Abstract
The Doppler shift caused by toroidal plasma rotation in DIII-D complicates a comparison of the frequency of toroidicity-induced Alfven eigenmodes (TAE) to theoretical predictions, but also separates toroidal modes in frequency space and provides information about the radial location of the modes. Two independent techniques for estimating the mode frequency and Doppler shift are presented: one based upon the spectrum of multiple toroidal modes and one that utilizes the measured toroidal rotation of the plasma. Both methods indicate the presence of multiple TAE modes located between the q=1 and y=3/2 surfaces. The frequencies determined by the two methods agree within 20%, consistent with their estimated uncertainties.
Highlights
Toroidicity-induced Alfvh eigenmodes (TAE) have been observed in experiments in the DII-D (Heidbrink er a1 1991, Strait et al 1993, Turnbull et al 1993) and Tokamak fusion test reactor (TFTR)(Wong et al 1991, 1992, Durst et al 1992) tokamaks
1 depends on the assumption that each family of spectral peaks corresponds to a family of TAE modes at the same radial location, so that they have the same frequency in the plasma frame and Doppler shifts generated by the same plasma rotation frequency
There is very good agreement between two essentially independent methods for estimating the frequency of TAE modes in the toroidally rotating plasma frame. These results allow the radial location of the mode to be estimated from the magnitude of the Doppler shift
Summary
Toroidicity-induced Alfvh eigenmodes (TAE) have been observed in experiments in the DII-D (Heidbrink er a1 1991, Strait et al 1993, Turnbull et al 1993) and Tokamak fusion test reactor (TFTR)(Wong et al 1991, 1992, Durst et al 1992) tokamaks. The TAE mode is a discrete mode which was predicted to exist in toroidal plasmas, with a frequency which lies in the toroidicity-induced gap in the shear Alfvtn-wave spectrum (Cheng et al 1985, Cheng and Chance 1986). This mode is of concern for fusion reactors because of the possibility of resonant interaction with the fusion alpha particles, leading to rapid loss of the alpha particles and failure of thermonuclear ignition. Experimental efforts are in progress to understand the conditions under which this mode becomes destabilized (Strait et al 1993)
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