Computational studies of giant edge islands and unpaired X-points in HSX and W7-X by manipulating coil currents
Abstract
We present magnetic configurations in the Helically Symmetric eXperiment (HSX) and Wendelstein 7-X (W7-X), in which the edge magnetic structure exhibits island chains which are spatially larger than the previously reported configurations. These ``giant" island chains (with rotational transform ι=4/3 or 4/4 for HSX and ι=5/6, 5/5 or 5/4 for W7-X) are obtained by reducing the coil current in main coil 6 for HSX and non-planar coil 5 for W7-X (i.e. the coil nearest the up-down symmetric cross-section ϕ=36∘ for W7-X and ϕ=45∘ for HSX). This appears a sufficient (but not necessary) condition for giant islands. The giant islands create X-point legs which transport plasma to the plasma-facing components (PFCs). In the most extreme cases, the island O-points leave the domain of the field line map and the divertor legs of the remaining ``unpaired" X-points do not close around the island. We show for W7-X, via the construction of quadratic flux-minimising surfaces, that these island size trends can mostly be interpreted as changes in magnitude of a resonant perturbation on a changing resonant ``unperturbed" magnetic surface. We use the anisotropic heat diffusion code EMC3-Lite to find ``giant island" W7-X configurations which are promising for PFC heat loads. These configurations significantly degrade the neoclassical transport performance but allow exploration of novel divertor regimes; for example, we show that the internal island pitch can be increased. This leads to favourable downstream/upstream plasma density ratios according to simple models; an attractive finding which motivates further investigation.
Related
- Manipulating the stability of crystallographic and magnetic sub-lattices: A first-order magnetoelastic transformation in transition metal based Laves phase
- A New Method For Manipulating Circuits, Application To Quantum Adders
- Probing and Manipulating Quantum Materials with Strong-field Terahertz and Mid-infrared Radiation
- Bistable topological edge states in polariton microcavities with unpaired Dirac cones
- Rewire and reset are all you need: Minimal resources for manipulating non-Abelions
BibTeX
@misc{davies2026computational,
title = {{Computational studies of giant edge islands and unpaired X-points in HSX and W7-X by manipulating coil currents}},
author = {Robert Davies and Dieter Boeyaert and Alexis Wolfmeister and Benedikt Geiger and Georg Harrer and Joachim Geiger and Louis Day and Lucas Sanchez-Garay},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2607.14722},
eprint = {2607.14722},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2607.14722},
}
RIS
TY - UNPB
TI - Computational studies of giant edge islands and unpaired X-points in HSX and W7-X by manipulating coil currents
AU - Robert Davies
AU - Dieter Boeyaert
AU - Alexis Wolfmeister
AU - Benedikt Geiger
AU - Georg Harrer
AU - Joachim Geiger
AU - Louis Day
AU - Lucas Sanchez-Garay
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2607.14722
UR - https://arxiv.org/abs/2607.14722
AB - We present magnetic configurations in the Helically Symmetric eXperiment (HSX) and Wendelstein 7-X (W7-X), in which the edge magnetic structure exhibits island chains which are spatially larger than the previously reported configurations. These ``giant" island chains (with rotational transform ι=4/3 or 4/4 for HSX and ι=5/6, 5/5 or 5/4 for W7-X) are obtained by reducing the coil current in main coil 6 for HSX and non-planar coil 5 for W7-X (i.e. the coil nearest the up-down symmetric cross-section ϕ=36^∘ for W7-X and ϕ=45^∘ for HSX). This appears a sufficient (but not necessary) condition for giant islands. The giant islands create X-point legs which transport plasma to the plasma-facing components (PFCs). In the most extreme cases, the island O-points leave the domain of the field line map and the divertor legs of the remaining ``unpaired" X-points do not close around the island. We show for W7-X, via the construction of quadratic flux-minimising surfaces, that these island size trends can mostly be interpreted as changes in magnitude of a resonant perturbation on a changing resonant ``unperturbed" magnetic surface. We use the anisotropic heat diffusion code EMC3-Lite to find ``giant island" W7-X configurations which are promising for PFC heat loads. These configurations significantly degrade the neoclassical transport performance but allow exploration of novel divertor regimes; for example, we show that the internal island pitch can be increased. This leads to favourable downstream/upstream plasma density ratios according to simple models; an attractive finding which motivates further investigation.
ER -