EXPERIENCE WITH DISPLEX GM-TYPE REFRIGERATORS ON MAGNETIC-RESONANCE-IMAGING CRYOSTATS

Two-stage Gifford-McMahon (GM) type refrigerators have been in use for over 10 years on magnetic resonance imaging (MRI) cryostats for the p urpose of reducing the helium boil-off rate. This paper describes the experience that we at APD Cryogenics have had in applying Displex(R) G M-type refrigerators for cooling the cold shields in MRI cryostats. Th is experience includes the initial interface design work that matches refrigerator capacity and operating temperature to the cryostat heat l oads, the means of installing the expander so that it can be easily se rviced, and the means to minimize the heat transfer losses between the refrigerator and cold shield. Once a unit is in operation, the concer n is for reliable operation and long periods of operation between serv ice. Operating experience has shown that the original goals of extendi ng the period between refilling the cryostat with liquid helium and op erating reliably for long periods between maintenance have been met. D ata that have been gathered also provide a basis for further improveme nts which will have the net effect of reducing the lifetime cost of co oling superconducting MRI magnets.