A NUMERICAL-SIMULATION OF THE L-H TRANSITION IN JET WITH LOCAL AND GLOBAL-MODELS OF ANOMALOUS TRANSPORT

A numerical study of the dynamics of the L-H transition in JET was don e using models of anomalous transport which depend either on local or on global plasma parameters. Comparison with experimental results show s that the best agreement is reached when using a global model for red ucing chi(e), chi(i) and D in the region where shear becomes large (e. g., outside the q = 1 surface). Thus the LH transition manifests itsel f as a sudden drop of the transport coefficients everywhere outside th e q = 1 surface, not only in a narrow layer near the plasma edge. The slow improvement of plasma confinement which follows such a fast trans ition could then be attributed to the dependence on the local plasma p arameters of the transport coefficients in the plasma core.