Electrically insulating materials for centrifugal mirrors

TL;DR

This paper investigates the use of hexagonal boron nitride as an electrically insulating material in centrifugal mirror fusion devices, combining computational modeling and plasma exposure tests to evaluate its performance.

Contribution

It presents a comprehensive assessment of hBN's suitability as an insulating material in centrifugal mirrors through modeling and experimental plasma exposure.

Findings

hBN shows promising thermal and electrical properties for fusion applications.

Erosion mechanisms like sputtering and grain ejection were less severe in hBN than in silicon carbide.

Computational models predict good performance of hBN under fusion-relevant conditions.

Abstract

The centrifugal mirror confinement scheme incorporates supersonic rotation into a magnetic mirror device, which stabilizes and heats the plasma. This concept is under investigation in the Centrifugal Mirror Fusion Experiment (CMFX) at the University of Maryland. Plasma rotation is driven by an axial magnetic field and a radial electric field that lead to velocity drifts in the azimuthal direction. An electrically insulating material is required to prevent the applied voltage from shorting on the grounded chamber. Hexagonal boron nitride (hBN) is a promising candidate material for plasma-facing components in future centrifugal mirrors due to its exceptional thermal and electrical properties. However, its performance under intense particle and heat fluxes characteristic of the plasma edge in fusion devices remains largely unexplored. Computational modeling for ion- and neutron-material interactions was carried out with RustBCA and OpenMC, respectively, and predicts relatively good performance in comparison to other insulating materials. Material coupons were then exposed to plasma in PISCES-A at UCSD and CMFX. A load-locked sample feedthrough was constructed and installed on CMFX to test coupons. Two erosion mechanisms were identified -- sputtering and grain ejection -- both of which were more apparent in silicon carbide than hBN.