| Presentation: | submitted: | by: |
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| lll_icc07.pdf | 2007-03-06 17:36:43 | Lynda LoDestro |
Linear MHD Stability Analysis of the SSPX Spheromak
Author: Lynda L. LoDestro
Requested Type: Poster Only
Submitted: 2006-12-18 18:01:56
Co-authors: J. Jayakumar, B.I. Cohen, E.B. Hooper, H.S. McLean, L.D. Pearlstein, R.D. Wood, LLNL; A.D. Turnbull, GA; C.R. Sovinec, UW
Contact Info:
LLNL
P.O. Box 808
Livermore, CA 94551
USA
Abstract Text:
Past analysis of SSPX has included reconstruction of the equilibria assuming simple profile forms with a few parameters for the current profile and minimizing the RMS error with respect to magnetic measurements near the vessel wall. The results typically show a good correlation between the toroidal mode numbers n of measured magnetic fluctuations and the presence of low-order rational surfaces at the same n in the reconstructed q profile. Recent progress in SSPX has resulted in high electron temperatures and good core-plasma energy confinement (Te > 350eV and radial electron thermal diffusivity approaching tokamak L-mode values). Together, these results suggest that the quality of magnetic surfaces in SSPX is sufficiently good that a standard toroidal linear MHD stability analysis of the observed fluctuations is appropriate.
In this paper we apply a variety of computational tools to assess linear MHD stability in SSPX. Equilibria are generated by the 1&1/2D Corsica code. Beginning with reconstructed equilibria, plasma β is artificially elevated well above SSPX β's, until DCON (fast-running stability assessment based on crossings) predicts robust ideal instability. With this equilibrium we performed a benchmark of an ideal-MHD internal kink, using GATO (linear toroidal ideal-MHD eigenvalue code) and NIMROD (nonlinear, non-ideal, 3D initial-value code, run in linearized mode with small or vanishing transport coefficients) and obtained excellent agreement in growth rates and eigenfunctions. For an external-mode benchmark, an SSPX-like equilibrium was generated with vanishing current on the open field-lines (GATO assumes a vacuum outside the separatrix); excellent agreement was again obtained. We are now applying these tools to analyze SSPX discharges and to assess β limits, and will report progress.
* Work performed under the auspices of the US DOE by University of California Lawrence Livermore National Laboratory under contract W–7405–ENG–48; by General Atomics under Grant DE-FG03-95ER54309
Characterization: A1,E2
Comments:
Group with Harry Mclean
