Self-shadowing, gaps and leading edges on Tore Supraʹs inner first wall

Operation with the actively cooled inner first wall of Tore Supra shows that even such a large area limiter is subjected to anomalous heat deposition where the plasma contacts the limiter. This can be modelled by a parallel convective heat flux with a e-folding length of the order of a millimetre. In some extreme cases, associated with lower hybrid heating in a low density plasma, the situation could degenerate into a runaway situation associated with large carbon influx into the discharge and ending with the rupture of elements. The analysis of the heat flux deposition on this limiter is complicated by the need to take shadowing effects into account, which are becoming significant because of the small scale phenomenon involved. It is shown that only a small fraction of the front faces is wetted by the parallel heat flux and that very disparate heat fluxes co-exists on each element.