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Internal magnetic probing results of driven and decaying HIT-SI discharges

Author: Roger J Smith
Requested Type: Poster Only
Submitted: 2011-06-06 18:04:11

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

Contact Info:
University of Washington
AERB Bldg, Room 120
Seattle, Wa   98195
USA

Abstract Text:
The Helicity Injected Torus (HIT-SI) is a spheromak device driven by two helicity injectors configured as ½ toroidal pinch handles attached to opposite sides of the confinement volume and driven sinusoidally in quadrature at 14.5 kHz. Steady magnetic helicity injection, by purely inductive means, is thereby achieved. HIT-SI has a minor radius of 20 cm with the magnetic axis at 33 cm. Recently, large DC toroidal currents of 3 times the injector currents added in quadrature have been produced suggesting that a spheromak entity, or separatrix, exists within the confinement volume containing flux separate from flux threading the injectors. The equilibrium volume is probed with a mid-plane retractable internal magnetic probe array that spans a full outboard minor radius. Peak toroidal fields of up to 60 mT are measured near the magnetic axis during the driven phase. During the decay phase, after the injectors are turned off, an axisymmetric equilibrium ensues for 0.65 ms. Initially, the decaying equilibria departs from the Taylor state for HIT-SI and shows evidence of finite  and a Grad Shafranov (GS) shift. Later during the decay the equilibria relaxes to the Taylor state. Internal probing results will be presented for the driven and decaying phase and a GS solver will be used to fit the decay phase yielding a complete magnetic description of the equilibrium. Work supported by USDoE.

Characterization: A3

Comments:
With other HIT group posters