Abstract: An elongated cryogenic envelope includes a support-spacer for locating a plurality of refrigeration tubes at selected radial and circumferential locations within a vacuum chamber formed between inner and outer coaxial tubes. The support-spacer includes a high-thermal-conductivity ring surrounding the inner tube and a plurality of hollow epoxy-fiberglass, titanium-tipped spokes extending between the outer tube and the high-thermal-conductivity ring surrounding the inner tube.

Abstract: A plurality of cryogenic envelope sections are joined together to form a power transmission line. Each of the sections is comprised of inner and outer tubes having multilayer metalized plastic spirally wrapped within a vacuum chamber formed between the inner and outer tubes. A refrigeration tube traverses the vacuum chamber, but exits one section and enters another through thermal standoffs for reducing heat-leak from the outer tube to the refrigeration tube. The refrigeration tube passes through a spirally wrapped shield within each section's vacuum chamber in a manner so that the refrigeration tube is in close thermal contact with the shield, but is nevertheless slideable with respect thereto.

Abstract: A dewar vessel adapted to have fluid pumped therefrom to reduce its internal pressure and temperature has a porous plate located in the path of the pumped fluid. For a given fluid pressure and viscosity, the pores are sized to provide a sufficiently low pressure drop across the plate while still providing a sufficiently large surface area for the transfer of heat between the vessel and the pumped fluid. A sheet-like liquid-retaining collar extends from the interior wall of the dewar container toward the center thereof so that the container liquid is restrained from moving along the container's inner wall when the container is tilted.