Physics of ELM power fluxes to plasma facing components and implications for ITER

Abstract

A comparison of the spatial and temporal evolution of the filamentary structures observed during type-I ELMs is presented from a variety of diagnostics and machines. The filaments are elongated in the perpendicular (poloidal) direction and both the radial and poloidal size appears to increase linearly with the minor radius of the machine. The filaments spend between 50 and 100 μs rotating toroidally/poloidally with velocities close to that of the pedestal. Subsequently their rotation velocity decreases and the filaments propagate radially. At the time of separation each filament contains up to 2.5% of the energy released by the ELM. In both the connected and separated stages the dominant loss mechanism is ion parallel transport. The target e-folding length is observed to be correlated with the radial size of the filaments. This may suggest that the physics that drives the size of the filaments also determines the target power e-folding lengths.