RF and magnetic priming of relativistic magnetrons

Abstract

Summary form only given. Research is underway to investigate two techniques for priming of relativistic magnetrons for rapid startup and reduced mode competition: 1) RF priming experiments with a 2 MW magnetron signal 2) Magnetic-priming simulations by an azimuthally-varying axial magnetic field. Experiments utilize the MELBA-C (Titan) 6-vane, relativistic magnetron which operates with parameters: V=-300 kV, I=1-10 kA, e-beam pulselength=0.5 /spl mu/sec, microwave power=100-500 MW, microwave frequency in L-band: 1-1.3 GHz. The ceramic insulator enables operation down to 8.5 E-8 Torr. The RF priming source is a 2 MW, 2.2 /spl mu/sec, pulsed magnetron from AFRL operating at 1.3 GHz. The microwaves are injected into 1 of the 3 open coupling slots in the MELBA-C relativistic magnetron. Magnetic priming consists of imposing N/2 azimuthal variations in the axial magnetic field of an N-vane magnetron. Such optimal magnetic priming has been demonstrated in low voltage experiments and high voltage simulations to cause rapid startup of magnetrons by pre-bunching the electrons into the N/2 electron spokes desired for the pi-mode. A highly idealised model of magnetic priming uncovered a parametric instability, which draws electrons into N/2 spokes that extend to the anode even in the absence of RF fields.