Speaker
Description
In our contribution, we will present the latest developments of the sorption-based three-stage Joule-Thomson cryocooler for the Dutch Einstein Telescope pathfinder. In order to meet the unprecedented sensitivity demand of Einstein Telescope, there is a need for achieving cryogenic cooling of the mirror systems to temperatures near 10 K. This is addressed in a consortium comprising of the University of Twente (EMS), Demcon Kryoz and Cooll. The consortium is developing a zero-vibration cooling system by employing a sorption-based compressor, originally developed for space applications. This technology operates without moving parts and hence eliminates potential vibration sources. Compression is achieved with thermally-driven adsorption-desorption cycles. Pressure buffers will regulate the pulsating downstream flow of the sorption compressor, hence enabling continuous cryogenic cooling power at the Joule-Thomson restrictions. The cooler chain consists of three stages: a 35 K neon stage, 18 K hydrogen stage and at last a 8K helium stage. The current baseline delivers 50 mW of cooling power at 8 K to cool the payloads of ETpathfinder. The sorption cooler design is fully scalable due to the modular sorption compressor cells and is therefore also able to meet the requirements of the ET payloads.
Furthermore, in our cooler design, several principles are applied to avoid flow-induced vibrations. The helium gas will flow at full gas-phase at the cold tip, hence eliminating potential vibrations from liquid boiling effects close to the connection of the cold tip with the suspension wires. Moreover, the required thermal connection is minimized at temperatures near 10 K due to the conductivity peak of the suspension wires in this temperature range. This will minimize the mechanical connection and therefore vibrations that can be transferred from the background towards the payload. More examples of minimizing flow-induced vibrations are the prevention of transition to turbulence, suppression of secondary flow instabilities in bended pipes and avoiding violent boiling at the LN2 precooler interfaces. In the concept phase, several feasibility tests were performed; vibration measurements were performed using the AFM on an U-shaped tube to evaluate flow-induced vibrations and extensive lifetime testing was done on the compressor cell design in order to meet the lifetime requirements.
This technology will be benchmarked in the ETpathfinder facility. In previous space application studies, a TRL 5 was demonstrated at the University of Twente and the aim of this consortium is to reach TRL7 at ETpathfinder. The consortium started in 2024 and we are currently in the assembly phase with the aim to complete the integration of the first system at the High Pressure Lab of the University of Twente in the summer of this year, followed by the verification phase. In parallel, the assembly of the cooler subsystems for ETpathfinder has started beginning of this year in preparation for the integration in Maastricht.
In our efforts, we will demonstrate our latest developments for the zero-vibration cryocooler for ETpathfinder.