Testing of a high temperature radiatively cooled Li/Ta heat pipe in Magnum-PSI

In this paper we present results from plasma testing and thermal analysis of a lithium filled tubular heat pipe used as a replaceable plasma facing component (PFC) with no direct cooling. The tantalum envelope (19 mm diameter by 197 mm long) was heated on its side wall using a hydrogen plasma beam in the linear plasma device Magnum-PSI. A single continuous plasma pulse lasting ˜2 h was carried out with the isothermal zone of the heat pipe operating at a temperature of ˜1000 °C for the whole time with the main heat removal via thermal radiation. Target tilting was used to vary the peak surface heat flux in the range 7.5–13 MW/m2. The tilting also increased the magnetic field component normal to the return flow of lithium via the sintered niobium wick to ˜0.85 T. Near infra-red thermography was used to measure the surface temperature. Heating power was increased until liquid lithium escaped through a crack in the heat pipe near the beam center. The impact of the lithium leak on the plasma was benign compared to that expected from leaks in helium or water cooled PFCs. The operating limit due to magnetohydrodynamic effects is calculated.