Spectroscopic studies of homogeneous thin carbon erosion films on mirrors and flakes with a high deuterium content formed in tokamak T-10

Abstract

Redeposited hydrocarbon films on plasma facing elements in tokamaks accumulate hydrogen isotopes. In the present study such films were made to redeposit on stainless steel mirror substrates as thin films and without any substrate as bare flakes with high deuterium content, under deuterium-plasma discharges inside T-10 tokamak vacuum chamber. These films were subjected to spectral characterizations through Fourier-transform infrared (FT-IR), electron paramagnetic resonance (EPR), and photoluminescence techniques. IR spectra showed the presence of two main deuterium states as observed by the CD 2,3 sp 3 stretching modes at 2100–2200 cm −1 and the CD 2 sp 3 bending modes at 600–1100 cm −1. Among these, CD 3 stretching mode at 2217 cm −1 may serve as a control for deuterium desorption during the cleanup process of the reactor. As a comparative measure, C60 films were also studied, the luminescence excitation spectrum of which showed similarity in peak positions with tokamak bare flakes pertained to sp 2 luminescence centers. The observed spectral differences are mainly due to more localized sp 2 states for C60 and sp 3 states for tokamak flakes. EPR spectra of the bare flakes showed the defective states with a high spin density, ∼10 19 cm −3 which serve as luminescence quenching centers, and provide a path for hydrogen isotopes adsorption.