Patent GB-622148-A (GB)
Title: Improvements in and relating to means for imparting high energy to charged particles
IPC: H05H13/04
Filed: 1947-01-03
Abstract: 622,148. Magnetic induction accelerators. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 3, 1947, No. 281. Convention date, Jan. 5, 1946. [Class 39 (i)] Apparatus for imparting high energy to charged particles comprises a time-varying magnetic field linking the orbital path of the particles and an additional intermittentlyacting electric field acting at a selected portion of the path. The annular chamber 10 is highly evacuated and provided on its interior surface with a conductive coating, e.g. silver, formed with spaced gaps to act as a highfrequency electrode system. The conductive coating may have additional longitudinal uncoated gaps to minimize the circulation of induced currents. A laminated iron core 11, opposed pole-pieces 12, 13, and series-connected coils 25, 26 surround the chamber 10, the faces 12<11>, 13<11> of the pole-pieces being doubly tapered. An opening 16 permits cooling air to be circulated. The thermionic cathode 40 and electrodes forming the electron gun are supported by a stem 43 within the region of influence of the magnetic field of pole-pieces 12<11>, 13<11>, and a target lies near the inner periphery of the tube. Energizing voltage pulses are applied to the injecting electrodes by means of a winding 56 on a small core 57 of high permeability. The winding 56 produces a voltage pulse which is applied to the grid of a thyratron 64 which permits the discharge of a capacitor 68 through winding 53 and a consequent abrupt injection of electrons into vessel 10. Some of these electrons are accelerated to a fixed orbit having a speed within 1 per cent of the velocity of light. A voltage pulse arising from the reversal of flux due to magnetic variations at pole-pieces 20, 21 affects winding 71 and a thyratron 81. This causes a voltage drop across a resistor 85 and biasses an oscillator valve 89 to set up voltages on the accelerating electrodes of the betatron, and accelerate the electrons. These voltage oscillations are terminated by means of transformer 104, 105 which applies a voltage adjustable in phase to the resistor 107, and triggers thyratron tube 103 at the desired time. The firing of tube 103 brings the anode 114 to a lower voltage and current flow in tube 81 ceases. The electrons spiralling inwards impinge on the target and liberate X-rays. Alternatively, weakening of the magnetic guide field may allow outward spiralling of the orbit and impingement on the electron gun or a target nearby. In a modification, Fig. 8, a glass vessel 120 has inner and outer conductive coatings 121, 125, e.g. of silver, connected together by metal rings 127, 128, the inner coating being longitudinally divided as well as laterally divided by tapered gaps 123 in the metallic coating. The spacing between gap 123 and ring 127 is substantially a quarter of the wave-length of the desired frequency of the field across gap 123. The input transmission line 130, 131 is matched in impedance with the gap 123. This gap may taper from 30-60‹. The quarter-wave system attached thereto may be replaced by a halfwave system or a cavity resonator resonant at the operating frequency. Specification 574,812 and 585,992 are referred to.