Shielding of liquid metal targets in plasma of linear devices

Abstract

We apply a 0D model of shielding for simulations of liquid Li exposure experiments in He plasma of the Magnum-PSI linear device. The model accounts for all the most essential processes in the vapor cloud and plasma–surface interactions. The simulation results are in good agreement with the target surface temperature measurements. A factor of 10 increase in the erosion flux leads to a 100 °C decrease in the surface temperature, still giving a reasonable agreement with experiments. Therefore, the temperature measurements are inconclusive with respect to determining whether enhanced erosion takes place or not. We observe that only 10% of the eroded material is redeposited, while several other works suggest up to 99% redeposition. We show that low redeposition is a consequence of the low electron temperature, about 0.3 eV, in the vapor cloud and that the ratio of the ionization length to the transverse cloud size is the critical parameter to look at. Hence, the redeposition factor is not a universal quantity and can vary in quite a broad range depending on the plasma parameters and machine geometry.