Credit: SLAC National Accelerator Laboratory
Schematic of the interior of SLAC's superconducting electron gun. Electrons coming from a photocathode (brown) on the right gain energy inside a superconducting cavity (dark blue), which is cooled to nearly absolute zero temperature inside a vessel filled with liquid helium (light blue). A magnetic field (magenta) bundles the electrons into a tight beam, which exits the gun on the left.