This paper addresses technical problems of thermal contact conductance or resistance which inevitably occurs in most cryogenic engineering systems. The main focus of this paper is to examine what kind of physical factors primarily influences the thermal contact resistance and to suggest how it can be minimized. It is a good practical rule that the contact surface must have sub-micron roughness level with no oxide layer and be thinly covered by indium, gold, or Apiezon-N grease for securing sufficient direct contact area. The higher contact pressure, the lower the thermal contact resistance. The general description of this technique has been widely perceived and reasonable engineering results have been achieved in most applications. However, the detailed view of employing these techniques and their relative efficacies to reduce thermal contact resistances need to be thoroughly reviewed. We should consider specific thermal contact conditions, examine the engineering requirements, and execute each method with precautions to fulfil their maximum potentials.

Review : Thermal contact problems at cryogenic temperature

Cryostats that operate below 1 K have additional requirements involving the need for extremely small heat leaks and alternative cooling methods. This chapter describes the design and operation of a cryostat operating at 50 mK for the Cryogenic Dark Matter Search experiment. Included are descriptions of the cooling and thermal insulation system, seal design, fabrication and operations. Valuable data is provided on the thermal conductivity of Kevlar and the calculation of joint conductance. The particular issue of using only radiopure materials in the cryostat construction is also covered. A list of lessons learned from the cryostat operation is provided.

Design and Operation of a Large, Low Background, 50 mK Cryostat for the Cryogenic Dark Matter Search

We present two different techniques for achieving low resistance ($<$20 n$\rm \Omega$) contacts between copper and aluminium at cryogenic temperatures. The best method is based on gold plating of the surfaces in an e-beam evaporator immediately after Ar plasma etching in the same apparatus, yielding resistances as low as 3 n$\rm \Omega$ that are stable over time. The second approach involves inserting indium in the Al/Cu joint. For both methods, we believe key elements are surface polishing, total removal of the aluminum oxide surface layer, and temporary application of large (typ. 11 kN) compression forces. We believe the values for gold plated contacts are the lowest ever reported for a Cu/Al joint of a few $\rm cm^{2}$. This technology could simplify the construction of thermal links for advanced cryogenics applications, in particular that of extremely low resistance heat switches for nuclear demagnetization refrigerators.

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

The detectors of the Super Cryogenic Dark Matter Search experiment at SNOLAB (SuperCDMS SNOLAB) will operate in a seven-layered cryostat with thermal stages between room temperature and the base temperature of 15 mK. The inner three layers of the cryostat, which are to be nominally maintained at 1 K, 250 mK, and 15 mK, will be cooled by a dilution refrigerator via conduction through long copper stems. Bolted and mechanically pressed contacts, flat and cylindrical, as well as flexible straps are the essential stem components that will facilitate assembly/dismantling of the cryostat. These will also allow for thermal contractions/movements during cooldown of the sub-Kelvin system. To ensure that these components and their contacts meet their design thermal conductance, prototypes were fabricated and cryogenically tested. The present paper gives an overview of the SuperCDMS SNOLAB sub-Kelvin architecture and its conductance requirements. Results from the conductance measurements tests and from sub-Kelvin thermal modeling are discussed.

Thermal conductance modeling and characterization of the SuperCDMS-SNOLAB sub-Kelvin cryogenic system

We present two different techniques for achieving low resistance (<20 n
 $$\Omega $$
 ) contacts between copper and aluminium at cryogenic temperatures. The best method is based on gold plating of the surfaces in an e-beam evaporator immediately after Ar plasma etching in the same apparatus, yielding resistances as low as 3 n
 $$\Omega $$
 that are stable over time. The second approach involves inserting indium in the Al/Cu joint. For both methods, we believe key elements are surface polishing, total removal of the aluminum oxide surface layer, and temporary application of large (typ. 11 kN) compression forces. Such contacts are not demountable. We believe the values for gold plated contacts are the lowest ever reported for a Cu/Al joint of a few $$\mathrm{cm}^{2}$$
 . This technology could simplify the construction of thermal links for advanced cryogenics applications, in particular that of extremely low resistance heat switches for nuclear demagnetization refrigerators.

Very Low Resistance Al/Cu Joints for Use at Cryogenic Temperatures

http://inspirehep.net/record/1402733/files/fermilab-pub-14-522-ppd.pdf

Thermal conductance measurements of bolted copper joints for SuperCDMS

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Thermal conductance measurements of bolted copper joints for SuperCDMS