β-Limiting MHD instabilities in improved-performance NSTX spherical torus plasmas
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.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- NSTX Research Team
- DOE Contract Number:
- AC02-76CH03073; AC05-00R22725; W-7405-ENG-36; FG02-99ER54524; FG02-99ER54523
- OSTI ID:
- 1017356
- Journal Information:
- Nuclear Fusion, Vol. 43, Issue 5; ISSN 0029-5515
- Publisher:
- IOP Science
- Country of Publication:
- United States
- Language:
- English
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-Limiting MHD instabilities in improved-performance NSTX spherical torus plasmas
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