An ionization wave detection system for long air gap discharges

Understanding the ionization process is essential for elucidating the mechanisms of long air gap discharges. However, existing commercial camera and photodetectors face significant challenges in capturing ionization and propagation dynamics in long air gap discharges due to the rapid evolution (10⁶ ∼ 10⁷ m/s) of ionization waves, the wide dynamic range of emission intensities, and the requirement for precise spatial calibration. To address these limitations, this study presents an Ionization Wave Detection System (IWDS), designed based on a 16-channel photomultiplier tube (PMT) assembly. By adopting single-lens catadioptric optical imaging design, the IWDS is equipped with a viewfinder window for synchronized spatial calibration and provides a spatial resolution of at least 6 mm per channel, ensuring precise observation of discharge evolution. Additionally, the subsequent analogue signal processing and acquisition units provide the IWDS with a wide range of adjustable gain (up to 1 × 10⁶) and a sampling rate of 200 MSa/s, enabling continuous recording for up to 32 ms, in which the bandwidth of the electrical module is 45 MHz. The system was successfully employed to investigate the rapid evolution of ionization wave across various discharge stages, including initial streamer discharge, re-illumination phenomena, and dark periods. A comparative analysis with existing experimental and simulation data underscores the IWDS’s significant potential for spatio-temporal diagnostics of ionization wave in long air gap discharges.