Cryogenic Accessories
Used to minimize heat leak into the sensor and cryogenic system, cryogenic wire has a much lower thermal conductivity (and higher electrical resistivity) than copper wire. The most common type of cryogenic wire is phosphor bronze. This wire is available in one-, two-, and four-lead configurations. Four-lead configurations are available as Quad-twist™ (two twisted pairs) or Quad-lead™ (ribbon). Wire gauge is 32 or 36 AWG, with polyimide or polyvinyl formal (Formvar®) used to insulate the wires. Other common cryogenic wires include manganin, nichrome heater wire, and HD-30 heavy duty copper wire.
For high-frequency signals, Lake Shore provides various coaxial cables: ultra-miniature coaxial cables and semi-rigid coaxial with a stainless steel center conductor.
The most common electrical connections are solder joints. Solder can also be used to install various sensors to improve thermal heat sinking. Common solders are indium solder and 90/10 Pb/Sn. Indium solder is used for various applications including sensor installation to provide excellent thermal contact with the sample. 90/10 Pb/Sn solder is used for applications requiring a higher temperature (liquidus point of 575 K and solidus point 458 K). Ostalloy® 158 solder is used as a seal for demountable vacuum cans and electric feedthroughs in cryogenic systems.
Epoxies are used to install and fasten sensors, while providing thermal contact and electrical insulation, with the sample. Epoxy can also be used for mechanical attachment and joints. Stycast® 2850FT is a black epoxy resin, and has a thermal expansion coefficient that is matched to copper. A silver-filled, low-temperature conducting epoxy provides excellent strength, along with electrical and thermal conductivity.
Thermal greases are used to install and fasten sensors, while providing thermal contact and electrical insulation, with the sample. Apiezon N and Apiezon H greases are suitable for enhancing thermal contact, especially for sensors inserted into cavities. Apiezon N is for low temperature applications, while H is for high temperature.
The most common varnish for cryogenic installations is VGE-7031 varnish. It has good chemical resistance, bonds to a variety of materials, and has a fast tack time.
Lake Shore also supplies heat sink bobbins, a beryllium oxide heat sink chip, and a four-lead resistance sample holder. Cartridge heaters and vacuum feedthrough products are also available.