Experimental study on dissipative characteristics of cathode plasma of coaxial magnetically insulated transmission lines based on microwave interferometry

Abstract

Flash x-ray radiography is an important diagnostic in hydrodynamic experiments to provide fluoroscopic imaging of fast-moving dense targets. In order to obtain multiple images of an object at different times in an experiment, a flash x-ray accelerator is required to output multiple pulses. For the induction voltage adder (IVA) multi-pulse accelerator, it is important to study the effect of the cathode plasma generated by the front pulse in magnetically insulated transmission lines (MITLs) on the transmission of the subsequent pulses. In this paper, a coaxial MITL experimental platform based on the “QiangGuang-I” accelerator is established to study the dissipation characteristics of the cathode plasma, and its working condition is similar to that of MITLs in typical IVA accelerators. In the experiment, a stable magnetic insulation is formed in the coaxial MITL, and the current loss along the line can be ignored. The microwave interferometer is used to measure the evolution of cathode plasma density over time for hundreds of microseconds after the pulse disappears. The measurement results of microwave interference show that the line-averaged density of the plasma in the anode–cathode gap is above 1 × 1018 m−3, and the time for the plasma density to decrease to 1 × 1016 m−3 is about 600 μs. The expansion velocity of the plasma after a pulse is much lower than that during the pulse. In addition, the dissipation characteristics of the cathode plasma with different electrical parameters of the pulses are compared and analyzed.