A Cryogenic Geophone with stable response from Room Temperature to millikelvin

Abstract

With the development of pulse-tube cryocoolers, the availability and use of low-temperature environments have increased exponentially in recent years. However, replacing liquid helium with a mechanical cooling device has, since its introduction, highlighted the need to attenuate the mechanical vibrations generated by the cryocooler itself. In the case of dilution refrigerators, which are capable of reaching temperatures on the order of few mK, the issue of mechanical vibrations reaching the experimental setup is, in many situations, extremely critical. This has led to the development of several customized experimental approaches aimed at attenuating vibrations. However, the inertial measurement of vibrations at cryogenic and, in particular, ultracryogenic temperatures has relied on customized sensors, since no commercially available, calibrated instruments exist for measurements at these temperatures. Nevertheless, many research groups employ commercial geophones that are recalibrated at low temperatures. This approach, however, is not free from systematic errors and presents significant challenges in quantitatively assessing the absolute response. In this work, we describe the development of cryogenic geophones exhibiting an almost temperature-independent response, from room temperature down to approximately 10 mK.