Avoidance of Tearing Mode Locking and Disruption with Electro-Magnetic Torque Introduced by Feedback-based Mode Rotation Control in DIII-D and RFX-mod

Authors: M. Okabayashi, P. Zanca, E.J. Strait, A.M. Garofalo, J.M. Hanson, Y. In, R.J. La Haye, L. Marrelli, P. Martin, R. Paccagnella, P. Piovesan, C. Piron, L. Piron, D. Shiraki, F.A. Volpe, and the DIII-D and RFX-mod Teams

Abstract: Disruptions caused by tearing modes (TMs) are considered to be one of the most critical roadblocks to achieving reliable, steady-state operation of tokamak fusion reactors. Here we have demonstrated a very promising scheme to avoid such disruptions by utilizing the electro-magnetic (EM) torque produced with 3D coils that are available in many tokamaks. In this scheme, the EM torque to the modes is created by a toroidal phase shift between the externally-applied field and the excited TM fields, compensating for the mode momentum loss due to the interaction with the resistive wall and uncorrected error fields. Fine control of torque balance is provided by a feedback scheme. We have explored this approach in two vastly different devices and plasma conditions: DIII-D and RFX-mod operated in tokamak mode. In DIII-D, the plasma target was high βN plasmas in a non-circular divertor tokamak. In RFX-mod, the plasma was ohmically-heated plasma with ultralow safety factor in a circular limiter discharge of active feedback coils outside the thick resistive shell. The DIII-D and RFX-mod experiments showed remarkable consistency with theoretical predictions of torque balance. The application to ignition-oriented devices such as International Thermonuclear Experimental Reactor (ITER) would expand the horizon of its operational regime. The internal 3D coil set currently under consideration for edge localized mode suppression in ITER would be well suited to this purpose.

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Presented at: the 25th IAEA Fusion Energy Conference, St. Petersburg, Russia, 13-18 October 2014.

Published as: 25th IAEA Fusion Energy Conference Proceedings [EX/P2-42] on IAEA Physics website
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Download PPPL-5072 (pdf 4.5 MB / 8pp)
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