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The opening process of thermal plasma contacts in a post-arc channel after current zero in a flat-type gas-blast quenching chamber

The electrical resistivity of a post-arc channel after current zero was measured along the nozzle axis in a flat-type gas-blast quenching chamber. In the chamber, iron electrodes were intentionally adopted, since Fe spectral lines at wavelengths of 426 and 443 nm have much higher radiation intensities than those of , F or Cu at temperatures below 5000 K. Observation of the two Fe spectral lines permitted determination of temperature T and iron vapour concentration in the post-arc channel up to s after current zero. On the other hand, of gas contaminated with iron vapour was theoretically calculated on the basis of the simplified first Chapman - Enskog approximation. Use of this calculation result made it possible to estimate of the post-arc channel from the measured T and . The estimation result revealed that increased more dramatically at the nozzle throat than at other axial locations, reaching at after current zero. Furthermore, on the basis of the axial distribution of , the concept of `thermal plasma contacts' was developed to interpret behaviour of the post-arc channel.