ITT_121341 - Cryo-free QHR Fridge

The National Physical Laboratory (NPL) requirement is for a refrigerator to house one of our Cryogenic Current Comparators (CCC). Currently the system is mounted in a dewar of helium to provide the necessary temperature, but this requires refilling periodically and we wish to move to a closed setup which does not need additional cryogens for sustained periods of operation. The asset must therefore: 1) Allow the existing CCC components to be mounting in the cold space of the fridge. 2) Hold a steady temperature of 4 K or less for a sustained period. 3) Not require any additional liquid cryogens for cool-down or whilst running.