Rapid ionization of Xe/Ar mixtures in nanosecond discharges exploiting post-pulse field reversals

Abstract

Enhanced post-pulse electric field reversals of Ar, Xe, and XeAr mixture gases in capacitively coupled nanosecond discharges are investigated with Particle-In-Cell simulations in the context of maximizing electron density. The electric field reversal occurs at the falling edge of the voltage pulse and induces electron oscillatory movement in the plasma bulk region. The amplitude of field reversals is affected by driven voltage and the ratio of bulk length to gap distance. Exploiting the field reversal with a so called Plasma frequency dependent Square Wave (PSW) in an optimal gas mixture leads to the highest electron density. Specifically, for a 250 V PSW XeAr mixture case, the electron density is 2.2 times higher compared to a 1 kV DC pure Xe case even if the driven voltage is 4 times less than DC voltage. In 250 V PSW cases, XeAr mixture plasma has 1.2 times higher average electron density and 1.2 times electron temperature in the sheath region than a pure Xe plasma. With a narrower bulk region, the XeAr plasma has an enhanced field reversal and this leads to higher and faster growing electron density and electron temperature than a Xe plasma. For applications using Xe plasmas, XeAr mixture plasmas with PSW can be exploited for high electron density and temperature at reduced costs.