Design and construction of an enhanced thermal conductivity measurement set-up in the temperature range of 1.8 K to 50 K at CERN

Abstract Within the goals of the High-Field Magnet (HFM) program at CERN, ongoing research focuses on achieving magnetic flux densities of up to 16 T using superconducting coils. Understanding the thermal properties of composite materials used as impregnation resins or insulation layers in superconducting magnets is crucial for the design of effective cooling methods. To this end, a new test stand was built at CERN in the Cryogenic Laboratory, to extend the investigation of thermal properties to a lower temperature range compared to the conventional cryocooler-based set-ups stopping at around 3 K, by linking a closed He II circuit to this system. This circuit enables to pre-cool helium gas, then gets it condensed by expansion through a Joule-Thomson valve before it gets pumped continuously via a roots pump, allowing to extend the measurement capabilities down to 1.8 K. The He II circuit is coupled to the cryocooler’s cold head via a gas-gap heat switch, enabling the He circuit to be thermally decoupled from the warmer cryocooler head for measurements at the lowest temperature. By varying base temperatures of the experimental platform, providing the cooling power either by the cryocooler or by the He circuit, a steady-state heat flux measurements can be ensured from 1.8 K up to 50 K. This work details the design and construction of this new enhanced test stand for thermal conductivity measurements at a lower temperature range, and its validation by measuring a reference sample.