He$^+$ and Xe$^+$ velocities near the presheath-sheath boundary in a He/Xe discharge

Abstract

The oopd1 particle-in-cell Monte Carlo collision (PIC-MCC) code is used to simulate He/Xe discharge in order to determine the velocities of helium and xenon ions at the presheath-sheath boundary in two ion species plasmas. Nine cases were simulated, seven of which are He/Xe mixtures with varying helium partial pressure and then two cases, one for pure helium and one pure xenon, while the discharge pressure is kept at 0.7 mTorr. As the partial pressure of helium is increased the velocities at the presheath-sheath boundary also increase for both ion species. In all cases thexenon ions reach the presheath-sheath boundary at approximately their own sound speed and the helium ions reach the boundary at a velocity which is much lower than their sound speed.