A NEW CONFIGURATION FOR LIQUID-HELIUM-TEMPERATURE CRYOGENIC COOLERS

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 SUCHAS 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 DATABASE WILL INDICATE APPROPRIATE VALUES FOR CRITICAL DESIGN PARAMETERS FOR USE DURING PHASE II TO CONSTRUCT PROTOTYPES.