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Title: Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX

Abstract

We present results for the 3D nonlinear simulations of neutral-beam-driven compressional Alfv´en eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX). Hybrid MHD-particle simulations for the H-mode NSTX discharge (shot 141398) using the HYM code show unstable CAE modes for a range of toroidal mode numbers, n = 4 - 9, and frequencies below the ion cyclotron frequency. It is found that the essential feature of CAEs is their coupling to kinetic Alfv´en wave (KAW) that occurs on the high-field side at the Alfv´en resonance location. We frequently observe high-frequency Alfv´en eigenmodes in beam-heated NSTX plasmas, and have been linked to flattening of the electron temperature profiles at high beam power. Coupling between CAE and KAW suggests an energy channeling mechanism to explain these observations, in which beam driven CAEs dissipate their energy at the resonance location, therefore significantly modifying the energy deposition profile. Nonlinear simulations demonstrate that CAEs can channel the energy of the beam ions from the injection region near the magnetic axis to the location of the resonant mode conversion at the edge of the beam density profile. Furthermore, a set of nonlinear simulations show that the CAE instability saturates due to nonlinear particle trapping, and amore » large fraction of beam energy can be transferred to several unstable CAEs of relatively large amplitudes and absorbed at the resonant location. Absorption rate shows a strong scaling with the beam power.« less

Authors:
ORCiD logo [1];  [1];  [2];  [1];  [1];  [2];  [1]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Univ. of California, Los Angeles, CA (United States)
Publication Date:
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
Contributing Org.:
University of California, Los Angeles, California 90095, USA The simulations reported here were carried out using resources of the National Energy Research Scientific Computing Center (NERSC).
OSTI Identifier:
1358658
Alternate Identifier(s):
OSTI ID: 1346987; OSTI ID: 1363699
Grant/Contract Number:
AC02-09CH11466; SC0011810; DESC0011810
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 24; Journal Issue: 4; Related Information: http://arks.princeton.edu/ark:/88435/dsp018p58pg29j; Journal ID: ISSN 1089-7674
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; beam-plasma interaction; numerical simulations; waves; resonance; plasmas; absorption; conversion; frequency; spectrum; tokamaks

Citation Formats

Belova, Elena V., Gorelenkov, N. N., Crocker, N. A., Lestz, J. B., Fredrickson, E. D., Tang, S., and Tritz, K.. Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX. United States: N. p., 2017. Web. doi:10.1063/1.4979278.
Belova, Elena V., Gorelenkov, N. N., Crocker, N. A., Lestz, J. B., Fredrickson, E. D., Tang, S., & Tritz, K.. Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX. United States. doi:10.1063/1.4979278.
Belova, Elena V., Gorelenkov, N. N., Crocker, N. A., Lestz, J. B., Fredrickson, E. D., Tang, S., and Tritz, K.. Fri . "Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX". United States. doi:10.1063/1.4979278. https://www.osti.gov/servlets/purl/1358658.
@article{osti_1358658,
title = {Nonlinear simulations of beam-driven Compressional Alfv´en Eigenmodes in NSTX},
author = {Belova, Elena V. and Gorelenkov, N. N. and Crocker, N. A. and Lestz, J. B. and Fredrickson, E. D. and Tang, S. and Tritz, K.},
abstractNote = {We present results for the 3D nonlinear simulations of neutral-beam-driven compressional Alfv´en eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX). Hybrid MHD-particle simulations for the H-mode NSTX discharge (shot 141398) using the HYM code show unstable CAE modes for a range of toroidal mode numbers, n = 4 - 9, and frequencies below the ion cyclotron frequency. It is found that the essential feature of CAEs is their coupling to kinetic Alfv´en wave (KAW) that occurs on the high-field side at the Alfv´en resonance location. We frequently observe high-frequency Alfv´en eigenmodes in beam-heated NSTX plasmas, and have been linked to flattening of the electron temperature profiles at high beam power. Coupling between CAE and KAW suggests an energy channeling mechanism to explain these observations, in which beam driven CAEs dissipate their energy at the resonance location, therefore significantly modifying the energy deposition profile. Nonlinear simulations demonstrate that CAEs can channel the energy of the beam ions from the injection region near the magnetic axis to the location of the resonant mode conversion at the edge of the beam density profile. Furthermore, a set of nonlinear simulations show that the CAE instability saturates due to nonlinear particle trapping, and a large fraction of beam energy can be transferred to several unstable CAEs of relatively large amplitudes and absorbed at the resonant location. Absorption rate shows a strong scaling with the beam power.},
doi = {10.1063/1.4979278},
journal = {Physics of Plasmas},
number = 4,
volume = 24,
place = {United States},
year = {Fri Mar 10 00:00:00 EST 2017},
month = {Fri Mar 10 00:00:00 EST 2017}
}

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