Population Inversion in a Magnetized Expanding Thermal Plasma

A weakly magnetized expanding hydrogen plasma was investigated by means of optical emission spectroscopy. In the tail of the expansion, highly excited H atoms were found, which were responsible for the color change in the jet from red to blue. Several mechanisms that can produce higher excitation states of the H atom were investigated. After determining the production rates of each excited level, the dominant production route of highly excited H atoms was determined to be a mutual H₂ ⁺-H^- recombination.