MEASUREMENT OF 2-DIMENSIONAL ELECTRON DENSITY DISTRIBUTION OVER EXTINGUISHING ATMOSPHERIC ARC USING HIGHLY SENSITIVE SHACK-HARTMANN TYPE LASER WAVEFRONT SENSOR

摘要

Optical measurement of 2-dimmentional electron density distributions over extinguishing arc channels is a promising method for developing highly reliable gas circuit breakers. However, the measurement sensitivity of a standard optical system with potential of acquiring a 2-dimmentional electron density distribution by only a single measurement is limited to relatively high electron densities above around 1023m-3. Here, a Shack-Hartmann type laser wavefront sensor incorporating microlens arrays with a long focal length of 238 or 467mm was investigated in order to achieve the improvement of the measurement sensitivity by two orders of magnitude. The highly sensitive sensor was applied to pulsed arcs in 3-mm air gap between rod-to-rod tungsten electrodes with a diameter of lmm. 2-dimmentional electron density distributions over the extinguishing arc discharges with currents of several amperes showed that the sensor with 467-mm microlens arrays achieved measurement sensitivity of 1021m-3 and electron densities in the gap between the electrodes were lower than those around the gap ranging from 1021 to 1022m-3. These experimental results are important for researching and clarifying the process of unstable arc extinguishing.