Giant edge localized modes (ELMs) play an important role in the transport of plasma at the edge of tokamaks with a divertor. The loss of plasma, by mechanisms that are not well understood, causes very high power loading on parts of the wall structure. The flows of particles and energy have been determined on a rapid time-scale for the first time in JET. The soft X ray measurements have a complex structure and show a rapid onset of the instability. They prove that some plasma is lost outside the divertor and that recycling occurs to well within the separatrix. The implications of the results for the ELM instability mechanism and the design of tokamaks are discussed.
Discharge optimization and the control of edge stability