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Heat transport in a plasma is investigated. On Tore Supra, such a perturbation is induced at the edge by the ergodic divertor. The main experimental features are temperature modulations and a transport barrier which allows no loss of confinement in the core plasma. An analysis of both temperature field and magnetic perturbation indicates clearly delimited regions of strong and weak transport that are related to the loss of memory on a field line due to the transverse diffusion. Furthermore, the perturbation is strongly space-dependent. This implies non local transport and a region (separatrix) in which the chirikov parameter is less than one. This analysis leads to a 1-dimensional analytical model which recovers modulations. A transport barrier is also expected, assuming a dissymetrical transport process around the separatrix. A mapping transport code has also been developed which takes the basic features of the ergodic divertor into account. The transport barrier can be attributed to non diffusive transport out of islands located around the separatrix. The trapping mechanisms in these islands, combined with some small level of transverse transport, reduce the probability for particles to flow back to the perturbed region. A dissymetrical process then appears and allows for a transport barrier.

Additional information

Authors: FÉRON S, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Report: EUR-CEA-FC-1616 FR (1997) 159pp.
Availability: Available from Association Euratom-CEA, CEN Cadarache, 13108 Saint-Paul-lez-Durance (FR)
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