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Title: Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point

Abstract

The destabilization of ideal internal kink modes by trapped fast particles in tokamak plasmas with a “shoulder”-like equilibrium current is investigated. It is found that energetic particle branch of the mode is unstable with the driving of fast-particle precession drifts and corresponds to a precessional fishbone. The mode with a low stability threshold is also more easily excited than the conventional precessional fishbone. This is different from earlier studies for the same equilibrium in which the magnetohydrodynamic (MHD) branch of the mode is stable. Furthermore, the stability and characteristic frequency of the mode are analyzed by solving the dispersion relation and comparing with the conventional fishbone. The results suggest that an equilibrium with a locally flattened q-profile, may be modified by localized current drive (or bootstrap current, etc.), is prone to the onset of the precessional fishbone branch of the mode.

Authors:
 [1]; ;  [2]
  1. Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, Sichuan 610031 (China)
  2. State Key Lab of Nuclear Physics and Technology, School of Physics, Peking University, Beijing 100871 (China)
Publication Date:
OSTI Identifier:
22600036
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 7; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BOOTSTRAP CURRENT; COMPARATIVE EVALUATIONS; DISPERSION RELATIONS; EQUILIBRIUM; MAGNETOHYDRODYNAMICS; PARTICLES; PLASMA; PRECESSION; STABILITY; TOKAMAK DEVICES; TRAPPING

Citation Formats

Wang, Xian-Qu, Zhang, Rui-Bin, and Meng, Guo. Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point. United States: N. p., 2016. Web. doi:10.1063/1.4958645.
Wang, Xian-Qu, Zhang, Rui-Bin, & Meng, Guo. Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point. United States. doi:10.1063/1.4958645.
Wang, Xian-Qu, Zhang, Rui-Bin, and Meng, Guo. 2016. "Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point". United States. doi:10.1063/1.4958645.
@article{osti_22600036,
title = {Trapped fast particle destabilization of internal kink mode for the locally flattened q-profile with an inflection point},
author = {Wang, Xian-Qu and Zhang, Rui-Bin and Meng, Guo},
abstractNote = {The destabilization of ideal internal kink modes by trapped fast particles in tokamak plasmas with a “shoulder”-like equilibrium current is investigated. It is found that energetic particle branch of the mode is unstable with the driving of fast-particle precession drifts and corresponds to a precessional fishbone. The mode with a low stability threshold is also more easily excited than the conventional precessional fishbone. This is different from earlier studies for the same equilibrium in which the magnetohydrodynamic (MHD) branch of the mode is stable. Furthermore, the stability and characteristic frequency of the mode are analyzed by solving the dispersion relation and comparing with the conventional fishbone. The results suggest that an equilibrium with a locally flattened q-profile, may be modified by localized current drive (or bootstrap current, etc.), is prone to the onset of the precessional fishbone branch of the mode.},
doi = {10.1063/1.4958645},
journal = {Physics of Plasmas},
number = 7,
volume = 23,
place = {United States},
year = 2016,
month = 7
}
  • The internal kink mode is destabilized by trapped high-energy particles, leading to a new branch of the internal kink dispersion relation with a real frequency near the average trapped-particle precession frequency and a growth rate of the same magnitude. This trapped particle branch of the dispersion relation is investigated numerically for a variety of particle distributions. Mode growth rate and frequency is found as a function of plasma ..beta.., density, and trapped-particle energy and distribution. The high-energy trapped particle sources considered are neutral beam injection, ion-cyclotron heating, and fusion alpha particles. Relevance for various plasma heating schemes is discussed.
  • The internal kink mode is destabilized by trapped high energy particles, leading to a new branch of the internal kink dispersion relation with a real frequency near the average trapped particle precession frequency and a growth rate of the same magnitude. This trapped particle branch of the dispersion relation is investigated numerically for a variety of particle distributions. Mode growth rate and frequency are found as a function of plasma ..beta.., density, and trapped particle energy and distribution. The high energy trapped particle sources considered are neutral beam injection, ion cyclotron heating, and fusion alpha particles. Relevance for various plasmamore » heating schemes is discussed.« less
  • Cited by 5
  • New experimental observations are reported on the structure and dynamics of short-lived periodic (1, 1) “fishbone”-like oscillations that appear during radio frequency heating and current-drive experiments in tokamak plasmas. For the first time, measurements can directly relate changes in the high energy electrons to the mode onset, saturation, and damping. In the relatively high collisionality of Alcator C-Mod with lower hybrid current drive, the instability appears to be destabilized by the non-resonant suprathermal electron pressure—rather than by wave-particle resonance, rotates toroidally with the plasma and grows independently of the (1, 1) sawtooth crash driven by the thermal plasma pressure.
  • The effects of thermal trapped particles on the internal kink mode are studied using drift kinetic theory. For equal electron and ion temperatures, the trapped particles increase the marginal poloidal beta at [ital q]=1 substantially. For unequal temperatures, drift resonance with the hotter species is destabilizing and can lead to instability below the ideal magnetohydrodynamics threshold. An electrostatic potential is weakly stabilizing for the internal kink. At high beta, fluctuations of trapped particle modes couple to the internal kink mode and can lead to large displacements of the central region.