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| Hauptseite > Publikationsdatenbank > Beryllium erosion in pure D and nitrogen seeded limiter plasmas in JET |
| Hauptseite > Publikationsdatenbank > Beryllium erosion in pure D and nitrogen seeded limiter plasmas in JET |
| Abstract | FZJ-2021-01672 |
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2021
Abstract: Beryllium erosion in pure D and nitrogen seeded limiter plasmas in JETT. Dittmar, J. Romazanov, S. Aleiferisc, D. Borodin, S. Brezinsek, A. Drenika, A. Huber, E. Pawelecb, S. Silburnc, V. S. Neverovd, and the JET contributors*Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germanya Max-Planck-Institut für Plasmaphysik, 85748 Garching b. München, Germayb University of Opole, Institute of Physics, Oleska 48, Opole, Polandc UKAEA-EURATOM Association, Culham Science Centre, Abingdon, OX14 3DB, UKdNational Research Centre “Kurchatov Institute”, Moscow 123182, Russian Federationt.dittmar@fz-juelich.deBeryllium (Be) is the material used for the inner and outer limiters of the JET tokamak and will be the plasma-facing material of the first wall in the ITER fusion experiment. The erosion of Be is a main driver for fuel retention due to the build-up of hydrogen rich Be-codeposits and is responsible for a large fraction of the tungsten sputtering in the divertor by material migration of Be from the main chamber into the W divertor. Besides physical sputtering there is evidence that chemically assisted physical sputtering (CAPS) play an important role in Be erosion [1]. Contrary to physical sputtering CAPS relies additionally on chemical processes for the Be erosion, and therefore erosion yields are very sensitive regarding surface temperature and chemical composition. A series of similar JET limiter discharges (Bt = 2.4 T, Ip = 1.9 MA, ne,core ~ 7–8·1019 m-³, Te ~ 1.9 keV) in deuterium, comparable to studies in unseeded discharges in earlier experiment [2] was performed. Fast, continuous repetition of identical discharges ratcheted up the limiter base temperature and allowed to study the influence of the limiter surface temperatures (450...640 K) on the interaction of the plasma with the beryllium components. Compared with previous studies, the edge plasma temperature during the limiter heat-up phase was decreased from ~15 eV to less than 5 eV, thus, the impact energy of the projectiles dropped accordingly. Additionally, plasma density variations were performed at elevated limiter temperature and reduction of CAPS. Besides VIS and UV spectroscopic observation at the midplane contact point, additional narrowband filtered camera images of Be, BeD and Be II allow a direct comparison of emission patterns with ERO 2.0 modeling [3]. Similar discharges were also carried-out with nitrogen and neon seeding in order to study suppression of CAPS by nitrogen species. In this contribution, we will give an overview of the available experimental data on CAPS and discuss the influence of surface temperature and ion energy. Moreover, we show that the nitrogen gives raise to an cumulative, surface temperature independent reduction of BeI, BeII and molecular BeD measured intensities and discuss that this reduction is likely due to a suppression of chemical erosion of the beryllium. [1] C. Björkas, et al. Plasma Phys. Control. Fusion 55 (2013) 074004[1] S. Brezinsek, et al., Nuc. Fus. 54 (2014) 103001[3] D. Borodin, et al., this conference* See the author list of E. Joffrin et al. published in Nuclear Fusion Special issue 2019, https://doi.org/10.1088/1741-4326/ab2276
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