Thermal contact conductance of demountable in vacuum copper-copper joint between 14 and 100 K

Thermal contact conductance (TCC) at material interfaces has a great impact upon the efficiency of cooling in cryogenic instruments, and is thus a crucial design parameter. Lack of reliable numerical data for demountable in vacuum bare (uncoated, dry, and without interposers) copper-copper joints prompted us to carry out systematic studies of TCC over the temperature range 14-100 K. We measured TCC as function of applied force for the contacts with surface roughness R(a) = 0.2, 1.6, and 3.2 μm. It is seen that with increasing temperature, the TCC of bare Cu-Cu contact initially rises following a generic power law dependency T(γ) with γ = 1.25 ± 0.02, reaching a maximum value at 40-50 K. TCC then decreases as temperature continues to rise towards 100 K. We show results that match those in the literature from low (4-20 K) and high (100-300 K) temperature domains, resulting in a unified smooth curve of temperature dependency of TCC for bare Cu-Cu joints. Temperature dependence is then described in a phenomenological model, accounting for the effects of changes in bulk conductivity and surface hardness with temperature. This model consistently explains the observed power law dependence of TCC as function of applied force and changes caused by roughness of contact surfaces.