US3471630A - Particle accelerators - Google Patents

Description

Oct. 7, 1969 w, F, G|BBQN$ ET AL 3,471,630

PARTICLE ACCELERATORS Filed Jan. 25, 1968 2 Sheets-Sheet 1 Inventors W F. G/BBo/ms K, h/ATKI V B M, 4,64% v da.

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Oct. 7, 1969 w GIBBONS ET AL 3,471,630

PARTICLE ACCELERATORS Filed Jan. 23, 1968 2 Sheets-Sheet 2 Inventor: W E GIBBO/VS WAT (Ml y [mt-n1, v M% United States Patent US. Cl. 17450.61 Claims ABSTRACT OF THE DISCLOSURE A tubular chamber for a particle acceleratoris made from a number of sections each of which consists of a metal tube divided longitudinally into at least two members by electrically insulating strips. The members are secured to the strips in a vacuum-tight manner.

This invention relates to particle accelerators of the type in which charged particles are accelerated along a curved or straight path in an evacuated tubular chamber. Such particle accelerators employing tubular chambers will hereafter be referred to as of the type specified and include accelerators of the betatron and synchrotron types employing gradually-increasing magnetic accelerating fields, and also linear accelerators employing constant electric accelerating fields.

Where particle accelerators of the type specified are of large size, the evacuated tubular chamber is usually built up from a number of sections of electrically insulating material. An all-metal construction is not suitable since this would allow electric currents to circulate with undesirable results.

Glass, ceramics, and epoxy resins are commonly used. A conductive coating may be put onto the inner surface of some or all of the sections of the chamber. The coating inside each section is sometimes formed in two electrically isolated parts so that it may be used for beam deflection. The conductive coating may also be used to facilitate the removal of any electric charge which may build up. Ceramic and glass chambers are very expensive because of the close dimensional tolerances to which they must necessarily be made. Epoxy resin sections are cheaper but suffer from the serious disadvantage that gases are evolved from the resin due to radiation produced by the charged particles being accelerated. This leads to defocusing of the beam of particles.

According to the present invention a tubular chamber for a particle accelerator of the type specified includes a plurality of sections each comprising a metal tube divided longitudinally into at least two members separated from one another by strips of electrically insulating material to which the members are secured in a vacuum-tight manner.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a transverse sectional view of an accelerator chamber;

FIGURE 2 is a side elevation view of part of one section of the accelerator chamber of FIGURE 1',

FIGURE 3 is a longitudinal sectional view showing how two sections of the chamber are joined together; and

FIGURE 4 is a transverse view of part of FIGURE 3.

The drawings illustrate, not necessarily to scale, an embodiment in which a chamber section of elliptical crosssection is formed from two metal members joined along the major axis of the section.

3,471,630 Patented Oct. 7, 1969 Referring to FIGURES l and 2, two metal members 10 and 11 are each formed into an approximately semielliptical shape as shown to form the main part of the section. outwardly-directed flanges are formed along the longitudinal edges of each section. The two sections are joined to two strips of ceramic material 12 and 13 by means of intermediate U-shaped metal fillets 14, 15, 16 and 17, as shown in FIGURE 1. The'metal members must be joined to the ceramic strips in a vacuum-tight manner so that the complete accelerator chamber may be evacuated. The four joints shown in FIGURE 1 are all made in the same way, and that between metal member 10 and ceramic strip 12 will be described in greater detail.

The upper surface of the strip 12 is covered with a metallised film and one side of the fillet 14 is brazed'to this film. The other side of the fillet 14 and the flange along one edge of the metal member 10 are then welded together.

Strengthening ribs 18 may be pressed into the metal members if required.

In order to simplify the connection of adjacent sections of the chamber, each end of a section has a ceramic endring 19 fastened to it. FIGURES 2, 3 and 4 illustrate the method of attaching the end-ring to the metal members and ceramic strips. As shown in FIGURE 4, an end-ring 19, of elliptical shape, has its side surfaces metallised as at 20, except for two small areas 21 on the major axis of the ellipse. The ends of each metal member are rolled back to form a flange, and these flanges are brazed to the metallised areas of the end-ring as shown in FIGURE 3. The non-metallised areas 21 of the end-ring are provided so that the two metal members making up a section are electrically insulated from one another. The mechanical connection between the end-ring and the ceramic strips must be made by using an epoxy-resin adhesive or a low melting-point glass.

FIGURE 3 also illustrates how two sections of the accelerator chamber are fastened together. To the side of each end-ring remote from the metal members is se cured, by brazing, a metal ring 22 of U-shaped section. Two adjacent sections are fastened together by welding the two adjacent metal rings together, as shown.

Since the complete accelerator chamber is in the form of a closed ring, then either each section will have to be slightly curved along its length, or alternatively the curve may be formed by the connections between adjacent sections of the chamber. Electrical connections will have to be provided between the metal members of some or all of the sections in order to facilitate charge removal. In the embodiment described the two members of each section are electrically insulated from one another. This is so that the two members of a section may be used as beam deflector plates when an electric potential is applied to them and also to avoid encircling the varying magnetic field of the accelerator with an electrically conduct- "ng path.

In some applications it is desirable to be able to heat the sections of the chamber. In such a case the metal members may be' made from a high-resistance material such as titanium or constantan, and they may then be heated simply by the passage of an electric current through the members. Ceramic materials have been mentioned as suitable for the insulating strips. However, other materials, such as glass, are also suitable. The important consideration is that it must be possible to form a vacuumtight seal between the insulating strips and the metal members. I

The accelerator chambers of particle accelerators of the type specified are usually of elliptical cross-section, but this is not essential, and chambers of different crosssection may be made.

The methods described of forming the joints between the metal members,the ceramic strips and the end-rings are only by way of example, and other methods are known to those skilled in the art.

The main advantage of sections made in accordance with the invention is their relatively low cost and simplicity of manufacture. The metal members and fillets are easily formed, and the only complexity introduced 1's in the forming of the seals between metal and ceramic components.

. What we claim is:

: 1. A tubular chamber for a particle accelerator of the type specified which includes a plurality of sections each comprising a metal tube divided longitudinally into at least two members separated from one other by strips of electrically insulating material, each member being secured to each insulating strip in a vacuum-tight manner by means of an intermediate metal fillet individual to that member.

2. A chamber as claimed in claim 1 in which each section of the chamber has an end-ring of electrically insulating material secured to each end.

3. A chamber as claimed in claim 2 in which the endrings of two adjacent sections are secured to one another by means of intermediate metal fillets.

4. A chamber as claimed in claim 1 in which said electrically insulating material is a ceramic material.

5. A chamber as claimed in claim 1 in which the members are made from a metal having a high electrical resistance.

References Cited UNITED STATES PATENTS 2,775,643 12/1956 Scott.

LEWIS H. MYERS, Primary Examiner D. A. TONE, Assistant Examiner US. 01. x.R. 313-317; 328-256

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