Title: Model for current drive induced crash cycles in W7-X

Abstract

In the Wendelstein 7-X (W7-X) stellarator, the vacuum rotational transform, ι, has a flat radial profile and does not cross any major rational resonance. Nevertheless, during plasma operation the ι–profile can be strongly modified by electron cyclotron current drive in such a way that the resulting ι-profile passes through low-order rational values, and this can trigger magnetohydrodynamic (MHD) events. Indeed, W7-X plasmas are sometimes subject to repetitive collapses of core confinement, which can be observed regardless of the direction in which the EC current is driven. Even though the origin of these MHD instabilities is under investigation, the crashes may be connected to the formation of magnetic islands and magnetic reconnection. In the present work, we try to shed light on the dynamics of different events happening during the course of sawtooth cycles in W7-X by proposing a model that combines a slow current diffusion with a recipe for fast relaxation that conserves the corresponding helical flux (Kadomtsev 1975 Fiz. Plazmy 1 710–15). We also propose a simple model based on Taylor relaxation (Taylor 1974 Phys. Rev. Lett. 33 1139), (Taylor 1986 Rev. Mod. Phys. 58 741) to predict the nonlinear redistribution of plasma current caused by the largest ofmore » the observed events.« less

Authors:

Aleynikova, K. ^[1]; Hudson, Stuart R.  ^[2];

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• Search DOE PAGES for ORCID "0000-0003-1530-2733"

Helander, Per  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-0460-590X"

Kumar, Arunav  ^[4];

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Geiger, Joachim  ^[3];

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Hirsch, M. ^[3]; Loizu, J. ^[5]; Nührenberg, C. ^[3]; Rahbarnia, Kian  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-5550-1801"

Qu, Zhisong  ^[4];

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• Search DOE PAGES for ORCID "0000-0003-4628-6983"

Gao, Yu  ^[3];

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• Search DOE PAGES for ORCID "0000-0001-8576-0970"

Thomsen, H. ^[3]; Turkin, Y. ^[3]; Zanini, Marco  ^[3]

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• Search DOE PAGES for ORCID "0000-0002-8717-1106"

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+ Show Author Affiliations

1. Max Planck Institute for Plasma Physics, Greifswald (Germany); Max Planck-Princeton Center for Fusion and Astro Plasma Physics, Princeton, NJ (United States)
2. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
3. Max Planck Institute for Plasma Physics, Greifswald (Germany)
4. Australian National Univ., Canberra, ACT (Australia)
5. Ecole Polytechnique Federale Lausanne (EPFL) (Switzerland)

Publication Date:

Mon Dec 06 00:00:00 EST 2021

Research Org.:

Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Org.:

USDOE; Euratom Research and Training Programme; Swiss National Science Foundation (SNSF); Simons Foundation

Contributing Org.:

W7-X Team

OSTI Identifier:

1878183

Grant/Contract Number:  

AC02-09CH11466; 633053; 560651

Resource Type:

Accepted Manuscript

Journal Name:

Nuclear Fusion

Additional Journal Information:

Journal Volume: 61; Journal Issue: 12; Journal ID: ISSN 0029-5515

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; stellarator; sawtooth; reconnection; equilibria