Hydrogen-Reduced Carbonization by Acetylene Discharges

A pure acetylene discharge has been used to deposit thin carbon films onto the wall of a toroidal device, demonstrating in situ carbonization of magnetic fusion devices. The H-atom content of films deposited at different wall temperatures is measured by IR absorption, ERD, and 15N nuclear reaction techniques. Compared with a methane discharge, the acetylene discharge gives a rapid deposition rate, a high C-atom density, and a low H-atom film density. The 50% reduction of H/C atomic ratio is particularly desirable to suppress the enormous hydrogen desorption in tokamak discharges.