Electrical Breakdown of Ice at Cryogenic Temperatures
An ice or ice-silica compound system is attractive for electrical insulation at cryogenic temperatures. A sample of ice without silica was found to have a breakdown strength of 0.3 MV/cm for ac voltages, and 0.6 MV/cm for impulse voltages. The breakdown strength of an ceicesilica compound system was 0.7 MV/cm for ac voltages. There were no visible macroscopic cracks in the sample, but microscopic cracks and voids may exist, since partial discharges were observed at about half the value of the ac breakdown voltage. The relationship between partial discharges and microscopic voids, and the voltage-time characteristics of this insulation system were studied.
Effect of electrode ice layer on prebreakdown current in liquid nitrogen
The effect of ice on dc prebreakdown events was investigated using a needle-to-plane electrode system in liquid nitrogen at 77.3 K. It was found that H/sub 2/O ice has marked effects on prebreakdown current, corona onset voltage and breakdown voltage. The breakdown voltage at atmospheric pressure depends on microscopic cracks in H/sub 2/O ice. >
Kinetic Theory of Dense Fluids. XII. Electronic and Ionic Motion in Liquid He4I and Liquid He3
The mobilities of positive and negative charge carriers in liquid He3 and He4I are calculated and the resultant agreement with experiment is excellent. The negative carrier is taken to be an electron. Due to electrostriction and density fluctuations the effective mass of the electron is of the order of 100 electron masses. In addition, the disorder of the liquid leads to incoherences in the scattering of the electron from atomic pseudopotentials. The positive carrier is taken to be He2+. An extension of the theory of Rice and Allnatt, using the ideas introduced by Mazo and Kirkwood, leads to a formula for the mobility in terms of a quantum‐mechanical temperature. Electrostriction increases the density about an ion and the dissipation arises about equally from the short‐range repulsive forces and the Coulomb and van der Waals attractive forces. Both calculations involve only basic considerations and there are no adjustable parameters in the theory.The computed effective mass of the negative carrier in He3 ...