β-limiting MHD instabilities in improved-performance NSTX spherical torus plasmas

J. E. Menard, M. G. Bell, R. E. Bell, E. D. Fredrickson, D. A. Gates, S. M. Kaye, B. P. LeBlanc, R. Maingi, D. Mueller, S. A. Sabbagh, D. Stutman, C. E. Bush, D. W. Johnson, R. Kaita, H. W. Kugel, R. J. Maqueda, F. Paoletti, S. F. Paul, M. Ono, Y. K.M. PengC. H. Skinner, E. J. Synakowski

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84 Scopus citations

Abstract

Global magnetohydrodynamic (MHD) stability limits in the National Spherical Torus Experiment (NSTX) have increased significantly recently due to a combination of device and operational improvements. First, more routine H-mode operation with broadened pressure profiles allows access to higher normalized β and lower internal inductance. Second, the correction of a poloidal field coil induced error-field has largely eliminated locked tearing modes during normal operation and increased the maximum achievable β. As a result of these improvements, peak β values have reached (not simultaneously) βT = 35%, βN = 6.4, (βN) = 4.5, βN/li = 10, and βP = 1.4. High βP operation with reduced tearing activity has allowed a doubling of discharge pulse-length to just over 1 s with sustained periods of βN ≈ 6 above the ideal no-wall limit and near the with-wall limit. Details of the β-limit scalings and β-limiting instabilities in various operating regimes are described.

Original languageEnglish
Pages (from-to)330-340
Number of pages11
JournalNuclear Fusion
Volume43
Issue number5
DOIs
StatePublished - May 2003

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