Spectroscopic measurement of atomic and molecular deuterium fluxes in the DIII-D plasma edge

Molecular deuterium fluxes into the edge of deuterium-fuelled L-mode discharges are measured using passive visible spectroscopy of D₂ emission lines. Comparison with the atomic deuterium influx measured using D_α emission suggests that a significant fraction of the plasma edge fuelling from the walls is in the form of D₂. Molecular deuterium flux is observed in both the divertor and main chamber regions but is roughly a factor 100 smaller near the inner main chamber wall and roughly a factor 1000 smaller near the outer main chamber wall, when compared with the divertor region. Very high levels of molecular D₂ excitation are measured, with ground state D₂ rotational population temperatures T_rot up to 10 000 K and vibrational population temperatures T _vib up to 30 000 K. Comparisons between rotational population temperatures and the local electron density suggest that T_rot can be used as a reasonably good indicator of electron density in the D₂ line emission region. In recombining, detached divertor operation, estimates of the enhanced volume recombination rate due to the presence of vibrationally-excited D₂ suggest that the effect of molecular-assisted volume recombination could be comparable in magnitude to that of normal D⁺ volume recombination (EIR).