Tokamak configurations with a divertor generally exhibit edge localized modes (elms) which play an important role in controlling the edge plasma. Many different sorts of elm have been classified, but the plasma properties are most substantially changed by the giant elms which cause the loss of a substantial fraction of the plasma energy and particles over a short time interval of approx 100mus. This leads to a very high power loading of parts of the tokamak wall structure. The details of the very fast processes involved in the loss of plasma are not understood. Using a set of highly time-resolved diagnostics, the flow of both energy and particles during giant elms has been determined for the first time in the mark 1 Jet divertor. These results are determined mainly from a comprehensive set of soft X-ray cameras which have several views fo the divertor region. Observations in the soft X-ray region are able to provide important information because fo the very high electron temperatures achieved just within the separatrix. The soft X-ray measurements have a remarkably complex structure with very rapid flashes being observed both from the divertor plates and from regions well within the separatrix. The divertor flashes are from bremsstrahlung from hot plasma electrons which strike the divertor plates and those inside the plasma are from a local enhancement of the plasma density caused by recycling particles. The measurements prove that the plasma energy is deposited both in the divertor and other areas of the vessel, and that of the particles lost many are recycled to well within the separatrix. The implications of the measurements for the elm instability mechanism and the design of tokamaks are discussed.
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