Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns

JET Contributors, V. Parail, T. Ahlgren, L. Aho-Mantila, M. Airila, C. Björkas, K. Heinola, A. Lahtinen, K. Nordlund, E. Safi, S.-P. Pehkonen, Elina Pajuste, A. Jarvinen, I. Jepu

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Data on erosion and melting of beryllium upper limiter tiles, so-called dump plates (DP), are presented for all three campaigns in the JET tokamak with the ITER-like wall. High-resolution images of the upper wall of JET show clear signs of flash melting on the ridge of the roofshaped tiles. The melt layers move in the poloidal direction from the inboard to the outboard tile, ending on the last DP tile with an upward going waterfall-like melt structure. Melting was caused mainly by unmitigated plasma disruptions. During three ILW campaigns, around 15% of all 12376 plasma pulses were catalogued as disruptions. Thermocouple data from the upper dump plates tiles showed a reduction in energy delivered by disruptions with fewer extreme events in the third campaign, ILW-3, in comparison to ILW-1 and ILW-2. The total Be erosion assessed via precision weighing of tiles retrieved from JET during shutdowns indicated the increasing mass loss across campaigns of up to 0.6 g from a single tile. The mass of splashed melted Be on the upper walls was also estimated using the high-resolution images of wall components taken after each campaign. The results agree with the total material loss estimated by tile weighing (similar to 130 g). Morphological and structural analysis performed on Be melt layers revealed a multilayer structure of re-solidified material composed mainly of Be and BeO with some heavy metal impurities Ni, Fe, W. IBA analysis performed across the affected tile ridge in both poloidal and toroidal direction revealed a low D concentration, in the range 1-4 x 10(17) D atoms cm(-2).

Original languageEnglish
Article number086009
JournalNuclear Fusion
Volume59
Issue number8
Number of pages21
ISSN0029-5515
DOIs
Publication statusPublished - Aug 2019
MoE publication typeA1 Journal article-refereed

Fields of Science

  • 114 Physical sciences

Cite this

JET Contributors, Parail, V., Ahlgren, T., Aho-Mantila, L., Airila, M., Björkas, C., ... Jepu, I. (2019). Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns. Nuclear Fusion, 59(8), [086009]. https://doi.org/10.1088/1741-4326/ab2076