Fusion Science and Technology / Volume 56 / Number 3 / October 2009 / Pages 1353-1365
Technical Papers / Tore Supra Special Issue
The main key to achieving high-power long-duration discharges on Tore Supra, the actively cooled toroidal pump limiter (TPL) is the main plasma-facing component, handling high heat fluxes. The heat pattern on the TPL presents features of both localized and large-area limiters (mixed influences of parallel and cross-field heat fluxes). The combination of the toroidal field ripple and the flat surface results in a peaked heat flux pattern with large private flux areas on the surface. The apparent heat flux decay length is shorter than 10 mm and varies by less than 10% with the plasma conditions. The conduction/convection is modeled within 5% by the heat flux deposition code TOKAFLUX. The heat pattern is further modified by the contribution of suprathermal particles (ion ripple losses, fast electrons). Altogether, the relation of the peak heat flux to a given injected power is consistent with modeling made during TPL design. The thermal response of the elements is also in line with the design, with a typical thermal time constant of 1 s and steady-state surface temperature during long discharges. An important issue being investigated concerns the growth of material deposits; they accumulate in shadowed areas and especially just along the frontier to plasma-wetted areas. In 2009, the limiter is still in operation and several thematics are still being actively investigated, such as the effect of the material deposits on the operation, the long-time-scale behavior of the tile to heat sink bond, and the deuterium retention.