Hybrid vapor cooled power lead for cryostat

A power lead (1) for a cryostat (83) has high temperature superconducting (HTSC) conductors (7) extending inward toward a pool (93) of liquid cryogen in the cryostat (83) in series with normal conductors (21) extending from the HTSC conductors (7) to outside the cryostat. Tubular shrouds (31, 35, 37) vented to atmosphere direct a flow of cryogen vapor along the HTSC conductors (7) to maintain them superconducting, and along the normal conductors (21) to remove Joule heat and heat leakage along the normal conductors. In one embodiment, a pool of liquid nitrogen maintained within a tubular inner shroud (35) is the principal coolant for the normal conductors (21). Helium vapor is circulated over the HTSC conductors and is then directed by an outer tubular shroud (37) around the inner tubular shroud (35) to provide additional cooling for the normal conductors (21). Flexible connectors (13) at one end of each of the HTSC conductors (7) accommodate for individual thermal contractions of these conductors.