Power lead for penetrating a cryostat

A vapor cooled multiple circuit power lead carrying power at a given power level for penetrating a cryostat having a cryogen chamber containing a cryogen at a predetermined temperature said power lead comprising:

• a tubular enclosure;
• divider means dividing said tubular enclosure into an inner section extending from an inner end of said tubular enclosure outward to said dividing means, and an outer section extending outward from said divider means to an outer end of said enclosure;
• a plurality of lead elements laterally spaced within said tubular enclosure to form multiple circuits and each including an inner high temperature superconducting section extending through said inner section of said tubular enclosure and comprising an inner conductor composed of a material which is superconducting below an intermediate temperature between said predetermined temperature and ambient temperature at said given power level, and an outer normal conductor section extending through said outer section of said tubular enclosure and comprising an electrically insulating central support, an electrically insulating sleeve concentric with said central support and forming therebetween an annular chamber, and normal elongated outer conductor means wound spirally in said annular chamber and extending across said annular chamber to form helical flow passage means;
• and
• means introducing a flow of cryogen vapor into said inner end of said inner section of said tubular enclosure to flow outward and cool said inner conductors below said intermediate temperature, flow directing means at said divider means directing said flow of cryogen vapor from said inner section into said helical flow passage means, and vent means venting said cryogen vapor from said helical flow passage means adjacent said outer end of said tubular enclosure.