Heat dissipation due to microvibrations in low temperature experiments

Abstract: Ultra-sensitive photodetectors on-board space missions need very low temperatures to keep a good resolution. Cryo-coolers, such as pulse-tubes, help maintaining these conditions within a cryostat. In return however, they generate micro-vibrations. These micro-vibrations dissipate enough heat to cause temperature fluctuations at the detector's support, thus lowering the detector's resolution. The first objective is to establish a test bench almost from scratch. The test bench includes a dummy representing the detector's support. The next objectives is to verify that we can measure heat dissipation at the dummy, corresponding to very low values of power ; and finally, to find a link between mechanics and heat dissipation. The dummy consists of a mass suspended by Kevlar chords and is mounted on the cold plate of a cryostat. From the cryostat enclosure, we were able to generate micro-vibrations at the suspended mass and to carry out acceleration and temperature measurements. At 4 K, we were able to measure heat dissipation only around the suspended mass resonance modes. As a first quantitative result, we found that an acceleration of thousands µg (g is the gravitational acceleration) on the cold plate dissipates hundreds of nano-watts. However, these are preliminary results and we will need to improve the test bench for future measurement campaigns.