Analysis of Ion Density at Sheath Region Affected by Moving Speed of Vacuum Arc Cathode Spot Using Three-Dimensional Electromagnetic Thermal Fluid Simulation

Vacuum arc discharge has been used in a wide range of fields such as circuit breakers, ion plating, and surface treatment. In vacuum arc discharges, the cathode spots move rapidly and irregularly, and it is necessary to obtain the factor which control the cathode spot movement for industrial applications. It is assumed that the movement of cathode spot is caused by the transport of ions, which leads to the field electron emission and the thermionic electron emission. The transport of ions from the original cathode spot forms the potential hump which depends on the ion density, and causes the increment of electric field density on the advance side of cathode spot. In this research, the velocity of cathode spot is set as parameter for elucidating the relation between ion density and current density at the sheath region, and aims to elucidate the critical ion density for causing the cathode spot movement.