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Abstract

An anomalous state of the plasma boundary has been found in divertor and limiter discharges near the density limit in the ASDEX Tokamak. The plasma parameters are no longer constant on flux surfaces near the boundary. A toroidally symmetric belt shaped region with densities above the central value and very low temperatures develops at the inner side of the torus. Strongly enhanced radiation from impurity ions in low ionization states is emitted from this plasma region while the mean impurity concentration of the discharge remains unchanged. The drastic change of the parameters in the plasma boundary might be explained by a thermal instability which can appear if the parallel heat conduction time is longer than the local cooling time. This implies that the transverse energy flow from the central plasma to the inner boundary is small. This limitation of heating power in the plasma boundary might be the cause of the density limit of Tokamaks.

Additional information

Authors: NIEDERMEYER H MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, GARCHING BEI MUENCHEN (GERMANY), MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, GARCHING BEI MUENCHEN (GERMANY)
Bibliographic Reference: WRITE TO MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, 8046 GARCHING BEI MUENCHEN (GERMANY), MENTIONING REPORT IPP III/90, 1983
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