Two-dimensional particle simulation on the behavior of multi-charged copper ions in the cathode spot of a pulsed vacuum arc discharge.

The behavior of multicharged ions in the cathode spot of pulsed copper vacuum arc is studied by the 2D3V electrostatic Particle-In-Cell Direct Simulation Monte Carlo method. This method tracks the position and velocity of electrons, neutrals, and copper ions charged from +1 to +4 simultaneously, which couples with external circuit physics as well as heat conduction at the cathode. The general thermofield electron emission developed in recent years is used in the vacuum arc simulation. The simulation starts from complete vacuum until the arc current reaches the steady state at about 3 A limited by the external circuit, and the arc voltage is between 20 and 30 V. During the discharge, the cathode temperature increases from room temperature to around 8000 K. The breakdown process is visualized by the distribution of ion density at different stages of arc discharge: from a small volume of cathode spot to a conductive current path between electrode gaps. The vacuum arc plasma is found to be highly ionized, with an average charge state slightly above two and electron density on the order of 1020 cm−3. The positively charged ions move in the direction from the cathode to anode, which is opposite to the direction of the applied external field. Ion energies at the steady state increase from 20 to 200 eV when charge states increase from +1 to +4. This indicates that the electrostatic acceleration of ions is caused by a dynamic space-charge field in the breakdown process of pulsed vacuum arc discharge. [ABSTRACT FROM AUTHOR]