Experimental investigations of multilayer insulation

Multilayer insulation (MLI), using alternate layers of shield and spacer in high vacuum, is the most effective cryogenic insulation developed to date. Due to unpredictable changes in parameters such as winding pressure, uniform contact pressure and interstitial pressure, accurate theoretical prediction of MLI performance is very difficult. Thus, an experimental investigation has been carried out on a few indigenous MLI materials. The investigations are centred on the influence of the number of layers and layer density, with the cold boundary at the same temperature as liquid nitrogen. The experiments have been carried out using a cylindrical vessel with guard vessels on the top and bottom flat surfaces. The interstitial pressure, which depends on conditions pertaining to specific parameters, such as outgassing rate of materials, cryopumping speed and time for evacuation, has also been measured. The results are compared with those obtained from a theoretical analysis carried out for the same combination of shield and spacer materials.