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Evaluation of Magnetic Diagnostics for MHD Equilibrium Reconstruction of LHD Discharges

Author: Aaron C Sontag
Requested Type: Poster Only
Submitted: 2011-06-10 15:18:56

Co-authors: J. Hanson, S. Lazerson, J. H. Harris, S. Sakakibara, Y. Suzuki

Contact Info:
Oak Ridge National Laboratory
PO Box 2008
Oak Ridge, TN   37830
USA

Abstract Text:
Evaluation of Magnetic Diagnostics for MHD Equilibrium Reconstruction of LHD Discharges*

A. C. Sontag [1], J. Hanson [2], S. Lazerson [3], J. H. Harris [1], S. Sakakibara [4], Y. Suzuki [4]

1) Oak Ridge National Laboratory, Oak Ridge, TN, USA
2) Auburn University, Auburn, AL, USA
3) Princeton Plasma Physics Laboratory, Princeton, NJ, USA
4) National Institute for Fusion Science, Toki City, Gifu, Japan

Accurate reconstruction of MHD equilibrium parameters is an important tool for understanding the confinement and stability of magnetically confined toroidal plasmas. In tokamak plasmas, equilibrium reconstruction is used to determine the current and pressure profiles near the edge of the plasma in order to evaluate proposed mechanisms for ELMs [ , ]. In order to help understand the mechanisms for ELMs in stellarators, the V3FIT code will be used to reconstruct non-axisymmetric stellarator equilibria [ ]. The V3FIT code uses the VMEC code [ ] to calculate the 3D equilibrium state in conjunction with a non-linear, least-squares minimization routine to find the equilibrium solution that best matches a set of measurements. The Large Helical Device (LHD) is a superconducting, heliotron type device with over 25 MW of heating power that is capable of achieving both high-beta (~5%) and high density (>1 x 1021/m3) [ ]. This high performance capability as well as the ability to drive tens of kiloamperes of toroidal plasma current leads to deviations in the equilibrium magnetic geometry from the vacuum flux surfaces. The present work is a study of the ability of the V3FIT code to reliably reconstruct the plasma equilibrium state for a variety of LHD discharge types using the existing diagnostics. The initial study is performed using a diagnostic set consisting of the measured coil currents, the total plasma current and a set of 24 saddle loops mounted on the vacuum vessel. The accuracy of the reconstructed plasma parameters using this initial diagnostic set is assessed. Future work is planned to expand the diagnostic set used during reconstruction to include existing diamagnetic loops, magnetic pickup coils, measured ion and electron pressure profiles, and the measured iota profile.

*Supported by U.S. DOE Contract DE-AC05-00OR22725

References


[i] P.B. Snyder, et al., Nucl. Fusion 47 (2007) 961.
[ii] T.H. Osborne, et al., J. Phys. Conf. Ser. 123 (2008) 012014.
[iii] J.D. Hanson et al., Nucl. Fusion 49 (2009) 075031.
[iv] S.P. Hirshman and D.K. Lee, Comput. Phys. Commun. 39 (1986) 161.
[v] A. Komori, et al., Fusion Sci. and Tech. 58 (2010) 1.

Characterization: A5,A7

Comments:

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