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Title: Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model

Abstract

Alfvén Eigenmodes (AE) can be destabilized by energetic particles in neutral beam injection (NBI) heated plasmas through inverse Landau damping and couplings with gap modes in the shear Alfvén continua. In this paper, we describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system using the reduced MHD equations, density and parallel velocity moments for the energetic particles as well as the geodesic acoustic wave dynamics. A closure relation adds the Landau damping and resonant destabilization effects in the model. We apply the model to study the Alfvén modes stability in TJ-II, performing a parametric analysis in a range of realistic values of energetic particle β ($$\beta_{f}$$ ), ratios of thermal/Alfvén velocities ($$V_{\rm th}/V_{\rm A0}$$ ), energetic particle density profiles and toroidal modes (n) including toroidal and helical couplings. The study predicts a large helical coupling between different toroidal modes and the destabilization of helical Alfvén eigenmodes (HAE) with frequencies similar to the AE activity measured in TJ-II, between 50–400 kHz. The analysis has also revealed the destabilization of GAE (global Alfvén eigenmodes), TAE (toroidal Alfvén eigenmodes) and EPM (energetic particle modes). For the modes considered here, optimized TJ-II operationsmore » require a $$\rlap{-} \iota$$ profile in the range of $[0.845, 0.979]$ to stabilize AEs in the inner and middle plasma. AEs in the plasma periphery cannot be fully stabilized, although for a configuration with $$\rlap{-} \iota = [0.945, 1.079]$$ , only $n=7, 11, 15$ AE are unstable with a growth rate 4 times smaller compared to the standard $$\rlap{-} \iota = [1.54, 1.68]$$ case and a frequency of 100 kHz. Finally, we reproduce the frequency sweeping evolution of the AE frequency observed in TJ-II as the $$\rlap{-} \iota$$ profile is varied. The AE frequency sweeping is caused by consecutive changes of the instability dominant modes between different helical families.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Universidad Carlos III de Madrid (Spain)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1394310
DOE Contract Number:  
AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 57; Journal Issue: 12; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Varela, Jacobo, Spong, Donald A., and Garcia, Luis. Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model. United States: N. p., 2017. Web. doi:10.1088/1741-4326/aa83c4.
Varela, Jacobo, Spong, Donald A., & Garcia, Luis. Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model. United States. https://doi.org/10.1088/1741-4326/aa83c4
Varela, Jacobo, Spong, Donald A., and Garcia, Luis. 2017. "Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model". United States. https://doi.org/10.1088/1741-4326/aa83c4.
@article{osti_1394310,
title = {Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model},
author = {Varela, Jacobo and Spong, Donald A. and Garcia, Luis},
abstractNote = {Alfvén Eigenmodes (AE) can be destabilized by energetic particles in neutral beam injection (NBI) heated plasmas through inverse Landau damping and couplings with gap modes in the shear Alfvén continua. In this paper, we describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system using the reduced MHD equations, density and parallel velocity moments for the energetic particles as well as the geodesic acoustic wave dynamics. A closure relation adds the Landau damping and resonant destabilization effects in the model. We apply the model to study the Alfvén modes stability in TJ-II, performing a parametric analysis in a range of realistic values of energetic particle β ($\beta_{f}$ ), ratios of thermal/Alfvén velocities ($V_{\rm th}/V_{\rm A0}$ ), energetic particle density profiles and toroidal modes (n) including toroidal and helical couplings. The study predicts a large helical coupling between different toroidal modes and the destabilization of helical Alfvén eigenmodes (HAE) with frequencies similar to the AE activity measured in TJ-II, between 50–400 kHz. The analysis has also revealed the destabilization of GAE (global Alfvén eigenmodes), TAE (toroidal Alfvén eigenmodes) and EPM (energetic particle modes). For the modes considered here, optimized TJ-II operations require a $\rlap{-} \iota$ profile in the range of $[0.845, 0.979]$ to stabilize AEs in the inner and middle plasma. AEs in the plasma periphery cannot be fully stabilized, although for a configuration with $\rlap{-} \iota = [0.945, 1.079]$ , only $n=7, 11, 15$ AE are unstable with a growth rate 4 times smaller compared to the standard $\rlap{-} \iota = [1.54, 1.68]$ case and a frequency of 100 kHz. Finally, we reproduce the frequency sweeping evolution of the AE frequency observed in TJ-II as the $\rlap{-} \iota$ profile is varied. The AE frequency sweeping is caused by consecutive changes of the instability dominant modes between different helical families.},
doi = {10.1088/1741-4326/aa83c4},
url = {https://www.osti.gov/biblio/1394310}, journal = {Nuclear Fusion},
issn = {0029-5515},
number = 12,
volume = 57,
place = {United States},
year = {2017},
month = {9}
}