Magnetic priming experiments on a long pulse, relativistic magnetron

Summary form only given. Initial magnetic priming experiments performed on the UM/Titan relativistic magnetron (6-vane, -300 kV, 5-10 kA, 0.3-0.5 mus) have shown improvements in magnetron performance over baseline operation. In the current experimental setup, three, 4-cm magnetic wires (Mu-Metal) are located within the cathode structure, centered beneath the emission region, and spaced 120 degrees apart. These wires produce magnetic perturbations with N/2 azimuthal symmetry (for pi-mode in an N vane magnetron). Because of the close proximity of the priming structures to the cathode surface, the magnetic perturbations are strongest in the region where the electrons are emitted into the magnetron interaction space. Results from experiments using the non-symmetric extraction-waveguide load array showed a dramatic reduction in pi-mode starting current (2.4 kA primed vs. 3.4 kA unprimed). Magnetic priming increased the percentage of pi-mode shots from 35% (unprimed) to 58% (primed). Preliminary data also show significant reductions in magnetron startup time as well as time to peak power for the pi-mode. Pi-mode peak power was increased by almost a factor of 2 in the magnetically primed case. The mean pulse width of pi-mode shots showed a slight, but statistically significant increase in the magnetic priming case (90 ns unprimed vs. 105 ns primed). Data obtained using the symmetric extraction-waveguide load array showed similar trends in magnetron performance improvement. Pi-mode mean starting current was reduced by magnetic priming (3.6 kA unprimed vs. 1.4 kA primed). Magnetic priming increased the percentage of pi-mode shots (46% unprimed vs. 50% primed). The series-2 magnetic priming case also showed a modest reduction in the time to peak power of the pi-mode shots. With the available number of shots, reductions in magnetron pi-mode startup time in the series-2 primed case versus the unprimed case could not be proven to be statistically significant using a t-test. Fut- re simulations and experiments will utilize different Mu-Metal wire lengths and diameter, as well as magnetic priming structures in the relativistic magnetron anode