Experimental, numerical and analytical evaluation of j×B -thrust for fast-liquid-metal-flow divertor systems of nuclear fusion devices

Abstract

Divertor systems of fusion devices exhaust intense heat loads from the plasma, which degrades solid plasma-facing components (PFCs). Fast liquid metal (LM) flow divertors may be more advantageous for this purpose. However, LMs have risk of piling due to intense magnetohydrodynamic (MHD) drag. Despite this, severe deceleration of the flow could be countered with the injection of currents that are transverse to external magnetic fields, allowing to thrust the flow with jxB forces. The injection of currents as an approach to propel LM-divertor flows has remained experimentally understudied. This article focuses on the evaluation of jxB-thrust and finding its drawbacks. This paper evidences that the simple operation of a LM-flow divertor with jxB-thrust, without any of the instabilities caused from reactor plasmas or parasitic currents, already presents intrinsic challenges.

jxB-thrust was experimentally tested with free-surface-LM flows, a vertical magnetic field and and externally applied current. Experiments were reviewed with a theoretical model, showing agreement in the trends of theory and experiments. Full 3D-MHD-free-surface flow simulations were also performed with FreeMHD and confirmed the sensitivity to unstable flow behavior in LM systems when applying external currents. Furthermore, excessive power requirements are expected for the implementation of jxB-thrust at the reactor scale, making these systems inefficient for commercial devices.