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Title: Drift waves in helically symmetric stellarators

The local linear stability of electron drift waves and ion temperature gradient modes (ITG) is investigated in a quasihelically symmetric (QHS) stellarator and a conventional asymmetric (Mirror) stellarator. The geometric details of the different equilibria are emphasized. Eigenvalue equations for the models are derived using the ballooning mode formalism and solved numerically using a standard shooting technique in a fully three-dimensional stellarator configuration. While the eigenfunctions have a similar shape in both magnetic geometries, they are slightly more localized along the field line in the QHS case. The most unstable electron drift modes are strongly localized at the symmetry points (where stellarator symmetry is present) and in the regions where normal curvature is unfavorable and magnitude of the local magnetic shear and magnetic field is minimum. The presence of a large positive local magnetic shear in the bad curvature region is found to be destabilizing. Electron drift modes are found to be more affected by the normal curvature than by the geodesic curvature. The threshold of stability of the ITG modes in terms of {eta}{sub i} is found to be 2/3 in this fluid model consistent with the smallest threshold for toroidal geometry with adiabatic electrons. Optimization to favorable driftmore » wave stability has small field line curvature, short connection lengths, the proper combination of geodesic curvature and local magnetic shear, large values of local magnetic shear, and the compression of flux surfaces in the unfavorable curvature region.« less
Authors:
;  [1]
  1. Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706-1609 (United States)
Publication Date:
OSTI Identifier:
20782346
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 12; Journal Issue: 11; Other Information: DOI: 10.1063/1.2130313; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ASYMMETRY; BALLOONING INSTABILITY; CHARGED-PARTICLE TRANSPORT; DRIFT INSTABILITY; EIGENFUNCTIONS; EIGENVALUES; ELECTRON DRIFT; ELECTRON TEMPERATURE; ELECTRONS; GEOMETRY; ION TEMPERATURE; MAGNETIC FIELDS; MAGNETIC MIRRORS; MAGNETIC SURFACES; MIRRORS; PLASMA; PLASMA CONFINEMENT; PLASMA DRIFT; SHEAR; STABILITY; STELLARATORS; SYMMETRY; TEMPERATURE GRADIENTS