HOME PROGRAM REGISTRATION HOTEL TRANSPORTATION SUBMIT ABSTRACT ABSTRACT LIST PROGRAM COMMITTEE MORE ON MADISON	Understanding spheromak formation and evolution by ideal and resistive MHD modeling Author: Hooper E. Bickford Coauthor: the LLNL SSPX team and the U. Wisc. NIMROD team Institution : LLNL Abstract text: Formation and evolution in SSPX are modeled using ideal MHD [1], hyperresistive transport of helicity and current [2], and resistive MHD. CORSICA reconstructs equilibria from magnetic probe data, and includes many reduced physics models (e.g. transport). Resistive MHD modeling uses NIMROD [3], applied to earlier studies of spheromaks [3, 4]. We report NIMROD modeling with comparison to experiments. Flux conserver geometry and bias magnetic flux are close to those in SSPX. Many experimental features are reproduced semi-quantitatively or better, including spheromak geometry, magnetic field strengths at the flux conserver, and profiles of j/B and q. Magnetic fluctuation amplitudes are large, although “magnetic probe” fields at the flux conserver (5-10% RMS) are much less than in the central current column. Mode frequencies are an order-of-magnitude lower in the simulation than the experiment. Because these modes are observed to rotate as a “rigid-body”, artificial rotation is applied in the code. The near-wall rotation speed matching experiment is roughly the sound speed. The resulting velocity profile is nearly unidirectional; in the unrotated simulation the average azimuthal velocity is small with peak velocities ± 1/4 of the applied wall velocity. Other plasma characteristics are marginally affected. Magnetic field puncture plots demonstrate chaotic behavior. Hyperresistive modeling had good agreement with the experimental time history for a hyperresistivity coefficient of 0.01 volt-weber. The extent to which this model and value are consistent with resistive MHD modeling is being studied. Work performed under the auspices of the U. S. DOE by U. of California LLNL under contract No. W-7405-Eng-48. [1] E. B. Hooper, et al. Nucl. Fusion 39, 863 (1999). [2] E. B. Hooper and L. D. Pearlstein, Plasma Phys. Reports 28, 765 (2002). [3] C. R. Sovinec, et al., Phys. Plasmas 10, 1727 (2003); C. R. Sovinec, et al., Phys. Plasmas 8, 475 (2001). [4] R. H. Cohen, et al., Nucl. Fusion 43, 2903 (2003).