Radio frequency induced electron currents in ITER

Abstract

The perspectives of radio frequency mode conversion and fast wave current drive are examined for ITER. It is found that power cannot efficiently be coupled to the ion Bernstein wave because of the width of the ion-ion hybrid evanescence region; this excludes mode conversion as a feasible current drive method. Fast wave current drive is equally rendered difficult by the size of the machine. Except at the lowest frequencies, electron absorption is in competition with absorption by the different ion species. In particular, if there is contamination by Be from the coating, absorption by the Be impurity is not negligible. At these lower frequencies both central and off-axis current drive is possible. At high frequency another fast wave current drive window exists near the second harmonic cyclotron frequency of tritium but its efficiency is degraded when highly energetic tritium tails are formed.