In this paper, the sensitivity of switching-off voltage spikes of SiC MOSFET and Si IGBT to stray inductance at the same voltage and current levels is compared and analyzed. The influence of the geometric structure of simple stacked busbar on its stray inductance is analyzed and the general guiding principle of busbar design is given. Aimed at the three-level circuit topology involved in this project, based on the analysis of its working principle and commutation circuit, the stray inductance network of stacked busbar is successfully extracted with the help of finite element simulation software ANSYS Q3D, and the idea of optimizing stray inductance of maximum commutation circuit is putted forward. A set of three-level AC-DC-AC power electronic device is designed, and a series of iterative optimization design and optimization results analysis of the busbar of the device are made.

In this paper, a transmission line circuit model of a magnetically insulated transmission line(MITL) system has been developed for a 15 MA Z-pinch driver (CZ-15). The current loss characteristics of multi-level MITLs and the ion emission due to expansion of anode and cathode plasma during the PHC and inner-MITL region are analyzed. The temporal and spatial distribution of current loss of outer-MITL and ion current of the PHC and inner-MITL of the CZ-15 driver are obtained. 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 achieve fully magnetic insulation. Electron emission at the start of load current and the duration is about 25 ns, which is short for a single pulse and has little effect on the rising edge and peak value of the load current. The waveform of the electron flow functioning as time resembles a saddle shape, whose amplitude goes up first, then it goes down, and then increase 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. During the inner-MITL region, the main positive ion species are protons and Oxygen 2%2B. At the beginning, the ion loss current of proton is larger than that of Oxygen 2%2B, 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 increase 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 about 18 MA and hold voltage about 2.3 MV, the peak load current is about 13.5 MA.

No abstract

A transmission line circuit model was conducted to compare the performances of the two-level 2.5 Ω magnetically insulated transmission lines (MITLs) system of a 5-MA linear-transformer-driver (LTD) accelerator for two kinds of typical loads, including bremsstrahlung electron beam diodes and Z-pinch loads. Both the electron current loss in the pulse front during the magnetic insulation setup process and the electron flow distribution in the magnetic insulation steady state were analyzed. When the accelerator drives an electron beam diode load with impedance of 1.20 Ω (a single level), the duration of the magnetic insulation setup is about 12 ns, the current loss is about 130 kA in a single MITL level, the maximum electron flow current is about 50 kA in the end of MITL, and its amplitude decreases gradually after the steady magnetic insulation is established. When the accelerator drives a Z-pinch load with length of 1.5 cm, radius of 1.2 cm, and mass of 0.3 mg/cm, the duration of the magnetic insulation setup is almost zero, the maximum electron flow current in the end of MITL can reach about 55 kA (a single level), and the waveform of the electron flow resembles a saddle shape, which reaches the peak at the pinch stagnation time.

In order to minimize the initial energy storage of tens of MA-class Z-pinch accelerators, an intelligent optimization method was developed based on the transmission line code circuit model and PSOGSA algorithm. Using several input parameters, the four overall parameters of the Z-pinch accelerator could be fast determined, including the connection and parallel combination of LTD cavities, the outer radius of the stack-MITL system, and electrical length of monolithic radial transmission lines. The optimization method has been verified by comparing the results with the Z-300 and Z-800 conceptual designs. By means of this intelligent optimization, some factors that affect the initial energy storage on high-current Z-pinch accelerators have been investigated, such as the operating electrical fields, the diameter of the stack-MITL system, and the inner diameter of the LTD cavity. The suggestions for designing relatively low-cost, efficient LTD-based accelerators have been proposed.