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

摘要

The CH A-X molecular band is measured upon seeding the hydrogen plasma in the linear plasma generator Pilot-PSI [electron temperature T_e=0.1-2.5 eV and electron density n_e = (0.5-5) × 10~(20) m~(-3)] with methane. Calculated inverse photon efficiencies for these conditions range from 3 up to >10~6 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 T_e < 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 n_e > 5 × 10~(20) m~(-3) and 0.1 eV < T_e < 1 eV. These results form a framework for in situ carbon erosion measurements in future fusion reactors such as ITER.