The Optistat™Dry is based on a Gifford-McMahon (GM) Cryocooler. The major components in the cooling system are the cold head (Sumitomo RDK-101D), the compressor (either water or air-cooled) and high pressure lines. They form the basis of a sealed circuit containing helium gas which is used as the cooling medium. The cold head is where the Gifford-McMahon refrigeration cycle takes place. It is connected to a compressor by two gas lines and an electrical power cable. One of the gas lines supplies high pressure helium gas to the cold head, the other gas line returns low pressure helium gas to the compressor. The compressor provides the necessary helium gas flow rate at the high and low pressure for the cold head to convert into the desired cooling power at the first and second stages of the cold head.