Thermal Isolation in Microcalorimeter Measurements

Microcalorimeter measurements must be carried out in a thermally stable environment, e.g. thermally shielded from outside influences. But DC and RF signals still need to pass through such thermal shielding. While the heat conductivity of DC signal lines is usually not critical for the actual measurements, the thermal insulation of the RF transmission line is vital and one of the biggest challenges in many calorimeter experiments. Usually, commercial coaxial lines or rectangular waveguides are good heat conductors, thus the thermal isolation section (TIS) for a microcalorimeter set-up is often custom made. This work is about the design and test of TISs for the waveguide bands R 900 (75–110 GHz), R 1.4k (110–170 GHz), and R 1.8k (140–220 GH). Scattering parameter measurements of microcalorimeter feeding lines and effective efficiencies of transfer standards as well as thermal simulations are presented, and the results are discussed.