THE TIME BEHAVIOR OF RADIAL ELECTRIC-FIELDS AT THE L-H TRANSITION FROM THE OBSERVATION OF RIPPLE-TRAPPED IONS

The density of ripple-trapped ions is strongly influenced by negative radial electric fields that can compensate the grad B drift. This dens ity can be monitored with a time resolution of about 100 mu s by the m easurement of charge-exchange neutral particle fluxes. According to Mo nte Carlo and Fokker-Planck calculations these fluxes should respond w ith a time delay of less than 200 mu s, if the halfwidth of the electr ic field is reasonably large (a few centimetres). In the experiment, r ise 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, w here the flux measurement does not show any indication for a fast drop of the fields.