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.
Mechanisms underlying the retention of fuel species in tokamaks with carbon plasma-facing components are presented, together with estimates for the corresponding retention of tritium in ITER. The consequential requirement for new and improved schemes to reduce the tritium inventory is highlighted and the results of ongoing studies into a range of techniques are presented, together with estimates of the tritium removal rate in ITER in each case. Finally, an approach involving the integration of many tritium removal techniques into the ITER operational schedule is proposed as a means to extend the period of operations before major intervention is required.
We observe emission of protons and Hn+ (n up to 4) at room temperature from field ionization of thick films of water adsorbed on Pt or Pd, not on W tips. This differs from previous field ionization experiments of water, all of which show hydrated proton emission. Our observations are explained by the ionic dissociation of water on Pt and Pd surfaces. These thick film experiments are made possible by a special local water supply arrangement. An ion point source based on this ionization process is shown to produce nanobeams of light ions suitable for high resolution ion microscopy.
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