Drift waves in helically symmetric stellarators

Journal Article · Tue Nov 15 00:00:00 EST 2005 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.2130313· OSTI ID:20782346

Rafiq, T; Hegna, C ^[1]

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1. Engineering Physics Department, University of Wisconsin, Madison, Wisconsin 53706-1609 (United States)

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 drift 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.

• OSTI ID: 20782346
• Journal Information: Physics of Plasmas, Vol. 12, Issue 11; Other Information: DOI: 10.1063/1.2130313; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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