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Weakly collisional ions trapped in the toroidal field ripples at the outer plasma edge can be prevented from escaping from the plasma due to grad B-drift by a counteracting radial electric field. This leads to an increase in the density of ripple-trapped ions, which can be monitored by the analysis of charge exchange neutrals. The paper describes a novel method, that allows one to measure aspects of the radial electric field at the plasma edge, especially its time behaviour, with a time resolution of about 100 µs. A few results obtained with this new method (published earlier) can be summarised by the statement, that a radial electric field with more than about 5 kV/m could not be detected before the L/H-transition, and that after the onset of the transition the field grows to not more than about 10 kV/m in 1 to 2 ms. The further growth of the field to 20 kV/m or, as shown in this paper, to more than 40 kV/m may need times longer than 100 ms. The present paper confirms these earlier observations, but adds some conditions that should be fulfilled to really exclude rapid jumps of the field at the transition.

Additional information

Authors: HERRMANN W ET AL, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/315 EN (1998) 31pp.
Availability: Available from the Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
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