Magneto-Fluid Dynamics Seminar

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A 'Supersonic' Ballooning Stability Problem in Sheared Subsonic Flow

Speaker: E. Hameiri, CIMS

Location: Warren Weaver Hall 1013

Date: Wednesday, October 2, 1996, 1:30 p.m.

Synopsis:

Sheared toroidal plasma rotation was shown recently to reduce the growth rate of ballooning modes in a tokamak, and ultimately to stabilize them when Ω becomes a significant fraction of the Alfven wave toroidal frequency. We analyze the case of a much lower (but realistic) flow shear, with dΩ/dq on the order of the slow magnetosonic wave toroidal frequency. We consider both subsonic and supersonic values of dΩ/dq. The supersonic case is novel in that the energy integral δW is not bounded from below. The integral can nevertheless be modified and we prove that when the modified version becomes negative there is an odd number of unstable ballooning modes. When it is positive, there can be an even number of such modes (but stability in the subsonic case). These results are borne out by both analytical and numerical calculations.