Recent results in the hard-tube MILO experiment

Summary form only given, as follows. The hard-tube MILO (magnetically insulated transmission line oscillator) is an all stainless steel, brazed version of the gigawatt-class, L-band tube reported by Calico et al. (1995). The Calico MILO generated a 1.5-GW, 60-ns FWHM microwave pulse using a 500-kV, 60-kA, 500-ns electron beam, while the hard-tube MILO generates a 1.8-GW, 170-ns FWHM microwave pulse using a 500-kV, 60-kA, 300-ns electron beam. We show that this improved performance is due to suppression of unwanted electron emission from the cathode in the region of the first two tube cavities. We also report on experiments to identify the breakdown mechanism in the vacuum radome for the Vlasov antenna which is used as a high-power microwave load for both MILO experiments. Finally, experimental results are presented for an optimized version of the hard-tube MILO that computer simulations have shown should generate over 3.0 GW.