Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| approved | sherwood_summary-1.pdf | 2026-03-03 14:40:35 | Atul Kumar |
| approved | sherwood_summary.pdf | 2026-03-03 13:16:33 | Atul Kumar |
Abstracts
Author: Atul Kumar
Requested Type: Consider for Invited
Submitted: 2026-03-04 16:07:15
Co-authors: A. Kumar, D. Nath, W. Tierens, J.D. Lore, R. Wilcox, G. Ronchi, M. Shafer, O. Sahni, M.S. Shephard, B. Van Compernolle, R.I. Pinsker, A. Demby, O. Schmitz
Contact Info:
Oak Ridge National laboratory
1 bethel Valley Road
Oak Ridge, TN 37831
United States
Abstract Text:
The recent demonstration of high-power helicon operations on DIII-D provides a promising path toward efficient mid-radius current drive in advanced tokamak regimes, but it may introduce new plasma–material interaction (PMI) challenges associated with rectified RF sheath potentials near antenna structures. We apply STRIPE, an integrated framework for RF-driven PMI, combining 2D SOLPS background plasmas, 3D RF sheath modeling, geometry-specific sputtering yields, and 3D whole-device impurity transport simulations with GITR(m), to quantify carbon erosion and global impurity dynamics in two H-mode discharges with antenna–plasma gaps of 7 cm and 4 cm and coupled RF powers of 150 kW and 250 kW, respectively. Simulations predict rectified sheath potentials of 2–5 kV localized near lower antenna regions where the field lines intersect surfaces at grazing angles, accelerating ions to multi-keV energies. Effective sputtering yields are obtained by integrating energy- and angle-resolved binary-collision yields with 3D ion energy–angle distributions computed using GITR, capturing curvature, magnetic incidence, and sheath acceleration effects. Carbon self-sputtering dominates erosion, with yields up to ~8 atoms/ion, while RF-accelerated D⁺ contributes ~1% of the total erosion flux. Reducing the antenna–plasma gap increases gross erosion by more than an order of magnitude and enhances core penetration (~58% versus ~35% of the helicon-sourced carbon), demonstrating nonlinear coupling between sheath voltage and plasma accessibility of impurities. Nevertheless, the helicon-induced carbon source remains smaller than the divertor-derived source and does not produce measurable core contamination. Predicted core impurity levels remain low and consistent with experimental observations showing no increase in global carbon content during helicon operation. Under future high-Z wall conditions, helicon-driven erosion could become a more significant main-chamber impurity source.
Characterization: 2.0
Comments: