History
W. E. Gifford and R. C. Longsworth, in 1960's, invented the so-called Basic Pulse Tube Refrigerator. The modern PTR was invented by Mikulin by introducing orifice in Basic pulse tube in 1984. He reached a temperature of 105 K. Soon after that, PTR’s became better due to the invention of new variations. This is shown in figure 3, where the lowest temperature for PTR’s is plotted as a function of time.
At the moment, the lowest temperature is below the boiling point of helium (4.2 K). Originally this was considered to be impossible. For some time it looked as if it would be impossible to cool below the lambda point of 4He (2.17 K), but the Low-Temperature group of the Eindhoven University of Technology managed to cool to a temperature of 1.73 K by replacing the usual 4He as refrigerant by its rare isotope 3He. Later this record was broken by the Giessen Group that managed to get even below 1.3 K. In a collaboration between the groups from Giessen and Eindhoven a temperature of 1.2 K was reached by combining a PTR with a superfluid vortex cooler.
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