hermally induced decomposition of hard and soft amorphous hydrocarbon films was investigated by thermal effusion spectroscopy. Released species were detected by a sensitive quadrupole mass spectrometer using two different experimental setups for thermal effusion. Species released in a molecular beam setup were detected in direct line of sight to the sample surface, while species released in a remote UHV oven had no direct line of sight to the mass spectrometer. Soft, hydrogen-rich carbon films exhibit a desorption maximum at T≈740 K while hard films with a low hydrogen content have their maximum at T≈870 K. Additionally, the spectrum of released species differs dramatically between hard and soft films. We found a significant redeposition of species released from soft films. From the redeposited fraction of material we estimated an average redeposition probability of about 50% for species released from soft films.
Abstract:Tungsten (W) films with thicknesses ranging between 1 and 12 m deposited by magnetron sputtering on silicon substrates were used as a model system for comparing the deuterium (D) retention measured by both temperature programmed desorption (TPD) and nuclear reaction analysis (NRA). Samples were loaded with deuterium ex-situ with an ECR plasma at 370 and 600 K with an energy of 38 eV per deuteron. To avoid diffusion of D into the silicon substrate and to increase adhesion a copper interlayer was applied. The results show that all implanted D atoms were retained exclusively in the W films. The distribution of D is homogenous throughout the W layer with an atomic fraction of 3±0.4×10 -3 . With increasing W thickness the D profile extends to correspondingly larger depths with practically identical D concentration. For W films with a thickness lower than the NRA information depth of about 8 μm the total retained D amount measured by TPD and NRA is in excellent agreement. As expected, for films thicker than the NRA information depth, TPD deviates from NRA.
Abstract. The deuterium inventory in tungsten-coated divertor tiles used during the first full-tungsten plasma-facing wall phase of ASDEX Upgrade was measured by various analysis methods. The D inventory in the inner divertor was still dominated by codeposition with residual carbon, whereas it was dominated by trapping in the thicker vacuum plasma sprayed tungsten layers at the outer divertor. The total inventory in the divertor area decreased by a factor of 5 ~ 10 compared to the period of carbon-dominated plasma-facing wall.
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