Numerical and experimental study on the characteristics of 4 K gas-coupled Stirling-type pulse tube cryocooler

•A novel gas-coupled SPTC was developed, which features extremely compact structure.•The gas-coupled characteristic is numerical studied and validated by experiment.•A negligible phase interaction is found between the two gas-coupled stages.•Mixed sphere diameter regenerator will not help to achieve better cooling performance than constant diameter regenerator. A novel gas-coupled Stirling-type pulse tube cryocooler (SPTC), coupling with a colder-stage at the cold head of pre-cooling stage, has been presented, which features extremely compact structure. The gas-coupled characteristics, such as interaction of phase distribution, mass flow distribution and available energy regenerator loss, have been numerical and experimental studied. A negligible phase interaction is found between the two gas-coupled stages, which means the phase of each stage can be optimized individually. The colder-stage regenerator material diameter has a significant effect while its inertance tube size has a weak effect on mass flow distribution. The sphere-type colder-stage regenerator has a different available energy loss mechanism with the mesh-type regenerator of pre-cooling stage. At present, the prototype achieves a no-load temperature of 4.94 K. A cooling power of 12.4 mW/6 K can be achieved with an input power is 270 W and a precooling power of 12.43 W/77 K.