Patent GB-706186-A (GB)
Title: Improvements in or relating to betatrons
IPC: H05H11/00
Filed: 1950-10-30
Abstract: 706,186. Magnetic induction accelerators. SIEMENS-REINIGER-WERKE AKT.-GES. Oct. 30, 1950 [Oct. 31, 1949], No. 26458/50. Class 39(1) In an arrangement for introducing electrons in a narrow beam into the stabilizing guiding field zone of a betatron, the electrons are guided on a direct path from an electron gun arranged in the plane of the equilibrium orbit and outside the orbit, azimuthally transversely through the stabilizing guiding field into a deflector arranged inside the orbit, and from the deflector azimuthally outwardly into the stabilizing guiding field zone. The electrons are injected with a velocity corresponding to the guiding field strength obtaining at the time of the time of the injection at the point of introduction. As shown, the electron gun is located within a tubular extension 4 of the envelope, and comprises focusing electrodes 9, 10, an accelerating electrode 11, and deflecting plates 12, 13 for adjusting the electron beam path. The deflecting plate 12 and the accelerating electrode 11 are connected together and to the wall coating 15. The electron beam is magnetically screened by making the electrodes of soft iron. The deflector for introducing the beam into the circle 16 along the inner boundary of the guiding field consists of an S-shaped plate 20 and two counter plates 21, 22. An additional plate 23 provides for adjusting the entry of the beam into the deflector. Cages 24, 25 adjacent the deflector inlet collect secondary electrons. The voltages, dimensions and curvatures of the two parts of the deflector are chosen so that the electron beam is brought to a focus inside the deflector and emerges as a narrow beam. As shown in Fig. 6 the first part 21 of the deflector has a portion reduced in cross-section to that of the second part 22. The electrodes of the electron gun and of the deflector are mounted between two ceramic bars 29, Fig. 2. to form a structural unit. The bars 29 are screwed to the ceramic end closure 5 of the envelope extension 4. Metallic coatings on the inner surfaces of the bars 29 are connected to the wall coating 15. Metallic strips on the outer surfaces of the bars 29 provide the leads for the deflector electrodes. The terminals for these leads are connected to them through contact springs. A deflecting system 26 guides the accelerated electrons through the envelope at 3. The guiding field is preferably maintained constant during injection. This may be effected by the use of an auxiliary coil surrounding only the accelerating field, or by the use of an abruptly saturable magnetic core bridging the central air gaps. With the guiding field not maintained absolutely constant the electron gun is designed to deliver a divergent beam. The injection voltage and the guiding field strength are such that electrons leaving the deflector perform only small radial oscillations, and the radial dependence of the guiding field in the region of the first rotations of the electrons is such that the electrons perform approximately two rotations for each radial oscillation. Specification 466,836 is referred to.