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

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4 Author(s)
Westerhout, J. ; FOM Institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, Trilateral Euregio Cluster, P. O. Box 1207, 3430 BE Nieuwegein, The Netherlands ; Lopes Cardozo, N.J. ; Rapp, J. ; van Rooij, G.J.

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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.

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Applied Physics Letters  (Volume:95 ,  Issue: 15 )