Evaluation of Vibration Characteristics of a 1.5 W 4 K Pulse Tube Cryocooler with Improved First Stage Cooling Capacity

Abstract Pulse tube (PT) cryocoolers are extensively utilized in various applications, including dilution refrigerators for quantum computers and physical property measurement systems that require minimal mechanical vibration-induced noise. In the field of physical and chemical applications, there is a growing need for enhanced first stage cooling capacity. To address this demand, Sumitomo Heavy Industries (SHI) has developed RP-182C2S as an upgrade to our existing 1.5 W 4 K PT cryocooler, RP-182B2S. This upgrade offers a substantial improvement in first stage cooling capacity, increasing its specification from 36 W at 48 K to 42 W at 45 K, while maintaining the specific second cooling capacity and interface on the cylinder side. From a vibration standpoint, increasing the cooling capacity can potentially have negative effects on vibration characteristics. This is primarily due to factors such as the larger cylinder size and changes in operating pressure conditions. Another factor to consider is the alteration in the gas intake and exhaust direction of the cold head piping, transitioning from a horizontal design (used in 1.0 W 4 K PT cryocoolers) to a vertical design (implemented in 1.5 W 4 K PT cryocoolers). These modifications may also impact the vibration characteristics. Moreover, while vibration measurements of cryocoolers are typically conducted in room temperature environments, it is essential to perform such measurements in cryogenic environments to achieve more accurate and realistic results. In this study, we developed a test bench enables vibration measurements in a second stage condition at 4.2 K. We used this setup to conduct vibration measurement on RP-182C2S as well as RP-182B2S and RP-082B2S which served as the comparative cryocoolers. The evaluation results indicate that RP-182C2S demonstrates nearly identical vibration characteristics to RP-182B2S in terms of displacement and acceleration. Additionally, it was suggested that adjusting the direction of the piping can help mitigate vibration levels in a specific direction.