Cavendish Laboratory : John Ashmead's helium liquefier
Cavendish Laboratory
<p style='text-align: justify;'>Due to the increasing demand for liquid helium, Kapitza's liquefier was replaced by a new machine constructed by John Ashmead in 1949. Liquid helium was produced by a Joule-Thomson expansion rather than adiabatic cooling. Both the helium liquefier and the closed-cycle hydrogen liquefier were enclosed in a single container, which reduced the need for hydrogen purification, the time needed to start the machine and the explosion hazard. (Longair, 2016, p.308)</p>