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The sequence of processes leading to a density limit disruption has been analysed experimentally in detail for an ohmically heated plasma. During the density increase in the gas feeding phase, a boundary cooling and a steepening of the electron temperature gradient was observed by ECE-diagnostics. A sudden increase of the total radiative loss occurs when the radiative power equals approximately the ohmic input power. The plasma then detaches from the limiters and the development of MHD-mode activity is observed. The electron temperature profile evolution was recorded continuously with a time resolution of 1.0 E-4 sec. The presence of rotating or locked magnetic islands became visible as typical deformations of the radial profile. An m = 2 mode in the outer plasma region was coupled with an m = 1 mode deeper inside the plasma. The overlapping of two modes is believed to bring about a stochastisation of magnetic field lines in a sizeable part of the plasma cross-section, i.e. inside the q = 2 surface. This rapidly leads to the final energy quench of the density limit disruption. It occurs in TEXTOR in approximately 1 msec.

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: Article: 18th European Conference on Controlled Fusion and Plasma Physics, Vol. II (1991) pp. 45-48
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