Title: Impact of ideal MHD stability limits on high-beta hybrid operation

Abstract

The hybrid scenario is a candidate for stationary high-fusion gain tokamak operation in ITER and DEMO. To obtain such performance, the energy confinement and the normalized pressure β_N must be maximized, which requires operating near or above ideal MHD no-wall limits. New experimental findings show how these limits can affect hybrid operation. Even if hybrids are mainly limited by tearing modes, proximity to the no-wall limit leads to 3D field amplification that affects plasma profiles, e.g. rotation braking is observed in ASDEX Upgrade throughout the plasma and peaks in the core. As a result, even the small ASDEX Upgrade error fields are amplified and their effects become visible. To quantify such effects, ASDEX Upgrade measured the response to 3D elds applied by 8 2 non-axisymmetric coils as N approaches the no-wall limit. The full n = 1 response profile and poloidal structure are measured by a suite of diagnostics and compared with linear MHD simulations, revealing a characteristic feature of hybrids: the n = 1 response is due to a global, marginally-stable n = 1 kink characterized by a large m = 1; n = 1 core harmonic due to q_min being just above 1. A helical core distortion ofmore » a few cm forms and affects various core quantities, including plasma rotation, electron and ion temperature, and intrinsic W density. In similar experiments, DIII-D also measured the effect of this helical core on the internal current profile, providing useful information to understand the physics of magnetic flux pumping, i.e. anomalous current redistribution by MHD modes that keeps q_min > 1. Thanks to flux pumping, a broad current profile is maintained in DIII-D even with large on-axis current drive, enabling fully non-inductive operation at high β_N up to 3.5 - 4.« less

Authors:

Piovesan, Paolo ^[1]; Igochine, V. ^[2]; Turco, F. ^[3]; Ryan, D. A. ^[4]; Cianciosa, M. R. ^[5]; Liu, Y. Q. ^[6]; Marrelli, L. ^[1]; Terranova, D. ^[1]; Wilcox, R. S. ^[7]; Wingen, A. ^[5]; Angioni, C. ^[2]; Bock, A. ^[2]; Chrystal, C. ^[7]; Classen, I. ^[8]; Dunne, M. ^[2]; Ferraro, N. M. ^[9]; Fischer, R. ^[2]; Gude, A. ^[2]; Holcomb, C. T. ^[10]; Lebschy, A. ^[2] more »; Luce, T. C. ^[11]; Maraschek, M. ^[2]; McDermott, R. ^[2]; Odstrcil, T. ^[2]; Paz-Soldan, C. ^[11]; Reich, M. ^[2]; Sertoli, M. ^[2]; Suttrop, W. ^[2]; Taylor, N. Z. ^[7]; Weiland, M. ^[2]; Willensdorfer, M. ^[2] « less

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+ Show Author Affiliations

1. Consorzio RFX, Padova (Italy)
2. Max-Planck-Institut fur Plasmaphysik, Garching (Germany)
3. Columbia Univ., New York, NY (United States)
4. Univ. of York, York (United Kingdom)
5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
6. Culham Science Centre, Abingdon (United Kingdom)
7. Oak Ridge Associated Univ., Oak Ridge, TN (United States)
8. DIFFER, Nieuwegein (The Netherlands)
9. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
10. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
11. General Atomics, San Diego, CA (United States)

Publication Date:

Thu Oct 27 00:00:00 EDT 2016

Research Org.:

Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States); General Atomics, San Diego, CA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC)

Contributing Org.:

The ASDEX Upgrade Team; The DIII-D Team; The EUROfusion MST1 Team

OSTI Identifier:

1336246

Alternate Identifier(s):

OSTI ID: 1375933; OSTI ID: 1376540

Grant/Contract Number:  

FC02-04ER54698; AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Plasma Physics and Controlled Fusion

Additional Journal Information:

Journal Volume: 59; Journal Issue: 1; Journal ID: ISSN 0741-3335

Publisher:

IOP Science

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY; hybrid scenario; MHD stability; 3D equilibrium