Speaker
Mr
Abhijit Sen
(India)
Description
We report on an analytic calculation of Delta_prime, the tearing mode stability index, in a toroidal tokamak geometry with an equilibrium sheared toroidal flow. A flow modified external kink equation is derived and a boundary layer formalism is adopted. The ``outer'' solutions of this equation, obtained analytically using a perturbation theory are matched asymptotically to the analytic ideal ``inner'' solutions to get a closed expression for Delta_prime in terms of the plasma parameters. Our calculations are a generalization of the earlier work by Hegna and Callen [Phys. Plasmas 1, 2308 (1994)] that was done in the absence of flow. In the cylindrical limit we also recover the results of Gimblett et al [Phys. Plasmas 3, 3619 (1996)] that shows the destabilizing effect of purely axial flows. For a purely toroidal flow the various flow dependent terms of the ``inner'' solutions are compared and the nature of their contributions analyzed to delineate their influence on Delta_prime. We also extend our results to include finite beta corrections and nonlinear modifications arising from considerations of finite width of the island in the calculation of Delta_prime. Our analytic expressions should prove useful in providing a rigorous basis for assessing the validity of various ansatz for Delta_prime that are currently being used to explain experimental data and to benchmark
MHD code calculations of this stability index.
Country or International Organization of Primary Author
India
Primary author
Mr
Abhijit Sen
(India)
Co-authors
Dr
Debasis Chandra
(Institute for Plasma Research)
Prof.
P. K. Kaw
(Institute for Plasma Research)
