Thomson scattering diagnostics of decay processes of Ar/SF₆ gas-blast arcs confined by a nozzle

Because of its instability, it is difficult to measure precisely the electron density (n_e) of a long-gap decaying arc discharge in a circuit breaker. However, it is well known that it is an essential parameter for the determination of success or failure of the current interruption in a circuit breaker. In this paper, the spatiotemporal evolutions of the electron density were successfully measured in decaying SF₆ gas-blast arc discharges formed with a long gap (50 mm) in a confined nozzle using laser Thomson scattering. Pure Ar gas and an 80%Ar/20%SF₆ mixture gas were used as the arc quenching media at atmospheric pressure. After reducing the current to zero, both the measured n_e and arc radius in the Ar/SF₆ gas arc clearly decayed more rapidly than in the pure Ar gas arc.