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Evidence for Separatrix Formation and Sustainment with Steady Inductive Helicity Injection

Author: Brian S. Victor
Requested Type: Consider for Invited
Submitted: 2011-06-02 18:34:33

Co-authors: T.R.Jarboe, A.C.Hossack, D.A.Ennis, B.A.Nelson, R.J.Smith, C.Akcay, C.J.Hansen, G.J.Marklin, N.K.Hicks, J.S.Wrobel

Contact Info:
University of Washington
AERB Rm 120, Box 352250
Seattle, WA   98105
USA

Abstract Text:
The Helicity Injected Torus with Steady Inductive Helicity Injection (HIT-SI) has achieved a breakthrough in the development of a new, more efficient current drive method for magnetic confinement fusion. HIT-SI accomplishes helicity injection current drive on a spheromak of major radius 0.3 m with two injectors driven sinusoidally at 14.5 kHz. The injectors are operated 90 degrees out of phase to give constant helicity injection. Results include the first sustainment of toroidal plasma current of over 50 kA at up to 3 times the injected currents added in quadrature. Separatrix toroidal currents--currents not linking the helicity injectors--are sustained at up to 40 kA. A simplified model of the separatrix and injector current paths that agree with magnetic measurements will be presented. Internal magnetic probe profiles show a rough match to Taylor equilibria. Results are achieved in HIT-SI during deuterium operations immediately after helium operation. At the beginning of the shot a large magnetic eigenstate having n=1 symmetry like the injectors is produced. The eigenstate then makes a rapid transition to produce a weak toroidal current that the injectors begin building up with considerable n=1 activity. As the toroidal current grows the n=1 activity decreases while the helicity injection rate remains constant, indicating an evolution to a more quiescent, direct current drive. This new observed growth and sustainment of toroidal current through multiple injector cycles using steady inductive helicity injection is an important step in demonstrating the viability of this current drive method. Work supported by USDoE.

Characterization: A3,D3

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