Spectrum of prebreakdown light and temporal correlation of prebreakdown current and light pulses at a point cathode in hexane

Prebreakdown current and light emission were investigated at a 3 micron tip radius needle cathode in hexane stressed by a dc power supply. A gap separation of 5 mm was used, producing a nominal electric field of 10⁹ V/m. The spectral intensity of the light emission was measured in intervals of 10 nm for wavelengths ranging from 330 to 620 nm. Spectral peaks were detected at 430, 510, and 590 nm which corresponded to an intense spectral band at 431.25 nm produced from hydrocarbon reactions like those found in the sun s atmosphere, and a spectral line at 590 nm that is associated with hydrocarbons at high pressure. The temporal correlation of the light and current pulses was also determined. The results from the correlation sjuggested that the current leads the light by one to six nanoseconds. The resolution of this measurement was limited by the effective sampling period of 2.5 nsec.