Surface composition and structure of divertor tiles following the JET tokamak operation with the ITER-like wall (original) (raw)
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Investigation of tungsten-coated divertor tiles at the JET tokamak with the ITER‐Like Wall
HNPS Proceedings
Materials migration in fusion plasma devices and fuel retention in plasma-facing components are issues of great importance for the safe operation of fusion devices. The underlying mechanisms require a good understanding in order to make predictions regarding the lifetime of wall components and to assess the amount of fuel retained in the machine mainly in co-deposited layers. To reduce fuel inventory and to investigate plasma-wall interactions a large-scale experiment at the JET (Joint European Torus) tokamak is realized: operation with the ITER-Like Wall (JET-ILW) which comprises beryllium and tungsten. The current work reports on the post-mortem analysis of W/CFC tiles retrieved after the first deuterium-deuterium campaign at JET-ILW. Specimens from different areas of the divertor have been analyzed by means of several techniques including nuclear reaction analysis and Rutherford backscattering employing a deuterium beam. In addition, X-ray fluorescence spectroscopy and scanning e...
Fusion Engineering and Design, 2019
Tungsten-coated divertor tiles 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 intensities 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 tiles due to higher powers used.
Spectrometric analysis of inner divertor materials of JET carbon and ITER-like walls
Fusion Engineering and Design, 2018
One of main reasons of the Joint European torus (JET) transformation from the carbon (JET-C) to ITER-like (JET-ILW) wall was high tritium retention of carbon. In order to compare the tritium retention, samples of analogous positions of the plasma-facing side of vertical tiles No. 3 of two campaigns: JET-C (2008-2009) and JET-ILW (2011-2012) were cut out. Temperature-programmed tritium desorption spectrometry in He + 0.1% H 2 gas flow showed that JET-C sample without a tungsten coating had by a factor of > 20 higher surface concentration of tritium than JET-ILW tungsten-coated sample: 4.9 × 10 13 and 1.7-2.2 × 10 12 T atoms/cm 2 respectively. Installation of metallic plasma facing wall in the JET was a unique possibility to collect from the vacuum vessel the first wall erosion products (EP)dust and flakes. Selected EP were investigated by means of energy dispersion X-ray (EDX), electron spin resonance (ESR), infrared and Raman spectrometry. EDX analysis shows presence of metallic impurities and carbon as a main component. Investigations with ESR spectrometry allows to estimate presence of two main paramagnetic centresg = 2.002 and g = 2.12. Infrared spectra show presence of inorganic oxides. The obtained results supplement the information about composition of the EP from fusion devices.
Journal of Nuclear Materials
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 mm 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 mm 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.
Surface analysis of tiles and samples exposed to the first JET campaigns with the ITER-like wall
Physica Scripta, 2014
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.
Ion beam micro analysis of deposits at tokamak divertor surfaces
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
Cross sections of deposited layers in the Joint European Torus (JET) were analysed using the nuclear micro analysis at the Tandem Laboratory, Uppsala University. For deuterium and beryllium the nuclear reactions 2 D( 3 He,p) 4 He and 9 Be( 3 He,p n ) 11 B were exploited for analysis. Typically the analyses have been made with 10 lm spatial resolution and a sensitivity of better than one atomic percent for beryllium or deuterium in carbon matrix. Comparing several different surface treatment techniques shows that polishing the sample surface give very good optical surface information but that some amount of deuterium and beryllium probably is removed. For good quantitative results the measurement can either be done on a rough surface or the top of the polished surface can be cut off.
Microanalysis of deposited layers in the inner divertor of JET with ITER-like wall
Nuclear Materials and Energy
In JET with ITER-like wall, beryllium eroded in the main chamber is transported to the divertor and deposited mainly at the horizontal surfaces of tiles 1 and 0 (high field gap closure, HFGC). These surfaces are tungsten coated carbon fibre composite (CFC). Surface sampleswere collected following the plasma operations in 2011-2012 and 2013-2014 respectively. The surfaces, as well as polished cross sections of the deposited layers at the surfaces have been studied with micro ion beam analysis methods (μ-IBA).Deposition of Beand other impurities, and retention of D is microscopically inhomogeneous. Impurities and trapped deuterium accumulate preferentially in cracks, pits and depressed regions, and at the sides of large pits in the substrate (e.g. arc tracks where the W coating has been removed). With careful overlaying of μ-NRA elemental maps with optical microscopy images, it is possible to separate surface roughness effects from depth profiles at microscopically flat surface regions.
R&D on full tungsten divertor and beryllium wall for JET ITER-like wall project
Fusion Engineering and Design, 2007
The ITER reference materials have been tested separately in tokamaks, plasma simulators, ion beams and high heat flux test beds. In order to perform a fully integrated material test JET has launched the ITER-like Wall Project with the aim of installing a full metal wall during the next major shutdown. As a result of R&D projects in 2005-2006, bulk tungsten tiles are foreseen at the outer horizontal target and tungsten coating at the other divertor tiles. In some regions of the main chamber, beryllium coated Inconel tiles and bulk beryllium tiles are utilised which include marker tiles as erosion diagnostics. This paper gives an overview of the R&D carried out in the frame of the ITER-like Wall Project on the development of an inertially cooled bulk tungsten tile design and the characterization of tungsten and beryllium coating technologies.
Physica Scripta, 2016
As a complementary method to RBS, GDOES (Glow Discharge Optical Emission Spectrometry) was used to investigate the depth profiles of W, Mo, Be, O and C concentrations into marker coatings (CFC/Mo/W/Mo/W) and the substrate of divertor tiles up to a depth of about 100 m. A number of 10 samples cored from particular areas of the divertor tiles were analyzed. The results presented in this paper are valid only for those areas and they can not be extrapolated to the entire tile. Significant deposition of Be was measured on Tile 3 (near to the top), Tile 6 (at about 40 mm from the innermost edge) and especially on Tile 0 (HFGC). Preliminary experiments seem to indicate a penetration of Be through the pores and imperfections of CFC material up to a depth of 100 m in some cases. No erosion and a thin layer of Be (< 1 m) was detected on Tiles 4, 7 and 8. On Tile 1 no erosion was found at about 1/3 from bottom.
Tritium distributions on W-coated divertor tiles used in the third JET ITER-like wall campaign
Nuclear Materials and Energy
Tritium (T) distributions on tungsten (W)-coated plasma-facing tiles used in the third ITER-like wall campaign (2015-2016) of the Joint European Torus (JET) were examined by means of an imaging plate technique and βray induced x-ray spectrometry, and they were compared with the distributions after the second (2013-2014) campaign. Strong enrichment of T in beryllium (Be) deposition layers was observed after the second campaign. In contrast, T distributions after the third campaign was more uniform though Be deposition layers were visually recognized. The one of the possible explanations is enhanced desorption of T from Be deposition layers due to higher tile temperatures caused by higher energy input in the third campaign.