Multi-time electron density imaging over arc discharges around the current zero point

摘要

Framing Shack–Hartmann type laser wavefront sensors were developed for obtaining time evolutions of two-dimensional electron density images over single SF_6 and air arc discharges with decaying arc currents. An SF_6 arc discharge showed initial drastic shrinking of the diameter of the filamentary arc column and subsequent rapid electron density reduction from 10~(23)m~(?3) to less than 10~(21)m~(?3) around the point of arc extinction. On the other hand, an atmospheric arc discharge around the current zero had almost constant electron densities of 10~(21–22) m~(?3) regardless of the presence or absence of the arc current. A current-basis study showed that the observed constant electron densities could be residual ones surrounding the arc column with electron densities of 10~(20) m~(?3) and contributing less to the arc current.