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Density limits and the evolution of disruptions were studied on TEXTOR for different wall materials facing the plasma surface. A systematic extension of the density limit was found over a large current range when the metallic wall was first exchanged for a carbon and later for a boron-carbon coated wall. The maximum attainable density nearly doubled when metallic impurities were replaced by low Z-impurities such as boron and carbon. With a neutral beam additional heating power of 3.2 MW, average densities exceeding 1.0 E20/m3 were obtained. The maximum density observed scales as the square root of the auxiliary heating power. The sequence of processes leading to a density limited disruption was analysed experimentally for ohmically heated plasmas. During the density increase in the gas feeding phase a boundary cooling by radiation and a steepening of the electron temperature gradient was observed. The electron temperature profile evolution showed a structure which could be interpreted as a filamentation of the plasma current. The decay of the plasma current after the energy quench was governed either by the resistance of the cold plasma or by the electric time constant of the TEXTOR liner.

Additional information

Authors: WAIDMANN G, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE);KUANG G, Institut für Plasmaphysik, Kernforschungsanlage Jülich GmbH, Jülich (DE)
Bibliographic Reference: Report: Jül-2448 EN (1991) 30 pp.
Availability: Available from Zentralbibliothek der Kernforschungsanlage Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
Record Number: 199110639 / Last updated on: 1994-12-02
Original language: en
Available languages: en