ELECTROMAGNETIC BEARINGS FOR MINIATURE HIGH SPEED TURBOEXPANDERS IN SPACE-BORNE CRYOCOOLERS

CRYOGENIC COOLING OF ADVANCED SENSORS IS BEING INVESTIGATED, PARTICULARLY CRYOCOOLERS THAT USE MINIATURE HIGH-SPEED TURBOEXPANDERS.A MINATURE ELECTROMAGNETIC BEARING (EMB) DESIGN FOR CRYOGENIC TURBINES IS BEING UNDERTAKEN TO OVERCOME THE LIMITATIONS OF GAS BEARINGS. THE PROPOSED EMB, BECAUSE IT IS NON-CONTACTING, IS EXPECTED TO SHOW ULTRA-HIGH RELIABILITY OVER EXTENDED PERIODS OF CRYOCOOLER OPERATION. BECAUSE THE EMB OPERATES AT CRYOGENIC TEMPERATURES,IT ALLOWS A SUBSTANTIAL REDUCTION IN THE TURBOEXPANDER HEAT LEAK ASSOCIATED WITH THE WARMER TEMPERATURES NEEDED BY GAS BEARINGS. THIS REDUCTION IN TURBOEXPANDER HEAT LEAK IS ANTICIPATED TO RESULT IN A SUBSTANTIAL LOWERING OF CRYOCOOLER INPUT POWER THAT CAN LEAD TO MAJOR REDUCTIONS IN SPACECRAFT POWER AND WEIGHT. IN ADDITION TO MAJOR ADVANCES IN SPACE-BORNE CRYOCOOLER PERFORMMANCE, THIS PROGRAM, WHEN SUCCESSFUL, WILL ADVANCE EMB TECHNOLOGY TO FAR HIGHER LEVELS OF MINIATURIZATION AND SPEED THAN HAVE BEEN ACHIEVED TO DATE. THIS TECHNOLOGY ALSO WILL BENEFIT EARTH-BOUND APPLICATIONS WHERE GOALS OF ULTRA-LOW TEMPERATURES ARE HINDERED BY HEAT LEAKS IN TURBINES, INCLUDING REFRIGERATORS FOR SUPERCONDUCTING MAGNETS IN PARTICLE ACCELERATORS AND MAGNETIC RESONANCE IMAGING SYSTEMS.