Effect of impurity ions on ion current flowing into an ion sensitive probe during N₂ and H₂ seeding in hydrogen plasma

We attempt to interpret the different trends of collected ion currents of the Langmuir probe and the ion sensitive probe (ISP) observed during N₂ and H₂ seeding in hydrogen plasmas in the divertor simulation experimental module (D-module) in GAMMA10/PDX. The current measured at the ion collector electrode of the ISP shows two distinct bumps. Results can be interpreted with the aid of spectroscopic measurements related to the dominant reaction processes, where nitrogen-induced molecule-activated-recombination (N-MAR) mechanisms produce various ion species, resulting in different measured currents. These experimental findings provide a further understanding of the most relevant plasma-neutral processes occurring in a detached-like plasma scenario in the presence of nitrogen, a candidate for impurity seeding in ITER. (author)