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Author: Dylan P. Brennan
Requested Type: Poster
Submitted: 2017-03-17 14:48:53

Co-authors: M.R. Halfmoon, A.J. Cole, D.J. Rhodes, J.M. Finn

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

Abstract Text:
The resistive magnetohydrodynamic (MHD) stability of tokamak configuration that is driven unstable to the m/n=2/1 mode by increasing pressure is studied in a reduced model that includes a drift-kinetic slowing down distribution of trapped energetic ions, variations in the magnetic shear, plasma rotation and a resistive wall. The energetic ion contribution is integrated to the perturbed pressure, and entered into an asymptotic matching formalism for the resistive MHD dispersion relation. The equilibria are stable for beta=0 and the marginal stability values beta(rp,rw) < beta(rp,iw) < beta(ip,rw) < beta(ip,iw) (resistive plasma, resistive wall; resistive plasma, ideal wall; ideal plasma, resistive wall; and ideal plasma, ideal wall) are computed. Toroidal magnetic field line curvature is included to model trapping in the particle distribution, in an otherwise cylindrical model. The particles and pressure can affect the mode both in the core region where there can be low and reversed shear and outside the resonant surface in significant positive shear. The results show that the energetic ions damp and stabilize the mode when orbiting in significant positive shear, and drive the mode unstable in reversed shear regions. The effect of rotation is included in the drift-kinetic ion model, where it modifies the four beta limits discussed above.