Studies of impurity migration in TEXTOR by local

Studies of impurity migration in TEXTOR by local tracer injection a Kirschner , a Wienhold , a Borodin , a, b Björkas , c Hoey , a, c Matveev , A. P. D. C. O. Van D. S. Brezinseka, A. Kretera, M. Laengnera, K. Ohyad, V. Philippsa, A. Pospieszczyka, a a a U. Samm , B. Schweer , and TEXTOR team a. Institut für Energie- und Klimaforschung – Plasmaphysik, Forschungszentrum Jülich, Assoziation EURATOM-FZJ, Trilateral Euregio Cluster, 52425 Jülich, Germany, b. Department of Physics, University of Helsinki, Finland, c. Department of Applied Physics, Ghent University, B-9000 Ghent, Belgium, d. Institute of Technology and Science, The University of Tokushima, Japan. Motivation ERO modelling results ● Modelled 13 C deposition efficiencies local deposition efficiencies. According modelling needs assumption of enhanced re-erosion (factor f. Enh) of re-deposits to match. f. Enh=5, RN=1 RI=0. 1, RN=1 ● 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? The 3 D Monte Carlo code ERO background - plasma Cx+, CHy 0, + re-eroded/ reflected particles CH 4 ● Assuming reflection for hydrocarbons according to MD (RI=0. 1, RN=1) - to simulate observed 13 C deposition efficiency: f. Enh~35 for reference case, f. Enh=10 -15 for low injection case surface ● Assuming f. Enh=5 for re-erosion and RN=1 - to simulate observed 13 C deposition efficiency: RI=0. 8 -0. 9 for reference case, RI=0. 6 -0. 7 for low injection case surface (substrate C, CR, Be) plasma-wall-interaction: impurity transport: • physical sputtering/ reflection • chemical erosion (CD 4, Be. D) • deposition from background • redeposition of eroded species • ionisation, dissociation • friction, thermal force • Lorentz-force • cross field diffusion 13 CH 4 13 C deposition Low Injection Case: Reference Case: tracer experiments Experimental set-up: horizontal observation Modelled and simulated profiles of Test limiter after exposure: vertical observation Reference: 0. 3% polished C surface toroidal limiter (46 cm) ● 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% limiter lock test limiter 13 CH Conclusions RI=0. 1, RN=1 polished C surface Limiter tip injection rate position Reference Low injection 4 Reference ~1⋅1019/s 46 cm Low injection ~1⋅1018/s 46. 2 cm Biased test limiter (300 V) ~1⋅1019/s 47 cm Deposition efficiency: #deposited 13 C on test limiter #injected 13 CH 4 atoms Biased test limiter: 1. 7% polished C surface ● Measured 13 C f. Enh in ERO 35 D+ 10 -15 5 -10 deposition efficiency increases with impact energy and reduced flux of depositing species re-deposit substrate Erosion: Y Re-erosion: f. Enh×Y FEnh = F(Ein, Gin) ● “Standard” assumptions in ERO lead to large 13 C 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. Forschungszentrum Jülich | Institute of Energy and Climate Research – Plasma Physics | Association EURATOM - FZJ