Simulations of Cathode Plasma Expansion in Vacuum*

Vacuum arcs are a concern in many high voltage applications: accelerator cavities, spacecraft charging, ion sources, and pulsed power systems. In many cases an arcing event is a failure mode, while in others it may be the intended mode of operation. Understanding the initiation of a vacuum arc is critical to mitigating or controlling them. This work aims to clarify some of the elements of initiating arcs that are not well-understood.

 

A typical description of vacuum arc discharge involves a cathode (K) plasma forming that propagates to an anode (A), creating a conducting pathway, or arc. The timescale for some of the processes is quite fast (single ns’s) and there is indication that the speed of neutral and/or ion emission from the cathode is ~20,000 m/s. Furthermore, there is evidence that the cathode and anode might be acting in coordination but without an intervening plasma.

 

PIC-DSMC simulations are performed to investigate the speed of AK gap closure and ask questions related to cathodic material transiting the gap to the anode. The simulations are performed with Aleph, a massively parallel electrostatic low temperature plasma simulation capability. The numerical requirements for simulating such a large range of densities and high speeds are enormous and will be discussed.