Non-immersed apertured foilless diodes for the recirculating linear accelerator

Summary form only given. Nonimmersed apertured foilless diode designs have been developed for the Recirculating Linear Accelerator (RLA). They produce intense relativistic electron beams of low transverse velocities similar to those produced by foil diode designs. The anode foil is replaced by a four-range-thick anode plate with an aperture on axis. This configuration drastically increases the shot rate since there is no need for frequent foil changes and lengthy diode cavity pumpdowns. The performance of these diodes is currently being investigated with the low-energy (1.5-MV) RLA injector and the 4-MV IBEX accelerator. A diode configuration with a large (7-cm) A-K gap and a very thin 6-mm-diameter cathode shank was investigated in detail. It appears that the electron beam is focused by counterstreaming protons emitted from the anode aperture plate, which intercepts the outer section of the electron beam. MAGIC simulations based on this assumption have reproduced quite well both the amplitude and the time evolution of the experimentally observed electron beams. A ~600-A ion current can focus 15 kA of the electron beam through the 3-cm anode aperture