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Title: Nonlinear simulations of beam-driven Compressional Alfén Eigenmodes in NSTX

Abstract

Results of 3D nonlinear simulations of neutral-beam-driven compressional Alfvén eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX) are presented. 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 Alfvén wave (KAW) that occurs on the high-field side at the Alfvén resonance location. High-frequency Alfvén eigenmodes are frequently observed 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. 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 transferredmore » 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

Creator(s)/Author(s):
; ; ; ; ; ;
Publication Date:
DOE Contract Number:  
AC02-09CH11466
Product Type:
Dataset
Research Org.:
Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Sponsoring Org.:
U. S. Department of Energy
Keywords:
Compressional Alfven Eigenmodes
OSTI Identifier:
1562031
DOI:
10.11578/1562031

Citation Formats

Belova, E V, Gorelenkov, N N, Crocker, N A, Lestz, J B, Fredrickson, E D, Tang, S, and Tritz, K. Nonlinear simulations of beam-driven Compressional Alfén Eigenmodes in NSTX. United States: N. p., 2017. Web. doi:10.11578/1562031.
Belova, E V, Gorelenkov, N N, Crocker, N A, Lestz, J B, Fredrickson, E D, Tang, S, & Tritz, K. Nonlinear simulations of beam-driven Compressional Alfén Eigenmodes in NSTX. United States. doi:10.11578/1562031.
Belova, E V, Gorelenkov, N N, Crocker, N A, Lestz, J B, Fredrickson, E D, Tang, S, and Tritz, K. 2017. "Nonlinear simulations of beam-driven Compressional Alfén Eigenmodes in NSTX". United States. doi:10.11578/1562031. https://www.osti.gov/servlets/purl/1562031. Pub date:Sat Apr 01 00:00:00 EDT 2017
@article{osti_1562031,
title = {Nonlinear simulations of beam-driven Compressional Alfén Eigenmodes in NSTX},
author = {Belova, E V and Gorelenkov, N N and Crocker, N A and Lestz, J B and Fredrickson, E D and Tang, S and Tritz, K},
abstractNote = {Results of 3D nonlinear simulations of neutral-beam-driven compressional Alfvén eigenmodes (CAEs) in the National Spherical Torus Experiment (NSTX) are presented. 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 Alfvén wave (KAW) that occurs on the high-field side at the Alfvén resonance location. High-frequency Alfvén eigenmodes are frequently observed 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. 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 = {10.11578/1562031},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2017},
month = {4}
}

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