Laser Micromachined, Monolithic Cathodes for Cathode Priming of a Relativistic Magnetron

Abstract

Summary form only given. Experiments have been performed on a relativistic magnetron using innovative monolithic cathodes (Al). These new types of cathodes are fabricated utilizing KrF laser ablation of surfaces to enhance the local E field. Two new types of cathodes invented are: projection ablation lithography (PAL) and ablation line focused (ALF) cathodes. PAL cathodes are fabricated by ablating a demagnified-projected pattern onto the surface thereby creating metal cloth, ALF cathodes use a cylindrical lens to focus the laser beam into a single line; these focused laser lines are then ablated into patterns using a stepper motor controlled with LabVIEW. A novel technique for priming N-cavity magnetrons has been invented at the University of Michigan; this technique, priming, utilizes N/2 discrete, azimuthal, electron emission regions around the cathode circumference to prebunch electrons into pi-mode symmetry. Cathode priming experiments and simulations are performed on a relativistic, 6-vane, magnetron. This magnetron is powered by the MELBA-C accelerator with parameters: 0.3 MV, 1-10 kA and 300-500 ns pulselength. Microwave start-oscillation time for PAL cathode priming decreased an average of 10 ns when compared to the unprimed case. Simulations of cathode priming have been performed using the 3D particle-in-cell, MAGIC code. These simulations show pi-mode start-up times decrease from 28 ns with no priming down to 14 ns when cathode priming is imposed. Also, 3D simulations show suppression of undesired magnetron modes (2pi/3), for effective pi-mode-locking