Decrease of breakdown voltages for micrometer-scale gap electrodes for carbon dioxide near the critical point: Temperature and pressure dependences

We performed measurements of breakdown voltages as a function of environmental pressure with 1-mum-gap tungsten electrodes for high-pressure carbon dioxide up to supercritical conditions at different temperatures (305.65, 308.15, and 313.15 K). Breakdown voltage curves exhibit an inflection at around 3 MPa and a drastic decrease near the critical point. The location of the drastic decrease shifts to the high-pressure range and the sharpness and depth decrease with increased temperature. The breakdown voltage in pressure environments higher than that at the inflection point was analyzed systematically using the Townsend theory and density fluctuations. Moreover, comparison with breakdown voltage measurements by 10-mum-gap electrodes indicates that one factor inducing the inflection and the decrease might be electron attachment to existing clusters in dense carbon dioxide. (C) 2003 American Institute of Physics.