Improved-confinement plasmas at high temperature and high beta in the MST RFP

Journal Article · Thu Jan 01 00:00:00 EST 2009 · Nuclear Fusion

DOI:https://doi.org/10.1088/0029-5515/49/10/104020· OSTI ID:1015748

Chapman, B. E. ^[1]; Ahn, J. W. ^[1]; Almagri, A. F. ^[1]; Anderson, J. ^[1]; Combs, Stephen Kirk ^[2]; Foust, Charles R ^[2]; Kaufman, M. ^[1]

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1. University of Wisconsin, Madison
2. ORNL

We have increased substantially the electron and ion temperatures, the electron density, and the total beta in plasmas with improved energy confinement in the Madison Symmetric Torus (MST). The improved confinement is achieved with a well-established current profile control technique for reduction of magnetic tearing and reconnection. A sustained ion temperature > 1 keV is achieved with intensified reconnection-based ion heating followed immediately by current profile control. In the same plasmas, the electron temperature reaches 2 keV, and the electron thermal diffusivity drops to about 2 m(2) s(-1). The global energy confinement time is 12 ms. This and the reported temperatures are the largest values yet achieved in the reversed-field pinch (RFP). These results were attained at a density similar to 10(19) m(-3). By combining pellet injection with current profile control, the density has been quadrupled, and total beta has nearly doubled to a record value of about 26%. The Mercier criterion is exceeded in the plasma core, and both pressure-driven interchange and pressure-driven tearing modes are calculated to be linearly unstable, yet energy confinement is still improved. Transient momentum injection with biased probes reveals that global momentum transport is reduced with current profile control. Magnetic reconnection events drive rapid momentum transport related to large Maxwell and Reynolds stresses. Ion heating during reconnection events occurs globally, locally, or not at all, depending on which tearing modes are involved in the reconnection. To potentially augment inductive current profile control, we are conducting initial tests of current drive with lower-hybrid and electron-Bernstein waves.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1015748
• Journal Information: Nuclear Fusion, Vol. 49, Issue 10; ISSN 0029--5515
• Country of Publication: United States
• Language: English