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The automatic ambipolarity derived for NC diffusion results from the assumption that the plasma is in equilibrium, rather than any specific property of NC transport. It further assumes that there is no other mean source or damping of toroidal momentum ignoring, for example, anomalous toroidal viscosity. If the NC fluxes were intrinscially ambipolar, it is not obvious what process can carry the observed radial currents from biased internal probes or the current required to neutralise the ion orbit loss current near the plasma edge. In the original NC analysis by Galeev and Sagdeev, the ion and electron fluxes are functions of E(r), the radial electric field. This predicts a current driven by the applied probe voltage which is consistent, both in magnitude and in its variation with voltage, with that measured in TEXTOR. In a stochastic magnetic field, electron escape along the magnetic field can be balanced by increased NC ion flux. This can explain the measured behaviour of the radial electric field in TEXT, and the general behaviour of impurities during enhanced MHD activity.

Additional information

Authors: STRINGER T E, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(94)38 EN (1994) 6 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199411465 / Last updated on: 1994-12-06
Original language: en
Available languages: en