Pulse shortening in the improved magnetically insulated transmission line oscillator

Magnetically insulated transmission line oscillator (MILO) is a crossed field device designed specifically to generate microwave power at the gigawatt level, which is a major hotspot in the field of high-power microwaves (HPM) research at present. An improved MILO has been developed in our laboratory. When the improved MILO is driven by a 550kV, 54kA, 80ns electron beam, HPM is generated with power of 3.2 GW, frequency of about 1.76 GHz, and duration of 40 ns. In order to lengthen the duration of the radiated microwave pulse, a long-pulse accelerator, whose voltage is about 450 kV and impedance is about 15 Ω, is employed to drive the improved MILO. In experiments, the diode voltage is increased gradually from about 350 kV to about 460 kV. When the diode voltages are 375 kV, 438 kV and 458 kV, the corresponding microwave power are 0.7 GW, 1.8 GW and 2.3 GW, and the pulse duration are 110 ns, 100 ns, and 65 ns respectively. It is obvious that pulse shortening is observed in the experiments. The simulation and experimental results confirm that the leading reason for pulse shortening is the remarkable voltage variation in the experiments. In conclusion, a sufficiently flat voltage pulse is crucial to achieving a longer microwave pulse.