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

The evolution of the energy, momentum and particle transport through the L-H transition are determined in JET NBI heated discharges. Both normal and periodic L-H transitions are studied. It is found that all of the transport coefficients drop at the transition over a wide radial region and not just in the edge region as was previously thought to be the case. Indeed it is shown by two different modelling techniques that the conventional model in which the transport changes in a narrow region at the edge cannot explain the time behaviour of the electron temperature. Measurements of the fluctuation level by reflectometry also show a very fast drop over a wide radial region