Table top, pulsed, relativistic electron gun with GV/m gradient

Abstract

We present the design and performance characteristics of a compact, high voltage pulser with 150 ps rise time, 0.2 to 2 ns adjustable flat top and up to 1 MV amplitude on a 80 Ohm load or up to 0.5 MV on a 20 Ohm load, at 1 Hz repetition rate. Combination of a laser triggered SF6 and a liquid gap is used to form the fast rising pulse and maintain a low jitter between the laser, external trigger, and the high voltage pulsed output. The dark current and breakdown studies with this pulse applied between the electrodes of a diode indicate that fields up to 1 GV/m could be supported by stainless steel and copper cathodes without breaking down. The dark current from a conditioned cathode in a background pressure of 10−7 Torr is below the detection limit of 0.5 mA of our system. Photoemission studies had been conducted with 300 kV applied between copper cathode and stainless steel anode seperated by 2 mm. KrF laser of 5 eV photon energy and 20 ns FWHM was used to irradiate the cathode. In these preliminary measurements, 3 nC charge and corresponding quantum efficiency of 3.5×10−4 have been obtained. Future plans include increasing the gradient to GV/m range, decreasing the laser pulse duration to ps and subps range and increasing the electron energy to a few MeV.