GB711916A - Improvements in and relating to apparatus for accelerating charged particles - Google Patents

Abstract

711,916. Magnetic induction accelerators. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 19, 1951 [Nov. 18, 1950], No. 27086/51. Class 39(1) A betatron started synchrotron has two sets sets of windings devoid of ferromagnetic material 31-34 and 86-89, Fig. 1, windings 31-34 producing the betatron accelerating and guiding fields and windings 86-89 a guiding field during the synchrotron acceleration, and the windings and acceleration path for the charged particles, preferably electrons, are enclosed in an evacuated tank 1. Windings 86-89 may operate alone or in conjunction with windings 31-34 during the synchrotron acceleration. Tank 1 is preferably of iron or steel, and is evacuated via tube 2. Cover plates 3, 4 are secured to cylinder 5 by screws 6 and gaskets 7 of synthetic rubber. Copper liner 10 absorbs eddy currents to prevent the time varying magnetic fields from extending to the tank 1, and the parts thereof are held together by screws 14. The gun 17 for injecting intermittent bursts of electrons may be constructed as described in Specification 685,444 and is supported within hollow tube 18 of stainless steel, through which the cathode conductors pass. The gun is adjustably mounted by means of flexible bellows 25, the vacuum being maintained by plate screw and gasket seals at either end thereof. The adjustments are carried out by screwing nuts 30 up or down on threaded stud 29; there may be several studs 29. Betatron windings 31, 32, 33, 34 devoid of ferromagnetic material comprise hollow tubes 35 through which water may be circulated for cooling. They are connected in series so the current flows in the same direction through all the windings, and supplied by conductors 36 sealed through tank 1 by insulators 37, plates 38, screws 39, gaskets 40. The windings are carried from liner 10 by dielectric spacers 42, supports 43, 44, 45, 46, spacers 47, 48 and dielectric shims 49, 50, 51 52. The assembly is strengthened by dielectric spokes 53 contacting cylinders 55 against which they are pressed by spreaders 56. The latter comprise dielectric blocks 57 59, studs 58 and dielectric nuts 60 which can be tightened to control the degree of pressure. Spacers 47, 48 are held apart by dielectric spacer 61, and pressure is exerted between liner 10 and cylinder 62 by means of cylindrical spacers 63, 64 engaged by spreaders 65 similar to 56. A cylindrical dielectric member may be made by winding glass cloth impregnated with an organic resin around a steel mandrel, and after curing the member is stripped from the mandrel and machined to the desired dimensions. The organic resin may be of diallyl phthalate and diethylene glycol maleate together with a polyvinyl formal resin obtained by the partial hydrolysis of polyvinyl acetate and the reaction of the partially hydrolized product with formaldehyde. The design of the coils 31-34 to satisfy the betatron acceleration and stability conditions is discussed. Shims 49-52 allow for vertical adjustment of the coils during assembly to correct for field discrepancies. The synchrotron acceleration is obtained by an open circuited coaxial line resonator 70. The outer and inner conductors 71, 72 and also further conductors 73 within 72 comprise a plurality of copper wires secured together by an organic resin, such as that already referred to, and extend over about 60 degrees of the circumference. Wires 71 may be hollow for water-cooling. Wires 72, 73 define an R.F. field free space within 72 through which the electrons pass, and 71, 72, 73 are preferably, but not necessarily, slotted at 79, 80, 81 to prevent eddy currents. Outer conductor 71 which also acts as an electrostatic shield is secured to cover plate 12 by copper plate 75, clamping members 76 and bolts 77, and 72 and 73 are soldered to plate 75. The structure is strengthened by arcuate dielectric member 78. The resonator frequency is equal to or a multiple of the rotation frequency of the electrons. During the synchrotron acceleration, the guide field windings 86, 87, 88, 89 are energized to keep the electrons at approximately the same radius. There windings are disposed in circumferential slots in spacers 47, 48, and may comprise hollow water-cooled tubes 90. Windings 86-89 are so connected that current in the outer windings 87, 88 flows in the same direction as in 31-34 while that in the inner windings 86, 89 flows in the opposite direction. Outer windings 87, 88 may be slightly'further apart than the inner windings. A suitable energizing and synchronizing circuit is described with reference to Figs. 5 and 6 (not shown). The arrangement may be such that' after synchrotron acceleration the electrons spiral inwardly or outwardly to a target to generate X-rays which pass out through a slot in 71 and groove 113 to a window in the tank 1, Fig. 2 (not shown). Specifications 574,812, 622,148 and 665,828 also are referred to.