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The dependence of global and local confinement upon plasma current and poloidal field is studied in an analysis of JET data from a series of current ramp experiments. In such experiments the current profile is transiently decorrelated from its steady state shape over a period lasting more than ten confinement times. Global confinement is shown to depend not only on total current but also on some measure of the current distribution, such as the internal inductance. The origin of this dependence is found in the local analysis to be the dependence of diffusivity upon the poloidal field. A weak shear dependence of diffusivity is observed in the outer half of the plasma. Predictive transport calculations, in which the electron-ion thermal diffusivities are based on a critical temperature gradient model, are made; the calculations reproduce the measured temperature profiles to within the measurement errors. Simple mathematical expressions linking global to local confinement are used to demonstrate that the results from the global and local analysis are fully consistent.

Additional information

Authors: CHALLIS C D ET AL., JET Joint Undertaking, Abingdon, Oxon. (GB);KRAMER G J, FOM Instituut voor Plasmafysica, Rijnhuizen, Nieuwegein (NL)
Bibliographic Reference: Report: JET-P(92)15 EN (1992) 19 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199210775 / Last updated on: 1994-12-02
Original language: en
Available languages: en
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