D.c. breakdown voltage characteristics in supercritical helium: breakdown in nonuniform fields

✍ Scribed by S. Nakayama; D. Ito

• Publisher: Elsevier Science
• Year: 1986
• Tongue: English
• Weight: 778 KB
• Volume: 26
• Category: Article
• ISSN: 0011-2275
• DOI: 10.1016/0011-2275(86)90189-x

✦ Synopsis

This Paper describes the results of an experimental study on the d.c. breakdown voltage characteristic of supercritical helium under a non-uniform electric field. The study was carried out to further the development of superconducting magnets cooled by supercritical helium. At a certain density value, Pc, a maximum breakdown voltage is observed in the breakdown voltage versus density characteristic. In the case of a negative needle electrode, the breakdown voltage is proportional to the density, p, below pe When p > Pc, the breakdown voltage becomes almost independent of the density. The Pc versus temperature curve, obtained from measurements at different temperatures, agrees well with a pseudo-critical line, which is the phase transition line between the pseudo-gas and pseudo-liquid phase of supercritical helium. The breakdown mechanism of supercritical helium in the pseudo-liquid phase is different from the mechanism in the pseudo-gas phase. The breakdown voltage in the pseudo-liquid region was equal to the breakdown voltage of liquid helium.