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icc_11_proceedings.pdf2011-08-29 17:03:25David Ennis
icc_11.pdf2011-08-25 16:11:53David Ennis

Overview of HIT-SI Results and Plans

Author: David A. Ennis
Requested Type: Consider for Invited
Submitted: 2011-06-10 12:39:37

Co-authors: B. S. Victor, A. C. Hossack, C. Akcay, C. J. Hansen, T. R. Jarboe, G. J. Marklin, B. A. Nelson, R. J. Smith

Contact Info:
University of Washington
430 AERB, Box 352250
Seattle, WA   98195-2
USA

Abstract Text:
Experiments in the Helicity Injected Torus-Steady Inductive (HIT-SI) spheromak have achieved record spheromak current amplification during operation in deuterium plasmas. HIT-SI investigates steady inductive helicity injection to form and sustain an equilibrium in a high-beta spheromak geometry using two semi-toroidal injectors. In each injector the toroidal flux and induced loop voltage are sinusoidally oscillated in phase at a frequency of ~15 kHz. During standard operations the two HIT-SI injectors are 90 degrees out of phase with each other, producing a constant rate of overall helicity injection with all applied power delivered into the plasma, rather than to the plasma facing surfaces. The lack of electrodes make HIT-SI an ideal platform for clean studies of helicity injection current drive and current-profile relaxation. The HIT-SI diagnostic suite includes: FIR interferometry, IDS, bolometry, high speed camera, flux loops, internal and surface magnetic probes. Recent operations in deuterium plasmas have produced toroidal plasma currents greater than 50 kA, current amplification (I_tor/I_inj_quad > 3), and poloidal flux amplification (Psi_pol/Psi_inj_quad > 10). High performance deuterium discharges are achieved by initially conditioning the plasma-facing alumina surface of the HIT-SI confinement volume with helium plasmas. During subsequent deuterium operation the alumina surface strongly pumps deuterium, thereby limiting the density in the confinement volume. Additional measurements during high current deuterium discharges demonstrate reduced current and electron density fluctuations, impurity O III ion temperatures up to 50 eV and a toroidal current persistence for 0.6 ms after the injectors are shut off. Construction is underway on the new HIT-SI3 configuration with three injectors mounted on the same side of the conīŦnement volume. The three-injector arrangement will allow the injectors to continuously drive current more effectively, generate rotation of the equilibrium plasma, while also providing improved access for diagnostics and neutral pumping. Progress and plans for the HIT-SI3 modification will be presented. Work supported by USDoE and ARRA.

Characterization: A3

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University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011