At present, magnetic imagers rely upon manual replenishment of liquid helium as a means of cooling the superconducting magnets. This project will establish the feasibility of a miniature, closed-cycle cryocooler to eliminate this expensive and wasteful practice, thereby dramatically reducing the cost of cryogenic refrigeration. By incorporating the integration of heat exchangers and expansion engines in a concentric tube configuration, this cryocooler will exploit the advantages of both counterflow and regenerative heat exchange, resulting in excellent heat exchange efficiency over the entire temperature span from 300 K down to 4.5 K. The nominal power consumption by the warm compressor is less than 500 W per 1 W of cooling at 4.5 K. In addition, the new configuration is less susceptible to gas contamination than a regenerative cycle (Gifford-McMahon or Stirling) used in combination with a Joule-Thomson stage, which is easily blocked with condensed contaminants. The first objective of the Phase I project is to finalize the integral heat exchanger and expansion engine configuration. Then, major components such as valves and the drive mechanism will be designed. Using these physical designs, a performance algorithm will be developed that will be used to build a data base. This data base will indicate appropriate values for critical design parameters for use during Phase II to construct prototypes.Anticipated Results/Potential Commercial Applications as described by the awardee: A small-capacity, liquid-helium-temperature cryocooler that is highly efficient, reliable, and easily manufactured has been long awaited. Such a closed-cycle cryocooler will have many immediate applications, since it will eliminate the need to replenish liquid helium periodically in superconducting magnet systems. In research, the field of high-energy physics is concentrating on all aspects of superconducting magnets. The most immediate commercial application for the new cryocooler is for magnetic resonance imagery In addition to cooling magnets, the new cryocooler could be used to increase the sensitivity of many sensors (e.g., infrared), both space- and earth-based, by allowing operation at 4.5 K.Topic 15: High Energy Physics Technology And Research
