Type-I ELM mode structure observed by divertor thermography in ASDEX Upgrade

In the ASDEX Upgrade tokamak, power deposition structures on the outer divertor target surfaces during type-I Edge Localised Modes (ELMs) have been discovered by infra red thermography. These structures are radially and toroidally separated non-axisymmetric spirals. They are most obvious about 80 mm away from the toroidal symmetric strike zone on the target plates. The spiral structure of the power load is caused by a toroidally structured energy release in the outer midplane during the non-linear phase of a type-I ELM cycle as shown by basic field line tracing. The resulting structures correspond to values around z(m) n ≈ 12 and m ≈ 50 (for q₉₅ ≈ 4)