We present experimental
results of the probing of a ‘current-zero like' (CZ-like) air arc in a model high
voltage gas circuit breaker geometry with active optical diagnostic techniques.
Namely, we apply both shadowgraphy and Speckle imaging in an effort to obtain
qualitative and quantitative information, respectively, about the physical
phenomena involved. With the former technique, the boundary layer between the
arc and the imposed gas flow and the transonic flow features can be readily
revealed. The latter technique yields quantitative information about the
two-dimensional density field with the help of a generalization of the
Gladstone-Dale law. Under the assumption of local thermal equilibrium, one may
estimate the corresponding temperature distribution along the arc plasma
channel and the surrounding gas flow.