Experimental Investigation of Cooling Capacity of 4K GM Cryocoolers in Magnetic Fields

4K GM cryocoolers are inevitably exposed to the magnetic field inMRI systems. The cooling capacity of a 4K GM cryocooler is strongly dependent on the heat capacity of the magnetic regenerator materials, such as HoCu2, Er3Ni and Gd2O2S(GOS). In order to clarify the effect of the magnetic field on acryocooler's performance, we measured the cooling capacity of Sumitomo Heavy Industries, Ltd. (SHI) 1W 4K GM cryocoolers in magnetic fields up to 2.0 T. It is found that the impact of a magnetic field on the cooling capacity with a HoCu2/GOS hybrid regenerator is much smaller than that with a HoCu2 regenerator.