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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:
ORCiD logo [1];  [1]; ORCiD logo [1]; ORCiD logo [2]
  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:
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

Citation Formats

Belova, E. V., Fredrickson, E. D., Lestz, J. B., and Crocker, N. A. Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U. United States: N. p., 2019. Web. doi:10.1063/1.5116357.
Belova, E. V., Fredrickson, E. D., Lestz, J. B., & Crocker, N. A. Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U. United States. doi:10.1063/1.5116357.
Belova, E. V., Fredrickson, E. D., Lestz, J. B., and Crocker, N. A. Thu . "Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U". United States. doi:10.1063/1.5116357.
@article{osti_1561973,
title = {Numerical simulations of global Alfvén eigenmodes excitation and stabilization in NSTX-U},
author = {Belova, E. V. and Fredrickson, E. D. and Lestz, J. B. and Crocker, N. A.},
abstractNote = {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 stabilization 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.},
doi = {10.1063/1.5116357},
journal = {Physics of Plasmas},
number = 9,
volume = 26,
place = {United States},
year = {2019},
month = {9}
}

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