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Title: Simulation study of high-frequency energetic particle driven geodesic acoustic mode

High-frequency energetic particle driven geodesic acoustic modes (EGAM) observed in the large helical device plasmas are investigated using a hybrid simulation code for energetic particles and magnetohydrodynamics (MHD). Energetic particle inertia is incorporated in the MHD momentum equation for the simulation where the beam ion density is comparable to the bulk plasma density. Bump-on-tail type beam ion velocity distribution created by slowing down and charge exchange is considered. It is demonstrated that EGAMs have frequencies higher than the geodesic acoustic modes and the dependence on bulk plasma temperature is weak if (1) energetic particle density is comparable to the bulk plasma density and (2) charge exchange time (τ{sub cx}) is sufficiently shorter than the slowing down time (τ{sub s}) to create a bump-on-tail type distribution. The frequency of high-frequency EGAM rises as the energetic particle pressure increases under the condition of high energetic particle pressure. The frequency also increases as the energetic particle pitch angle distribution shifts to higher transit frequency. It is found that there are two kinds of particles resonant with EGAM: (1) trapped particles and (2) passing particles with transit frequency close to the mode frequency. The EGAMs investigated in this work are destabilized primarily by themore » passing particles whose transit frequencies are close to the EGAM frequency.« less
Authors:
; ;  [1] ;  [1] ;  [2]
  1. National Institute for Fusion Science, Toki 509-5292 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
22490164
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CHARGE EXCHANGE; ELECTRON TEMPERATURE; GEODESICS; INCLINATION; ION BEAMS; ION DENSITY; ION TEMPERATURE; LHD DEVICE; MAGNETOACOUSTIC WAVES; MAGNETOHYDRODYNAMICS; PLASMA DENSITY; PLASMA SIMULATION; SLOWING-DOWN; TRAPPING; VELOCITY