Simulation of the First Wall Shielding During Upward VDE in Demo

Abstract First simulations of the DEMO first wall damage during the upward VDE of 0.6 GJ residual plasma energy in the core have been performed using the TOKES code. The simulations revealed two qualitatively different modes of the hot plasma core cooling. In the first of them, we proposed to call the weak shielding mode, the estimation of tungsten amount, vaporized from the wall during VDE is reduced from 5.7 kg for simulation without the shielding to 5∙10-4 kg, the melted pool depth at the wall surface remains almost the same 158 μm without shielding and 140 μm for the weak shielding; the amounts of melted W are 77 kg and 23 kg correspondingly. In the second one – the fast radiation cooling mode – which arises due to 15% increase of the initial core energy loss rate, the vaporized W penetrates directly to the hot core and radiates the plasma energy at least 5 times faster than in the weak shielding mode. As a result, the entire vertically displaced core is cooled by radiation during less than 1 ms, the W amount, vaporized during VDE is reduced to 0.8 kg, the melted pool depth is 92 μm and the amount of melted W is 60 kg.