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Ion and electron temperatures of up to 5 keV have been obtained within 10 cm of the last closed flux surface (LCFS) in hot-ion H-modes with 18 MW of NBI heating. The ion temperature profiles appear to have "pedestals" which scale with power per particle in H-modes. In L-modes pedestal temperatures are an order of magnitude lower. This difference can be explained by the one order of magnitude difference in particle residence time in the two confinement modes. In H-modes, the resulting pressure pedestals contribute typically 40%, and up to 5 MJ, to the plasma stored energy, explaining about half of the confinement improvement over L-mode conditions. The remaining improvement occurs across the entire plasma, but most notably in the periphery. There is ample evidence that ions with energies in the keV range escape to and beyond the LCFS, and account for most of the loss of power in the ion channel. The report includes results from energy discriminating probes in the scrape-off layer and an analysis of the characteristics of the heat strike zones in the X-point configuration. The observed boundary ion temperatures have far-reaching implications for fusion reactivity, power handling, wall erosion and impurity production in reactor conditions. They suggest that it is possible to bring the entire volume of a reactor plasma to thermonuclear temperatures, with a considerable boost to the overall thermonuclear reactivity.

Additional information

Authors: WEISEN H, Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Lausanne (CH);BERGSAKER H, Manne Siegbahn Institute of Physics, Stockholm (SE);ERENTS S K, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);MCCRACKEN G, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);ZHU J, AEA Fusion, Culham Laboratory, Abingdon, Oxon. (GB);CAMPBELL D ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(91)16 EN (1991) 46 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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