Identification of Mercier instabilities in Alcator C-Mod tokamak

Journal Article · Fri Dec 01 04:00:00 EST 2000 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.1323758· OSTI ID:40205967

In, Y; Ramos, J J; Hastie, R J; Catto, P J; Hubbard, A E; Hutchinson, I H; Marmar, E; Porkolab, M; Snipes, J; Wolfe, S ^[1]

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1. and others

During current ramp-up discharges, highly localized magnetohydrodynamic (MHD) fluctuations were observed on the electron cyclotron emission diagnostics of Alcator C-Mod tokamak [I. H. Hutchinson , Phys. Plasmas 1, 1511 (1994)]. The electron temperature profile was hollow, while the density profile was weakly decreasing. Assuming that the equilibration time was short enough to quickly thermalize ions the pressure profile was also found to be hollow. Using this pressure profile as an additional constraint to the EFIT program, an equilibrium with reversed shear was constructed having a q(0)>>1. The localized MHD activity was observed near the inner q=5 rational surface in this reconstructed equilibrium, where the Mercier criterion for ideal MHD stability was violated because of the reversed pressure gradient (dp/dr>0), q>1 and moderate shear. When kinetic effects were added, the ideal Mercier mode was finite ion Larmor radius stabilized. However, ion Landau damping was found to be strong enough to drive a kinetic Mercier instability.

• Sponsoring Organization: (US)
• OSTI ID: 40205967
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 7; ISSN 1070-664X
• Publisher: The American Physical Society
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ELECTRON TEMPERATURE
LANDAU DAMPING
LARMOR RADIUS
MERCIER CRITERION
MODE RATIONAL SURFACES
PRESSURE GRADIENTS
REVERSED SHEAR