Observation of Confined Current Structures in JET High Temperature Pedestals and Transient ELM Suppression
We report the identification of a localized current structure inside the JET plasma. It is a field aligned closed helical ribbon, carrying current in the same direction as the background current profile (co-current), rotating toroidally with the ion velocity (co-rotating). It appears to be located at an n=1 rational surface at a flat spot in the plasma pressure profile, at the top of the pedestal, and not in the gradient region. The current structure appears spontaneously in low density, high pedestal temperature, high rotation plasmas, and can last up to 1s, a time comparable to a local resistive time. It considerably delays the appearance of the first ELM, and regulates transport across the separatrix.