Measurement of the dissipation time of plasma density in a striation on TCA
Some of the pellets injected into TCA show strong localised features which are very luminous and may result in an abrupt change in pellet trajectory. These features, termed "positive" striations, can dominate pellet ablation and it is interesting to determine the nature of the plasma around them. The plasma density is sufficiently high to cause considerable pressure broadening of emitted spectral line features. A visible spectrometer equipped with an OMA multichannel detector observing the working gas Balmer beta emission shows a wide Lorentzian line shape, characteristic of pressure broadening. The temporal resolution of this measurement is much lower than the whole pellet interaction, so this only gives a time averaged measurement of the density. A system has been developed to measure the temporal evolution of this plasma density and emission intensity, as the gas in a striation dissipates into the plasma bulk with a bandwidth of over 10 MHz. This paper describes the experiment and the measurement of the dissipation time, and compares the measured density in a positive striation to that predicted by theoretical models of pellet ablation in a tokamak plasma.
Bibliographic Reference: Paper presented: 18th European Conference on Controlled Fusion and Plasma Physics, Berlin (DE), June 3-7, 1991
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Record Number: 199110447 / Last updated on: 1994-12-02
Original language: en
Available languages: en