Conceptual design of a pre-loaded liquid lithium divertor target for NSTX-U

P Rindt,N.J Lopes Cardozo,J.A.W Van Dommelen,R Kaita,M.A Jaworski

doi:10.1016/j.fusengdes.2016.08.020

Abstract

In this work, a conceptual design for a pre-filled liquid lithium divertor target for the National Spherical Torus Experiment Upgrade (NSTX-U) is presented. The design is aimed at facilitating experiments with high lithium flux from the plasma facing components (PFCs) in NSTX-U and investigating the potential of capillary based liquid lithium components. In the design, lithium is supplied from a reservoir in the PFC to the plasma facing surface via capillary action in a wicking structure. This working principle is also demonstrated experimentally. Next, a titanium zirconium molybdenum (TZM) prototype design is presented, required to withstand a steady state heat flux peaking at 10MWm−2 for 5s and edge localized modes depositing (130kJ in 2ms at 10Hz). The main challenge is to sufficiently reduce the thermal stresses. This is achieved by dividing the surface into brushes and filling the slots in between with liquid lithium. The principle of using this liquid “interlayer” allows for thermal expansion and simultaneously heat conduction, and could be used to significantly reduce the demands to solids in future PFCs. Lithium flow to the surface is analyzed using a novel analytical model, ideally suited for design purposes. Thermal stresses in the PFC are analyzed using the finite element method. The requirements are met, and thus a prototype will be manufactured for physical testing.

Highlights

In the process towards a commercially viable fusion reactor, one of the major challenges lies in the integrity and lifetime of materials
The design is aimed at facilitating experiments with high lithium flux from the plasma facing components (PFCs) in National Spherical Torus Experiment Upgrade (NSTX-U) and investigating the potential of capillary based liquid lithium components
Lithium is supplied from a reservoir in the PFC to the plasma facing surface via capillary action in a wicking structure

Summary

Introduction

In the process towards a commercially viable fusion reactor, one of the major challenges lies in the integrity and lifetime of materials. The plasma facing material considered for ITER, erodes too quickly for a commercial reactor [1]. A liquid is not vulnerable to erosion, because when material is removed it can be replenished. Another advantage is that any particles from the plasma retained in the liquid can be filtered out when the liquid is circulated, which can reduce the tritium inventory for example. LL allows for a low recycling operating regime, due to its great affinity with hydrogen species. This can lead to enhanced plasma performance [5,6]

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Discussion

Conclusion