Studies of impurity migration in TEXTOR by local tracer injection A. Kirschnera, P. Wienholda, D. Borodina, C. Björkasa,b, O. Van Hoeyc, D. Matveeva,c, S. Brezinseka, A. Kretera, M. Laengnera, K. Ohyad, V. Philippsa, A. Pospieszczyka, U. Samma, B. Schweera, and TEXTOR teama aInstitut für Energie- und Klimaforschung – Plasmaphysik, Forschungszentrum Jülich, Assoziation EURATOM-FZJ, Trilateral Euregio Cluster, 52425 Jülich, Germany, bDepartment of Physics, University of Helsinki, Finland, cDepartment of Applied Physics, Ghent University, B-9000 Ghent, Belgium, dInstitute of Technology and Science, The University of Tokushima, Japan. Motivation ERO modelling results ● Former tracer injection experiments in TEXTOR lead to very small local deposition efficiencies. According modelling needs assumption of enhanced re-erosion (factor fEnh) of re-deposits to match. ● Possibly enhanced re-erosion of re-deposits: determines resulting net-deposition and thus important for wall life time. ● Study the influence of flux and energy of depositing tracer species on resulting deposition efficiency ⇒ involved mechanisms? Modelled 13C deposition efficiencies RI=0.1, RN=1 fEnh=5, RN=1 The 3D Monte Carlo code ERO CH4 Cx+,CHy0,+ re-eroded/ reflected particles background - plasma surface (substrate C, CR, Be) surface plasma-wall-interaction: physical sputtering/ reflection chemical erosion (CD4, BeD) deposition from background redeposition of eroded species impurity transport: ionisation, dissociation friction, thermal force Lorentz-force cross field diffusion ● Assuming reflection for hydrocarbons according to MD (RI=0.1, RN=1) - to simulate observed 13C deposition efficiency: fEnh~35 for reference case, fEnh=10-15 for low injection case ● Assuming fEnh=5 for re-erosion and RN=1 - to simulate observed 13C deposition efficiency: RI=0.8-0.9 for reference case, RI=0.6-0.7 for low injection case Modelled and simulated profiles of 13C deposition Reference Case: Low Injection Case: 13CH4 tracer experiments Experimental set-up: Test limiter after exposure: horizontal observation vertical observation toroidal limiter (46cm) limiter lock test limiter Reference: 0.3% polished C surface ● Reference case: RI>~0.9 needed to reproduce measured profile ● Low injection case: profile shape reproduced also for smaller RI Low injection rate : 0.71% Conclusions Erosion: Y Re-erosion: fEnh×Y re-deposit D+ substrate RI=0.1, RN=1 fEnh in ERO Reference 35 Low injection 10-15 Biased test limiter 5-10 polished C surface 13CH4 injection rate Limiter tip position Reference ~1⋅1019/s 46cm Low injection ~1⋅1018/s 46.2cm Biased test limiter (300V) 47cm Biased test limiter: 1.7% ● Measured 13C deposition efficiency increases with impact energy and reduced flux of depositing species ● “Standard” assumptions in ERO lead to large 13C deposition efficiencies (55% for reference, 34% for low injection, 42% for biased limiter case) ● ERO needs enhanced re-erosion and/or increased ion reflection – enhancement smallest for biased limiter. FEnh = F(Ein, Gin) polished C surface Deposition efficiency: #deposited 13C on test limiter #injected 13CH4 atoms