Integrated Modelling with COCONUT of Type‐I ELMs at JET

When modelling ELMy H-mode plasmas the strong interaction between the core plasma and the scrape-offlayer (SOL) must be accounted for. The 1.5D core code JETTO [1] and the 2D SOL fluid-code EDGE2D [2] have been combined to provide a consistent picture of the transport across the separatrix, resulted in the coupled code COCONUT [3]. The ELM-crash itself is modelled in an ad hoc manner, by which the perpendicular diffusive transport within the ETB is enhanced for a short time (≈ few 100 μs). An ELM is triggered if the normalised pressure gradient exceeds a critical threshold, αc, specified by the MHD-stability analysis [4]. COCONUT simulations indicate that the neutral penetration changes the ETB transport behaviour qualitatively such as it reduces convection [5]. But since the same power enters the ETB from the core, a reduction in the convected out.ux to the SOL leads to a peak in the radial pressure gradient profile earlier in the ELM cycle. As a consequence, the ELM frequency increases, a tendency which is indeed seen in experiment. This paper concentrates on the modelling of type-I ELMy H-mode, pure-D JET plasmas, seeking to match experimental results for different scans of gas-puff, pedestal parameters (such as nped, Tped and ν *ped). The effects on ELM frequency, power-exhaust, a detailed analysis of the time-dependence of ELM-crashes and the reformation of the pedestal are discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)