Two-stage joule-thomson cryostat with gas supply management system, and

Abstract

A two-stage Joule-Thomson cryostat (10) has a first-stage cryostat (12) with a helical-coil heat exchanger (14) and and isenthalpic gas expansion orifice (20) that discharges a mixture of cooled gas and cryogenic liquid into a liquid cryogen plenum (26). A second-stage cryostat (30) with a helical coil heat exchanger (32), wound to a larger diameter than the first-stage heat exchanger coil (14), is wound around and in thermal contact with the liquid cryogen plenum (26). This arrangement achieves a high degree of interstage heat transfer and cooling of the gas flowing in the second-stage heat exchanger coil (32) by the liquid cryogen in the first-stage liquid cryogen plenum (26). In operation, a gas flow management system (60), designed for rapid cooldown, initially passes a first gas of high specific refrigerating capacity through both stages (12 and 30). When the stages and structure are sufficiently cooled to the near-vicinity of the normal boiling temperature of the first gas, the flow of the first gas through the second-stage cryostat (30) is discontinued, and flow of a second gas of lower normal boiling temperature than the first gas is passed through the second stage cryostat (30). The flow of the first gas continues through the first-stage cryostate (30).