(EX/4-5Rc) Modelling of Material Damage of CFC and W Macro-Brush Divertor Targets under ELMs and Disruptions at Plasma Gun Facilities and Prediction for ITER

B.N. Bazylev1), G. Janeschitz2), I. Landman1), S. Pestchanyi1), A. Loarte3), G. Federici4), M. Merola4), J. Linke5), J. Compan5), T. Hirai5), O. Ogorodnikova6), A Zhitlukhin7), V. Podkovyrov7), N. Klimov7), V. Safronov7), I. Garkusha8)
1) Forschungszentrum Karlsruhe GmbH, IHM, Karlsruhe, Germany
2)Forschungszentrum Karlsruhe GmbH, Fusion, Karlsruhe, Germany
3)EFDA Close Support Unit Garching, Boltmannstr.2, D-85748 Garching bei München, Germany
4)ITER International Team, Garching Working Site, Boltmannstr.2, D-85748 Garching bei München, Germany
5)Association Euratom- Institut für Plasmaphysik Jülich, D-5245 Jülich, Germany
6)Département de Recherches sur la Fusion Contrôlée, Association Euratom-CEA, CEA-Cadarache F-13108, Saint Paul Lez Durance Cedex, France
7)SRC RF TRINITI, Troitsk, 142190, Moscow Region, Russia
8)Institute of Plasma Physics of the National Science Centre, Kharkov Institute of Physics and Technology, 61108 Kharkov, Ukraine

Abstract.  Operation of ITER at high fusion gain is assumed to be the H-mode. A characteristic feature of this regime is the transient release of energy from the confined plasma onto plasma facing components (PFCs) by multiple ELMs, which can play a determining role in lifetime of PFCs as well as the transient power fluxes during disruptions. The expected energy fluxes on the ITER divertor during transients are: Type I ELM of 0.5-4 MJ/m2 during 300-600 μs, and disruptions of 2-13 MJ/m2 during 1-3 ms. CFC and tungsten macrobrush armour are foreseen as PFC for ITER divertor. During the intense transient events in ITER the evaporation, surface melting and melt splashing (W) are seen as the main mechanisms of PFC erosion. Due to rather different heat conductivities of CFC fibers, a noticeable erosion of the PAN fibers may occur at a rather small heat loads at which the damage to the tungsten armour is not substantial. The expected erosion of the ITER plasma facing components under transient energy loads can be properly estimated by numerical simulations validated against target erosion experiments at the plasma gun facility QSPA-T, in which components manufactured according to the EU specifications for the ITER divertor targets have been tested, and at the plasma gun facilities MK-200UG and QSPA-Kh50.The measured material erosion data have been used to validate the codes, PEGASUS, MEMOS, PHERMOBRID and FOREV-2, which are then applied to model the erosion of the divertor and main chamber ITER PFCs under the expected loads in ITER. Numerical simulations performed for the expected ITER-like loads demonstrated: a significant erosion of the CFC target is expected for ITER-like loads in excess of 0.5 MJ/m2; the W macrobrush structure is effective in preventing gross melt layer displacement during ELM-like loads leading to the overall erosion of W. Optimisation of macrobrush geometry in order to minimize erosion under ITER-like transient loads has been carried out. The erosion of the dome armour and the gaps between the divertor cassettes under the radiation from the plasma shield is numerically investigated for ITER disruption conditions. Different mechanisms of melt splashing are analyzed and implemented in the code MEMOS. For estimation of the W crack formation an analytical model that links the crack depth with the characteristic size of the crack mesh is proposed.

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