Helium Refrigeration During the 50 Years Since the 1968 Brookhaven Summer Study

Before the 1968 Brookhaven summer study, there were commercial helium liquefiers and refrigerators. Machines that are common today started just before the 1968 summer study. The 1968 summer study led to a use of superconductivity in physics. Improved refrigeration followed. This paper shows the developments in helium refrigeration that led to the machines that are the mainstay of modern physics. Changes in helium refrigeration led to improvements in MRI, nuclear magnetic resonance, and superconducting RF cavities. These changes are continuing today.