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

Measurements of the spatial decay of H 2 vibrational, rotational, and kinetic temperatures T vib , T rot , and T kin 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 H 2 + surface collisions. These accommodation probabilities are used to calculate the steady-state rate at which H 2 carries energy away from the plasma column. The power loss due to heating of H 2 neutrals is found to be quite significant, being only 2 x weaker than radiation cooling in the higher neutral pressure (detached) discharges. The H 2 vibrational temperature T vib is found to be the most important neutral channel for carrying energy out of the plasma - more important than either kinetic temperature T kin or rotational temperature T rot .