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Feedback-assisted extension of the tokamak operating space to low safety factor (Articolo in rivista)

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Feedback-assisted extension of the tokamak operating space to low safety factor (Articolo in rivista) (literal)

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Hanson J.M.; Bialek J.M.; Baruzzo M.; Bolzonella T.; Hyatt A.W.; Jackson G.L.; King J.; La Haye R.J.; Lanctot M.J.; Marrelli L.; Martin P.; Navratil G.A.; Okabayashi M.; Olofsson K.E.J.; Paz-Soldan C.; Piovesan P.; Piron C.; Piron L.; Shiraki D.; Strait E.J.; Terranova D.; Turco F.; Turnbull A.D.; Zanca P. (2014)
Feedback-assisted extension of the tokamak operating space to low safety factor
in Physics of plasmas; AMER INST PHYSICS, CIRCULATION & FULFILLMENT DIV, 2 HUNTINGTON QUADRANGLE, STE 1 N O 1, MELVILLE, NY 11747-4501 (Stati Uniti d'America)
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Hanson J.M.; Bialek J.M.; Baruzzo M.; Bolzonella T.; Hyatt A.W.; Jackson G.L.; King J.; La Haye R.J.; Lanctot M.J.; Marrelli L.; Martin P.; Navratil G.A.; Okabayashi M.; Olofsson K.E.J.; Paz-Soldan C.; Piovesan P.; Piron C.; Piron L.; Shiraki D.; Strait E.J.; Terranova D.; Turco F.; Turnbull A.D.; Zanca P. (literal)

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Article number: 072107 / Physics of Plasmas (Online) e-ISSN: 1089-7674 / http://www.scopus.com/inward/record.url?eid=2-s2.0-84904094280&partnerID=q2rCbXpz (literal)

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http://scitation.aip.org/content/aip/journal/pop/21/7/10.1063/1.4886796 (literal)

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1,2,12,14,19,22 : Department of Applied Mathematics and Applied Physics, Columbia University, New York, NY 10027-6900, United States; / 3,4,10,11,16,17,18,21,24 : Consorzio RFX, Corso Stati Uniti 4, 35127 Padova, Italy; / 5,6,8,9,20,23 : General Atomics, P.O. Box 85608, San Diego, CA 92186-5608, United States; / 7,15 : Oak Ridge Institute for Science and Education, Oak Ridge, TN 37830-8050, United States; / 13 : Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, NJ 08543-0451, United States; / 1 : Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, United States. (literal)

Titolo

Feedback-assisted extension of the tokamak operating space to low safety factor (literal)

Abstract

Recent DIII-D and RFX-mod experiments have demonstrated stable tokamak operation at very low values of the edge safety factor q(a) near and below 2. The onset of n = 1 resistive wall mode (RWM) kink instabilities leads to a disruptive stability limit, encountered at q(a) = 2 (limiter plasmas) and q 95 = 2 (divertor plasmas). However, passively stable operation can be attained for q(a) and q 95 values as low as 2.2. RWM damping in the q(a) = 2 regime was measured using active MHD spectroscopy. Although consistent with theoretical predictions, the amplitude of the damped response does not increase significantly as the q(a) = 2 limit is approached, in contrast with damping measurements made approaching the pressure-driven RWM limit. Applying proportional gain magnetic feedback control of the n = 1 modes has resulted in stabilized operation with q 95 values reaching as low as 1.9 in DIII-D and q(a) reaching 1.55 in RFX-mod. In addition to being consistent with the q(a) = 2 external kink mode stability limit, the unstable modes have growth rates on the order of the characteristic wall eddy-current decay timescale in both devices, and a dominant m = 2 poloidal structure that is consistent with ideal MHD predictions. The experiments contribute to validating MHD stability theory and demonstrate that a key tokamak stability limit can be overcome with feedback. (literal)

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