Atomic radiation of a recombining nitrogen plasma

International audienceShock layer radiation from atomic lines can represent the main source of radiation in the afterbody region of a space capsule during Earth entry. Studying the kinetics of excited states of atomic nitrogen is therefore important to correctly predict its corresponding radiation. The CentraleSupelec plasma torch facility provides a stable equilibrium plasma and can be used to study plasma kinetics and radiation in a controlled environment. Previous experiments were performed to supply measurements of excited states of molecular nitrogen in a nonequilibrium recombining flow. We extend these measurements to atomic lines to get measurement of excited states of atomic nitrogen. We performed optical emission spectroscopy from VUV to NIR and obtain measurements of atomic nitrogen states above 10eV. The VUV region allow access to low energy states of nitrogen. A departure from Boltzmann distribution is observed for the high excited states and their densities tend to be equal to the Saha-Boltzmann distribution. This was previously predicted and is experimentally observed in this paper. These results may be used to validate kinetic codes