(EX/4-5Rd) Modelling of ITER Edge Plasma Dynamics Following Type I ELMs and Consequences for Tokamak Operation
1) Forschungszentrum Karlsruhe, IHM, FUSION, P.O. Box 3640, 76021 Karlsruhe, Germany
2) EFDA Close Support Unit, Boltmannstr.2, D-85748 Garching by München, Germany
3) State Research Centre TRINITI, 142190, Moscow Region, Troitsk, Russian Federation
Abstract. The reference regime for ITER is the H-mode in which the stationary operation will be repetitively interrupted by outbreaks of the ELMs. At each ELM the lost DT plasma produces surface damages and following contamination of the confined plasma. The transient energy release concerns also the poloidal magnetic field that undergoes substantial changes drastically broadening the footprint of the power flux. Thus computer modelling for ITER implies enhanced plasma transport across both the magnetic surfaces and the field lines ending at the vessel walls, multi-species plasma and neutral inflow in real toroidal configuration, account of poloidal field coils and plasma currents, line radiation losses, and injections of noble gases mitigating the disruptions. In order to predict the expected fluxes and consequent contamination of the vessel, a collaboration research has been developed in frame of fusion programme of EU and RF. The FZK (Karlsruhe, Germany) performs numerical modelling for the high energy fluxes relevant to ITER transient events and the TRINITI (Troitsk, Russia) experiments with a powerful plasma gun aiming at validation the codes. The paper will describe the physics basis employed to model the transient loads in ITER and summarise the main results of the experimental and modelling studies. The carbon fibre composite (CFC) and tungsten targets are investigated. The computer modelling revealed that significant impurity contamination of the edge plasma can occur, which can cause the collapse of the confinement at lesser ELM sizes than that determined by armour lifetime limitations. At the plasma gun facility MK-200 UG, experiments were carried out on the interaction of hot magnetized plasma streams with CFC and W targets. Plasma impact was investigated at the loads relevant to hard disruptions and Type I ELMs of ITER. First experiments aimed at impurity generation were performed in order to quantify the evaporation thresholds of W and CFC. Radiation properties of evaporated carbon were studied.
First simulations showed that ELMs do not clean the plasma from impurities. The tolerable ELM size was estimated as 1 MJ/m2 for ELM frequency of 0.5 Hz. Latest modelling results on the energy distribution over the vessel surface during ELM and post-ELM stages will be presented, accounting also for neutral influxes into the confinement regions.
Full paper and slides available (PDF)