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The effect of edge-localized modes (ELM) on confinement in ohmic H-modes has been investigated by analysing the rates of change of global parameters such as the electron content and the stored energy as a function of ELM frequency. In double-null H-modes, ELMs are found to expel on average 2% of the electron content and 2.5% of the stored energy. In single-null discharges which are separated by more than 2.2 cm from the inner wall, larger ELMs are observed which expel on average between 3% and 7% of the electron content and between 3% and 12% of the stored energy. When the plasma-wall distance is reduced, ELM frequencies increase and ELM amplitudes decrease. Quasi-stationary H-modes are obtained for f(ELM) approximately equal to 130 Hz in double-null plasmas and for f(ELM) in the range 50 Hz to 300 Hz in single-null plasmas, depending upon the plasma-wall distance and the ELM amplitude. The reduction in particle confinement due to the ELMs is sufficient to bring the ratio of particle to energy confinement times below 8-12 depending upon the ELM size and frequency.

Additional information

Authors: WEISEN H ET AL, École Polytechnique Fédérale de Lausanne, Centre de Recherches en Physique des Plasmas (CH)
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 38 (1996) pp. 1415-1419
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