Investigation of particle diffusion and suprathermal electrons in a magnetized helium plasma column

Studying radiative properties of magnetized helium plasma via high-resolution spectroscopy identified close correlations between the particle diffusion and suprathermal electrons for different modes of operation of the MISTRAL installation. The standard diagnostic emission lines in neutral helium (1s3d D-3-1s2p P-3, 1s3s S-3-1s2p P-3, 1s3d D-1-1s2p P-1, and 1s3s S-1-1s2p P-1) show anomalous ratios that are related to enhanced particle diffusion and suprathermal electron generation. The supplementary investigation of singlet/triplet Rydberg series (transitions 1snd D-3-1s2p P-3 and 1s5p P-1-1s2s S-1) as well as ionic lines (HeII, transitions n = 3-4 at 469 nm and n = 4-6 at 656nm) allowed quantitative characterization. Simulations carried out with the atomic physics code SOPHIA demonstrate that simultaneous implementation of diffusion processes and suprathermal electrons matches all experimental findings. Single consideration, however, of either diffusion or hot electrons is in contradiction to the proposed extended set of HeI and HeII emission lines. The high precision achieved with the LSJ-split level structure of SOPHIA coupled to Langmuir probe measurements allowed to conclude to a Bohm type diffusion in MISTRAL. (C) 2014 AIP Publishing LLC.