The FACET facility will involve relocation, refurbishment and upgrading of accelerator components at SLAC to provide beams at a new facility in Sector 20 of the SLAC linac. The goal of the FACET facility is to deliver high quality beams for plasma wakefield accelerator research. The facility will be located upstream of the injector for SLAC's Linac Coherent Light Source, as illustrated in the figure below. It will use the upstream two kilometers of the SLAC linac and a new experimental area at Sector 20 in the existing linac tunnel.

By installing a new focusing system at Sector 20, the SLAC linac electron beam can be focused and compressed in length to sizes appropriate for plasma wakefield accelerator research. Comparable power densities for positron beams will be provided with the addition of an upstream positron bunch compressor in Sector 10. A shielding wall at the end of Sector 20 will allow access to the upstream portion of the linac during LCLS operations.

The FACET facility features six main components:

 The SLAC Linac  Bunch Compression System
 
The SLAC Linac

The 40 year old SLAC linear accelerator is still the largest linac in the world and provides unique electron and positron beams for research. FACET uses the first two-thirds of the linac to accelerate electrons and positrons to an energy of 23 GeV.

 Bunch compression system

A three stage magnetic bunch compression system is used to deliver electron and/or positron bunches to the FACET IP that are 17µm (or 57 fsec) long. With 3 nC of charge per bunch this corresponds to a peak current of over 20 kiloAmps. The bunches are initially compressed as they transit from the damping ring to sector 2 of the main linac at an energy of 1.2GeV. From sector 2 to 10 the bunches are accelerated to a mean energy of 9GeV and compressed a second time in a magnetic chicane. The final kilometer of linac boosts the beam to a mean energy of 23GeV where the bunch is compressed a third and final time in the new Sector 20 chicane.