This note concerns two very important parts of most beam instrument systems; diffusion pumps and water chillers. As we'll see below, the two can be intimately connected.

Many SEMs, TEMs and other electron beam instruments contain one or more diffusion pumps as part of their vacuum systems. These are usually vertically-oriented cylindrical objects, perhaps 30 cm high, wrapped in several turns of copper tubing. They are usually placed behind or below the instrument's column, and typically handle high vacuums for tungsten filaments, or backing for ion pumps with other emitter types. Generally, these units are fairly maintenance-free; a change of oil every few years may be all that is required.