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The density of ripple-trapped ions is strongly influenced by negative radial electric fields that can compensate the grad Beta drift. This density can be monitored with a time resolution of about 100 us by the measurement of charge-exchange neutral particle fluxes. According to Monte Carlo and Fokker-Planck calculations these fluxes should respond with a time delay of less than 200 µs, if the halfwidth of the electric field is reasonably large (a few centimetres). In the experiment, rise times of the fluxes after the L-H transition are longer or about 1 ms; jumps of the electric field in much shorter times can be excluded under such circumstances. The same is found for the H-L transition, where the flux measurement does not show any indication for a fast drop of the fields.

Additional information

Authors: HERRMANN W, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);HEIKKINEN J A, VTT, Helsinki (FI);KURKI-SUONIO T, HUT, Helsinki (FI)
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 40 (1998) pp. 683-687
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