Cleaning of carbon materials from flat surfaces and castellation gaps by an atmospheric pressure plasma jet

Abstract

A study of the removal of carbon layers from flat and castellated surfaces by a plasma jet source operated in open atmosphere is presented. Amorphous hydrogenated carbon films deposited on silicon substrates, on aluminium made castellated surfaces, and graphitic carbon plates were used. The erosion effects of plasmas generated either in pure argon, nitrogen or in their mixtures with hydrogen, ammonia, oxygen are compared. Highest erosion was obtained with nitrogen and nitrogen/oxygen plasmas. Plasmas in argon and containing hydrogen, and ammonia have shown a low erosion rate. A large removal rate by pure nitrogen plasma jet of 3.2mg/min was found by scanning graphitic carbon flat surfaces for optimum process parameters. Adding small quantities of oxygen led to a removal rate enhancement by a factor of 3. Finally, the integral removal rate of amorphous hydrogenated carbon deposited in gaps 23mm deep and 0.5mm wide was of the order of 0.35mg/min. The layer elimination was more efficient at the top and at the bottom of the gaps, precisely where the thickest codeposits develop in a nuclear fusion device.