After the superinsulation invention by P. Petersen, quite a little time has passed — only several decades. However the concept of superinsulation operation mechanism has suffered

multiple variations. In the course of time these models have allowed to develop a modern superinsulation.

P. Petersen placed screens made of aluminium foil in a vacuum volume and separated them by means of glass-fibre mats. Instead of foil, a polymer film with thin aluminium layers being applied on its both sides is most widely used now.

A number of competing concepts exists as to the heat transfer mechanism in superinsulation. These concepts were sufficiently true in order to develop a sufficiently effective superinsulation. However, in the process of operation of big cryogenic objects, researchers have noted that our ideas on thermal processes in superinsulation are not correspond to reality.

Using the latest views on superinsulation, one can make the following definition.

Screen-vacuum heat insulation (superinsulation) is a system of parallel or concentric (coaxial) gas-permeable metal films applied on a substrate being separated from other by a porous padding manufactured from a material with a high heat resistance coefficient providing a small degree of heat radiation absorption and a small degree of accommodation of the inter-screen gas molecule energy at a high and stable adsorption ability of the metal films.

At the present time, a polyethyleneterephthalate film with the thickness of 12-15 p. m with thin layers of aluminium of 0.5 p. m thick being applied thereon on both sides are widely used as screens [10, 11]. A low heat conductivity of the film and a small thickness of the aluminium layer reduce the heat transfer along the layers and increase the superinsulation effectiveness in industrial products. For the insulating pad thin-fibre (with the fibre thickness up to one micron) glass materials with low gas release are used. As the distance between the screens is sufficiently large (the packing density normally lies within 10-50 screens/cm), the screen-vacuum insulation operates most effectively at practically the same low pressure values as the pure vacuum insulation, i. e. at the pressure values below 10-2 Pa. However the effectiveness of such insulation is far higher than the vacuum and powder-vacuum insulation. The present-day industrial superinsulation provides a heat flow at the level of 0.3-0.5 W/m2. Such heat inflow values are realised at the screen number of 45-75, i. e. at the thickness values less than 0.1 m and a small insulation layer mass [11]. The best superinsulation samples within the temperature range of 10 — 350K are characterised by the effective heat conductivity coefficient equal to (2-3)*10-5 W/(m*K), i. e. significantly less that with other heat insulation types. This parameter provides for the preferable superinsulation application for the protection against heat inflows of devices operating at cryogenic temperatures. [11].

A peculiarity of superinsulation is the non-additivity of thermal resistance in respect to the number of screens and the fact that the thermal resistance of insulation practically cease increasing when a certain number of layers has been reached [12].