The Thermal Conductance of Sapphire Ball Based Detector Clamps

TL;DR

This study measures the thermal conductance of sapphire ball clamps used in low-temperature detectors, revealing temperature-dependent conductance values that align with thermal boundary resistance models.

Contribution

First direct measurement of thermal conductance for sapphire ball clamps at millikelvin temperatures, providing data crucial for detector design.

Findings

Conductance of sapphire-on-copper clamp: 660^{+360}_{-210} (T/K)^{3.1} nW/K

Conductance of sapphire-on-silicon clamp: 380^{+190}_{-120} (T/K)^{2.8} nW/K

Conductance consistent with thermal boundary resistance

Abstract

In order to provide secure clamping with a low thermal conductance, some low temperature detectors are held with point contact sapphire ball clamps. While this method is increasingly common, the thermal conductance across this interface has not been well studied. We present a direct measurement of the thermal conductance of such clamps between 200 and 600~mK, with a clamping force of approximately 2.7~$\pm0.3$~N/clamp. The thermal conductance of a single sapphire-on-copper clamp was found to be 660$^{+360}_{-210}$~$(T/K)^{3.1}$~[nW/K]. For a sapphire-on-silicon clamp the conductance was found to be 380$^{+190}_{-120}$~$(T/K)^{2.8}$~[nW/K]. The conductance measured is consistent with thermal boundary resistance.