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In order to minimise the radiation losses, it is desirable to keep the plasmas in nuclear fusion devices free of high-Z impurities. The walls of TEXTOR and other tokamaks are covered therefore with thin layers of amorphous carbon layers (a-C:H) or amorphous carbon/boron layers (a-C/B:H). The sputtering behaviour of these layers was studied under bombardment by Ar(+) ions with energies of 1.5 keV and current densities of a few mA/cm2. Investigations of these coatings were carried out in order to measure the velocity distribution of the sputtered atoms and the sputtering yields by laser induced fluorescence in the vacuum ultraviolet. The velocity distribution and absolute density of sputtered H (121.6 nm), D (121.5 nm), B (249.8 nm), C (127.8 nm) and O (130.2 nm) have been measured. A Thompson-distribution can be fitted to the experimental points. The best fit gives surface energies of about 1.0 eV for H- or D-, 7.6 for C- and 5.6 for B-atoms. The velocity distribution of atomic oxygen could not be fitted with a single value for the surface energy, but with the superposition of two Thompson-distributions with energies of 0.5 and 4.8 eV. For H-atoms, the sputtering yield shows a strong dependence on the fluence. The effect is considerably stronger for a-C:H than for a-C/B:H layers.

Additional information

Authors: PASCH E, Forschungszentrum Jülich GmbH, Institut für Plasmaphysik (DE)
Bibliographic Reference: Report: Jül 2647 DE (1992) 119 pp.
Availability: Available from Zentralbibliothek der Forschungszentrum Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
Record Number: 199310022 / Last updated on: 1994-11-29
Original language: de
Available languages: de