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  4. Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma
 
research article

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Varela, J.
•
Cooper, W. A.  
•
Nagaoka, K.
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February 1, 2020
Nuclear Fusion

The aim of the present study is to analyze the stability of the pressure gradient driven modes (PM) and Alfven eigenmodes (AE) in the large helical device (LHD) plasma if the rotational transform profile is modified by the current drive of the tangential neutral beam injectors (NBI). This study forms a basic search for optimized operation scenarios with reduced mode activity. The analysis is performed using the code FAR3d which solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations for density and parallel velocity moments of the energetic particle (EP) species, including the effect of the acoustic modes. The Landau damping and resonant destabilization effects are added via the closure relation. On-axis and off-axis NBI current drive modifies the rotational transform which becomes strongly distorted as the intensity of the neutral beam current drive (NBCD) increases, leading to wider continuum gaps and modifying the magnetic shear. The simulations with on-axis NBI injection show that a counter (ctr-) NBCD in inward shifted and default configurations leads to a lower growth rate of the PM, although strong n = 1 and 2 AEs can be destabilized. For the outward shifted configurations, a co-NBCD improves the AEs stability but the PM are further destabilized if the co-NBCD intensity is 30 kA T-1. If the NBI injection is off-axis, the plasma stability is not significantly improved due to the further destabilization of the AE and energetic particle modes (EPM) in the middle and outer plasma region.

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Type
research article
DOI
10.1088/1741-4326/ab60cf
Web of Science ID

WOS:000520150300001

Author(s)
Varela, J.
Cooper, W. A.  
Nagaoka, K.
Watanabe, K. Y.
Spong, D. A.
Garcia, L.
Cappa, A.
Azegami, A.
Date Issued

2020-02-01

Publisher

IOP Publishing Ltd

Published in
Nuclear Fusion
Volume

60

Issue

2

Article Number

026016

Subjects

Physics, Fluids & Plasmas

•

Physics

•

lhd

•

stability

•

mhd

•

alfven modes

•

neutral beam current drive

•

neutral beam injection

•

neoclassical tearing mode

•

electron-cyclotron waves

•

number ballooning modes

•

noninductive current

•

bootstrap current

•

heliotron/torsatron system

•

alfven eigenmodes

•

high-performance

•

stabilization

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SPC  
Available on Infoscience
April 2, 2020
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/167793
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