A comparison of low-n Mercier unstable Wendelstein stellarators and quasi-interchange modes in tokamaks
Fuente:
arXiv
Saved in:
| Main Authors: | , , , , , , , |
|---|---|
| Format: | Preprint |
| Published: |
2025
|
| Subjects: | |
| Online Access: | |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| _version_ | 1866918123493392384 |
|---|---|
| author | Ramasamy, Rohan Zhang, Haowei Geiger, Joachim Nührenberg, Carolin Smith, Håkan M. Lackner, Karl Igochine, Valentin team, the JOREK |
| author_facet | Ramasamy, Rohan Zhang, Haowei Geiger, Joachim Nührenberg, Carolin Smith, Håkan M. Lackner, Karl Igochine, Valentin team, the JOREK |
| contents | Mercier's criterion is typically enforced as a hard operational limit in stellarator design. At the same time, past experimental and numerical studies have shown that this limit may often be surpassed, though the exact mechanism behind this nonlinear stability is not well understood. This work aims to contribute to our current understanding by comparing the nonlinear evolution of Mercier unstable Wendelstein stellarators to that of nonlinearly stable quasi-interchange modes in tokamaks. A high mirror, very low $ι$, W7-X-like configuration is first simulated. A second case is then considered using experimental reconstructions of intermediate $β$ W7-AS discharges, where saturated low-n modes were observed experimentally, with sustained MHD signatures over tens of milliseconds. The possible reasons for the discrepancies between experiment and simulation, and the observation of partial reconnection in contrast to flux pumping are discussed, in view of reproducing and designing for operation of stellarators beyond the Mercier stability limit. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2505_03987 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | A comparison of low-n Mercier unstable Wendelstein stellarators and quasi-interchange modes in tokamaks Ramasamy, Rohan Zhang, Haowei Geiger, Joachim Nührenberg, Carolin Smith, Håkan M. Lackner, Karl Igochine, Valentin team, the JOREK Plasma Physics Mercier's criterion is typically enforced as a hard operational limit in stellarator design. At the same time, past experimental and numerical studies have shown that this limit may often be surpassed, though the exact mechanism behind this nonlinear stability is not well understood. This work aims to contribute to our current understanding by comparing the nonlinear evolution of Mercier unstable Wendelstein stellarators to that of nonlinearly stable quasi-interchange modes in tokamaks. A high mirror, very low $ι$, W7-X-like configuration is first simulated. A second case is then considered using experimental reconstructions of intermediate $β$ W7-AS discharges, where saturated low-n modes were observed experimentally, with sustained MHD signatures over tens of milliseconds. The possible reasons for the discrepancies between experiment and simulation, and the observation of partial reconnection in contrast to flux pumping are discussed, in view of reproducing and designing for operation of stellarators beyond the Mercier stability limit. |
| title | A comparison of low-n Mercier unstable Wendelstein stellarators and quasi-interchange modes in tokamaks |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2505.03987 |