Model for current drive stabilization of neoclassical tearing modes
Jennifer Woodby, Eugenio Schuster, Glenn Bateman and Arnold H. Kritz
Physics of Plasmas, 15, 092504 (2008)
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Abstract
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A model derivation is presented for the effect of current drive on the saturated
width of magnetic islands driven by the neoclassical tearing mode
(NTM) instability in axisymmetric plasmas. The derivation is carried out
for continuous current drive as well as for modulated current that is driven
at the same angle as the island O-point. The results of the derivation are
implemented in a revision of the ISLAND module to compute saturated
magnetic island widths. It is found that the greatest stabilizing effect
of both modulated and continuous current drive on the island width is
achieved when current is driven at the island center. In addition, narrow
current drive is more effective at stabilizing the magnetic islands than wide
current drive, for which more current falls outside the island. When modulated
and continuous current drives are compared for equal total driven
current, the modulated current is shown to be more effective, particularly
as the offset from the island center increases.
