Abstract: Deuterium permeation during ion bombardment through tungsten membranes coated by amorphous carbon films was investigated and compared with the permeation through bare tungsten. The membrane was bombarded by D3+ ions with energies of 200 and 1200 eV/D at a temperature of 873 K. The thickness of the amorphous carbon film was 120–170 nm. Detailed characterization of the carbon films were performed using AFM, NRA, RBS, FIB/SEM and XPS. The influence of the carbon films on permeation were strong for both ion energies, but different for each energy. In the case of 200 eV/D ions, the film was completely removed by the end of permeation due to intensive chemical sputtering, the lag time of permeation was much longer than for the bare membrane, and the permeation rate rose to a maximum value close to the bare membrane and then decreased to lower values. In the case of 1200 eV/D, the films were sputtered only very slowly, the lag time was much longer than in the case of the bare membrane but shorter than at 200 eV/D, and the permeation rate increased steadily up to several percents of the incident flux.
Abstract: As was already observed experimentally, the erosion of tungsten (W) coated graphite (C) tiles in ASDEX-Upgrade (AUG) exhibits regular erosion patterns on the micrometre rough surfaces whose origin is not fully understood: surfaces inclined towards the magnetic field direction show strong net W erosion while surfaces facing away from the magnetic field are shadowed from erosion and may even exhibit net W deposition. This paper presents a model which explains the observed erosion/deposition pattern. It is based on the calculation of ion trajectories dropping through the plasma sheath region to the rough surface with combined magnetic and electrical fields. The surface topography used in the calculations is taken from atomic force microscope measurement of real AUG tiles. The calculated erosion patterns are directly compared with secondary electron microscopy images of the erosion zones from the same location. The erosion on surfaces inclined towards the magnetic field is due to ions from the bulk plasma which enter the sheath gyrating along the magnetic field lines, while the deposition of W on surfaces facing away from the magnetic field is due to promptly re-deposited W that is ionized still within the magnetic pre-sheath.
Abstract: Finely dispersed Ti-doped isotropic graphites with 4 at.% Ti have been manufactured using synthetic mesophase pitch 'AR' as raw material. These new materials show a thermal conductivity at room temperature of similar to 200 W/mK and flexural strength close to 100 MPa. Measurement of the total erosion yield by deuterium bombardment at ion energies and sample temperatures for which pure carbon shows maximum values, resulted in a reduction of at least a factor of 4, mainly due to dopant enrichment at the surface caused by preferential erosion of carbon. In addition, ITER relevant thermal shock loads were applied with an energetic electron beam at the JUDITH facility. The results demonstrated a significantly improved performance of Ti-doped graphite compared to pure graphite. Finally, Ti-doped graphite was successfully brazed to a CuCrZr block using a Mo interlayer. These results let assume that Ti-doped graphite can be a promising armour material for divertor plasma-facing components. (C) 2009 Elsevier B.V. All rights reserved.
Notes: ISI Document Delivery No.: 450FR xD;Times Cited: 1 xD;Cited Reference Count: 16 xD;13th International Conference on Fusion Reactor Materials (ICFRM-13) xD;DEC 10-14, 2007 xD;Nice, FRANCE
Abstract: The analysis of organic compounds in combustion exhaust particles and the chemical transformation of soot by nitrogen oxides are key aspects of assessment and mitigation of the climate and health effects of aerosol emissions from fossil fuel combustion and biomass burning. In this study we present experimental and analytical techniques for efficient investigation of oxygenated and nitrated derivatives of large polycyclic aromatic hydrocarbons (PAHs), which can be regarded as well-defined soot model substances. For coronene and hexabenzocoronene exposed to nitrogen dioxide under simulated diesel exhaust conditions, several reaction products with high molecular mass could be characterized by liquid chromatography-atmospheric pressure chemical (and photo) ionization-mass spectrometry (LC-APCI-MS and LC-APPI-MS). The main products of coronene contained odd numbers of nitrogen atoms (m/z 282, 256, 338), whereas one of the main products of hexabenzocoronene exhibited an even number of nitrogen atoms (m/z 391). Various reaction products containing carbonyl and nitro groups could be tentatively identified by combining chromatographic and mass spectrometric information, and changes of their relative abundance were observed to depend on the reaction conditions. This analytical strategy should highlight a relatively young technique for the characterization of various soot-contained, semi-volatile, and semi-polar reaction products of large PAHs.
Abstract: Carbon layers doped with Ti, V, W, and Zr to about 15 at.% were produced by means of magnetron sputter deposition, which distributes metal atoms homogeneously in the amorphous carbon matrix. The effects of thermal annealing to temperatures of 500-1300 K on the phase, crystallinity and distribution of the dopant were determined. X-ray diffraction (XRD), MeV ion beam analysis (IBA), and extended X-ray absorption fine-structure spectroscopy (EXAFS) were used for characterization. The three techniques deliver complementary information on different length scales of the diffusion and crystallization. All four metal dopants are in carbidic state with crystallites on the nanometer scale after annealing to 1100 K. Dopant diffusion of no more than 20 nm, even after heating at 1300 K for 2 h, was observed.
Abstract: Amorphous carbon layers doped with 8.5 at.% titanium (a-C:Ti) were produced by dual-source magnetron sputter deposition. To investigate the local atomic environment of Ti, EXAFS analysis was performed for as-deposited layers and after annealing to 700, 1100 and 1300 K, as well as for Ti and TiC bulk samples. After deposition of the a-C:Ti films, most Ti atoms are homogeneously distributed in an amorphous carbon matrix. Annealing to 700 K slightly increases the order in the Ti environment, but TiC-like crystallization is hardly existent. After annealing to 1100 K, clear correspondence to the TiC standard is observed. Annealing to 1300 K further increases the order and TiC crystallite size. Fitting of EXAFS data to a theoretical model was used to derive quantitative parameters for a-C:Ti layers, e.g., Ti-C and Ti-Ti distances and ordering parameters.
Abstract: The annealing of magnetron-sputtered carbon films doped with up to 8.5 at.% W, Ti, V, and Zr prior to the erosion experiments led to the formation of carbide cyrstallites of several nm. The total erosion yield by 30 and 200 eV D-1, impacting as D-3(+) projectiles, at 300 K and similar to 750 K was determined from film thickness changes measured by ion beam analysis. Doping with W, Ti, V, and Zr always reduces the total erosion yield by a factor of up to 20 compared to a pure C film. The temperature dependency of the metal erosion was observed. The methane production yield was studied by mass spectrometry. The CD4 production yield decreases less than the total yield or even increases. This implies that the distribution of the chemically eroded species is changed by the dopants. It can be speculated that the re-deposition of carbon is reduced by doping.
Abstract: The erosion by 30 and 200 eV/D at temperatures between 300 and 1100 K was investigated for magnetron-sputtered films, consisting of carbon and metal (2-7 at.% W, Ti, Zr) present as nanometer-sized carbide crystallites. The total erosion yield was determined from weight-loss measurements and film thickness changes measured by RBS. The chemical erosion yield was obtained from the CD4 signal of mass spectrometry. The total erosion yield of doped films is reduced by a factor of 3-20 compared to pure C films. The CD4 production yield decreases less implying that the distribution of the chemically eroded species was changed by the dopants. Therefore, measuring only CD4 production or its spectroscopic signature could yield to misleading values and interpretations.
