Spectroscopic investigation of channel initiation in hydrogen sparks

Coaxial cable discharges in hydrogen at a pressure of 2700 torr have been examined spectroscopically with nanosecond resolution by means of a wide-aperture monochromator and high-speed photomultiplier. From accurate measurements of absolute line and continuum intensities and line profiles, electron temperature and density are derived as functions of time and position in the gap. An ionization wave is observed moving from the cathode to the anode with a velocity of 2 × 10 7 cm sec -1 , leaving behind a highly conducting channel in a non-equilibrium state, with electron density and temperature unevenly distributed along the axis for lengths of time up to about 15 nsec.