The evolution of resistive ballooning modes in the banana-plateau collisionality regime
The theory of resistive ballooning modes relevant to the banana-plateau collisionality regime is studied using the recently developed neoclassical MHD equations. Employing the ballooning mode formulation and a multiple length scale analysis, a generalized set of poloidal flux surface averaged equations coupling the parallel ion flow velocity V{sub {parallel}i}, the vector potential A{sub {parallel}}, and the electrostatic potential {phi} are derived. A particularly simple case in which the parallel sound wave coupling reduces the order of the differential equation in the frequency range {vert bar}{omega}{vert bar} {much gt} {omega}{sub s}, where {omega}{sub s} = sc{sub s}/qR{sub 0}, s is the shear parameter, c{sub s} the sound speed and qR{sub 0} the connection length, is dealt with. The calculations show that a new class of localized pressure-gradient-driven ballooning modes with growth rates varying as ({upsilon}{sub e} + {mu}{sub e}){sup 1/2} is possible, where {upsilon}{sub e} is the electron collision frequency and {mu}{sub e} is the electron neoclassical poloidal flow viscous damping frequency. It is shown that the resistive ballooning modes are sensitive to variations of a parameter {eta} (= {vert bar} dlnP{sub 0}/dlnq {vert bar}) within the tokamak plasma. The enhanced ion polarization and pinch type currents are found to cause stabilization of resistive modes. Further, our model highlights a smooth transition from the Pfirsch-Schlueter to the (neoclassical) banana-plateau collisionality regimes. The relevance of these results to ISX-B experiments is briefly pointed out. 17 refs.
- Research Organization:
- Wisconsin Univ., Madison, WI (USA)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- FG02-86ER53218
- OSTI ID:
- 6631696
- Report Number(s):
- UW-CPTC-90-6; ON: DE90016672; TRN: 90-027156
- Country of Publication:
- United States
- Language:
- English
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