Pulse Tube Coolers for HTS Power Generation Systems

Superconducting generators and RF magnets will be the leading technologies for high electrical power systems on aircraft, spacecraft and ground based systems in future DoD applications. These systems employ High Temperature Superconducting (HTS) materialsoperating at cryogenic temperatures. Future HTS systems will employ Yttrium Barium Copper Oxide (YBCO) which requires cooling near 65K. At present, the more mature HTS conductor Bismuth Strontium Calcium Copper Oxide (BSCCO) requires cooling down to 30K.Two cooling requirements have been set forth. The HTS rotor coils and RF magnets will need 30W of cooling at 65K, while the HTS armature windings will require an order of magnitude higher cooling power at the same operating temperature. We propose todevelop cryocoolers that will meet both these requirements. A single-stage pulse tube cooler (PTC) will be developed to provide 300W at 65K, which may be used in cooling armature windings. The lower temperature requirement (30K) will be met by developinga two-stage PTC. In order to achieve high efficiency and reliability, and to reduce mass, both cryocoolers will employ a linear compressor. Inertance tubes will be used for optimum phase shift between pressure and mass flow. The pulse tube will betapered to minimize streaming losses.A study will be conducted to identify methods by which the weight and size of the cryocooler can be minimized. We anticipate that it will be possible to define a design that is more than 75% lighter overall (less than 130 lbs. total) than the Phase IIprototype unit (~505 lbs.) without compromising any of the performance, life and reliability requirements.We have developed strategic alliances with worldwide leaders of three different cryogenic markets. The strategic alliances involve direct partner participation in the Phase II program and include planning to transition to rate production during Phase III.