Thermoelectric currents and their role during ELM formation in JET

A recently developed numerical model, describing a self-amplification and structure formation process which is used to model the initial non-linear growth phase of edge-localized modes (ELMs), is applied to the JET tokamak. Connection length simulations of the magnetic topology, including only error fields, for JET reveal the existence of small, so-called short connection length flux tubes. Such a configuration is used as the starting point for the model. Thermoelectric currents are assumed to flow in the short connection length flux tubes and add additional magnetic perturbations which change the magnetic topology severely. The change in magnetic topology leads to the formation of new, much larger short connection length flux tubes that can conduct much larger currents through the plasma edge. The current density inside the flux tubes is assumed to be constant to calculate the total current. This self-amplification process leads to the formation of patterns, known as footprints, on various segments of the inner wall throughout the vessel. The resulting footprints and their relation to the observed ELM patterns during discharges are discussed.