High Vacuum Beryllium Thermal Switch Used to Isolate Cryo-Coolers 3" diameter gas gap style Beryllium switch. Beryllium (part with 3 holes) is at the leading and trailing locations of this assembly. A stainless steel bellows provides a high vacuum seal. While a titanium post down the ID of this assembly maintains a constant gap at temperature between the leading and trailing surfaces of Beryllium. When the gas is evacuated, this assembly can provide as much as 1000° K of insulation from end to end per Watt of input heat. back