Chemical sputtering measurements in Tore Supra by aftershot mass spectrometry outgassing studies
The global chemical sputtering yield for a tokamak with carbon walls has been estimated in Tore Supra by analysing the aftershot molecular outgassing with a differentially pumped mass spectrometer. Quantitative measurements of molecular outfluxes during plasma operation are difficult due to the strong cracking probability of the neutral species. The aftershot outgassing method takes advantage of the fact that just after the termination of the plasma, the molecular desorption responsible for chemical sputtering continues, although in a decreasing way. This avoids the plasma perturbation effect due to molecule cracking. Even though the analysis of the spectrum is difficult due to the complex decomposition pattern of organic compounds containing hydrogen and deuterium, the characteristic time evolution of the different outgassing species can help to deconvolute the mass spectrum. The contribution of second order hydrocarbons and of carbon monoxide to the total chemical erosion yield is also studied. The dependence of the yields on plasma flux and surface conditions is discussed, as well as the pros and cons of the method used.
Bibliographic Reference: Article: Journal of Vacuum Science and Technology A, Vol. 15 (1997) No. 5, pp. 2597-2604
Record Number: 199711710 / Last updated on: 1998-01-20
Original language: en
Available languages: en