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Author: Dylan P. Brennan
Requested Type: Poster
Submitted: 2018-03-01 14:29:11

Co-authors: Andrew J. Cole, Meng Li, Cihan Ak├žay, and John M. Finn

Contact Info:
Princeton University / PPPL
100 Stellarator Road
Princeton, NJ   08540

Abstract Text:
The stability boundaries of a reduced model of a tokamak in beta vs Omega, the ratio of thermal to magnetic energy vs the toroidal rotation frequency, are examined as the rotation varies across the Hall, Semi-Collisional and Inertial regimes of two fluid resonant layers, including real frequency plasma responses. The energetic ion contribution to the perturbed pressure is included in the model, where trapped energetic ions damp and stabilize the mode when orbiting in significant positive shear, and drive the mode unstable in reversed shear regions. The toroidal rotation frequency of the plasma is included in the drift-kinetic ion model, where it shifts the resonance between the finite frequency mode and the trapped ion precession. The equilibria are stable for low beta and the marginal stability values in beta and rotation are computed. The results are compared with extended MHD simulations using the NIMROD code, and recent experiments on DIII-D for rotational limits at fixed beta. The results show the Semi-Collisional regime to be most relevant to the experimental analysis, and the lowest limiting beta. The stability boundary is non-monotonic in Omega, and extends to lower beta as the finite frequency of the plasma response approaches the rotational frequency. The impact of the rotation in both the plasma layer responses, and the energetic ion response, must be taken into account to interpret the experimental results.