For disruptive science missions – such as to study the hot and energetic universe or the cosmic microwave background – where detectors operate at very low temperatures (down to 50 mK), the thermal susceptibility to microvibrations (such as from reaction wheels, thrusters or cryocoolers) may become critical.

This thesis aimed to gain an understanding of this thermal susceptibility, for cryogenic devices and systems crucial for such missions. We built a highly sensitive test bench dedicated to studying dissipation due to microvibration disturbance. Using bespoke actuation and sensing methods, we were able to induce sub-millig levels of mechanical excitation and observe sub-microwatt levels of dissipation. We quantified dissipation in a gas-gap heat switch (a cryogenic device ubiquitous in sub-Kelvin space applications) and studied the locations and nature of the phenomena causing it.

Our work has largely been experimentally focused. It has also been backed by a simple thermomechanical dissipation model to interpret our measurements. For mechanical excitation around 1 mgrms, we observed microvibration dissipation as high as 1 μW, at 1.2 K and 4.2 K. Large Q factors (>1000) of our heat switch (and variations thereof) were measured, allowing us to observe microvibration dissipation of flexible damped elements attached to our test object (e.g. instrumentation wiring) due to their forced oscillation.

Our work applies to cryogenic systems for low-temperature science missions, such as the future Athena X-ray space observatory, but also beyond space for quantum computers that also need very low and stable temperatures.​