ABSTRACT

Physics research in a wide variety of subfields requires vacuum. Vacuum is needed to create ultracold atoms for Bose-Einstein condensation or quantum computing, to create plasmas for nuclear fusion, to conduct particle physics experiments such as those at the Large Hadron Collider, and to keep surfaces clean at the atomic level so their physical and chemical properties can be studied. There are fewer molecules to carry the heat. Once the pressure falls below 10 Torr, the lack of gas molecules starts to have a stronger effect and the thermal conductivity drops. This change in thermal conductivity is important for the example of the thermal evaporator: because the pressure is low, little heat is transferred from the boat to the substrate, so heat damage to the substrate is minimized. The labeling usually just reads “psi,” even though it should read “psig.”.