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This paper addresses the physics of stochastic boundaries. The stochastic properties of magnetic field lines are related to the spectrum of the radial magnetic perturbation. The stochastic region, or divertor volume, is shown to be bounded to the edge plasma. On short scales, the stochasticity is not effective and parallel transport dominates, this defines the laminar region. On the long scales one recovers the proper stochastic features which characterize the ergodic regime. Theoretical predictions for the transport of energy, current and particles in the divertor volume are analysed for both the laminar and ergodic regimes. The experimental data shows good agreement with the predictions on electron transport. Regarding particle transport, the response is larger than expected and stochastic boundaries are characterized by significant screening properties compared to limiter shots. A decreased life time of the ions at the very edge of the plasma is expected. Screening effects are thus observed for species exhibiting large wall pumping capability, while He and Ne are weakly affected by the stochastic boundary. The plasma properties are in the ergodic volume lead to radiating layer investigations on Tore Supra. Stable operation has been achieved with 80% of radiated power and radio frequency heating up to 6 MW.

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Authors: GHENDRIH P, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);GROSMAN A, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);CAPES H, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Report: 1571 EN (1996) 76pp.
Availability: Available from Association Euratom-CEA, CEN Cadarache, 13108 Saint-Paul-lez-Durance (FR)
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