Thermal load on DED target plates

Abstract

At TEXTOR 94 the installation of a Dynamic Ergodic Divertor (DED) is foreseen to investigate the influence of a perturbation field at the high field side of the tokamak. The preliminary design has been described previously. The DED can be operated with a rotating field at frequencies in the range from 50 Hz to 10 kHz or with a stationary field (DC operation). In the preliminary design the thickness of the graphite tiles (target plates) was not finally defined: Thicker tiles can sustain higher heat loads but at high frequency operation of DED the perturbation field is weakened due to the skin effect in the graphite tiles. Between the back side of the target plates and the field coils an optional thermal insulation was foreseen. In this paper, the maximum temperatures and heat loads of the coils are discussed for the different design options. In the case of a rotating field, the heat is distributed poloidally almost uniformly and one dimensional heat diffusion calculation is appropriate. From the cooling time between discharges an 'equilibrium state' is found showing the heating and cooling of the target plates for longer sequences of equal discharges. At the DC operation of DED, the field causes 'hot stripes' on the DED divertor target plates due to increased heat fluxes compared to the rotating scenario. With a two dimensional model the maximum temperatures on both sides of the tiles are calculated.