Abstract
At present the effects of titanium getter films on tokamak walls are mainly studied by measuring the plasma parameters and there are only few experiments that study the effects by means of surface analysis. The aim of our experiment is to observe a titanium surface evaporated on a molybdenum substrate with ion scattering spectroscopy (ISS) which is very sensitive to the topmost layer of the surface. In the first experiment we try to distinguish the necessary thickness of Ti layers required to refresh the CO contaminated Ti surface due to burying the adsorbed gases. We derive a value of about 10 Å. The second experiment deals with the release rate of adsorbed H 2 from the Ti film by He + of Ar + ion bombardment using a residual gas analyzer. The intention was to simulate the hydrogen recycling from tokamak walls by plasma irradiation. We obtained a rate of less than 10 −2 atoms/ion. In a third experiment we measured the desorption cross section of CO adsorbed on Ti and Mo by He + or Ar + ion impact using ISS. As a demonstration of the applicability of ISS for measuring sputtering yields of thin films, we investigated Au layers on Mo substrates using Ar + ion impact at the energy of 2 keV. A yield of 2 atoms/ion with ± 50% uncertainty was obtained.
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