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Local transport and ideal ballooning stability in the L-phase and ELM-free H-phase in ASDEX are analysed by computer modelling. It is found that the diffusivities X(e) and D at the edge are reduced by a factor of six a few milliseconds after the H-transition. Local transport in the inner plasma improves at an early stage by a typical factor of two. A change in the collisionality regime of electrons and ions does not take place. During the L-phase and the quiescent H-phase ideal ballooning modes are found to be stable. Computer experiments further show that a significant reduction in the particle flux at the separatrix takes place which is closely connected with the H-transition process. This explains the observed buildup of a density shoulder on a millisecond time-scale and the drop of the particle flow into the divertor. A strong decrease of the electron heat conduction flux at the separatrix is, however, ruled out in ELM-free periods. On the assumption of electrostatic turbulence induced transport, these results are consistent with measured density fluctuation levels near the separatrix.

Additional information

Authors: BECKER G, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);MURMANN H, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 28 (1988) No. 12, pp. 2179-2186
Record Number: 198910198 / Last updated on: 1994-12-01
Original language: en
Available languages: en