Investigating the influence of ion mass on plasma characteristics in low temperature ExB plasmas using 2D-3V PIC-MCC simulations*

Presence of drifts and instabilities in low-temperature plasma with an inhomogeneous magnetic field in different E×B discharge devices leads to complex plasma characteristics. The plasma profile varies with input conditions (such as gas chemistry, bias voltage, magnetic fields, power and pressure). Previously [1], we have studied instabilities in the background plasma in the case of Hydrogen in a simplified geometry (in the context of negative ion source using a 7 mT Gaussian shape transverse magnetic field) using the 2D-3V PIC-MCC kinetic model. In this work, using the same geometry, we have performed a comprehensive computational investigation to investigate how ion mass affects the plasma characteristics and plasma transport. Using the same initial conditions, comparison is made for two different gases - Hydrogen and Xenon. Ions are un-magnetized in the case of the Xenon, but ions are partially magnetized in the case of the Hydrogen. Compared to the Hydrogen case, we observe high plasma density and low electron and ion temperature in the case of Xenon due to high ionization rate than Hydrogen. In the Xenon case, the potential gradient present in the system is small compared to the Hydrogen, implying a weak electric field. E×B drift instabilities are visible in the case of Hydrogen, however, we do not observe any such instabilities in the case of Xenon. Plasma transport across the magnetic field is significantly influenced by these instabilities [1]. Our investigations suggest that ion mass plays a significant role in plasma transport across magnetic fields.

[1]. The feasibility of resonance induced instabilities in the magnetic filter region of low temperature plasma based negative ion sources, AIP Conference Proceedings 2373, 080003 (2021)