On the use of quantitative Schlieren techniques in temperature measurement of leader discharge channels

Electrical discharges in long air gaps, referred to as 'leader discharges', usually propagate with transient thermal plasma channels. The gas temperature evolution of the channels plays a key role in the inception and development of leader discharges. This paper is aimed at investigating the use of quantitative Schlieren techniques in temperature measurement of the leader discharge channels. To do this, a calibrated Toepler's lens-type Schlieren system was set up to measure the radial temperature profile of leader discharge channels. The measurements were compared with the simulation results from a detailed numerical model which describes the thermal-hydrodynamic properties of the channel. The comparison shows that although a good agreement is obtained when the leader is propagating in a stable manner, the measurements of the temperature evolution at the axis of leader channel deviate significantly from the numerical simulation during the leader initiation stage. Apart from the limited spatial and temporal resolution of the Schlieren system, the deviation is also caused by the non-isobaric gas heating during leader inception. Based on the theoretical analysis and numerical simulation, we proposed several suggestions to the application of quantitative Schlieren techniques to measure the temperature of leader channels.