Understanding the Spatial structure of RF-induced SOL Modifications
Recent experimental characterization of Radio Frequency (RF) - induced Scrape-Off Layer (SOL) modifications in ASDEX-Upgrade (AUG), JET and Tore Supra (TS) is summarized. Geometrical aspects are emphasised: complex SOL patterns are evidenced by several indicators visualized in one or two dimensions transverse to magnetic field lines. Results are ascribed to inhomogeneous RF-induced SOL biasing around powered Ion Cyclotron Range of Frequencies (ICRF) antennas and associated E¥B0 density convection. Within a simple RF sheath model [Perkins1989], the shape of convective cells on TS can be interpreted in terms of RF sheath generation by parallel RF currents. Some lessons are drawn for future machines.