Structuring metallic coatings to reduce eddy currents and thermal noise in super insulation

The performance of multi-layered super insulation in cryogenic systems is highly dependent on the radiative properties of reflector foil surfaces. Aluminum coated polyester foils are utilized for their high reflectivity in the infrared spectrum. This coating is an electrical conductor and in applications with variable magnetic fields, eddy currents are induced in the coating. These eddy currents can have two effects. In high energy applications like for example superconducting fault current limiters, heat is dissipated in the super insulation, degrading its performance and potentially even damaging the super insulation. For high precision magnetic measurements using SQUIDs, switching ambient fields induce eddy currents in the super insulation which result in a transient response superposing the signal to be measured. This, in addition to a higher thermal noise background reduces the quality of the magnetic measurements. Our study developed Coolcat 2 NI with a 10?10 mm grid in the metallic coating. In this way the high reflectivity provided by the aluminum has been retained and the eddy currents were reduced to a level acceptable for different applications. Calorimetric and magnetic experiments are presented to show the merits of this structuring.