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Abstract

Pellets with velocities between 200 and 800 m/s and containing between 7 x 1.0 E17 and 3 x 1.0 E19 particles, that correspond to about 0.5 to 2 times the total number of particles contained in the plasma, were injected in the TCA tokamak. In ohmic conditions, varied plasma density and plasma current were investigated. The diagnostics used for the monitoring of the ablation processes were two CCD video cameras viewing the pellet path perpendicularly. Two photomultipliers monitoring the H(alpha) emission measured the total H(alpha) emission and the evolution of the pellet velocity in the plasma. H(alpha) emission from the ablation cloud showed significant spatial structure, indicating a complexity in the processes that govern the pellet ablation. Positive striations, curved trajectories and other varied interactions were observed. In particular, there were many examples of strong localised interactions in a region at half the minor radius, which showed a very strong enhancement of the ablation rate. The resulting penetration depths were much smaller than predicted theoretically. In plasma discharges of higher purity, obtained with the vacuum vessel freshly boronised, the amplitude of the striations appeared to be slightly reduced, and there was a change in the radial profile of the ablation rate. In the absence of strong striations, the plasma current had the strongest influence on the pellet penetration depth, which increased with lower plasma currents. This paper describes the dependence of pellet penetration on these parameters and other plasma conditions which may be compared to theoretical predictions.

Additional information

Authors: DUVAL B P, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Lausanne (CH);HOLLENSTEIN C, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Lausanne (CH);MARTIN Y ET AL., Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Lausanne (CH);DUTCH M, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Lausanne (CH)
Bibliographic Reference: Paper presented: 18th European Conference on Controlled Fusion and Plasma Physics, Berlin (DE), June 3-7, 1991
Availability: Text not available
Record Number: 199110445 / Last updated on: 1994-12-02
Category: PUBLICATION
Original language: en
Available languages: en
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