Removal of carbon deposited film and hydrogen retention control by low temperature H–C–N reactive plasmas

Control of tritium retention and its removal from the first wall of future fusion devices are the most crucial issues for safety and effective use of the fuel. Nitrogen injection into edge plasmas has been considered and tested as an effective method for suppression of carbon dust growth and reduction of hydrogen isotope inventory. In this paper we have investigated scavenger effects of nitrogen injected into H2/CH4 plasmas using a small helical device where low density (ne∼1016m−3) and low temperature (Te=5–10eV) hydrogen plasmas are generated in steady state condition like remote plasmas in fusion devices. It is shown from the comparison of the carbon film deposition and particle growth between those with and without N2 injection that the chemical erosion effects of nitrogen gas on the carbon film and particle growth strongly depends on the surface temperature. With increasing the surface temperature higher than ∼400K, the nitrogen chemical erosion significantly works to reduce the hydrocarbon deposition.