Particle confinement and magnetic fluctuations in tokamak discharges with gas puffing

Citation

Levine, Bruce Stephen (1980) Particle confinement and magnetic fluctuations in tokamak discharges with gas puffing. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/rrs7-xm92. https://resolver.caltech.edu/CaltechETD:etd-10102006-132249

Abstract

An experimental investigation has been made of particle confinement and magnetic fluctuations associated with short (< 1 msec) gas pulses into a Tokamak discharge. The fluctuations are measured with movable pairs of magnetic probes, each containing a poloidal and radial coil and inserted into the outer regions of the plasma.

When neutral gas is added and the current channel contracts, the fluctuation spectra are dominated by an m=2 mode that grows with the classical tearing-mode rate. When the gas feed is terminated, much broader spectra of modes with m up to 15 are observed. The modal frequencies are nearly integer multiples of 11 kHz. The m=2 mode dominates the poloidal spectra, while the radial spectra have numerous modes of appreciable amplitude. Time-delay measurements suggest that many of the higher-order (m > 3) modes originate in deformation of the m=2 and m=3 magnetic islands. A strong m=7 is found to be localized near the limiter in q(a) = 3.8 discharges, hence this mode is identified as an m=7, n=2, It is found that the m=2 mode becomes destabilized for discharges for which the peak puff density approaches the upper limit given by the Murakami scaling relation. The m=2 mode grows at a rate much slower than the classical tearing-mode rate. The threshold in peak puff density for this destabilization coincides with a degradation in particle confinement.

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