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Abstract

The ablation of carbon pellets injected into ECR-heated plasmas of Wendelstein 7-AS (W7-AS) has been investigated using a photographic technique with the aim of studying features of the ablation process in stellarator plasmas. The ablation rate profiles were measured assuming a proportionality of the C II radiation and the ablation rate. This assumption was confirmed experimentally and by simulations performed by a quasi-three-dimensional code. The fraction of continuum radiation, which is detected together with the C II line radiation (when using the light filters with finite spectral width), did not affect these measurements.

No significant drifts of pellet clouds in the toroidal, poloidal and radial directions were observed in the C II line (723nm) emission. From fast electron temperature measurements (Delta t = 10mu s) using ECE diagnostics, no indications of a pre-cooling wave were found.

A difference between the ablation rates for discharges with low and high plasma density, which lies beyond the error bars, was observed. A specific zone of enhanced ablation was detected at the plasma periphery at high density. The appearance of such ablation enhancement, points to the existence of an additional local heat flux. However, the mechanism that could explain the enhanced ablation phenomena at high plasma densities remains unclear.

Additional information

Authors: LEDL L, Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Greifswald (DE);BURHENN R, Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Greifswald (DE);LENGYEL L, Max-Planck-Institut fur Plasmaphysik, EURATOM Association, Teilinstitut Greifswald, Greifswald (DE);WAGNER F, Institut fur Plasmaforschung, Universitat Stuttgart (DE);SERGEEV V YU, St. Petersburg State Polytechnical University, St. Petersburg (RU);TIMOKHIN V M, St. Petersburg State Polytechnical University, St. Petersburg (RU);KUTEEV B V, St. Petersburg State Polytechnical University, St. Petersburg (RU);SKOKOV V G, St. Petersburg State Polytechnical University, St. Petersburg (RU);EGOROV S M, St. Petersburg State Polytechnical University, St. Petersburg (RU)
Bibliographic Reference: An article published in: Nuclear Fusion 44 (2004) pp.600-608
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://www.iop.org/EJ/S/UNREG/8j8IMOD95xY2MhZA9X4tEw/journal/NuclFus
Record Number: 200417557 / Last updated on: 2004-06-17
Category: PUBLICATION
Original language: en
Available languages: en