Magnetic Priming of a Relativistic Magnetron Utilizing Ferromagnetic Wires in the Cathode and Anode

Abstract

Magnetic priming experiments on the UM/ L-3-Titan relativistic magnetron (100 MW in L-band, -300 kV, ~3 kGauss), have shown suppression of unwanted modes and major reduction in starting currents for the pi-mode. Data from continuing experiments on magnetic priming at the cathode will be presented, as well as preliminary data on magnetic priming at the cathode and anode. Azimuthally-varying, axial-magnetic-perturbations are generated by three, 4 cm or 6 cm-long Mu-metal wires located just below the surface of 0.86 mm wall-thickness stainless steel tubing. The electron-emitting surface of the stainless steel is laser machined for field emission. Magnetic perturbations applied only at the cathode decay with increasing radius, hi order to maintain magnetic perturbations across the entire A-K gap, we also install three, magnetic-priming, Mu-metal wires inside holes drilled in the anode structure. Magnetostatics calculations have been performed for the case of magnetic wires embedded in the cathode and in the anode. Simulation results show strong perturbations at the cathode surface, which fall off slightly at small radii, but grow in intensity as the anode surface is approached. Data demonstrate that magnetic priming at the cathode significantly lowers (average factor of 2.5) the range of starting currents for pi-mode generation. The percentage of pi-mode shots was also increased by magnetic priming at the cathode by as much as 60% over unprimed shots. Experiments are reported concerning the effects of magnetic priming at both cathode and anode.