Two stage pulse tube cryocooler with intermediate heat exchanger for accessing regenerator cooling capacity

Conventional operation of closed-cycle two-stage GM-type Pulse Tube Cryocoolers (PTCs) usually relies on utilizing the cooling power of both the 1${}^{st}$ and the 2${}^{nd}$ stage. While the 1${}^{st}$ stage is required to precool the 2${}^{nd}$ stage to reach the lowest accessible temperature below 4K, it usually also provides enough cooling power to cool additional cryostat elements such as radiation shieldings. However, current applications in quantum physics have highlighted the need to additionally access heat sinks with intermediate temperatures and cooling powers, e.g. for cooling of superconducting wires. Here we will demonstrate a cooler configuration, where a third cooling stage is incorporated into the 2${}^{nd}$ stage regenerator. This third intermediate cooling stage allows to extract 4-5 W of cooling power at temperatures between 8 K and 9 K for a standard two-stage PTC with a cooling capacity of 1.6 W at 4.2 K. Most importantly, this approach does not reduce the performance of the main stage but the added intermediate regenerator stage instead allows to tap into hidden cooling power of the PTC.