252. A 22-Mev electron linear accelerator: N. A. Austin and S. C. Fult, Rev. Sci. Instrum.30, No. 4, 1959

Abstract

An electron linear accelerator that can produce electron energy over 26 Mev was made by Toshiba. Use of 2 pi /3 mode accelerator waveguide eliminates the pulse-shortening phenomena completely. The length of the buncher, which is as short as three free space wavelengths, improves the conversion efficiency. A tantalum disk heated by bombardment of electrons is used as cathode in the electron gun. The heating is effected by electrons emitted from a tungsten filament. The electron beam is homogenous and its diameter is small. The electron emission from the cathode can be varied by changing the voltage of bombardnent. As the space between the tungsten filament and the cathode disk is designed to work under space-charge limited conditions, fluctuations of filament voltage have little effect on the temperature of the cathode disk and the electron beam is kept very stable. Stability of a few parts per million is obtained by using a travelling wave tube, 3W20, as r-f oscillator with a transmission type cavity resonator in its feedback loop. The frequency of the oscillator is 2810 Mc. The continuous power output of the tube is rated at 4 watts. A pulsed travelling wave tube, 3W80, is used as amplifier andmore » produces r- f pulses of 10 mu sec with peak power up to 500 watts. The tube, 3W80, is triggered simultaneously with the main modulator and its power output is supplied to two krystrons, M-4614. The r-f power output is 5Mw from each of the two accelerator waveguide sections, each of which is about 180 cm long. Characteristics of the accelerator are as follows: Electron energy, 4 to 25 Mev; Peak current for 3.5 mu sec pulse, 400 ma, maximum; Pulse repetition rate, 1 to 360 pps and single pulse; Pulse sidth, 0.3, 0.6, 1.2, 2.5, 5.0 mu sec. (JAIF)« less