Sherwood 2015

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Energetic Ion Effects on Linear Tearing Mode Stability

Author: Michael R Halfmoon
Requested Type: Poster Only
Submitted: 2015-01-19 13:29:57

Co-authors: D.P. Brennan

Contact Info:
University of Tulsa
39A Linden Lane
Princeton, NJ   08540
United States

Abstract Text:
Previous analysis of toroidal confinement experiments has shown that energetic ions interact with and affect MHD mode stability, which has been extensively modeled and simulated for ideal MHD instabilities and resistive wall modes [1]. In addition, the 2/1 tearing mode was found to be damped or stabilized by energetic ions, with the most significant effects on the slow growing resistive mode [2]. This study focuses on the mode-particle interactions between energetic particles and pressure-driven, slow growing tearing modes which have been shown to be driven unstable in experiments as pressure increases[3]. In these simulations, a series of equilibria with fixed safety factor and varying pressure profiles are analyzed using the δf hybrid kinetic-mhd code in NIMROD. Our experimentally relevant equilibrium consists of a peaked pressure profile, a D-shaped poloidal cross section, and safety factor with finite shear to the magnetic axis. The mode is found to be damped and stabilized by the ions, consistent with previous results. The stabilizing effect is mainly due to trapped particle resonance, causing the tearing mode to have a finite frequency. To gain a better understanding of the underlying physics in these simulations, a high aspect ratio, step function equilibrium model based on Ref.[1] is investigated analytically to expand upon the tearing mode physics in the weakly unstable regime. We combine our computational and analytic tools in an effort to explain this damping and stabilizing effect.

1. B. Hu, and R. Betti, "Resistive wall mode in collisionless quasistationary plasmas." Physical Review Letters 93.10 (2004): 105002.
2. R. Takahashi et al, "Kinetic effects of energetic particles on resistive MHD stability." Physical Review Letters 102.13 (2009): 135001.
3.D.P. Brennan, et al "A Categorization of Tearing Mode Onset in Tokamaks via Nonlinear Simulation," Nucl. Fusion 45, 1178 (2005).
Supported by US DOE Grant DE-SC0004125


March 16-18, 2015
The Courant Institute, New York University