Effects of pressure near one atmosphere on prebreakdown current pulses at a needle cathode in hexane

Prebreakdown current pulses at a point cathode in highly purified liquid hexane have been observed to be affected by hydrostatic pressure from below one atmosphere to several atmospheres. Previously, careful combination of low-noise, high-bandwidth detection techniques had revealed these random currents actually to be well-separated bursts initiated at apparently random times, but each burst was a well-structured set of systematically spaced pulses with successive amplitudes related in an increasing linear manner. It has been observed that increasing the hydrostatic pressure reduces the duration of each burst and the number of pulses within it. A hybrid model for growth of the low-density region (LDR) has been developed by combining two earlier models in a mutually enhancing iteration, and reasonable agreement has been obtained with experimental observations. It appears that each burst corresponds to growth and dissipation of one LDR, and each set of increasingly larger pulses corresponds to breakdowns within the increasingly larger LDR as its potential changes during its expansion. An experimental means has been developed to vary hydrostatic pressure without exposure to gases, moving seals, contaminants, or changes in test liquid conditions other than pressure.<>