Analysis of RF Sheath-Driven Tungsten Erosion at RF Antenna in the WEST Tokamak

TL;DR

This paper introduces the STRIPE framework to analyze tungsten erosion caused by RF sheath effects at the WEST tokamak antenna, combining plasma modeling, RF sheath simulation, sputtering, and impurity transport to predict erosion patterns and compare with experimental data.

Contribution

The study provides a spatially resolved, predictive analysis of tungsten erosion due to RF sheath effects in WEST, integrating multiple simulation tools and validating results against measurements.

Findings

STRIPE captures RF sheath potentials exceeding 300 V.

Erosion patterns show poloidal and toroidal asymmetries due to RF effects.

Predicted tungsten erosion increases 30-fold from ohmic to ICRH phases, aligning with measurements.

Abstract

This study applies the newly developed STRIPE (Simulated Transport of RF Impurity Production and Emission) framework to interpret tungsten (W) erosion at RF antenna structures in the WEST tokamak. STRIPE integrates SolEdge3x for edge plasma backgrounds, COMSOL for 3D RF sheath potentials, RustBCA for sputtering yields, and GITR for impurity transport and ion energy-angle distributions. In contrast to prior work by Kumar et al. 2025 Nucl. Fusion 65, 076039, which focused on framework validation for WEST ICRH discharge 57877, the present study provides a spatially resolved analysis of gross W erosion at both Q2 antenna limiters under ohmic and ICRH conditions. Using 2D SolEdge3x profiles in COMSOL, STRIPE captures rectified sheath potentials exceeding 300 V, leading to strong upper-limiter localization. Both poloidal and toroidal asymmetries are observed and attributed to RF sheath effects, with modeled erosion patterns deviating from experiment - highlighting sensitivity to sheath geometry and plasma resolution. High-charge-state oxygen ions (O6+-O8+) dominate erosion, while D+ contributes negligibly. A plasma composition of 1 percent oxygen and 98 percent deuterium is assumed. STRIPE predicts a 30-fold increase in gross W erosion from ohmic to ICRH phases, consistent with W-I 400.9 nm brightness measurements. Agreement within 5 percent (ohmic) and 30 percent (ICRH) demonstrates predictive capability and supports STRIPE's application in reactor-scale antenna design.