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Title: Enhanced stabilisation of trapped electron modes by collisional energy scattering in tokamaks

The collisional stabilisation via energy scattering and pitch-angle scattering of micro-instabilities in tokamak plasmas is investigated by means of gyrokinetic simulations with a special emphasis on the often neglected energy scattering operator. It is shown that in the linear regime energy scattering has a negligible effect on Ion Temperature Gradient (ITG) modes but enhances the stabilisation of Trapped Electron Modes (TEM) in presence of nonzero ion temperature and density gradients. This stabilisation is sensitive to the model used for the energy restoring term in the collision operator. The contributions of parallel and drift motion to the total growth rate in velocity space are used to characterize the complex stabilisation mechanisms behind pitch-angle and energy scattering for a range of relevant parameters such as the magnetic shear, the collisionality, the logarithmic density gradient, and the logarithmic ion temperature gradient. It is shown that depending on these parameters, energy scattering stabilisation of TEM can be either due to a decrease of the contribution from drifting trapped electrons or to an increase of the contribution from the parallel motion of passing electrons. Finally, for a standard ITG/TEM case, the effect of energy scattering on the nonlinear heat and particle fluxes is investigated.
Authors:
; ;  [1] ; ;  [2]
  1. Aix-Marseille Université, CNRS, PIIM UMR7345, 13397 Marseille (France)
  2. Department of Physics, University of Bayreuth, 95440 Bayreuth (Germany)
Publication Date:
OSTI Identifier:
22490928
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 6; 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; COLLISIONS; COMPUTERIZED SIMULATION; DENSITY; HEAT FLUX; INCLINATION; ION DRIFT; ION TEMPERATURE; NONLINEAR PROBLEMS; PLASMA; SCATTERING; SHEAR; TEMPERATURE GRADIENTS; TOKAMAK DEVICES; TRAPPED ELECTRONS; VELOCITY