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Title: Collisionless microinstabilities in stellarators. II. Numerical simulations

Microinstabilities exhibit a rich variety of behavior in stellarators due to the many degrees of freedom in the magnetic geometry. It has recently been found that certain stellarators (quasi-isodynamic ones with maximum-J geometry) are partly resilient to trapped-particle instabilities, because fast-bouncing particles tend to extract energy from these modes near marginal stability. In reality, stellarators are never perfectly quasi-isodynamic, and the question thus arises whether they still benefit from enhanced stability. Here, the stability properties of Wendelstein 7-X and a more quasi-isodynamic configuration, QIPC, are investigated numerically and compared with the National Compact Stellarator Experiment and the DIII-D tokamak. In gyrokinetic simulations, performed with the gyrokinetic code GENE in the electrostatic and collisionless approximation, ion-temperature-gradient modes, trapped-electron modes, and mixed-type instabilities are studied. Wendelstein 7-X and QIPC exhibit significantly reduced growth rates for all simulations that include kinetic electrons, and the latter are indeed found to be stabilizing in the energy budget. These results suggest that imperfectly optimized stellarators can retain most of the stabilizing properties predicted for perfect maximum-J configurations.
Authors:
; ;  [1]
  1. Max-Planck-Institut f├╝r Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Wendelsteinstra├če 1, 17491 Greifswald, Germany and Max-Planck/Princeton Research Center for Plasma Physics, 17491 Greifswald (Germany)
Publication Date:
OSTI Identifier:
22218345
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 20; Journal Issue: 12; Other Information: (c) 2013 Euratom; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; APPROXIMATIONS; BOLTZMANN-VLASOV EQUATION; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DEGREES OF FREEDOM; DOUBLET-3 DEVICE; ELECTRON TEMPERATURE; G CODES; ION TEMPERATURE; NUMERICAL ANALYSIS; PLASMA; PLASMA CONFINEMENT; PLASMA SIMULATION; TEMPERATURE GRADIENTS; TRAPPED ELECTRONS; TRAPPED-PARTICLE INSTABILITY; WENDELSTEIN-7 STELLARATOR