VACUUM INSULATING PANEL - BASIC VACUUM CONSIDERATIONS

In the last ten years, the interest for more energy efficient and ''gr een'' insulating materials has led to intensive study of possible alte rnatives for CFC (chloro-fluoro hydrocarbons) based foams. Among these , evacuated insulating flat elements seem promising due to their high insulating value. When dis crete spacers are used as supporting elemen ts of metal foils or glass plates (transparency), excellent insulating properties of Dewars are expected to be preserved. Such a thin-wall f lat all-metal panel, with an array of supporting beads, is an UHV (ult ra high vacuum) chamber. Even if the pressure in the structure is in t he medium vacuum range, long operating time (5-10 years) sets requirem ents for tightness and low outgassing in the range, usually met in UHV practice. To achieve these goals, cleaning and pre-treatment of all c omponents, special welding techniques and proper bake out procedures a re essen tial. Some basic requirements, experimental procedures and re sults, obtained on test samples, are given.