CH spectroscopy for carbon chemical erosion analysis in high density low temperature hydrogen plasma

Abstract

The CH A-X molecular band is measured upon seeding the hydrogen plasma in the linear plasma generator Pilot-PSI [electron temperature Te =0.1-2.5 eV and electron density ne = (0.5-5) × 1020 m-3] with methane. Calculated inverse photon efficiencies for these conditions range from 3 up to 106 due to a steeply decreasing electron excitation cross section. The experiments contradict the calculations and show a constant effective inverse photon efficiency of ∼100 for Te <1 eV. The discrepancy is explained as the CH A level is populated through dissociative recombination of the molecular ions formed by charge exchange. Collisional de-excitation is observed for ne 5× 1020 m-3 and 0.1 eV< Te <1 eV. These results form a framework for in situ carbon erosion measurements in future fusion reactors such as ITER. © 2009 American Institute of Physics.