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Abstract

Experiments on the maximum attainable beta values of ASDEX discharges show that the limits of this parameter lie in the range of theoretical predictions. In a previous publication we have attempted to theoretically identify the corresponding instabilities. While no significant correlation to global plasma instabilities could be found, the two-dimensional MHD equilibria calculated on the basis of ASDEX experimental parameters turned out to be close to the marginal ideal ballooning limit. In the present work we extend this investigation to resistive ballooning modes. Separatrix bounded as well as limiter controlled plasma equilibria are considered. Because of the small aspect-ratio of ASDEX (A approximately equal to 4) all equilibrium as well as stability calculations are performed in full toroidal geometry. After the formulation of a system of four equations describing the resistive evolution of velocity and magnetic fields in the high-m stability limit in coordinate-invariant form and its Fourier approximation in the neighbourhood of a localization field line, we solve the resulting quasi- mode equations applying methods of finite-element discretization. We find complex growth rates gamma with positive real part for values of the toroidal mode number n below 100. Calculated values of Re{gamma} or= 10- 3-/tau-As-1 (with tau-A being the Alfven time) are small and therefore in agreement with the experimentally observed non-disruptive behaviour of the beta-p- limit. Thus we believe that the characteristic signatures which govern ASDEX high-beta-p discharges can be explained by resistive ballooning modes.

Additional information

Authors: ZEHRFELD H P, MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, GARCHING BEI MUENCHEN (GERMANY);GRASSIE K MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, GARCHING BEI MUENCHEN (GERMANY), MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, GARCHING BEI MUENCHEN (GERMANY)
Bibliographic Reference: WRITE TO MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, 8046 GARCHING BEI MUENCHEN (GERMANY) MENTIONING REPORT IPP 5/16, 1987
Record Number: 1989126058800 / Last updated on: 1989-03-01
Category: PUBLICATION
Available languages: en