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Impact of divertor configuration on recycling neutral fluxes for ITER-like wall H-mode plasmas

Abstract : It is well known since the last years that in JET, with the ITER-like wall, the performance of high-power Hmode plasmas strongly depends on the divertor magnetic topology. This is generally attributed to the effect of the magnetic field shaping on the neutral flux transport and pumping, which determine in high density H-mode plasmas the pedestal properties and finally the global confinement. In the present work we have analysed for different magnetic configurations the spatial distribution and the dynamic behaviour of the D emission. Experimental observations indicate that for certain configurations, the surface temperature and the D -emission anomalously increase on top of the inner divertor, which points to thermal outgassing there. This is the region where most Beryllium co-deposits accumulate and most Deuterium becomes trapped. The overheating at this region far from the strike point (SP) is observed to happen in magnetic configurations with reduced distance between the divertor material surface and the Separatrix (Clearance). The neutral flux that appears at the upper inner divertor during a few milliseconds after the ELM-crash, is by more than an order of magnitude larger than the puffing rate and dominates over the rest of the divertor recycling. Finally, a preliminary study describes how this thermal fuel outgassing from the co-deposited layers could be intentionally used as a Wall-conditioning technique with plasmas that focalise their particle and heat flux there. This could be used as a Wall isotope exchange technique or for Tritium recovery from regions where Be co-deposits accumulate in JET with the ITER-like wall.
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Submitted on : Tuesday, February 23, 2021 - 5:32:07 PM
Last modification on : Thursday, February 25, 2021 - 3:18:15 AM

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E de la Cal, U Losada, A Martín de Aguilera, A Shaw, E Solano, et al.. Impact of divertor configuration on recycling neutral fluxes for ITER-like wall H-mode plasmas. Plasma Physics and Controlled Fusion, IOP Publishing, 2020, 62, pp.035006. ⟨10.1088/1361-6587/ab5fb1⟩. ⟨hal-03150405⟩

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