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The role of neoclassical transport in determining the radial electric field in the presence of non-ambipolar loss mechanisms is discussed. It is pointed out that neoclassical fluxes are not generally automatically ambipolar. A simplified heuristic description of the NC loss process is then given and analytical expressions for the NC particle fluxes in the banana and plateau regimes are presented. The special case where other loss processes are either absent or ambipolar is discussed. Measurements of the radial profile of potential are described and it is pointed out how magnetic stochasticity may reverse the sign of E(r). Examples of ion orbits which enter the divertor are shown and an approximate estimate of the resulting ion loss current is described. This ambipolar condition which determines E(r) is discussed. A qualitative description of the way an electric field can reduce fluctuations and improve confinement is given. The NC transport of impurities is summarised and impurity transport in a stochastic magnetic field is discussed.

Additional information

Authors: STRINGER T E, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(93)70 EN (1993) 17 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199311558 / Last updated on: 1994-11-28
Original language: en
Available languages: en