An Analysis of Sheath Development of Cathode During the Instability Stage of Vacuum Arc

The purpose of this article was to investigate the dynamic evolution laws of the plasma between the gap during the instability phenomena in low-current vacuum arc using the simulation date comparison with the experimental data. The instability phenomena are characterized by high-frequency peaks of the arc voltage which are prior to the actual current chopping. Those peaks, which reach a level of more than ten times the normal arc voltage, have typical correspondence with the fluctuations of arc current and will result in a sudden chopping of the current through interaction with the elements of circuit. The fluctuations of arc voltage were classified into the types of long pulses and short pulses because of different characteristics on the duration time and oscillation morphology, which can summarize the peaks on the instability phenomena. The concepts of prearc cathode sheath and the cathode-emission intensity are proposed to reasonably explain the difference and connection between these two spikes. The distribution and motion of particles in the gap at different cathode-emission intensity, which demonstrating the development direction of the prearc cathode sheath and the relationship with the cathode-emission intensity, are simulated by the particle in cell-Monte Carlo collision (PIC-MCC). As a result, the relationship in the development of the prearc cathode sheath, the voltage spikes, and the intensity of cathode emission is summarized.