Comparative study of the decay process of LIP and gas arc in SF₆/N₂ gas mixture by Thomson scattering

The SF₆/N₂ gas mixture mitigates the challenges associated with the use and liquefaction problems of pure SF₆. It has great significance to analyze the decay characteristics of the plasma in it. Laser-induced plasma (LIP) and gas arc represent two distinct types of plasma, differing significantly in energy density and duration. This study utilized collective Thomson scattering diagnostics to investigate the temporal and spatial evolution of electron density of these two plasmas, with varying SF₆/N₂ mix ratios as the gas medium. Our findings indicate that initially, the electron density in gas arc is lower, and its decay rate is generally slower compared to LIP. However, as the SF₆ concentration increases, the decay process accelerates for both LIP and gas arcs. It is worth noting that when the SF₆ volume fraction exceeds 70%, the decay rate of electron density approaches that of pure SF₆ in both plasma types, suggesting a saturation effect near a 70% SF₆/N₂ mix ratio in terms of electron density decay.