Modeling wall ion fluxes in an RF discharge: insights from 2D PIC simulation

Global models of plasma discharges have been widely used to simulate plasma reactors in the fields of plasma processing and space propulsion [Chabert et al 2012, Grondein et al. 2016]. These models rely on accurate description of the ion current leaving the plasma: after undergoing a pre-sheath drop, the ions enter the sheath at Bohm velocity. The pre-sheath drop is characterized by an edge-to-center plasma density ratio $h_L$ and heuristic models were formerly derived to understand how this parameter varies with plasma temperatures and ion mean free path, based on one-dimensional (1D) transport theory [Chabert et al. 2011], and validated by 1D simulation [Lafleur et al. 2015]. A model of inductively coupled plasma (ICP) discharges was implemented into a 2D benchmarked particle-in-cell (PIC) code [Turner et al. 2012], running with various gases (Ar, He, Xe). These simulations show that the ion flux has a strong spatial dependency -- in agreement with former results [Lafleur et al. 2012] -- and that it is affected by the aspect ratio of the discharge reactor. The influence of dielectric walls is also investigated.