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Resistive MHD Simulations of HIT-SI plasmas

Author: Cihan Akcay
Requested Type: Poster Only
Submitted: 2011-08-10 00:39:42

Co-authors: C. C. Kim, T. R. Jarboe, B. A. Nelson

Contact Info:
University of Washington
Aerosapce and energetics resea
Seattle, WA   98195-2
USA

Abstract Text:
HIT-SI (Steady Inductive Helicity Injected Torus) is a current drive experiment that uses
two semi-toroidal helicity injectors driven at 5-15 kHz to generate steady inductive helicity
injection (SIHI). All the plasma-facing walls of the experiment are coated with an insulating material to guarantee an inductive discharge.
NIMROD is a 3-D extended MHD code that can only model toroidally-uniform geometries.
The helicity injectors of the experiment
are simulated as flux and voltage boundary conditions with odd toroidal symmetry.
A highly resistive, thin edge-layer approximates the insulating
walls. The simulations are initial-value calculations that use a zero $beta$ resistive MHD (rMHD) model with uniform
density. The Prandtl number ($Pr = 10$), and Lundquist number ($S = 10-100$) closely match the experimental values.
The zero-$beta$, constant-density rMHD predicts the qualititative, but not quantitative behavior of HIT-SI.
rMHD calculations show $n=0$ magnetic
energy growth and a current amplification exceeding unity: $frac{I_{tor}}{I_{text{inj}}}=1.2$ with $Itor$=24 kA,
whereas HIT-SI has demonstrated toroidal currents up to 55~kA with $Iamp=3$. While HIT-SI
has shown evidence for separatrix formation, rMHD calculations indicate an entirely stochastic magnetic structure during sustainment.
Future work includes running rMHD with density evolution and also including two-fluid effects like Hall MHD and electron inertia.

Characterization: D4

Comments:
To be presented with the rest of HIT-SI posters

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