Influence of toroidal and vertical magnetic fields on Ion Cyclotron Wall Conditioning in tokamaks

In the present paper, inter-machine studies of Ion Cyclotron Wall Conditioning (ICWC) have been performed in limiter (TEXTOR) and divertor (ASDEX Upgrade, AUG) tokamaks in the presence of toroidal (0.2-2.35 T) and vertical (0-0.04 T) magnetic fields using the conventional ICRF antennas without modifications in hardware. The ICWC effect on both machines was studied by analyzing the removal rate of marker gases which have been loaded to the walls by glow discharge beforehand. Several factors were identified which could have a crucial impact on the conditioning efficiency: (i) RF power coupled to the plasmas; (ii) RF power absorption scheme; (iii) superimposing an additional vertical magnetic field on the toroidal field (B(V) << B(T)). All the observed effects are analyzed in terms of RF plasma wave excitation/absorption and compared with the predictions from 1-D RF and 0-D transport codes. ICWC scenarios for ITER are proposed and analyzed. (C) 2009 Elsevier B.V. All rights reserved.