Title: Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U

Abstract

Three-dimensional nonlinear simulations of Alfvén eigenmodes in the subcyclotron frequency range demonstrate a robust physical stabilizing mechanism via modest off-axis beam injection, in agreement with experimental observations from the National Spherical Torus Experiment (NSTX-U). Experimental results from NSTX-U have demonstrated that neutral beam injection from the new beam sources with large tangency radii deposits beam ions with large pitch, which can very effectively stabilize all unstable Global Alfvén Eigenmodes (GAEs). Beam-driven GAEs have been linked to enhanced electron transport in NSTX, and the ability to control these modes will have significant implications for NSTX-U, ITER, and other fusion devices where super-Alfvénic fast ions might be present. Nonlinear simulations using the HYM code have been performed to study the excitation and stabilization of GAEs in the NSTX-U right before and shortly after the additional off-axis beam injection. The simulations reproduce the experimental finding, namely, it is shown that off-axis neutral beam injection reliably and strongly suppresses all unstable GAEs. Before additional beam injection, the simulations show unstable counter-rotating GAEs with toroidal mode numbers and frequencies that match the experimentally determined modes. Additional off-axis beam injection has been modeled by adding beam ions with large pitch and varying density. The complete stabilizationmore » occurs at less than 7% of the total beam ion inventory. New analytical theory of GAE (de)stabilization has also been derived, indicating a different interpretation for the GAE stabilization mechanism compared to previous publications.« less

Authors:

Belova, E. V.  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-1525-1027"
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Fredrickson, E. D. ^[1]; Lestz, J. B.  ^[1];

• Search DOE PAGES for author "Lestz, J. B."
• Search DOE PAGES for ORCID "0000-0002-6975-1537"
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Crocker, N. A.  ^[2]

• Search DOE PAGES for author "Crocker, N. A."
• Search DOE PAGES for ORCID "0000-0003-2379-5814"
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+ Show Author Affiliations

1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
2. Department of Physics &, Astronomy, University of California, Los Angeles, California 90095, USA

Publication Date:

2019-09-12

Research Org.:

Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

Sponsoring Org.:

USDOE

Contributing Org.:

NSTX-U Team

OSTI Identifier:

1561973

Alternate Identifier(s):

OSTI ID: 1561389

Grant/Contract Number:  

SC0011810; AC02-09CH11466; DESC0011810

Resource Type:

Accepted Manuscript

Journal Name:

Physics of Plasmas

Additional Journal Information:

Journal Volume: 26; Journal Issue: 9; Journal ID: ISSN 1070-664X

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

70 PLASMA PHYSICS AND FUSION TECHNOLOGY