Adhesive force distributions for tungsten dust deposited on bulk tungsten and beryllium-coated tungsten surfaces

Comprehensive measurements of the adhesive force for tungsten dust adhered to tungsten surfaces have been performed with the electrostatic detachment method. Monodisperse spherical dust has been deposited with gas dynamics techniques or with gravity mimicking adhesion as it naturally occurs in tokamaks. The adhesive force is confirmed to follow the log-normal distribution and empirical correlations are proposed for the size-dependence of its mean and standard deviation. Systematic differences are observed between the two deposition methods and attributed to plastic deformation during sticking impacts. The presence of thin beryllium coatings on tungsten surfaces is demonstrated to barely affect adhesion

DLC Thin Films and Carbon Nanocomposite Growth by Thermionic Vacuum Arc (TVA) Technology

The aim of this chapter is to report the results on synthesis DLC thin films and carbon nanocomposites by the versatile nanofabrication method based on plasma entitled thermionic vacuum Arc (TVA). TVA technology is based on the localized ignition of the arc plasma in vacuum conditions. Among thin film coating methods by vacuum deposition techniques with high purity, low roughness, and good adhesion on the substrates, TVA is one of the major suitable methods to become a powerful coating technology. Two or three different TVA discharges can be ignited simultaneously in the same chamber for multi-material processing using TVA and separate power supplies. These TVA discharges are localized and do not interfere with each other. Simultaneous two or three TVA discharges were already used for the production of alloy/composite of various materials. This is due to the high versatility concerning the configuration of experimental arrangements, taking into account the number of electron guns, symmetry of the electrodes, relative position of the anode versus cathode, and also the huge opportunity to combine the materials to be deposited: bi- and multi-layers, nanocomposites, or alloys in order to have specific applications. This chapter presents the comparative results concerning the surface-free energy information processing, the reflective index, the hardness, and the morphology to provide a coherent description of the diamond-like carbon films and carbon nanocomposites synthesized by thermionic vacuum arc (TVA) and related configurations where Me = Ag, Al, Cu, Ni, and Ti: binary composites (C-Me, C-Si) and ternary composites (C+Si+Me). The results include reports on the distribution in size, surface, geometry, and dispersion of the nanosized constituents, tailoring and understanding the role of interfaces between structurally or chemically dissimilar phases on bulk properties, as well as the study of physical properties of nanocomposites (structural, chemical, mechanical, tribological). The results presented here could have a great impact on the development of advanced materials and many manufacturing industries, as well as expanding the technologically important field of interface science where the control of the film-substrate interface would be critical

Effect of composition and surface characteristics on fuel retention in beryllium- containing co-deposited layers

We have investigated retention of deuterium in beryllium- containing, laboratory-made films whose properties resemble co- deposits observed on JET-ILW or predicted for ITER. The samples were prepared using High Power Impulse Magnetron Sputtering and Thermo-Vacuum Arc Deposition. We have observed that retention depends on the flux of D atoms on the growing film, but even more prominently on its composition, structure, and morphology. Especially, inclusion of carbon by 10-15 at.% in the layers can increase retention by a factor of 2-10. This we attribute to increasing number of defects as well as aromatic and aliphatic C-D bonds in the samples. Other impurities do not significantly alter the D inventory while more D is retained in samples with rough or highly modified surfaces. Our results show that reproducing the reported D concentrations of ~5 at.% in JET-ILW- like deposits requires keeping the sample temperature at 100- 200°C during the production phase and optimizing the uniformity of deposition fluxes. Data from Be-D samples further indicate that fuel retention in more ITER-relevant co-deposits would be around 1-2 at.%

Stability of beryllium coatings deposited on carbon under annealing up to 1073 K

Chemical reactions involving co-deposits in plasma facing components will occur under heat loads. Previous experiments in the Be-C-O system evidenced that compound formation may induce by itself the peel-off of deposits when C films are annealed in vacuum due to the simultaneous formation and mixing of Be2C and BeO. The present experiment investigates the reverse case, where Be films are deposited on graphite and annealed up to 1073 K. The delamination mechanism also exist and it is initialise at 973 K. However, it remains scarce since the carbide and oxide phases grow preferentially at different depths. The experiment points C as a source of dust in presence of Be in operative scenarious. Phase formation was followed by ion beam analysis, X-ray diffraction and electron microscopy.publishedVersio

The Properties of Binary and Ternary Ti Based Coatings Produced by Thermionic Vacuum Arc (TVA) Technology

A series of the multicomponent thin films (binary: Ti-C; Ti-Ag and ternary: Ti-C-Ag; Ti-C-Al) were fabricated by Thermionic Vacuum Arc (TVA) technology in order to study the wear resistance and the anticorrosion properties. The effects of Ti amount on the microstructure, tribological and morphological properties were subsequently investigated. TVA is an original deposition method using a combination of anodic arc and electron gun systems for the growth of films. The samples were characterized using scanning electron microscope (SEM) and a transmission electron microscope (TEM) accompanied by selected area electron diffraction (SAED). Tribological properties were studied by a ball-on-disc tribometer in the dry regime and the wettability was assessed by measuring the contact angle with the See System apparatus. Wear Rate results indicate an improved sliding wear behavior for Ti-C-Ag: 1.31 × 10−7 mm3/N m (F = 2 N) compared to Ti-C-Al coating wear rate: 4.24 × 10−7 mm3/N m. On the other hand, by increasing the normal load to 3 N an increase to the wear rate was observed for Ti-C-Ag: 2.58 × 10−5 mm3 compared to 2.33 × 10−6 mm3 for Ti-C-Al coating

Stability of beryllium coatings deposited on carbon under annealing up to 1073 K

Chemical reactions involving co-deposits in plasma facing components will occur under heat loads. Previous experiments in the Be-C-O system evidenced that compound formation may induce by itself the peel-off of deposits when C films are annealed in vacuum due to the simultaneous formation and mixing of Be2C and BeO. The present experiment investigates the reverse case, where Be films are deposited on graphite and annealed up to 1073 K. The delamination mechanism also exist and it is initialise at 973 K. However, it remains scarce since the carbide and oxide phases grow preferentially at different depths. The experiment points C as a source of dust in presence of Be in operative scenarious. Phase formation was followed by ion beam analysis, X-ray diffraction and electron microscopy

Deuterium plasma sputtering of mixed Be-W layers

In ITER, the first mirrors would be vulnerable to deposition from the first wall materials, namely beryllium (Be) and tungsten (W) in mixed compositions. In this study we investigate the capactively coupled RF plasma sputtering of such mixed Be-W deposits on rhodium-coated substrates, using deuterium as the process gas, and track the enrichment of W during the sputtering process. Experiments were conducted on Be-W deposits with W concentration varying from 2 to 8.3 at.%, and maximal deuterium ion energies in the plasma of 70 and 220 eV. The evolution of the W concentration in the deposits during the plasma sputtering depended considerably on both deuterium ion energy as well as the initial concentration of W in the films. With 220 eV sputtering, a rapid enrichment of W was observed, with all the W changing from BeW before sputtering to metallic W and its oxides after sputtering. With 70 eV sputtering, there was no net change in the W concentration, as long as the initial concentration of W in the film was below 4 at.%. Moreover, the W remained considerably in the state of BeW after the sputtering as well. However, a W enrichment was also observed with 70 eV sputtering, when the W concentration in the films was higher (8.3 at.%). The rate of W enrichment was also observed to increase monotonically with the increase in the initial concentration of W in the deposits. SDTrimSP simulations performed with experimental parameters indicate that sputtering yield of Be increases with W concentrations in the Be-W layers due to backscattering of D projectiles off W atoms. These studies show that low energy deuterium sputtering of mixed Be-W layers with low W concentrations, allows for removal of Be without rapidly enriching W in the films, making it a promising option for ITER

Fuel retention and erosion-deposition on inner wall cladding tiles in JET-ILW

The morphology of beryllium coatings on the Inconel inner wall cladding tiles after JET-ILW campaigns was determined. The focus was on: (i) fuel retention and its share in the overall fuel inventory; (ii) the change of the layer structure and composition. The study is motivated in the view of planned D-T operation in JET. Four tiles were examined: the initial not exposed; one exposed to two campaigns (ILW1-2) and two facing the plasma during ILW1-3. As determined with ion beam and microscopy methods, the initial Be layer (9.0 mu m thick) contained up to 4-5 at.% of impurities, mainly H, O, C, Ni. In the exposed tiles, the impurity content increases to 14-26 at.% (up to 20 at.% O, 1.7 at.% C, 1.0 at.% N, 1.3 at.% Ni and under 0.1 at.% W). The surface composition indicates gettering of O and a long-term retention of N. The Be thickness on the tile exposed to ILW1-2 was between 7.6 and 9.7 mu m, thus indicating erosion in some areas, while the thickness after ILW1-3 increased to 10-12 mu m. The D content was in the range 1.2-3.4x10(17) cm(-2) after ILW1-2 and 3.2-10x10(17) cm(-2) after ILW1-3 on most of the analyzed area, but in the limiter shadow values up to 58 x10(17) cm(-2) were measured. Taking into account the total area of the Be-coated inner wall cladding tiles, the lower limit of D inventory amounts to 5.3x10(22) atoms corresponding to about 176 mg, i.e. somewhat greater than the amount determined on Be limiters. The formation and spalling-off of Be-O particles was revealed

Interaction of nitrogen ions with beryllium surfaces

The interaction of energetic nitrogen projectiles with a beryllium surface is studied using a highly sensitive quartz crystal microbalance technique. The overall mass change rate of the beryllium sample under N2+ ion impact at an ion energy of 5000 eV (i.e. 2500 eV per N) is investigated in situ and in real-time. A strong dependency of the observed mass change rate on the nitrogen fluence (at constant flux) is found and can be attributed to the formation of a nitrogen-containing mixed material layer within the ion penetration depth. The presented data elucidate the dynamics of the interaction process and the surface saturation with increasing nitrogen fluence in a unique way. Basically, distinct interaction regimes can be discriminated, which can be linked to the evolution of the surface composition upon nitrogen impact.Steady state surface conditions are obtained at a total cumulative nitrogen fluence of ∼80 × 1016 N atoms per cm2. In dynamic equilibrium, the interaction is marked by continuous surface erosion. In this case, the observed total sputtering yield becomes independent from the applied nitrogen fluence and is of the order of 0.4 beryllium atoms per impinging nitrogen atom

Deuterium Retention and Release Behavior from Beryllium Co-Deposited Layers at Distinct Ar/D Ratio

Beryllium-deuterium co-deposited layers were obtained using DC magnetron sputtering technique by varying the Ar/D2 gas mixture composition (10/1; 5/1; 2/1 and 1:1) at a constant deposition rate of 0.06 nm/s, 343 K substrate temperature and 2 Pa gas pressure. The surface morphology of the layers was analyzed using Scanning Electron Microscopy and the layer crystalline structure was analyzed by X-ray diffraction. Rutherford backscattering spectrometry was employed to determine the chemical composition of the layers. D trapping states and inventory quantification were performed using thermal desorption spectroscopy. The morphology of the layers is not influenced by the Ar/D2 gas mixture composition but by the substrate type and roughness. The increase of the D2 content during the deposition leads to the deposition of Be-D amorphous layers and also reduces the layer thickness by decreasing the sputtering yield due to the poisoning of the Be target. The D retention in the layers is dominated by the D trapping in low activation binding states and the increase of D2 flow during deposition leads to a significant build-up of deuterium in these states. Increase of deuterium flow during deposition consequently leads to an increase of D retention in the beryllium layers up to 300%. The resulted Be-D layers release the majority of their D (above 99.99%) at temperatures lower than 700 K