SLAC National Accelerator Laboratory is home to the linear accelerator (linac), the longest modern building on Earth. At nearly 2 miles long, above ground, the building houses klystrons that generate powerful microwaves. Below ground, these waves accelerate electrons to nearly the speed of light.

Formerly Stanford Linear Accelerator Center, the lab's name was changed in 2008 as SLAC underwent a shift from a focus on particle physics to a broader, multi-program laboratory with research across a range of areas including X-ray science, chemistry, materials sciences, astrophysics and many others.

Today the accelerator is divided into three sections that generate high-energy electrons for three facilities:
1. The Linac Coherent Light Source (LCLS), where the electron beam generates some of the world’s brightest X-ray laser pulses. 
2. LCLS-II, an upgrade to LCLS that is now under construction. In this section the original copper accelerator is being replaced by a new superconducting niobium-based particle accelerator that will be cooled to almost absolute zero using liquid helium. 
3. FACET, where scientists test advanced acceleration technologies that could dramatically shrink particle accelerators. FACET closed to make way for LCLS-II construction and will reopen after an upgrade as FACET-II.

Tour Facilities