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In a simple one-fluid cylindrical model of the transport and dissipative effects, the family of the magnetic states of the tokamak which correspond to a vanishing entropy production in the confinement region are characterised by a definite relation or "state equation", involving the relevant parameters of the discharge. The change in entropy production is investigated when the current density profile is rearranged by a perturbation which conserves the poloidal magnetic flux. It is shown that for a sufficiently short time interval (t2 much less than tau(E).tau(s), where tau(E) is the energy confinement time and tau(s) is the resistive time), neighbouring bifurcating equilibria exist which can be reached with a flux conserving transition and with increase of the magnetic entropy. The family of these new states can also be characterised by a state equation involving the relevant discharge parameters. When the state equations of the two families are simultaneously satisfied by the same set of parameter values, a flux conserving, entropy increasing transition may take place between states of the two families. The modifications of the current density and temperature profiles involved in the transition are investigated, as well as the discharge parameter conditions necessary for the transition to occur.

Additional information

Authors: MINARDI E, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(90)71 EN (1990) 34 pp.
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199110612 / Last updated on: 1994-12-02
Original language: en
Available languages: en