Micro ion beam analysis for the erosion of beryllium marker tiles in a tokamak limiter

JET Contributors, Jan Mlynar, L. Aho-Mantila, M. Airila, C. Björkas, E. Safi, Y. Zhou, S. K. Sipila , O. Asunta, M. Groth, A. Hakola, J. Karhunen, S. Koivuranta, T. Kurki-Suonio, B. Lomanowski, J. Lonnroth, A. Salmi, M. I. K. Santala, J. Varje, P. Siren

Research output: Contribution to journalConference articleScientificpeer-review

Abstract

Beryllium limiter marker tiles were exposed to plasma in the Joint European Torus to diagnose the erosion of main chamber wall materials. A limiter marker tile consists of a beryllium coating layer (7-9 mu m) on the top of bulk beryllium, with a nickel interlayer (2-3 mu m) between them. The thickness variation of the beryllium coating layer, after exposure to plasma, could indicate the erosion measured by ion beam analysis with backscattering spectrometry. However, interpretations from broad beam backscattering spectra were limited by the non-uniform surface structures. Therefore, micro-ion beam analysis (mu-IBA) with 3 MeV proton beam for Elastic back scattering spectrometry (EBS) and PIXE was used to scan samples. The spot size was in the range of 3-10 mu m. Scanned areas were analysed with scanning electron microscopy (SEM) as well. Combining results from mu-IBA and SEM, we obtained local spectra from carefully chosen areas on which the surface structures were relatively uniform. Local spectra suggested that the scanned area (approximate to 600 mu m x 1200 mu m) contained regions with serious erosion with only 2-3 mu m coating beryllium left, regions with intact marker tile, and droplets with 90% beryllium. The nonuniform erosion, droplets mainly formed by beryllium, and the possible mixture of beryllium and nickel were the major reasons that confused interpretation from broad beam EBS.
Original languageEnglish
JournalNuclear Instruments & Methods in Physics Research. Section B: Beam Interactions with Materials and Atoms
Volume450
Pages (from-to)200-204
Number of pages5
ISSN0168-583X
DOIs
Publication statusPublished - 1 Jul 2019
MoE publication typeA4 Article in conference proceedings
EventInternational Conference on Ion Beam Analysis (IBA) - Shanghai, China
Duration: 8 Oct 201713 Oct 2017
Conference number: 23

Fields of Science

  • 114 Physical sciences

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