Patent GB-663816-A (GB)
Title: Improvements in and relating to apparatus for the acceleration of electrons and ions
IPC: H05H13/04
Filed: 1946-07-18
Abstract: 663,816. Discharge apparatus. AKT.-GES. BROWN, BOVERI, & CIE. July 18, 1946 [Jan. 31, 1946], No. 21497/46. Class 39 (i). Relates to a linear or toroidal particle accelerator in which the particles pass repeatedly through high frequency electrical fields arranged in the direction of the moving particles and formed between conductors of a transmission line on which standing waves are established. In a linear accelerator, Fig. 2, the transmission line is galvanically uninterrupted, and comprises cylinders a1, b2, a3, b4 through which the particles pass, and wires b1, a2, b3, a4, interconnecting alternate cylinders. Voltage antinodes of the standing waves coincide with the gaps I-IV between the cylinders, and the arrangement is such that the particles are accelerated at each gap. This involves a progressive increase in the lengths of the cylinders, and of the standing wavelength. The standing wavelength is increased by the insertion of materials of high dielectric constant or permeability between the transmission line conductors, or by the use of inductances and condensers. The particles may be accelerated successively in two or more transmission lines energized as a symmetrical polyphase system. In a toroidal accelerator the particles pass repeatedly through one or more quarter-wave coaxial transmission lines under the control of a magnetic guiding field. The two coaxial lines 1a, 4a, Fig. 4, are energized in anti-phase. The line conductors continue beyond the short-circuiting points 10, 10a, but are open at the point 16 and are slit parallel to the particle orbit to prevent the flow of eddy currents. Betatron stabilization conditions are imposed on the magnetic field. To maintain synchronism between the particles and the accelerating voltage the radius of the particle path may be varied. The particles are introduced from a gun outside the acceleration tube proper with an excessive initial voltage and constrained to sweep along the inner wall of the tube where they are retarded by thin diaphragms to the correct synchronous voltage. As their voltage increases the radius of the particle orbit increases until the particles are no longer disturbed by the diaphragm. An additional rapidly increasing magnetic field may be used to force the particles away from the diaphragms. Alternatively the frequency of the accelerating voltage may be changed during the acceleration period, the constants of the transmission lines also being changed. The frequency change may be under the control of the particles passing through the plates of a condenser, and the transmission line constants may be changed by variation of the permeability of ferro-magnetic materials located between the transmission line conductors. In the acceleration of positive ions the accelerating frequency may be a multiple M of the circulating frequency, the multiple being decreased in steps. At each transition when the particles are out of synchronism with the accelerating field the radius of the particle path decreases and the circulating frequency increases until the next value of M is reached. The particles are brought out of synchronism at each transition when the radius of the particle orbit exceeds a certain value, for example by periodically changing the acceleration frequency or voltage, or the rate of change of the magnetic guiding field or by the design of the acceleration electrodes or of the magnetic pole-pieces. The particles may be abstracted after acceleration by means of an auxiliary steeply increasing magnetic field, and may strike an anti-cathode to produce X-rays, or may be led out of the tube by deflecting plates.