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NIMROD simulation of the HIT-SI experiment

Author: Cihan Akcay
Requested Type: Poster Only
Submitted: 2009-12-04 22:43:48

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

Contact Info:
University of Washington
Seattle, WA   98103

Abstract Text:
We present NIMROD simulation studies of current-drive, magnetic reconnection and
relaxation behavior of the HIT-SI experiment. HIT-SI (Steady Inductive Helicity
Injected Torus) is a spheromak that uses two semi-toroidal injectors to provide
steady inductive helicity injection (SIHI). SIHI produces and sustains a
spheromak by generating poloidal flux using relaxation current drive. Because
NIMROD can only model axi-symmetric geometries, the helicity injectors of the
experiment are modeled as flux (ψ_inj) and current (I_inj) boundary conditions.
We impose a tangential electric field on the annular regions of the tank (top
and bottom). One component of this tangential electric field provides the
applied voltage needed to drive the injector current. The second component
brings the injector flux in/out of the equilibrium region via Faraday's law. At
22 and higher toroidal modes the applied injector fields become well-localized
(to within 1%). Our simulations use a zero beta resistive MHD model with uniform
density. Lundquist number S and injector lambda, lambda_inj (=
μ_0*I_inj/ψ_inj) characterize the parameter space. S is the ratio of resistive
diffusion to Alfven transit time. For our simulations we set λ_inj=30, and
S=22. Our results to date show little relaxation during sustainment but do show
growth of the n=0 magnetic energy and an increase in plasma current during the
decay phase after the injectors are shut-off. We also present a new concept of
creating meshes on NIMROD that uses a combined and weighted average of the
vertices along a boundary to lay out a grid based on Boolean Sum Interpolation.
The meshing algorithm requires with no additional lines of code to treat
curved geometries. We expect it to improve the numerics of our simulations once
it is fully implemented.

Characterization: E10

Group with other HIT-SI posters

Princeton University

Innovative Confinement Concepts Workshop
February 16-19, 2010
Princeton, New Jersey

ICC 2010