Theoretical simulation of the closed currents near non-uniformly strongly heated surface of tungsten due to thermo-emf

Abstract

A problem of surface melting under the impact of plasmas is one of the most important in the development of future magnetic confinement fusion reactors. The expected high heat loads can lead to melting of tungsten chosen as the material of a divertor and the first wall of ITER. The tungsten melt can move under the action of forces and quickly deform a surface. This article shows that at high temperatures, a tungsten vapor can be considered as a conductive material with conductivity high enough to be taken into account during simulation of current through a sample. We describe the mechanism of current generation by the thermo-emf due to non-uniform heating of the vapor/condensed substance interface without external sources of charges. Even without direct contact with the external plasma, the density of this current is high enough to cause noticeable movement of the melt in an external magnetic field. Simulation shows that the melt moving observed at BETA may be caused not by a current of an electron beam but by non-uniformity of heating and can be reproduced by any other similar heat source in the external magnetic field.