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A simple isothermal model for the scrape-off layer (SOL) which includes effects of toroidal geometry and radial electric field, but ignores viscosity and plasma-neutral interactions, is presented. For finite toroidicity epsilon=a/R, and for the case of zero radial electric field E(r), the model predicts pressure asymmetry in favour of the outer target, and a non-zero radial current J(r) due to pressure gradient terms. For the case of non-zero E(r), J(r) is changed somewhat. The dependence of the current on the radial electric field, however, is too weak and non-monotonic against E(r), to explain experimental results on ion mobility obtained in biasing experiments on the Tokamak de Varennes. This may indicate that anomalous processes, not considered here, are controlling in TdeV. The direction of the pressure gradient driven current is inwards for normal toroidal field and outwards for the reversed field. The current can cause significant changes in radial flux in the SOL between the two field directions, for the case when the SOL width approaches the ion poloidal Larmor radius. Its effect on the SOL is proposed as a mechanism responsible for the dependence of the threshold power, needed to cause the L-H transition, on the direction of the toroidal field.

Additional information

Authors: CHANKIN A V, JET Joint Undertaking, Abingdon, Oxon (GB);STANGEBY P C, JET Joint Undertaking, Abingdon, Oxon (GB)
Bibliographic Reference: Report: JET-P(96) 12 EN (1996), 32pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon, OX14 3EA (GB)
Record Number: 199610986 / Last updated on: 1996-09-30
Original language: en
Available languages: en