Implicit particle-in-cell development for ion source plasmas

Particle-in-Cell (PIC) codes used to study plasma dynamics within ion sources
typically use an explicit scheme. These methods can be slow when simulating regions of high
electron density in ion sources, which require resolving the Debye length in space and the
plasma frequency in time. Recent developments on fully-implicit PIC models in curvilinear
geometries have shown that these spatial/time scales can be significantly decreased/increased
respectively, allowing for notable speed-ups in simulation time, and thus making it a potential
tool for studying the physics of ion sources. For this purpose, a charge and energy conserving
implicit PIC code has been developed in 1D to determine its potential for simulating bounded
plasmas. In this paper, we use this model to simulate a 1D benchmark of a bounded plasma
with fixed plasma density and electron/ion temperatures. The results are shown to compare
well to the benchmark and to the results using an explicit PIC code. It is shown that the total
amount of macro-particles used in the simulation is a better figure of merit for accurate results
than the standard particles per cell used in literature. Significant speed-ups in computation
time can be achieved for high plasma densities if the accuracy requirements are relaxed. In this
case, we demonstrate the ability of the implicit PIC code to speed-up simulation time by nearly
a factor of 12 compared to explicit PIC.