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epr_ct14_bsv.pdf2014-08-06 16:24:54Brian Victor

Sustained spheromaks with ideal n = 1 kink stability and pressure confinement

Author: Brian S. Victor
Requested Type: Consider for Invited
Submitted: 2014-05-30 10:31:12

Co-authors: T.R.Jarboe, B.A.Nelson, C.J.Hansen, A.C.Hossack, K.D.Morgan

Contact Info:
University of Washington
AERB Rm 120, Box 352250
Seattle, WA   98195
USA

Abstract Text:
Increasing the injectory frequency up to 68.5 kHz on the HIT-SI experiment produced, for the first time, sustained spheromaks with high-pressure confinement (β ≥ MHD β limit). Toroidal currents of 90 kA and current gains of nearly 4, a spheromak record, have been achieved. Equilibrium profiles of the sustained spheromak have a q profile with peak q < 1 indicating n = 1 kink stability. The injectors drive the edge of the plasma to a high λ (= μoj/B) with a low λ region forming in the center. Equilibrium profiles are generated by fitting to internal magnetic probe measurements and show kink stable profiles at injector frequencies of 14.5, 36.8, 53.5 and 68.5 kHz. Pressure confinement is consistently achieved at frequencies of 53.5 and 68.5 kHz, which is above the expected sound transit frequency, vi/a, of HIT-SI. Thus at these frequencies plasma propagation would be affected by the higher frequency imposed fluctuations. In addition the magnetic profiles have improved toroidal symmetry at higher injector frequencies. Equilibrium profiles at 53.5 and 68.5 kHz have β > 20%. The high, Mercier unstable, β and stability to ideal kink modes indicate imposed fluctuations may be interrupting the growth of pressure driven modes keeping the instability local and preserving global confinement. If a larger machine can repeat this result at higher temperatures, this method could provide an economical path to fusion. Work supported by USDoE.

Characterization: 1.2

Comments:

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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