Abstract Details
Abstracts
Author: Dov J Rhodes
Requested Type: Pre-Selected Invited
Submitted: 2017-03-17 12:07:00
Co-authors: A.J. Cole, D.P. Brennan, J.M. Finn, R. Fitzpatrick, M.E. Mauel, G.A. Navratil
Contact Info:
Columbia University
500 W. 120th St., Mudd 200
New York, New York 10027
United States
Abstract Text:
This study presents the first investigation of shaping effects on the stability and rotational stabilizability of MHD modes in a unified treatment addressing both plasma resistivity and wall resistivity. To explore a broad parameter space, a sharp-boundary model is developed based on a resistive-MHD model by Fitzpatrick [1], generalized to include toroidal curvature, up-down asymmetry and a resistive wall. The new model is used to examine linear mode onset over a range of beta spanning both tearing-dominated and wall-dominated behavior. Results show that rotation can raise the resistive-plasma resistive-wall (rp-rw) beta-limit up to the lower of two idealized limits; (i) a resistive-plasma ideal-wall (rp-iw) limit associated with the onset of a tearing-dominated instability, or (ii) an ideal-plasma resistive-wall (ip-rw) limit associated with the onset of a resistive-wall-dominated instability. The ordering of the two ideal limits, rp-iw and ip-rw, is observed to change depending on the plasma shape, safety factor and wall radius. In a cylindrical model, Brennan and Finn [2] showed that plasma rotation, or an equivalent feedback control with imaginary normal-field gain, can stabilize the mode up to the first ideal limit, typically rp-iw in a cylinder. Generalizing this approach to shaped toroidal geometry, the present study shows that the maximum rp-rw beta-limit achievable with rotation tends to peak at specific values of elongation and triangularity. Furthermore the window of optimal shaping is shown to coincide with an interchange of the ip-rw and rp-iw limits, corresponding to a transition between tearing-dominated and resistive-wall-dominated mode behavior. This work intends to provide insight into the dominant (tearing or resistive-wall) mode behavior observed in experiments and to guide larger codes in optimizing the shape of future devices. [1] R. Fitzpatrick, Phys. Plasmas 17, 112502 (2010). [2] D.P. Brennan and J.M. Finn, Phys. Plasmas 21, 102507 (2014).
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