Abstract
In this paper, the heat exchange process between the working gas and the regenerator materials is examined in the second-stage GM refrigerator. The temperature dependence of the cooling power is measured as a function of the phase angle between pressure and displacement oscillations of the working gas. It is found that the optimum phase angle maximizing the cooling power at a given temperature dramatically increases with decreasing temperature particular below 20 K. This behavior represents that the importance of the phase angle in order to increase the cooling power in the low temperature region.