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When the external injection of power is sufficiently high, a tokamak ohmically relaxed state with maximum entropy can no longer be sustained, and the plasma becomes resistively unstable. The instability is the result of a peculiar interaction between the edge resistivity , the current and the thermal transport at the edge of the current channel. The thresholds of the instability depend on the existence of a current pedestal and on the detachment of the current channel from the material limiters, combined with a sufficiently high ratio between the auxiliary power and the toroidal magnetic field and a sufficiently low toroidal current. In the paper the thresholds are expressed in a form which allows comparison with the experiments. The theoretical predictions are generally consistent with the observations on the H-transitions in tokamaks, in particular with the scalings observed in DIII-D and JIPP T-IIU.

Additional information

Authors: MINARDI E, JET Joint Undertaking, Abingdon, Oxon. (GB)
Bibliographic Reference: Report: JET-P(89)50 EN (1989)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 199010621 / Last updated on: 1994-12-01
Original language: en
Available languages: en