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Title: Trapped energetic electron driven modes with second stable regime in tokamak plasmas

Features of fishbone-like trapped energetic electrons driven modes (TEEMs), which are a particular manifestation of the fishbone gap modes, are investigated taking into account model radial profile and the pitch angle distribution of the energetic electrons (EEs). The TEEMs are found unstable only when the beta values of EEs β{sub h} (=pressure of the energetic electrons/pressure of magnetic field) are higher than certain critical values which are proportional to perturbed energy δW{sup ^}{sub c} of background plasma and much lower than that for traditional fishbone modes. In addition, TEEMs become stable again and enter a second stable regime when β{sub h} values are higher than second critical values. Furthermore, the modes can only be excited in plasmas which are stable for MHD instabilities. The real frequency and growth rate of the modes are approximately linear and parabolic functions of β{sub h}, respectively. The real frequency is very low but not zero in the vicinity of lower beta region, whereas it is comparable to the toroidal precession frequency of the EEs in higher critical beta region. The numerical results show that the second stable regime is easy to form when q = 1 flux surface is close to the magnetic axis. Suitable densitymore » gradient of EEs and magnetic shear are other two necessary conditions for excitation of the TEEMs.« less
Authors:
; ; ; ; ; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Southwestern Institute of Physics, Chengdu (China)
  2. Institute for Fusion Theory and Simulation, Zhejiang University, Hangzhou (China)
  3. (China)
  4. Southwest University for Nationalities, Chengdu (China)
Publication Date:
OSTI Identifier:
22304131
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 6; Other Information: (c) 2014 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; APPROXIMATIONS; INCLINATION; MAGNETIC FIELDS; MAGNETIC SURFACES; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA INSTABILITY; TAIL ELECTRONS; TOKAMAK DEVICES; TRAPPING