MINIATURE ELECTROMAGNETIC BEARINGS FOR CRYOGENIC APPLICATIONS

THERE IS A STRONG NEED FOR HIGH EFFICIENCY CRYOGENIC COMPRESSORS, WHICH CAN PUMP MODEST VACUUM LEVELS TO REDUCE THE TEMPERATURE OF THE LIQUID HELIUM USED IN COOLING SUPERCONDUCTING MAGNETS BELOW 4.2 K. ALTHOUGH HIGHLY RELIABLE AND CONTAMINATION FREE, SELF-ACTING GAS BEARINGS CANNOT OPERATE RELIABLY AT TEMPERATURES BELOW 70 TO 100 K OR PRESSURES BELOW ABOUT 0.4 ATM. HENCE, THE USE OF GAS BEARINGS IN A LOW PRESSURE, ULTRA-LOW TEMPERATURE COMPRESSORREQUIRES THAT THE BEARINGS OPERATE AT HIGHER TEMPERATURES AND PRESSURES, WITH THE CONCOMITANT EFFICIENCY PENALTY ASSOCIATED WITH HEAT AND FLOW LEAKAGES. AN ATTRACTIVE ALTERNATIVE TO GAS BEARINGS FOR THIS APPLICATION IS THE USE OF ELECTROMAGNETIC BEARINGS. MAGNETIC BEARINGS CAN OPERATE AT ANY TEMPERATURE AND PRESSURE, DOWN TO HARD VACUUM. HOWEVER, PRESENT MAGNETIC BEARING TECHNOLOGY IS NOT SUITABLE FOR APPLICATION TO HIGH-SPEED MINIATURE TURBOMACHINERY. THIS PROJECT DESCRIBES A NOVEL ELECTRO-OPTICAL POSITION SENSING SYSTEM THAT WILL ALLOW CONTROL OF HIGH-SPEED MINIATURE MAGNETIC BEARINGS. PHASE I OF THIS PROJECT WILL ASSESS THE FEASIBILITY OF THE CONCEPT BY DEMONSTRATING A BREADBOARD OPTICAL SENSING SYSTEM. IF PROVEN FEASIBLE, THE MAGNETIC BEARINGS WOULD BE DEMONSTRATED IN PHASE II BY BUILDING AND TESTING A PROTOTYPECRYOGENIC VACUUM COMPRESSOR.