On the asymmetries of ELM divertor power deposition in JET and ASDEX Upgrade

An analytical expression was derived for describing the divertor target power during ELMs based on the model discussed in [W. Fundamenski, R.A. Pitts, Plasma Phys. Control. Fus. 48 (2006) 109] where the power load arises from a Maxwellian distribution of particles released into the SOL region. The paper discusses a comparable simple extension of the model by introducing a non-zero characteristic velocity of the Maxwellian distributed particles. This way the experimentally observed temporal evolution as well as the in/out energy imbalance can be described. The extended model named free-streaming-particle (FSP) approach predicts a dependence of the ELM in/out energy balance of the pedestal Mach number as well as an inversion of the in/out balance by a change of the field line helicity as observed experimentally. From the FSP approach the value for E τ IR (see text) is predicted to be 18–25% in good agreement to the experimental data. A comparison to the various discussed mechanism for the ELM in/out asymmetry is presented.