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The formation and evolution of the cathode plasma in small-gap magnetically insulated transmission lines (MITLs) may lead to enormous current loss and even gap closure. This issue has been investigated through particle-in-cell/Monte Carlo collision simulations. Based on gas desorption from the cathode, the plasma is formed at the cathode when the emitted electrons collide with the desorbed gas contaminants. The expansion velocity and the electron and ion density distributions of the cathode plasma were analyzed. Rapid expansion of the plasma occurs when plasma instability increases due to a transverse magnetic mode in the MITL. Factors affecting the expansion velocity such as voltage amplitude and rate of gas desorption were examined. The simulation results indicated that a relatively high desorption rate of neutral gas resulted in a higher expansion velocity for the cathode plasma. This work extends our knowledge and understanding of cathode plasma dynamics in high-current MITLs. [ABSTRACT FROM AUTHOR]

In this paper, the evolution and dynamics of anode plasmas in high-power hollow cathode diodes were studied by particle-in-cell (PIC) simulation. The simulation results show that the ion flow emitted by the anode plasma layer and the increase of the electron current caused by the ion flow will cause a significant decline in the diode impedance in a short time. In addition, the expansion of the anode plasma layer will cause the diode impedance to decrease. The PIC simulation technique is also applied to a high-power hollow cathode diode of a 1.0 MV-LTD generator for anode plasmas, and the PIC simulation results were compared with the experimental data. [ABSTRACT FROM AUTHOR]

Surface evolution for a conductor electrode under pulsed megagauss (MG) magnetic field was investigated. Stainless steel rods with 3 mm diameter were driven by 8 MA, 130 ns (10%–90%) current pulse in a series of shots on the Primary Test Stand. Experimental data from two complementary diagnostic systems and simulation results from one-dimensional magneto-hydrodynamics code reveal a transition phase for instability development. The transition, which begins as the conductor surface starts to expand, lasts about 40 ns in the pulse. It ends after the thermal plasma is formed, and striation electrothermal instability growth stops but magneto-Rayleigh-Taylor instability (MRTI) starts to develop. An expanding velocity which grows to about 2.0 km/s during the transition phase was directly measured for the first time. The threshold magnetic field for thermal plasma formation on the stainless steel surface was inferred to be 3.3 MG under a rising rate of about 66 MG/μs, and after that MRTI becomes predominant for amplitude growth in surface perturbation. [ABSTRACT FROM AUTHOR]