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In future fusion reactors the net erosion of wall material will determine the lifetime of the first wall. A new technique has been developed to measure this erosion. A thin semi-transparent film of the redeposited material (a-C:H, a-C/B:H) is deposited on a glass substrate, to the back of which a fibre optic bundle is attached. Interference between light reflected at the glass/film interface and that reflected at the film/vacuum interface leads to periodic variation in reflectivity, which is measured with a photodiode. The setting of the glass substrate is not affected by vibration or movement occurring during a discharge. Reflectivity is high (12-28 %). Thickness resolution is in the nanometer range. First results show that in ohmic discharges the deposition rates in the scrape-off layer (SOL) of TEXTOR decrease with increasing central plasma density. In the case of discharges in trimethyl boron the rates increase at higher densities.

Additional information

Authors: WESCHENFELDER F, Forschungszentrum Jülich GmbH (KFA) (DE)
Bibliographic Reference: Report: Jül-2793 DE (1993) 108 pp.
Availability: Available from Zentralbibliothek der Forschungszentrum Jülich GmbH, Postfach 1913, 5170 Jülich (DE)
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