|poster.pdf||2006-02-22 14:06:36||Srinath Vadlamani|
Semi-Implicit Time-Stepping Algorithm used in MH4D for Simulations for Innovative Confinement Concept Fusion Devices
Author: Srinath Vadlamani
Submitted: 2005-12-21 15:08:16
Co-authors: U. Shumlak, G. Marklin, R. Lionello
PSI Center, Univ. of Washington
120 AERB, Box 352250
Seattle, WA 98195-2
The newly formed Plasma Science and Innovation Center (PSI Center)
at the University of Washington is improving existing MHD codes
to accurately model Emerging Concept (EC) devices.
Examination of the semi-implicit time stepping algorithm
implemented in the tetrahedral mesh MHD simulation code, MH4D,
is presented. The time steps for standard explicit methods,
which are constrained by the Courant-Friedrichs-Lewy (CFL)
condition, are typically small for simulations of EC
experiments due to the large sound and Alfven speeds.
The CFL constraint on time stepping is more severe with a tetrahedral mesh. The semi-implicit algorithm  removes the time step constraint from the fast waves, thus allowing
for larger time steps. We will present the implementation
method of this algorithm , and numerical results for
test problems in simple geometry. Also, we will present
the effectiveness in simulations of more complex geometry,
similar to the ZaP  experiment at the University of Washington.
Douglas S. Harned and D. D. Schnack, Semi-implicit method for long time
scale magnetohydrodynamic computations in three dimensions, JCP,
Volume 65, Issue 1, July 1986, Pages 57-70.
Roberto Lionello, Zoran Mikic and Jon A. Linker, Stability of Algorithms
for Waves with Large Flows, JCP, Volume 152, Issue 1, 10 June 1999, Pages 346-358.
U. Shumlak, B. A. Nelson, R. P. Golingo, S. L. Jackson, E. A. Crawford,
and D. J. Den Hartog, Sheared flow stabilization experiments in the ZaP flow
Zpinch, Phys. Plasmas 10, 1683 (2003).