3/1970 Fukushima ..315 3 [73] Assignee: The United States of America as represented by the United States Atomic Primary Examiner-Robert Segal Energy Commission Att0rneyRoland A. Anderson [22] Filed: Apr. 8, 1970 ABSTRACT- 21 A l. N 26,576 I pp 0 An electrostatic accelerated-charged-particle deflector includes a first electrode and a plurality of wire second elec- [52] US. Cl ..328/229, 313/80, 328/235 tr des atially mou ted with respect to each other and the Ill. first electrode to pen-nit the passage of the accelerated [58] Field of Search ..328/229, 233, 235; 313/80, charged particles between the fi t electrode and the Second 313/78 electrodes. A power supply is connected to establish a voltage 0 gradient between the first electrode and the wire electrodes [56] References cued normal to the direction of motion of the charged particles to UNITED STATES PATENTS interact'therewith and detlect the charged particles. The

potential gradient is established with the wire second elec- 2,850,669 9/1958 Geer ..313/78 X trode being electrically ositive in otential relative the first 3,325,713 6/1967 Seidl et al.- ..328/233 elem-ode 3,388,359 6/1968 Lambertson. .328/235 3,407,323 10/1968 Hand ..3 1 3/80 X 4 Claims, 2 Drawing Figures Pow/5, V SUPPLY ELECTROSTATIC ACCELERATED-CHARGED- PARTICLE DEFLECTOR CONTRACTUAL ORIGIN OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the U.S. Atomic Energy Commission BACKGROUND OF THE INVENTION This invention relates to an apparatus for accelerating charged particles to high energy in a closed orbit and more particularly to the extraction apparatus used to deflect the accelerated charged particles from their orbit.

In a charged-particle accelerator, such as a synchrotron, particles are accelerated in a closed orbit until the particles attain a desired energy level at which time the accelerated particles are used to strike targets of interest. The targets of interest may be inserted into the closed orbital path of the accelerated particles or the accelerated particles may be deflected from their closed orbit to strike a target outside of the orbit.

Conventionally, extraction of the charged particle beam in a closed-orbit accelerator is effected using magnetic particlebeam deflectors. The particle-beam deflectors must provide enough magnetic field bending to make the emergent particle beam clear the accelerator components in the orbital path while their fields should not affect the particle beam during acceleration. At the same time, the septum electrode that separates the extraction field from the main accelerator field must be thin enough so that it does not intercept any significant fraction of the accelerating charged-particle beam. The efficiency of the extraction deflector is inversely proportional to the thickness of the septum electrode. For example, if in slow extraction, the oscillation amplitude of the charged-particle beam increases by 0.39 inch per revolution, percent of the accelerated particle beam will strike a septum electrode 0.039 inch thick and the extraction efficiency of the deflector will be 90 percent. While this figure may be acceptable for accelerators of relatively low energy, it is not acceptable for accelerators of 200 BeV energy since the residual radiation caused by this loss is excessive. Accordingly, it is necessary in high-energy accelerators to maintain a high efficiency extraction system to effect minimal residual radiation. For example, with the 200 BeV proton synchrotron at the National Accelerator Laboratory an extraction efficiency of 99 percent is desired to minimize radiation. To achieve this efficiency, the septum electrode should be approximately 0.001 inch wide as viewed by the charged particle beam.

As stated, most beam-extraction-system designs utilize magnetic deflectors with current carrying septum electrodes cooled at the edges. The magnetic field achievable with this type of magnetic extraction decreases with decreasing septum electrode thickness. Where the septum electrode thickness is less than 0.005 to 0.010 inch, the maximum attained magnetic field in the deflector is so low that an electrostatic deflector becomes more effective than the magnetic deflector.

Conventional electrostatic deflectors embody two principal disadvantages. First, their septum electrodes are too thick to effect the high efficiency extraction of the charged-particle beam. Attempts to thin the septum electrode result in a mechanically unstable electrode. Second arcing between the septum electrode and the cathode electrode occurs as a result of field emission electrons from the cathode when high potential gradients are used.

It is therefore an object of the present invention to provide an improved electrostatic deflector for use in the extraction of accelerated charged particles.

It is another object of the present invention to provide an electrostatic charged-particle deflector including a septum electrode which provides minimal interaction with the accelerated particle beam.

It is another object of the present invention to provide an electrostatic charged-particle deflector capable of extracting charged particles at high efficiencies.

It is another object of the present invention to provide an electrostatic charged-particle deflector wherein interaction between the septum electrode and field emission electrons from the cathode is minimal.

It is another object of the present invention to provide an electrostatic charged-particle deflector capable of attaining greater potential gradients between the electrodes thereof than heretofore.

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

SUMMARY OF THE INVENTION The electrostatic deflector of the present invention in general comprises a first electrode and a plurality of second electrodes mounted in a plane spatially with respect to each other and with respect to said first electrode to permit the passage between the first electrode and the second electrodes of charged particles in a partial vacuum. Means are provided for establishing an electrostatic field between the first electrode and the second electrodes to deflect the charged panicles.

Further understanding of the present invention may best be obtained by consideration of the accompanying drawing wherein:

FIG. 1 is a schematic top view of an apparatus constructed according to the present invention; and

FIG. 2 is a schematic front view of the apparatus of FIG. 1.

As previously stated, the beam extraction system of a high energy particle accelerator such as the 200 BeV proton synchrotron, effects extraction of the accelerated proton beam by using magnets placed so thattheir magnetic fields interact with the beam to cause deflection and extraction thereof from the closed orbit. The embodiment of the present invention shown in FIGS. 1 and 2 is intended for use with such conventional magnetic deflectors and is used to provide the initial deflection of the accelerated particle beam from the closed orbit. Subsequent deflection and extraction of the beam is achieved using the conventional aforedescribed magnetic deflectors.

In FIGS. 1 and 2, a partially evacuated container 10 is shown as a housing in which a charged particle beam 12 is normally accelerated. It will be appreciated that the container 10 extends in a circle to provide the beam 12 a closed orbital path. A plurality of septum wire electrodes 14 are mounted in container 10 in a frame 16 so that they lie in a plane and are mutually parallel and mutually equispaced. The wire electrodes 14 are mounted so that their longitudinal axes are normal to the direction of the particle beam 12 and so that they do not intercept the particle beam 12 during beam acceleration. The frame 16 is C-shaped with the open end facing the charged particle beam 12 to avoid interaction therewith.

Spaced from the septum wire electrodes 14 is an electrode 18. The electrode 18 is mounted spatially with respect to the wire electrodes 14 and parallel to the plane thereof. The spacing between the wire electrode 14 and electrode 18 is sufficient to permit the passage therebetween of the charged particle beam 12A. Electrode 18 is cylindrical in shape with closed hemispherical ends. A power supply 20 is connected to the electrode 18 so that with the wire electrodes 14 grounded a potential gradient is established between the electrode 18 as a cathode and the wire electrodes 14.

In operation, the accelerated charged particle beam 12 has its accelerating orbit changed by a kicker magnet (not shown) so that the beam 12A is caused to perturb and pass between the septum wire electrodes 14 and the electrode 18. The electrostatic field generated by the potential gradient between the electrode 18 and the septum wire electrodes 14 causes the accelerated charged particle beam 12 to be deflected into the subsequent magnetic deflectors (not shown).

Potential gradients between the electrode 18 and wire electrodes 14 of kilovolts per centimeter were achieved with septum wire electrodes 14 one mil in diameter and a SO-mil spacing between wires. The spacing between the electrodes 18 and the septum wire electrodes 14 was 1 centimeter and the material of the

electrodes

14 and 18 was of a low density, high 2 material such as tungsten.

It will be appreciated that the electrostatic particle deflector as hereinbefore described provides a septum electrode which is not only thin in cross section as viewed by the accelerated beam, but one which is also thin in depth since the majority of the length of the total septum electrode is made up of the spacing between the wire electrodes. This construction greatly reduces power loss by interaction with the accelerated beam so that extraction efficiencies of 99 percent are effected. Further, it will be appreciated that the particle deflector also provides a septum electrode which is thin in cross section as viewed by field-emission electrons emitted from the electrically positive electrode 18. Thus, the structure inhibits arcing between the septum wire electrodes 14 and the cathode electrode 18 while permitting operation at potential gradients greater than heretofore.

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

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A charged-particle accelerator including means interacting with said charged particles for effecting acceleration of said particles in a partial vacuum; means for extracting said charged particles from said accelerator after acceleration; a

first electrode, a plurality of septum second electrodes spatially mounted with respect to each other and said first electrode to permit the passage of said accelerated particles between said first electrode and said septum electrodes, and means for establishing an electrostatic field between said first electrode and said septum electrodes normal to the direction of motion of said charged particles to interact therewith and deflect said charged particles.

2. The apparatus according to claim 1 wherein said septum second electrodes comprise a plurality of wires sized in crosssectional area relative the spacing therebetween to inhibit interaction between said septum electrodes and said charged particles, and wherein said electrostatic field generating means comprise means for establishing a potential gradient between said first electrode and said septum second electrodes with said septum second electrodes electrically positive in potential relative said first electrode.

3. The apparatus according to claim 2 wherein said septum second electrode wires are mounted in a plane parallel to the direction of motion of said particles with the longitudinal axes of said wires being mutually parallel and normal to the direction of motion of said charged particles, and wherein said septum electrode wires each have a cross section relative the spacing therebetween to inhibit interaction between said septum electrode wires and any field emission electrons from said first electrode.

4. The apparatus according to claim 2 wherein said septum second electrode wires each have their longitudinal axis mounted in a plane mutually parallel and normal to the direction of motion of said charged particles.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Inventor(s) f fid W. Maschke It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In claim 1, column 3, line 32, after the semicolon insert --said extraction means including.

Signed and sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050(10-69) USCOMNHDC 603764369 us. GOVERNMENT PRINTING OFFICE: I965 O36334

Claims

1. A charged-particle accelerator including means interacting with said charged particles for effecting acceleration of said particles in a partial vacuum; means for extracting said charged particles from said accelerator after acceleration; a first electrode, a plurality of septum second electrodes spatially mounted with respect to each other and said first electrode to permit the passage of said accelerated particles between said first electrode and said septum electrodes, and means for establishing an electrostatic field between said first electrode and said septum electrodes normal to the direction of motion of said charged particles to interact therewith and deflect said charged particles.

2. The apparatus according to claim 1 wherein said septum second electrodes comprise a plurality of wires sized in cross-sectional area relative the spacing therebetween to inhibit interaction between said septum electrodes and said charged particles, and wherein said electrostatic field generating means comprise means for establishing a potential gradient between said first electrode and said septum second electrodes with said septum second electrodes electrically positive in potential relative said first electrode.