Experimental investigation on the tilt angle performance of 4 K two-stage pulse tube cryocoolers for cosmic microwave background (CMB) telescopes

Recent helium re-condensing technology has been widely applied in the field of superconducting magnet. The pulse tube (PT) cryocoolers have achieved great application for its advantage of no moving parts in the cold end, high reliability, low vibration and noise. In our study, a two-stage PT cryocooler is employed to provide the cooling power for a nuclear magnetic resonance (NMR) superconducting magnet cryostat. In our tests, it has been shown that the superconducting magnet cryostat can realize a zero liquid helium boil-off during static operation. To obtain the liquid helium boil-off losses when the cryocooler is stopped, the cryocooler is shut down for seven hours continuously. The liquid helium evaporation rate test results show that the volume of liquid helium decreases from 63.6% to 56.3%, and the liquid helium evaporation rate is 0.83 L/h approximately. Based on the test results, the liquid helium will wholly evaporate in several days for similar superconducting magnet system even when the liquid helium cryostat is refilled.

Stirling type pulse tube cryocoolers are very attractive for cooling of diverse application because it has it has several inherent advantages such as no moving part in the cold end, low manufacturing cost and long operation life. To develop the Stirling-type pulse tube cryocooler, we need to design a linear compressor to drive the pulse tube cryocooler. A moving magnet type linear motor of dual piston configuration is designed and fabricated, and this compressor could be operated with the electric power of 100 W and the frequency up to 60 Hz. A single stage coaxial type pulse tube cold finger aiming at over 1.5 W at 80K is built and tested with the linear compressor. Experimental investigations have been conducted to evaluate their performance characteristics with respect to several parameters such as the phase shifter, the charging pressure and the operating frequency of the linear compressor.

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.

Transition edge sensors (TES) are extremely sensitive superconducting sensors, operating at 100 mK, which can be used to detect X-rays and Cosmic Microwave Background. The goal of our project is to design the electronics to read out an array of 10000 of these sensors by using microwave signals. However, we noticed the pulse tube used to maintain cryogenic temperatures caused interference in our readout. To determine the cause of the signal distortions, we used a detector with a 370 MHz sampling rate to collect and analyze sensor data. Although this data provided little information towards the nature of the noise, it was determined through a maintenance procedure than the 0.3 mm stainless steel wires were being vibrated due to acoustic waves, which distorted the signal. Replacing this wire appeared to cease the interference from the sensor data.

Investigation on a thermal-coupled two-stage Stirling-type pulse tube cryocooler

Small Stirling-type pulse tube cryocooler can be used to cool small optical devices due to the absence of moving elements in the cold head, long life, low vibration, and compactness. This paper reports a small two-stage Stirling-type pulse tube cryocooler that achieves a no-load minimum temperature of 20 K with 500 W of input electrical power and has 0.5 W@25 K cooling capacity. In addition to this, the effect of the second stage double-inlet on the P-U phase of the regenerator and the pulse tube is also simulated. The results show that the double-inlet has a significant effect on increasing the P-U phase difference between the inlet of the regenerator and the outlet of the pulse tube, which is much better than the effect of the length of inertial tube of this stage on the P-U phase.

Method for estimating off-axis pulse tube losses

Numerical simulation of a step-piston type series two-stage pulse tube refrigerator

Because of the absence of any moving components at the cold region, low vibration and high reliability, two stage GM type pulse tube refrigerator (PTR) is nowadays preferred compared to conventional GM refrigerator for cooling of superconducting magnets, SQUIDs, and cryopumping applications. The second stage regenerative material plays an important role in achieving low temperature below 20 K. Leads balls with 0.2 mm to 0.4 mm average diameter was selected as second stage regenerator matrix material while 200 mesh of SS 304 material was filled in the first stage. A two stage GM type PTR was developed. A rotary valve was fabricated and the valve timing effects on cooling performance of PTR were also studied. The valve timings were varied by the different width of rotor slit forming the flow area with stator ports. The lowest no-load temperature of 18.52 K and cooling capacity of 7 W at 29.58 K were obtained with an optimum frequency of 1.6 Hz, charging pressure of 16.5 bar.

The efficiency of 4 K Stirling type pulse tube cryocoolers (SPTCs) is rather low due to significant regenerator losses associated with the unique properties of helium around 4 K and the high operating frequencies. In this paper, regenerator performance at liquid helium temperature regions under high frequencies is investigated based on a single-stage SPTC precooled by a two-stage Gifford-McMahon type pulse tube cryocooler (GMPTC). The 4 K SPTC used a 10 K cold inertance tube as phase shifters for better phase relationship between pressure and mass flow. The effect of the operating parameters, including frequency and average pressure on the performance of the 4 K SPTC, was investigated and the first and second precooling powers provided by the GMPTC were obtained. To reduce the regenerator heat transfer losses, a multi-layer regenerator matrix, including Gd2O2S (GOS) and HoCu2, was used instead of a single-layer HoCu2 around 4 K. A theoretical and experimental comparison between the two types of regenerator materials was made and the precooling requirements for a regenerator operating at high frequencies to reach liquid helium temperatures were given, which provided guidance for the design of a three-stage SPTC.

The experimental investigation of a pulse tube refrigerator with a ‘L’ type pulse tube and two orifice valves

Intermediate cooling from pulse tube and regenerator in a 4 K pulse tube cryocooler

Hybrid J-T cryocooler is commonly employed in space detective missions requiring liquid helium temperature. In fact, nearly all the space applications of mechanical cryocoolers working at 4.5 K, having been launched or under development are hybrid J-T cryocoolers. For instance, mechanical cryocoolers used in Planck, JWST, SMILES, SPICA and so on, are all hybrid J-T cryocoolers. However, there is hardly any research on space 4.5 K hybrid J-T cryocooler in China. Key laboratory of space energy conversion technologies in Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS) has developed a 4.5 K J-T cooler precooled by two-stage pulse tube cryocooler. Base on this cryocooler, the influence of supply pressure and diameter of the J-T orifice on the cooling capacity of the J-T cooler is analyzed and experimentally studied. First of all, the influence of supply pressure and diameter of the J-T orifice is theoretically calculated. Then, experimental research is carried out. For the purpose of shortening experimental time, a two-stage GM cooler instead of pulse tube cooler is used to precool the J-T cycle. Firstly, open loop experiments are conducted because it’s much easier to adjust the supply pressure precisely. The mass flow rate of the J-T cooler rises monotonously as diameter of the J-T orifice decreases. However, the cooling capacity of the J-T cooler goes through an up and down process because the J-T effect turns to be worse when diameter of the J-T orifice increases. That is to say, performance of the J-T cooler turns to be worse when the diameter of the J-T orifice is larger than 34 μm. Based on the research of this paper, 34 μm J-T orifice may be the best choice of the hybrid J-T cooler. Besides, both mass flow rate and cooling power increase as supply pressure increases when supply pressure is below 2.0 MPa. In addition, the no load temperature of the J-T cooler rises with increasing supply pressure which is attributed to the flow resistance of the counter-flow heat exchangers. Secondly, three-stage oil-free linear J-T compressors are used to drive the J-T cooler, and the suction pressure and supply pressure of the three-stage compression system are 0.12 and 2.0 MPa, respectively. Finally, cooling power of 81.5 mW @4.48 K is achieved when the total power consumption of the J-T compressors is 102.7 W. And the temperature fluctuation at the evaporator is lower than ±0.05 K because the cooling capacity of the J-T cooler is provided by the vaporization of liquid helium.

Pulse tube (PT) cryocoolers with no moving parts in their cold ends are potentially able to replace conventional Gifford MacMahon (GM) cryocoolers for most applications. Over the past several years, CEA/SBT has undertaken basic research and prototype development of GM driven PT cryocoolers. Systematic studies have been carried out to characterize flow distribution and d.c. flow effects. Based on a good comprehension of these phenomena, several prototypes have been built and optimized for various customised applications. Their performance is presented in this paper.

The temperature of 1-2 K is crucial to the low-Tc superconducting and deep space exploration. The Joule-Thomson (JT) cryocooler coupled with a three-stage Stirling-type pulse tube cryocooler (SPTC) is an effective way of achieving the required low temperature and high efficiency. In this paper, a computational fluid dynamics (CFD) model is established for the JT cryocooler, in which the flow and heat transfer processes are simulated and analyzed. The distributions of precooling capacities are optimized by analyzing exergy losses caused by heat transfer. The effects of the three stage precooling temperatures, the precooling capacities and the high pressure before the JT valve on the cooling performance are also studied in depth. The no-load temperatures of 2.2 K and 1.42 K are achieved in the model with He-4 and He-3 as working fluids, respectively. The corresponding experimental verifications are underway.