Elsevier

Journal of Nuclear Materials

Volume 516, 1 April 2019, Pages 202-213
Journal of Nuclear Materials

Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall

https://doi.org/10.1016/j.jnucmat.2018.11.027Get rights and content

Highlights

  • Components from divertor corners in JET-ILW studied with IBA and SEM.

  • C/D co-deposition indicated on Inconel-600 blocks mounted on divertor carrier ribs.

  • C presence not essential for D retention in BeO layers on quartz microbalance covers.

  • Transport of C occurred only on centimeter scale in remote corners.

  • In-vessel oxidation of component surfaces by 18O tracer was measured.

Abstract

Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analysed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 μm were indicated, but typical values were on the order of a few hundred nm. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 μm were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

Introduction

Plasma-wall interactions, material migration and the resulting surface modification of plasma facing components are identified as key elements in the preparation for future fusion devices [1]. To facilitate material migration studies in the Joint European Torus (JET) with ITER-like wall [2,3], a significant number of probes have been installed; both in the divertor and in the main chamber [4]. Such probes are retrieved for ex-situ analysis during major shutdowns. The aim of this paper is to provide an analysis of deposited layers on components retrieved from remote corners in the JET divertor between 2012 and 2017, after three ITER-like wall campaigns (ILW-1 to ILW-3). Layer thickness, composition and depth profiles of atomic concentrations are investigated. Conclusions about material deposition are drawn while keeping in mind uncertainties and error sources related to the chosen analysis methods. Sample surface morphology and the presence of dust particles are also described. The analysed components are cubic blocks of Inconel-600 with side length 15 mm, referred to as spatial blocks (SB) and 76 mm long stainless steel covers for quartz microbalance (QMB) deposition monitors.

Section snippets

Sample descriptions and plasma exposure conditions

Five SB were included in the present study; SB 4, 5, 6, 8 and 9, all of which, while present in JET, were attached to the carbon ribs of the divertor carrier in Module 14 inner wide (IW) beneath and behind Tile 3. SB4-6 were in the machine between 2011 and 2012, during ILW-1 while SB8-9 were present from 2015 to 2016, during ILW-3. Two sets of four QMB covers each, numbered 1, 2, 3 and 5 were studied. The first such set was present in JET between 2012 and 2014, during ILW-2, except the cover

Spatial blocks 4–6 from ILW-1

ToF-ERDA measurements were performed on three sides of SB4-6: the side facing towards the plasma, the opposite one facing away from the plasma (referred to below as the backside) and one of the sides 90° from the plasma facing direction, opposite to the side fastened on the divertor carrier rib. The geometry of the ToF-ERDA setup was modified for the measurement on the side facing 90° from the plasma; entry angle was 30° and exit angle 15°. Deposited layers whose thickness decreased with the

Discussion

As stated in Section 3.1, out of all ToF-ERDA results presented here, only those from the 90° side of SB4-6 were compensated for ion-induced gas release. The results for D in Table 1 show that when such compensation is applied along with detection efficiency compensation, quantitative agreement between NRA and ToF-ERDA is achieved. Ideally, all ToF-ERDA results for species that can leave the sample as diatomic gases (here H, D 14N, 16O and 18O) should be compensated. This task is, however,

Summary and concluding remarks

Deposits on SB and QMB covers retrieved from remote corners in the JET-ILW divertor have been studied with IBA, SEM and EDS. Layer thicknesses on the order of 1 μm or more were found on the plasma facing side of SB6 from ILW-1, while all other layers on SB were limited to less than 1 μm. Typical layer thicknesses 90° from the plasma facing direction on the SB were a few hundred nm, with slightly thicker layers on SB8-9 from ILW-3 than on SB4-6 from ILW-1, due to the longer divertor plasma time

Data availability

The raw and processed data required to reproduce these findings are available to download from Mendeley Data via the links supplied with the online version of this paper.

Acknowledgments

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement number 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Work was performed under work package WPJET2. The Tandem Laboratory has been supported by grants from the Swedish Foundation for Strategic Research, grant number RIF14-0053, and the Swedish

References (29)

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See the author list of X. Litaudon et al., Nucl. Fusion 57 (2017) 102001.

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