English: A view of the Stanford superconducting linear accelerator, used to drive two infrared free-electron lasers. This view is from the head of the accelerator, where the filament power supply is held at approximately 100,000 volts between the two dark caps in the left of the frame. The hot filament discharges electrons in the insulated section in the right foreground, and these electrons accelerate toward the remainder of the structure which is at ground potential. Immediately beyond the large flat plate, the light stainless-steel segment houses a radio-frequency buncher which prepares the beam for the first superconducting segment, the injector, housed in the sky-blue dewar. This dewar is approximately 10 feet long and holds a w:liquid helium cooled w:niobium RF cavity structure, further shielded by a w:liquid nitrogen cooled outer jacket. Beyond this, another sky-blue dewar is visible. This second dewar consists of two twenty foot long superconducting accelerator sections which boost the electron beam energy to a few million electron volts. The tunnel housing the accelerator is 500 feet long and is buried four stories underground. On one occasion, a discharge of helium from the twenty-foot sections accumulated along the ceiling. This discharge was cold enough to liquefy the gas in the fluorescent ceiling lights, causing them to flicker purple and go out.