Deposition in the inner and outer corners of the JET divertor with carbon wall and metallic ITER-like wall

Rotating collectors and quartz microbalances (QMBs) are used in JET to provide time-dependent measurements of erosion and deposition. Rotation of collector discs behind apertures allows recording of the long term evolution of deposition. QMBs measure mass change via the frequency deviations of vibrating quartz crystals. These diagnostics are used to investigate erosion/deposition during JET-C carbon operation and JET-ILW (ITER-like wall) beryllium/ tungsten operation. A simple geometrical model utilising experimental data is used to model the time-dependent collector deposition profiles, demonstrating good qualitative agreement with experimental results. Overall, the JET-ILW collector deposition is reduced by an order of magnitude relative to JET-C, with beryllium replacing carbon as the dominant deposit. However, contrary to JET-C, in JET-ILW there is more deposition on the outer collector than the inner. This reversal of deposition asymmetry is investigated using an analysis of QMB data and is attributed to the different chemical properties of carbon and beryllium.EURATOM 63305

Overview of the JET ITER-like wall divertor

The work presented draws on new analysis of components removed following the second JET ITER-like wall campaign 2013–14 concentrating on the upper inner divertor, inner and outer divertor corners, life- time issues relating to tungsten coatings on JET carbon fibre composite divertor tiles and dust/particulate generation. The results show that the upper inner divertor remains the region of highest deposition in the JET-ILW. Variations in plasma configurations between the first and second campaign have altered ma- terial migration to the corners of the inner and outer divertor. Net deposition is shown to be beneficial in the sense that it reduces W coating erosion, covers small areas of exposed carbon surfaces and even encapsulates particles.EURATOM 633053RCUK Energy Programme EP/I50104

Assessment of erosion, deposition and fuel retention in the JET-ILW divertor from ion beam analysis data

Proceedings of the 22nd International Conference on Plasma Surface Interactions 2016, 22nd PSI.Post-mortem analyses of individual components provide relevant information on plasma-surface interactions like tungsten erosion, beryllium deposition and plasma fuel retention with divertor tiles via implantation or co-deposition. Ion Beam techniques are ideal tools for such purposes and have been extensively used for post-mortem analyses of selected tiles from JET following each campaign. In this contribution results from tiles removed from the JET ITER-Like Wall (JET-ILW) divertor following the 2013–2014 campaign are presented. The results summarize erosion, deposition and fuel retention along the poloidal cross section of the divertor surface and provide data for comparison with the first JET-ILW campaign, showing a similar pattern of material migration with the exception of Tile 6 where the strike point time on the tile was ∼ 4 times longer in 2013–2014 than in 2011–2012, which is likely to account for more material migration to this region. The W deposition on top of the Mo marker coating of Tile 4 shows that the enrichment takes place at the strike point location.Peer reviewe

Beryllium migration in JET ITER-like wall plasmas

JET is used as a test bed for ITER, to investigate beryllium migration which connects the lifetime of first-wall components under erosion with tokamak safety, in relation to long-term fuel retention. The (i) limiter and the (ii) divertor configurations have been studied in JET-ILW (JET with a Be first wall and W divertor), and compared with those for the former JET-C (JET with carbon-based plasma-facing components (PFCs)). (i) For the limiter configuration, the Be gross erosion at the contact point was determined in situ by spectroscopy as between 4% (E-in = 35 eV) and more than 100%, caused by Be self-sputtering (E-in = 200 eV). Chemically assisted physical sputtering via BeD release has been identified to contribute to the effective Be sputtering yield, i.e. at E-in = 75 eV, erosion was enhanced by about 1/3 with respect to the bare physical sputtering case. An effective gross yield of 10% is on average representative for limiter plasma conditions, whereas a factor of 2 difference between the gross erosion and net erosion, determined by post-mortem analysis, was found. The primary impurity source in the limiter configuration in JET-ILW is only 25% higher (in weight) than that for the JET-C case. The main fraction of eroded Be stays within the main chamber. (ii) For the divertor configuration, neutral Be and BeD from physically and chemically assisted physical sputtering by charge exchange neutrals and residual ion flux at the recessed wall enter the plasma, ionize and are transported by scrape-off layer flows towards the inner divertor where significant net deposition takes place. The amount of Be eroded at the first wall (21 g) and the Be amount deposited in the inner divertor (28 g) are in fair agreement, though the balancing is as yet incomplete due to the limited analysis of PFCs. The primary impurity source in the JET-ILW is a factor of 5.3 less in comparison with that for JET-C, resulting in lower divertor material deposition, by more than one order of magnitude. Within the divertor, Be performs far fewer re-erosion and transport steps than C due to an energetic threshold for Be sputtering, and inhibits as a result of this the transport to the divertor floor and the pump duct entrance. The target plates in the JET-ILW inner divertor represent at the strike line a permanent net erosion zone, in contrast to the net deposition zone in JET-C with thick carbon deposits on the CFC (carbon-fibre composite) plates. The Be migration identified is consistent with the observed low long-term fuel retention and dust production with the JET-ILW.EURATOM 63305

Deposition of impurity metals during campaigns with the JET ITER-like Wall

Post mortem analysis shows that mid and high atomic number metallic impurities are present in deposits on JET plasma facing components with the highest amount of Ni and W, and therefore the largest sink, being found at the top of the inner divertor. Sources are defined as "continuous" or "specific", in that "continuous" sources arise from ongoing erosion from plasma facing surfaces and specific" are linked with specific events which decrease over time until they no longer act as a source. This contribution evaluates the sinks and estimates sources and the balance gives an indication of the dominating processes. Charge exchange neutral erosion is found to be the main source of nickel, whereas erosion of divertor plasma facing components is the main source of tungsten. Specific sources are shown to have little influence over the global mid- and high-Z impurity concentrations in deposits.EURATOM 633053RCUK Energy Programme EP/I50104

Investigation of deuterium trapping and release in the JET divertor during the third ILW campaign using TDS

Selected set of samples from JET ITER-Like Wall (JET-ILW) divertor tiles exposed in 2015–2016 has been analysed using Thermal Desorption Spectrometry (TDS). The deuterium (D) amounts obtained with TDS were compared with Nuclear Reaction Analysis (NRA). The highest amount of D was found on the top part of inner divertor which has regions with the thickest deposited layers as for divertor tiles removed in 2014. This area resides deep in the scrape-off layer and plasma configurations for the second (ILW-2, 2013–2014) and the third (ILW-3, 2015–2016) JET-ILW campaigns were similar. Agreement between TDS and NRA is good on the apron of Tile 1 and on the upper vertical region whereas on the lower vertical region of Tile 1 the NRA results are clearly smaller than the TDS results. Inner divertor Tile 3 has somewhat less D than Tiles 0 and 1, and the D amount decreases towards the lower part of the tile. The D retention at the divertor inner and outer corner regions is not symmetric as there is more D retention poloidally at the inner than at the outer divertor corner. In most cases the TDS spectra for the ILW-3 samples are different from the corresponding ILW-2 spectra because HD and D2 release occurs at higher temperatures than from the ILW-2 samples indicating that the low energy traps have been emptied during the plasma operations and that D is either in the energetically deep traps or located deeper in the sample.EURATOM 63305

Investigation of deuterium trapping and release in the JET ITER-like wall divertor using TDS and TMAP

Selected set of samples from JET TER-Like Wall (JET-ILW) divertor tiles exposed both in 20132014 and 20112014 has been analysed using Thermal Desorption Spectrometry (TDS). The deuterium (D) amounts ob tained with TIS were compared with ion Beam Analysis (TBA) and Secondary ion Mass Spectrometry (SIMS) data. The hig amount of D was found on the top part of inner divertor which has regions with the thickest deposited layers. This area resides deep in the scrape-off layer. Changes in plasma configurations between the first 20112012 and the second 20132014 JET-IL W campaign altered the material migration towards the inner and the outer divertor come increasing the amount of deposition in the shadowed areas of the divertor base tiles. Retention on the outer divertor tiles is clearly smaller than on the inner divertor tiles. Experimental TDS spectra for samples from the top part of inner divertor and from the outer strike point region were modelled using TMAP program. Experimental deuterium profiles obtained with SIMS have been used and the detrapping and the activation energies have been adjusted Analysis of the results of the TMAP simulations enabled to determine the nature of traps in different samplesEURATOM 633053Finnish FundingAgency forTechnology and Innovation 4433/31/201

Deuterium retention on the tungsten-coated divertor tiles of JET ITER-like wall in 2015-2016 campaign

Tungsten-coated divertor files exposed during the third JET ITER-Like Wall (ILW) campaign in 2015-2016 (ILW-3) were studied with Secondary Ion Mass Spectrometry (SIMS). ILW-3 campaign contained more high-power plasma discharges and longer plasma time than the earlier ILW campaigns. Measurements showed increased beryllium (Be) deposition on the upper inner divertor, whereas on the outer divertor, Be deposition was lower than during the second campaign in 2013-2014 (ILW-2). Increased intensifies of nickel, molybdenum and tungsten were observed at the surface layer of the inner divertor Be dominated deposits. These layers are probably formed during the high-power plasma discharge phase near the end of the ILW-3 campaign. Compared to the earlier campaigns, D retention on the upper inner divertor was observed to on a similar level than after ILW-2, whereas at the lower inner divertor and most parts of the outer divertor, D retention was lower for ILW-3 than ILW-2. D retention was increased at lower part of outer divertor Tile 7, where Be deposition was slightly increased. Probable reason for the reduction is the higher surface temperature of the files due to higher powers used.Peer reviewe

Thermal desorption spectrometry of beryllium plasma facing tiles exposed in the JET tokamak

Corrigendum: 10.1016/j.fusengdes.2018.08.007.The phenomena of retention and de-trapping of deuterium (D) and tritium (T) in plasma facing components (PFC) and supporting structures must be understood in order to limit or control total T inventory in larger future fusion devices such as ITER, DEMO and commercial machines. The goal of this paper is to present details of the thermal desorption spectrometry (TDS) system applied in total fuel retention assessment of PFC at the Joint European Torus (JET). Examples of TDS results from beryllium (Be) wall tile samples exposed to JET plasma in PFC configuration mirroring the planned ITER PFC is shown for the first time. The method for quantifying D by comparison of results from a sample of known D content was confirmed acceptable. The D inventory calculations obtained from Ion Beam Analysis (IBA) and TDS agree well within an error associated with the extrapolation from very few data points to a large surface area.Peer reviewe

Surface analysis of tiles and samples exposed to the first JET campaigns with the ITER-Like Wall

This paper reports on the first post-mortem analyses of tiles removed from JET after the first campaigns with the ITER-like Wall (ILW) during 2011-2 [1]. Tiles from the divertor have been analysed by the Ion Beam Analysis (IBA) techniques Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) and by Secondary Ion Mass Spectrometry (SIMS) to determine the amount of beryllium deposition and deuterium retention in the tiles exposed to the scrape-off layer. Films 10-20 microns thick were present at the top of Tile 1, but only very thin films (<1 micron) were found in the shadowed areas and on other divertor tiles. The total amount of Be found in the divertor following the ILW campaign was a factor of ~9 less that the material deposited in the 2007-9 carbon campaign, after allowing for the longer operations in 2007-9.Comment: 10 pages, 5 figures. This is an author-created, un-copyedited version of an article accepted for publication in Physica Scripta. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i