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Author: Dylan P. Brennan
Requested Type: Poster
Submitted: 2016-02-15 15:20:07

Co-authors: Andrew J. Cole, Michael R. Halfmoon, Dov J. Rhodes and John M. Finn

Contact Info:
Princeton University / PPPL
P.O. Box 451
Princeton, NJ   08543

Abstract Text:
Differential flow between resonant surfaces can strongly affect the coupling and penetration of resonant components of toroidal resistive modes. These dependencies can affect the stability limits of pressure and current driven modes and the penetration thresholds of imposed fields. When the plasma response at a resonant surface has a finite frequency and flow, for example due to two-fluid effects or parallel dynamics, the results can be significantly modified from the simple visco-resistive result. This study presents a reduced analytic framework in a cylindrical tokamak to study two coupled mode components of a single mode resonant at surfaces with safety factor q=m/n and (m+1)/n, where m is the poloidal and n the axial wavenumber. Magnetic field line curvature is included to model toroidicity. The penetration thresholds and stability limits are calculated using asymptotic matching methods for the resistive modes, including differential flow between the resonant layers. The focus is on the Hall, Semi-Collisional, Resistive Inertial and Inertial regimes, with equilibrium, stability, toroidal rotation and boundary error field otherwise varied within the regimes of experiments. The model results are used to interpret calculations of experimental discharge stability including sheared flow profiles using the PEST-III and NIMROD codes. In particular, the focus is on how the differential flow can narrow the mode spectrum, in addition to modification of the stability. The results address error field penetration and beta limits in low-flow, low error field, two fluid regimes relevant to ITER experimental scenarios as well as current ITER-like discharges.

Supported by US DOE Grants DE-SC0014005 and DE-SC0014119