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The electric field induced second harmonic generation (E-FISH) technique has been widely utilized for the electric field measurement of atmospheric-pressure nonthermal plasmas. However, the measurement accuracy has not been quantified. Further, the E-FISH signal generation that is necessary to the evaluation of the measurement accuracy has been formulated only for the probe laser beam focused by a spherical lens and not for the cylindrical lens. Here, the E-FISH method utilizing the focusing cylindrical lens was studied for accurate one-dimensional (1D) electric field measurement of the primary-to-secondary transition phase of a single-filament positive streamer discharge generated in atmospheric-pressure air. A combination of numerical analysis and the E-FISH signal measurement was used to establish the radial distribution of the electric field vectors and the accompanying measurement accuracy. The E-FISH methodology captured a distinct evolution in the 1D electric field varying over timescales of ∼ 1  ns and length scales of 100  µ m. At the instant when the primary streamer arrived at the cathode, the electric field at 3 mm above the cathode surface was found to be as high as 225 Td, while the field at 10 mm above the cathode surface was as low as 5 Td. At the final stage of the primary-to-secondary transition phase completed in 3 ns from the primary streamer arrival at the cathode, the electric field at 3 mm above the cathode was found to be lower than that observed at 10 mm from the cathode; this finding is consistent with predictions made based on a previous model describing the initiation of the secondary streamer discharge and previously published electron density measurement. [ABSTRACT FROM AUTHOR]

Molded case circuit breakers (MCCBs) are used to provide overcurrent and short-circuit protection for low-voltage devices with rated currents of several hundreds of amperes. In MCCBs, some arc discharges have been observed to remain on the contacts and hardly move to the arc runners. Information about the temperature distribution over an air arc plasma is indispensable in investigating and clarifying such arc-commutation phenomena. We propose a new optical system that enables dynamic measurement of the two-dimensional temperature distribution over air arc via the two-line radiance ratio method. The system consists of a four hold-lens array, a high-speed video camera, and interference filters whose wavelengths correspond to the emission spectra of air arcs with metallic vapor. The dynamics of the air arcs in a mock MCCB was measured with this system. The anode root commutates to the runner, where its ambient temperature exceeds threshold Tth, by contrast, there was no clear threshold temperature for cathode-root commutation. The Tth was 8000 K and 6000–7000 K for Cu runners and Fe runners, respectively. Light emitting spheres, which were presumably molten droplets, were emitted from the anode root and often triggered the commutation of the cathode root. [ABSTRACT FROM AUTHOR]