Facility for Advanced Accelerator Experimental Tests-II (FACET-II)

The working space for experiments at FACET.

FACET-II is an accelerator-based user facility where experiments in beam-driven plasma wakefield particle acceleration are carried out. 
Menlo Park, California Location
2012 Start of Operations
120 (FY 2022) Number of Users


The Facility for Advanced Accelerator Experimental Tests-II (FACET-II) at SLAC National Accelerator Laboratory uses part of SLAC’s two-mile-long linear accelerator to generate high-density beams of electrons that help researchers design smaller, more powerful particle accelerators. The upgraded FACET-II facility builds upon years of valuable research from FACET, which operated from 2012 to 2016. With a state-of-the-art photoinjector, additional bunch compressor chicanes, and upgraded experimental area, FACET-II provides new capabilities for the development of advanced technologies for future accelerators. FACET-II provides electron beams optimized for the next generation of plasma wakefield accelerator experiments and is the only facility in the world capable of providing 10 GeV electron beams in support of accelerator science R&D.


A diverse set of research programs is enabled by the high-energy high-intensity electron beams and their interaction with lasers, plasmas, and solids. Primary elements of this program include demonstration of a 10 GeV plasma accelerator stage with preserved beam quality, development of ultra-high brightness beams from plasma-based injectors, developing high-intensity X-ray and Gamma-ray sources, and understanding strong-field QED phenomena. Novel diagnostics to characterize the extreme beams are being developed combining beam-physics, machine learning, and artificial intelligence. Future upgrades to deliver 10 GeV high intensity positron beams and upgrades to the 10 TW experimental laser systems are under development to exploit the full scientific potential of the facility.

Plasma Wakefield Acceleration

Electrons can “surf” on waves of plasma – a hot, ionized gas of charged particles thereby gaining very high energies in very short distances. This approach, called plasma wakefield acceleration, has the potential to dramatically shrink the size and cost of particle accelerators. Research at SLAC has demonstrated that a plasma can accelerate electrons to 1,000 times greater energies over a given distance than current technologies can manage.

Dielectric Wakefield Acceleration

When two well-spaced bunches of particles pass through a dielectric material, such as silica or diamond, their interaction with the material causes the first bunch to lose energy and the second to gain energy. FACET-II is the only facility that provides the high peak fields needed to test the highest possible acceleration with this technology.

Understanding the Universe

To learn more about the universe, we need to observe the behavior of both the smallest parts of nature and the largest phenomena in outer space. Researchers at FACET-II study the behavior of plasma processes expected to play a role in generating bright gamma ray bursts – the strongest and brightest explosions known to exist in outer space. The peak density and intensity of the facility’s electron beams allows researchers to study astrophysical phenomena in the lab and compare to observations and models of deep outer space.

Machine Learning and Artificial Intelligence

At FACET-II, the beams are so intense that they vaporize some traditional diagnostics so researchers are developing unique machine learning and artificial intelligence based techniques to measure the size, shape, and other characteristics of the facility’s electron beam. Importantly, machine learning and artificial intelligence techniques are non-invasive, meaning the facility’s beam can be studied without altering or intercepting it, thereby improving the quality and quantity of experiments. As these techniques are refined, they will be augmented to feedback on the accelerator to optimize the beam properties for a wide variety of User programs.

Reaching high energies

Going forward, FACET-II will try to create high-density beams of positrons, which are the antimatter particles of electrons. Physicists collide high-energy beams of electrons and positrons to probe the fundamental particles and forces that make up the universe. Positron beams behave differently in a plasma than electrons however and will require new approaches to optimize the plasma acceleration process. Much of the infrastructure to create positrons already exists at SLAC and a plan is being developed to restore this unique capability for our user community.