Power lead for penetrating a cryostat

A multiple circuit hybrid cryostat power lead has a plurality of laterally spaced, electrically isolated lead elements inside a tubular enclosure. Each lead element has an inner section with a high temperature superconducting (HTS) conductor inward of a divider in the tubular enclosure, and an outer normal conductor section outward of the divider. The outer sections of the lead elements have a pair of copper conductors spirally wound in an annular chamber between an electrically insulating central support and an electrically insulating sleeve to form helical flow passages. Cryogen vapor flows outward in the tubular enclosure inward of the divider over the HTS conductors, through a slotted heat exchanger electrically connecting the HTS and copper conductors at the divider, and through the helical flow passages to vents at outer terminals. Flow distribution in the helical passages is regulated either by a flow baffle diverting flow at an intermediate point in the helical flow passages through apertures in the sleeves into the tubular enclosure for mixing and reintroduction of the mixed cryogen vapor back into the helical passages through additional apertures in the sleeve outward of the flow baffle, or by individual thermally responsive valves in the flow passages.