Experimental study of a gas-coupled pulse tube cold finger with both active piston and cold inertance tube as phase shifters for 8 K applications

Abstract

Stirling-type pulse tube cryocoolers (SPTCs) working at temperatures below 8 K represent advantages in very long wave infrared detection, terahertz detection, etc. It is essential for SPTCs to obtain reasonable distribution of impedance to achieve good cooling performance. However, adjusting the distribution of impedance to an optimal value is hard as temperature decreases. It is critical for muti-stage SPTCs working at temperatures below 8 K to arrange appropriate phase shifter at each stage. This paper introduces a gas-coupled pulse tube cold finger with active piston and cold inertance tube as phase shifters for 8 K applications. The cold finger consists of pulse tube 1 (PT1) which works at liquid hydrogen temperatures and pulse tube 2 (PT2) which operates at liquid helium temperatures. Active piston is the phase shifter of PT1. It could adjust the impedance to any value theoretically under different operating conditions. The phase shifter of PT2 is cold inertance tube and gas reservoir. Cold inertance tube and gas reservoir has simple structure which makes it suitable for space applications. The impact of frequency and operating parameters of active piston on no-load temperature is investigated by experiments. A lowest no-load temperature of 5.16 K is achieved in experiments. The effect of temperature distribution of cold finger on cooling capacity at 8 K is also researched. A cooling capacity of 74 mW at 8 K can be obtained with the electric input power of 177.5 W and a pre-cooling capacity of 9.1 W/70 K.