HEPP Seminar Summer 2026 #6: M. da Silva Barros / O. Varley

Monday 18 May 2026, 16:00 → 17:00 Europe/Berlin

HGW-SR2 / GAR-D2

Gustavo Grenfell (Max Planck Institute for Plasma Physics - Garching), René Bussiahn (IPP Bereich Greifswald)

https://eu02web.zoom-x.de/j/68203618730?pwd=0ftcdSo212mi4VamayjXSCmZX0tUZJ.1

Meeting-ID: 682 0361 8730
Kenncode: 267281

 

16:00 → 16:30 M. Madeira (P): Fluid Turbulence Simulations in Geometries with Internal Magnetic Islands

Edge turbulence is a decisive factor in global plasma confinement, yet it remains significantly underdeveloped in both analytical theory and numerical simulations. This is especially true for stellarators when compared to tokamaks, due to the increased complexity of 3D geometries and the presence of magnetic islands. With the objective of reducing the gap, the fluid turbulence code GRILLIX has been recently extended to support 3D geometries [1] and, in particular, Wendelstein 7-X (W7-X).

While the magnetic islands in W7-X typically form the basis of the island divertor concept, the highest confinement is achieved in limiter configurations featuring internal magnetic islands [2]. This work aims to validate the new capabilities of GRILLIX by modelling W7-X’s 5/5 magnetic island chain in limiter configurations. The simulations successfully match the experimental plasma profiles and reproduce the characteristic "W-shaped" perpendicular flow. To study the impact of the island size on the radial electric field, a scan was conducted in a simplified circular toroidal geometry for two device sizes. It reveals a critical island width at which strong E x B flows develop [3], significantly increasing the electric field shear and leading to localized turbulence
suppression.

[1] Stegmeir A., Finkbeiner M.E., Pitzal C., Geiger J. and Jenko F. 2026 Comput.
Phys. Commun. 318 109874
[2] T. Andreeva et al 2022 Nucl. Fusion 62 026032
[3] A Bañón Navarro et al 2017 Plasma Phys. Control. Fusion 59 034004

Speaker: Miguel Da Silva Barros Madeira (IPP Bereich Greifswald)

2026_05_18_MMadeira_Progress_Talk.pdf

Abstract.pdf

16:30 → 17:00 O. Varley (P): Finite-Beta Effects on Divertor Island Topology in Optimised QI Stellarators with JOREK

Quasi-isodynamic (QI) stellarators with island divertors are promising candidates for future fusion reactors [1]. Experiments on W7-X and MHD modelling with HINT [2] have shown that divertor performance is highly sensitive to changes in magnetic topology. Increasing plasma beta can modify the size and position of magnetic islands, while also enhancing stochasticity. Recent studies further suggest that, in certain optimised QI stellarators, increasing beta may trigger a phase transition within the magnetic islands, leading to dramatic changes in island topology [3].

In this work, we use the fully implicit nonlinear MHD code JOREK to investigate these effects and compare the results against HINT calculations. Refined workflows are developed to improve the robustness of JOREK edge modelling. Initial studies show qualitative agreement between JOREK and HINT, although a free-boundary extension of JOREK is required to achieve quantitative agreement.

[1] A. Goodman et al. J. Plasma Phys. 91, E153 (2025).

[2] Y. Suzuki et al. Nucl. Fusion 46, L19 (2006).

[3] J. Geiger et al. 24th ISHW, Poster Session 1, Poster 42 (2024).

Speaker: Orin Varley

2026_05_18_HEPP_progress.pdf

Quasi-isodynamic (QI) stellarators with island divertors are promising candidates for future fusion reactors [1]. Experiments on W7-X and MHD modelling with HINT [2] have shown that divertor performance is highly sensitive to changes in magnetic topology. Increasing plasma beta can modify the size and position of magnetic islands, while also enhancing stochasticity. Recent studies further suggest that, in certain optimised QI stellarators, increasing beta may trigger a phase transition within the magnetic islands, leading to dramatic changes in island topology [3].

In this work, we use the fully implicit nonlinear MHD code JOREK to investigate these effects and compare the results against HINT calculations. Refined workflows are developed to improve the robustness of JOREK edge modelling. Initial studies show qualitative agreement between JOREK and HINT, although a free-boundary extension of JOREK is required to achieve quantitative agreement.

[1] A. Goodman et al. J. Plasma Phys. 91, E153 (2025).

[2] Y. Suzuki et al. Nucl. Fusion 46, L19 (2006).

[3] J. Geiger et al. 24th ISHW, Poster Session 1, Poster 42 (2024).