EVOLUTION OF TRANSPORT THROUGH THE L-H TRANSITION IN JET

The evolution of the energy, momentum and particle transport through t he L-H transition are determined in JET NBI heated discharges. Both no rmal 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 th at the conventional model in which the transport changes in a narrow r egion at the edge cannot explain the time behaviour of the electron te mperature. Measurements of the fluctuation level by reflectometry also show a very fast drop over a wide radial region.