Dr Gerrit Hogeweij (FOM)
AUG and JET, the largest present devices with high-Z PFC components, have identified requirements for stable H-mode operation, i.e. to keep heavy impurity concentrations sufficiently low, to avoid central accumulation, radiative collapses and disruptions. Limitations in the operational space which can be accessed in H-mode have been identified, e.g. (i) the need of operating at sufficiently high levels of gas puff, impeding access to low density regimes at low gas puff levels; (ii) central electron heating and/or frequent sawteeth may be needed to avoid W core accumulation. This paper starts with a short review of experimental results on erosion sources, edge (pedestal) transport, and core W transport. Then implications for ITER are discussed, concentrating on the effect of core W accumulation on the discharge evolution. In different ways the critical W concentration in ITER was assessed i.e. the maximal tolerable level without significantly perturbing the evolution of li, or the q and Te profiles. First, impurity transport (both neoclassical and anomalous) was modelled with the ZIMPUR code, in combination with ASTRA for the description of the bulk plasma parameters evolution with a scaling based transport model. The calculated critical W concentration is ~7 10-5 for the inductive scenario, and a factor 2-3 lower for the hybrid and steady state scenarios. Second, the current ramp-up phase in JET, AUG and ITER was modelled with the CRONOS suite of codes for different W concentrations. For ITER the expected plasma parameters for the baseline ITER ramp-up were used; for JET and AUG the experimental data (Te, ne, Zeff) were taken. The Bohm-gyroBohm model for thermal transport was used, and nW/ne profiles were assumed either flat or of the same (peaked) shape as measured in JET. The effects of flat and peaded W profiles are very different. The modelling results are in excellent agreement with experimental findings. As maximum tolerable W concentrations have now been calculated for different ITER scenarios, future work can concentrate on further quantify these limitations, using current understanding of neo-classical and anomalous W transport. This work was supported by EURATOM and carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
|Country or International Organisation||The Netherlands|
Dr Gerrit Hogeweij (FOM)
Dr Adrianus Sips (EFDA-JET) Dr Arne Kallenbach (Max-Planck-Institut f. Plasmaphysik) Dr Clemente Angioni (Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching, Germany) Dr Costanza Maggi (Max Planck Institut fuer Plasmaphysik) Dr Ernesto Lerche (ERM-KMS, Brussesl) Dr Giuseppe Calabro (ENEA) Dr Josef Schweinzer (IPP Garching) Dr Ralph Dux (IPP Garching) Dr Thomas Pütterich (Max-Planck-Institut für Plasmaphysik) Dr Vladimir Leonov (NRC "Kurchatov Institute")