Thermal conductance measurements of bolted copper joints for SuperCDMS

Abstract

Joint thermal conductance testing has been undertaken for bolted copper to copper connections from 60 mK to 26 K. This testing was performed to validate an initial design basis for the SuperCDMS experiment, where a dilution refrigerator will be coupled to a cryostat via multiple bolted connections. Copper used during testing was either gold plated or passivated with citric acid to prevent surface oxidation. Results obtained are well fit by a power law regression of joint thermal conductance to temperature and match well with data collected during a literature review.

Very low resistance Al/Cu joints for use at cryogenic temperatures

“…Furthermore, except for the measurements of Okamoto et al (see below), values in the range of 100-400 nΩ are encountered for forces of 3000 N, close to the recommended force for standard M4 stainless steel bolts [21]. This is consistent with the "conservative" approximation proposed in [22] for the thermal conductance of Cu-Cu bolted joints based on several earlier publications: G = 0.0624×T −0.00023 [WK −1 ] 1 . This translates into a contact resistance Rc of ≈400 nΩ using the Wiedemann-Franz law, which is comparable to the figure given above.…”

“…Numerous articles provide data on contact resistances between metals (see for instance [21,22,23,24,25,26]). We limit ourselves to the value of electrical resistance at low temperatures and do not consider their sometimes nonlinear temperature dependence, which is addressed in [26].…”