Experimental investigation of ELMs and associated fluctuations in JET

The paper gives a phenomenological classification of the ELM in JET. Both the temporal and the radial evolution of the ELM are investigated, and observations of significant changes in the electron density and pressure gradients during the ELM are presented, as well as density and magnetic field fluctuations associated with the ELM. Broadband turbulence (5-100 kHz) is generally observed during the D(alpha) event, and coherent precursor fluctuations at 50-80 kHz are observed 0.5-20 ms prior to some types of ELM. The density perturbations are localised to a narrow radial region at rho = 0.8-1.0, and there is evidence of a density pulse propagating outwards from this region during the ELM. The results are combined to give a description of the series of events constituting an ELM, and the interpretation of ELMs in terms of fluctuation induced transport is considered.