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The conditions for drift reversal in the Wendelstein VII-X advanced stellarator have been studied. The bounced averaged drifts in ballooning space have been evaluated as local stability of a plasma is commonly investigated after invoking the ballooning mode transformation. The calculations are perfomed in the straight field line Boozer magnetic coordinates. At low beta, the helically (toroidally) trapped particles have bounced averaged drift frequencies of the same (opposite) sign compared with the diamagnetic drift frequency. As beta increases, the fraction of trapped particles that experience drift reversal also increases (manifested by a change in the sign of the ratio of the drifts). This increase is attributed mainly to the modification of the grad-B drift due to the combination of a favourable variation of the radial gradient of the Jacobian and a steepening of the poloidal current flux gradient. Near the beta limit of 5%, nearly all the trapped particles become drift-reversed. This could have very favourable implications for anamalous transport in the WVII-X.

Additional information

Authors: CLEMENT D, Centre de Recherches en Physique des Plasmas, Lausanne (CH);COOPER W A, Centre de Recherches en Physique des Plasmas, Lausanne (CH)
Bibliographic Reference: Article: Proceedings of the 22nd EPS Conference on Controlled Fusion and Plasma Physics, Vol. 19C (1995), pp. III133-III136
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