Active and fast particle driven Alfven eigenmodes in Alcator C-Mod
- Massachusetts Institute of Technology Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)
Alfven eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where T{sub i}{approx_equal}T{sub e} and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfven eigenmode (TAE) damping rates between 0.5%<{gamma}/{omega}<4.5% have been observed in diverted and limited Ohmic plasmas. Unstable AEs are excited with a fast ion tail driven by H minority ion cyclotron radio frequency (ICRF) heating with electron densities in the range of n{sub e}=0.5-2x10{sup 20} m{sup -3}. Energetic particle modes or TAEs have been observed to decrease in frequency and mode number with time up to a large sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. In the current rise phase, unstable modes with frequencies that increase rapidly with time are observed with magnetic pick-up coils at the wall and phase contrast imaging density fluctuation measurements in the core. Modeling of these modes constrains the calculated safety factor profile to be very flat or with slightly reversed shear. AEs are found to be more stable for an inboard than for central or outboard ICRF resonances in qualitative agreement with modeling.
- OSTI ID:
- 20736567
- Journal Information:
- Physics of Plasmas, Vol. 12, Issue 5; Other Information: DOI: 10.1063/1.1865012; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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