Edge fluctuation measurements during X-point plasmas in Jet

The measurements of edge spikes in JET tokamak are discussed. The L to H transitions are considered. Local measurements of edge fluctuations are carried out and the effect on global particle and energy content are discussed. The plasma diagnostics is performed by means of Langmuir probes and pick-up coils near the X-point position, a poloidal D-γ array and a multichannel reflectometer and an ECE heterodyne radiometer viewing near the midplane. Comparison of the observed local perturbations with global changes leads to the conclusion that convection of particles, from the outer region of the plasma during the spikes, can be responsible for much of the observed reduction in plasma energy