Thermal design of the characterisation test setup of improved radiative heat exchanger fins for the Einstein Telescope

Abstract

This thesis focuses on the thermal design of a test setup to characterize future versions of improved fins with enhanced effective emissivity to improve cooling performance and reduce thermal noise for the radiative exchanger of the E-TEST prototype which demonstrated the feasibility of radiative cooling at cryogenic temperatures in the context of the Einstein Telescope. Thus, to validate such designs, a dedicated miniature exchanger was conceived, analyzed and dimensioned. The work began with a simplified thermal model to estimate how much heat the suspended fins that must be radiatively cooled down could tolerate while still reaching their target temperature of 25 [K], cooled against a sink at 10 [K]. This analysis showed that the system can accept about 3.5 [mW] of total heat for a first estimate of the emissivity of the fins of 0.8 with only a small fraction allowed from unwanted parasitic sources. Calculations of the error on the emissivity based on several parameters guided the design of key components such as tubes, cables and insulation. Then, a transient analysis examined how quickly the system cools down. Parameters change observation also showed how the objectives can vary. A more detailed 3D model using the ESATAN-TMS software is computed to compare these results and verify the assumptions. It provides a more realistic view of the temperature distribution across the miniature exchanger and statistically more accurate results. A transient analysis is also made for comparison. An improved model which reduces the complexity and the cost of such design is implemented as well as a multi-exchanger configuration to test the feasibility of the next phase. Overall, the study demonstrates that a compact test setup can be built to reliably measure the performance of improved fins in a cryogenic environment. Thus providing a solid foundation for future experimental campaigns.