Measurement and modeling of detached plasma cooling via ro-vibrational excitation of H2 neutrals in PISCES-A

Measurements of the spatial decay of H2 vibrational, rotational, and kinetic temperatures Tvib, Trot, and Tkin down the side port of the PISCES-A vacuum chamber, together with Monte-Carlo modeling, is used to obtain the accommodation probabilities for energy loss to the cold chamber walls during H2 + surface collisions. These accommodation probabilities are used to calculate the steady-state rate at which H2 carries energy away from the plasma column. The power loss due to heating of H2 neutrals is found to be quite significant, being only 2 × weaker than radiation cooling in the higher neutral pressure (detached) discharges. The H2 vibrational temperature Tvib is found to be the most important neutral channel for carrying energy out of the plasma - more important than either kinetic temperature Tkin or rotational temperature Trot.