PIC simulations of DC electronic currents collected by RF electrodes. Extrapolation to ICRF antennas

Experimental measurements have previously demonstrated the existence of DC electron currents collected on powered ICRF antenna structures, while at the same time ion current is measured by Langmuir probes at the other end of open flux tubes magnetically connected to the antenna. Such a configuration is tested numerically in this work by using the 2D electrostatic PIC code OOPIC. In simulations, the ICRF antenna is replaced by an RF electrode at one extremity of an open flux tube. At the other extremity of the open flux tube, the probe is modeled by a collecting electrode maintained at ground potential. RF and DC currents are computed on each boundary of the simulated box containing a magnetized plasma typical of tokamak SOL plasma parameters. Scans of RF voltage and frequency give clues about the nature of these currents.