SURFACE MODIFICATION OF VACUUM WALL BY CARBON AND ITS OUTGASSING

Carbon was deposited on the surface of a stainless steel tube by ECR (Electron Cyclotron Resonance) plasma with a CH4/H-2 gas mixture in order to reduce outgassing from the steel surface. The magnetic field for the ECR resonance was obtained by permanent magnets. The outgassing rates before and after the deposition were measured. The outgassing rate of water vapor from the coated surface after an exposure of 10(4) L water vapor is reduced to 1/70 after 5 min pumping and to 1/5 after 60 min pumping, reaching an outgassing rate of 7.6 x 10(-8) Pa m3 s-1 m-2. Depth profiling and the ratio of hydrogen atom to carbon atom in the carbon film were obtained. Comparison of activation energies of desorption (E(d)) measured by TDS (Thermal Desorption Spectroscopy) between the two different surfaces supports the reason of the improvement of the outgassing property by the carbon coating.