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Title: NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes

Abstract

Toroidal Alfvén eigenmodes (TAEs) are gap modes induced by the toroidicity of tokamak plasmas in the absence of continuum damping. They can be excited by energetic particles (EPs) when the EP drive exceeds other dampings, such as electron and ion Landau damping, and collisional and radiative damping. A TAE benchmark case, which was proposed by the International Tokamak Physics Activity group, is studied in this work. The numerical calculations of linear growth of TAEs driven by EPs in a circular-shaped, large aspect ratio tokamak have been performed using the Hybrid Kinetic-MHD (HK-MHD) model implemented in the NIMROD code. This HK-MHD model couples a δf particle-in-cell representation of EPs with the 3D MHD representation of the bulk plasma through moment closure for the momentum conservation equation. Both the excitation of TAEs and their transition to energetic particle modes (EPMs) have been observed. The influence of EP density, temperature, density gradient, and position of the maximum relative density gradient, on the frequency and the growth rate of TAEs are obtained, which are consistent with those from the eigen-analysis calculations, kinetic-MHD, and gyrokinetic simulations for an initial Maxwellian distribution of EPs. The relative pressure gradient of EP at the radial location of themore » TAE gap, which represents the drive strength of EPs, can strongly affect the growth rate of TAEs. It is demonstrated that the mode transition due to EP drive variation leads to not only the change of frequency but also the change of the mode structure. This mechanism can be helpful in understanding the nonlinear physics of TAE/EPM, such as frequency chirping.« less

Authors:
 [1];  [2];  [3];  [4];  [1];  [4]
  1. Univ. of Science and Technology of China, Hefei (China). CAS Key Lab. of Geospace Environment and Dept. of Modern Physics
  2. Univ. of Science and Technology of China, Hefei (China). CAS Key Lab. of Geospace Environment, Dept. of Modern Physics, and KTX Lab.; Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics
  3. SLS2 Consulting, San Diego, CA (United States)
  4. Dalian Univ. of Technology (China)
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States); Univ. of California, Oakland, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
Contributing Org.:
NIMROD Team
OSTI Identifier:
1540122
Alternate Identifier(s):
OSTI ID: 1415521
Grant/Contract Number:  
FC02-08ER54975; FG02-86ER53218; AC02-05CH11231; 13DE-AC02-05CH11231; DEFG02-86ER53218
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
Physics

Citation Formats

Hou, Yawei, Zhu, Ping, Kim, Charlson C., Hu, Zhaoqing, Zou, Zhihui, and Wang, Zhengxiong. NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes. United States: N. p., 2018. Web. doi:10.1063/1.4999619.
Hou, Yawei, Zhu, Ping, Kim, Charlson C., Hu, Zhaoqing, Zou, Zhihui, & Wang, Zhengxiong. NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes. United States. doi:10.1063/1.4999619.
Hou, Yawei, Zhu, Ping, Kim, Charlson C., Hu, Zhaoqing, Zou, Zhihui, and Wang, Zhengxiong. Mon . "NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes". United States. doi:10.1063/1.4999619. https://www.osti.gov/servlets/purl/1540122.
@article{osti_1540122,
title = {NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes},
author = {Hou, Yawei and Zhu, Ping and Kim, Charlson C. and Hu, Zhaoqing and Zou, Zhihui and Wang, Zhengxiong},
abstractNote = {Toroidal Alfvén eigenmodes (TAEs) are gap modes induced by the toroidicity of tokamak plasmas in the absence of continuum damping. They can be excited by energetic particles (EPs) when the EP drive exceeds other dampings, such as electron and ion Landau damping, and collisional and radiative damping. A TAE benchmark case, which was proposed by the International Tokamak Physics Activity group, is studied in this work. The numerical calculations of linear growth of TAEs driven by EPs in a circular-shaped, large aspect ratio tokamak have been performed using the Hybrid Kinetic-MHD (HK-MHD) model implemented in the NIMROD code. This HK-MHD model couples a δf particle-in-cell representation of EPs with the 3D MHD representation of the bulk plasma through moment closure for the momentum conservation equation. Both the excitation of TAEs and their transition to energetic particle modes (EPMs) have been observed. The influence of EP density, temperature, density gradient, and position of the maximum relative density gradient, on the frequency and the growth rate of TAEs are obtained, which are consistent with those from the eigen-analysis calculations, kinetic-MHD, and gyrokinetic simulations for an initial Maxwellian distribution of EPs. The relative pressure gradient of EP at the radial location of the TAE gap, which represents the drive strength of EPs, can strongly affect the growth rate of TAEs. It is demonstrated that the mode transition due to EP drive variation leads to not only the change of frequency but also the change of the mode structure. This mechanism can be helpful in understanding the nonlinear physics of TAE/EPM, such as frequency chirping.},
doi = {10.1063/1.4999619},
journal = {Physics of Plasmas},
number = 1,
volume = 25,
place = {United States},
year = {2018},
month = {1}
}

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