Test acceleration of Hokudai 45 MeV linear accelerator for nano-second pulsed electron beam generation

The short-pulse response of the electron gun which has been used for the Hokudai 45 MeV Linac was studied in order to generate a nano-second pulsed electron beam. A harmful reflection of the grid drive pulses, caused by the discontinuities of impedance at the input-terminal and at the grid-cathod assembly, was found. The insertion of a matching resistor across the gun input-terminal and the driving by a high voltage nano-second pulser (∼ 3 kV output peak voltage, 3 ns pulse width) with a large gird baias voltage was adopted to overcome these reflected signals. The characteristics of the accelerated beam were obtained; the measured by the pulse radiolysis method was about 30 - 45 Gray, and the pulse width was about 3.5 ns determined by the time-distribution of bremsstrahlung photons obtained by bombardment to a tungsten target with the electrons. (author)