Relaxation model of H-modes in JET
Several phenomenological aspects of H-modes are described using a single variational principle. The observed dependence of global confinement time on current, and the characteristics of local heat diffusivity for a relaxed energy state are discussed. It is possible to describe sawteething H-modes as those observed in JET and DIII-D from a single variational principle. This yields unique profiles of current and pressure, proportional to l/q(2) even if a mixing region exists. A relaxation model is adopted, making the free energy stationary with a constraint of constant helicity within the mixing surface and constant current in the confinement zone. The equilibria in the two regions are matched at the mixing radius. In the high beta(p) limit, the solution bifurcates into two equilibria with different radii of inversion. The equilibrium with the larger radius of inversion is identified with that of JET. The vanishing inversion radius could be of the type observed in ASDEX, which is sawtooth free. The mutual proportionality of the current and pressure profiles and the bifurcation of solution is shown to be a strict consequence of the finite pressure pedestal.
Bibliographic Reference: Report: JET-P(88)48 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 198910428 / Last updated on: 1994-12-01
Original language: en
Available languages: en