P. Starke (Sp), University of Augsburg (Germany); C. Adelhelm, M. Balden, U. Fantz, Max Planck
Institute for Plasma Physics, Garching (Germany)
Due to its excellent thermal and mechanical properties, carbon is intended to be applied in the divertor of future
fusion devices; however the main disadvantage is the formation of hydrocarbons when interacting with hydrogen
plasmas resulting in a high erosion yield. A promising method of reducing the erosion yield is doping of the carbon
materials which leads to a reduction of the effective carbon surface.
As reference material, different doped carbon layers were exposed to deuterium low pressure plasmas (ICP
discharges). The experimental setup provides homogeneous plasma parameters above the surface (several
square centimetres) and furthermore high fluences of incident ions compared to ion beam experiments. To obtain
erosion yields the relevant particle fluxes have to be determined. The incident ion flux towards the surface
(mainly D+) was measured using an energy resolved mass spectrometer. The absolute value of the carbon flux
was determined by weight loss; however time resolution was achieved by optical emission spectroscopy. Hence,
fluence resolved erosion yields were obtained. The experiments were carried out with an ion energy of 30 eV and
a surface temperature of 300 K. Here the ratio between atomic deuterium neutrals and ions is 150.
Amorphous carbon films with atomically disperse metal distribution a variation of the dopand concentration were
investigated. The erosion yields of the films strongly depend on the dopand concentration and show a strong
reduction with increasing fluence reaching values below 0.5%, which is the detection limit of the diagnostic
system. In addition the effect of the dopand distribution through carbidization on the erosion was studied by
heating the films to 1100 K before plasma treatment.