Multi-stage cold accumulation type refrigerator and cooling device including the same

An infrared telescope comprising a case, a first reflecting mirror disposed in said case, for reflecting infrared radiation entering said case from the outside of said case to a second reflecting mirror, said second reflecting mirror reflecting said infrared radiation from said first reflecting mirror to an infrared detector, a multi-stage cold accumulation type refrigerator, and a helium reservoir, said helium reservoir containing liquid helium for maintaining the temperature stability of said infrared detector, said multi-stage cold accumulation type refrigerator comprising a compressor disposed at an ordinary temperature, a helium gas as a common operating fluid to be compressed by said compressor, a plurality of thermal stages, at least one cylinder, and one or more expansion chambers and cold accumulators of different temperature levels, said thermal stages and said cylinders having outer surfaces, the improvements wherein at least one of said expansion chambers has a seal to prevent leakage of said helium gas, said seal being capable of sliding, wherein sliding resistance of said seal generates less heat than the theoretical generated refrigeration quantity of said expansion chamber, said theoretical generated refrigeration quantity being based on isothermal expansion in said expansion chamber;

• and a cold accumulating member of said cold accumulators is formed of an alloy or compound containing a rare earth metal.