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Empirical scaling laws for the confinement time tau (E) in tokamaks depend on dimensionless global plasma parameters in a way which is difficult to associate with some general plasma physics model. It is shown that such dependencies can arise form artefacts in the database used to derive the scaling expression. The artefacts involve inner relationships, for example collinearities between variables. For the International Thermonuclear Experimental Reactor (ITER) L-mode and H-mode databases it is shown that subsets of the scaling expressions are approximately constant. An alternative description of L-mode, edge localized mode (ELM)-free, small ELM and giant ELM H-mode data is given. A simple electrostatic physics model (plateau scaling) in which confinement is degraded by non-collisional processes, can describe global confinement data for all four confinement regimes; this common scaling features a multiplier C which is assigned a different value for each regime. The complex physics associated with magnetohydrodynamics (MHD) instabilities (ELM's, sawteeth, outer modes) is hidden in the multiplier C and attempts are made to uncover such physics. In these attempts global confinements are made to scale with physics models, electrostatics, MHD etc rather than physics variables.

Additional information

Authors: CHRISTIANSEN J P, JET Joint Undertaking, Abingdon, Oxon (GB);CORDEY J G, JET Joint Undertaking, Abingdon, Oxon (GB)
Bibliographic Reference: Report: JET-P(98)08 EN (1998) 14pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon, OX14 3EA (GB)
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