Acceleration gap for the Relativistic-Klystron Two-Beam Accelerator

We describe an acceleration gap and FODO quadrupole assembly for a prototype induction accelerator being constructed by FM Technologies for a joint LLNL/LBNL Relativistic-Klystron Two-Beam Accelerator (RK-TBA) technology test-bed experiment. The gap is designed for a 150 kV pulse with a 100 ns rise time and a 200 ns flat top provided by the induction cores. A demountable unit consisting of a reentrant geometry with alumina insulator and beam pipe was developed. Achieving the required longitudinal impedance, with the 1-1/8" beam pipe, required careful attention. We examined the electric field distribution, particularly at the opening to the beam pipe and at the insulator triple points. The magnet assemblies are distributed along the beam pipe. Each assembly consists of 12 parallelpipedal ceramic-8 magnet blocks arranged in a quadrupole Halbach configuration. This assembly is incorporated into a compact 50 cm induction modulator cell.