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The effect on the scrape-off layer (SOL) of changing the position of a tokamak limiter from the low field side (LFS) to the high field side (HFS) of the plasma is considered. Conservation of magnetic flux in the SOL requires that the area for flow of particles and energy, parallel to the magnetic field, is smaller on the HFS. The effect that this reduction in area has on the SOL is that the characteristic scrape-off thickness is increased and the plasma particle and energy densities are higher. Such increases observed in an experiment in JET are described in which the plasma was limited first on the LFS and then, during the same discharge, on the HFS. The magnitude of the effect was larger than expected. Evidence is presented which suggests that the observed enhancement of the effect on the SOL above expectations is due to a reduction in the Mach number at the limiter sheath when on the HFS.

Additional information

Authors: HARBOUR P J, JET Joint Undertaking, Abingdon, Oxon. (GB);LOARTE A, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(93)96 EN (1993) 27 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
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