Circuit simulation of current loss in magnetically insulated transmission line system in 15- MA Z-pinch driver

Abstract

In this paper, a transmission line circuit model of a magnetically insulated transmission line(MITL) system is developed for a 15-MA Z-pinch driver. The current loss characteristics of multi-level MITL and the ion emission due to the expansion of anode and cathode plasma in the post hole vacuum convolute(PHC) and inner-MITL region are analyzed. The spatiotemporal distribution of current loss of the outer-MITL and ion current of the PHC and inner-MITL of the 15 MA driver are obtained. The results show that the first electron emission happens at the end of constant-impedance MITL and the beginning of constant-gap MITL, and the end of constant-gap MITL firstly achieves fully magnetic insulation. Electron emission occurs at the start of load current and its duration is about 30 ns, which is short for a single pulse and has little effect on the rising edge nor peak value of the load current. The waveform of the electron flow varying with time resembles a saddle shape, whose amplitude first goes up, then comes down, and increases again. The electron flow current decreases from upstream to downstream in constant-gap MITL in space. The starting time of the loss current of the PHC is synchronized with the gap closing time. The loss current amplitude increases rapidly, reaching 4 MA at the peak load current time and 6.5 MA in the end. In the inner-MITL region, the main positive ion species are protons and oxygen 2+. At the beginning, the ion loss current of protons is larger than that of oxygen 2+, and then the protons are quickly magnetically insulated due to the small charge-to-mass ratio. The ion loss current of the inner-MITL region mainly increases after the peak load current time, and its peak value is 2.1 MA. Given the input conditions, the stack is going to deliver current of about 18 MA, the hold voltage is about 2.3 MV, and the peak load current is about 13.5 MA.