Improvement strategies for a low input power 4 K pulse tube cooler: Experiments and sage simulations

•Small scale low input power 4 K pulse tube cryocooler.•Stepwise optimization based on filling and geometry.•Improvement of the coefficient of performance by a factor 2.•Accurate modeling of PTCs Sage simulation models down to 4.2 K.•Sage simulations confirm the influence of the key parameters. Optimizing the design of a two-stage Pulse Tube Cryocooler (PTC) usually affects its geometry and regenerator filling. Here, this is demonstrated based on a recently developed small scale two-stage PTC, driven by a 1 kW Helium compressor with an initial base temperature of 5 K. The improvements are aimed at reducing the minimum temperature and maximizing the cooling performance around 4.2 K. By rescaling the geometry, while keeping the overall length constant, and implementing Gd2O2S (GOS) in the regenerator filling, the coefficient of performance (COP) can be doubled from 7×10-5 to 1.5×10-4. The simulations generated with the software Sage agree with the experimental results and describe the cooling performance accurately down to 4.2 K. This demonstrates that such simulations are important to optimize PTCs around liquid Helium temperatures.