DIII-D RESEARCH OPPORTUNITIES FORUM FOR THE 2013 EXPERIMENTAL CAMPAIGN Review | Direct submission with log-in | Request submission without log-in
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Title	99: Understand and control resistive wall mode stability in high-qmin plasmas
Name:	Jeremy Hanson hansonjm@fusion.gat.com	Affiliation:	Columbia University
Research Area:	Stability & Disruption Avoidance	Presentation time:	Requested
Co-Author(s):	J. Berkery, M. Lanctot, G. Navratil, S. Sabbagh, E. Strait, F. Turco	ITPA Joint Experiment :	Yes
Description:	The goals of this experiment are to understand and control the stability of the resistive wall modes encountered in 2012 experiments with betan ~ 3 and qmin ~ 3. The following questions will be addressed: (a)Is dependence of the RWM growth rate on plasma parameters, such as rotation, consistent with previously measured dependencies of the driven plasma response and the stability theory incorporating kinetic modifications to ideal MHD? (b)How do the driven plasma response and plasma rotation behave as the marginal stability boundary is crossed? (c)Can the transition to instability and associated beta collapses be avoided by controlling the plasma response using NBI feedback?	ITER IO Urgent Research Task :	No
Experimental Approach/Plan:	Reproduce DIII-D shot 150301, which suffers an unstable n=1 mode and beta collapse starting at t=2265 ms. Re-optimize error field correction using slow RWM feedback. Vary the injected NBI torque to determine the sensitivity of the stability to plasma rotation. Document the change in plasma response as marginal stability is approached using active MHD spectroscopy. Attempt to avoid beta collapse by maintaining a safe level of plasma response using NBI feedback.
Background:	Previous experiments have shown that the rotation-dependence of the driven plasma response is consistent with the predictions of a theory that includes kinetic modifications to ideal MHD [H. Reimerdes, et al, Phys. Rev. Lett. 106 (2011) 215002], and it is expected that unstable RWMs will exhibit a similar sensitivity. This experiment will provide crucial stability threshold data for comparison with predictions of kinetic stability codes such as MISK and MARS-K. Control of the driven plasma response has been demonstrated using NBI feedback below the no-wall beta limit [J. M. Hanson, et al, Nucl. Fusion 52 (2012) 013003]. However, control above the no-wall limit is expected to be more challenging due to the increased importance of kinetic effects, and the non-linear dependence of the plasma response on plasma stored energy. An assessment of this control technique in a regime near the RWM??s marginal stability point will establish its usefulness for disruption avoidance.
Resource Requirements:	At least 7/8 NBI sources, including both 210 sources
Diagnostic Requirements:	Magnetics, MSE, CER, Thomson scattering, ECE radiometer, density interferometer
Analysis Requirements:	Kinetic equilibrium reconstructions, ideal MHD and kinetic stability calculations
Other Requirements:	--