Low stiffness thermal straps for cryogenic applications

Abstract

In cryogenics, working together with cryocoolers, the thermal straps are a critical thermal element, since they thermally link the instrument with the cold source. In optical elements that work at cryogenic temperatures, the thermal path, and therefore the straps, must isolate them from the vibrations of the cryocoolers. Consequently, its stiffness is a characteristic to consider in the design. But, in the case of optical focal plane arrays, working at very low temperatures such as 50 mK, it can be resonant with the low frequency range of the cryocoolers, and its dissipation can break the superconducting state of the sensors, the basis of its functioning. It is therefore an undesired thermal effect derived from structural behavior. Design limitations impose the need for straps where stiffness is just as important as its conductance. The stiffness value needed is much lower than the one found in commercial straps. Therefore, this work highlights the design, and characterization tests of different strap prototypes in order to achieve the necessary resistivity and thermal conductivity for low cryogenic temperatures. The thermal straps were initially designed for the Cryostat facility for 2K Core Calibration (C2CC) a ground equipment for the ATHENA project (Advanced Telescope for High - ENergy Astrophysics, ESA).