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| # SLAC National Accelerator Laboratory
Aerial view of the former linear accelerator at SLAC National Accelerator Laboratory
**SLAC National Accelerator Laboratory**, originally named the **Stanford Linear Accelerator Center**, is a federally funded research and development center in [Menlo Park, California](/Menlo_Park,_California), United States. Founded in 1962, the laboratory is now sponsored by the [United States Department of Energy](/United_States_Department_of_Energy) and administered by [Stanford University](/Stanford_University). It is the site of the **Stanford Linear Accelerator**, a 3.2 km (2 mi) linear accelerator constructed in 1966 that could accelerate electrons to energies of 50 GeV.
Today, SLAC's research spans a broad program in [atomic](/Atomic_physics) and [solid-state physics](/Solid-state_physics), [chemistry](/Chemistry), [biology](/Biology), and [medicine](/Medicine) using X-rays from [synchrotron radiation](/Synchrotron_radiation) and a [free-electron laser](/Free-electron_laser), as well as experimental and theoretical research in [elementary particle physics](/Elementary_particle), [accelerator physics](/Accelerator_physics), [astroparticle physics](/Astroparticle_physics), and [cosmology](/Cosmology). The laboratory operates under the programmatic direction of the United States Department of Energy Office of Science.
## History
The entrance to SLAC in [Menlo Park, California](/Menlo_Park,_California)
Founded in 1962 as the **Stanford Linear Accelerator Center**, the facility is located on 172 hectares (426 acres) of [Stanford University](/Stanford_University)-owned land on [Sand Hill Road](/Sand_Hill_Road) in Menlo Park, California, just west of the university's main campus. The main accelerator is 3.2 km (2 mi) long, making it the longest linear accelerator in the world, and has been operational since 1966.
Research at SLAC has produced three [Nobel Prizes in Physics](/Nobel_Prize_in_Physics):
- **1976**: The discovery of the [charm quark](/Charm_quark) through the observation of the [J/ψ meson](/J/psi_meson).
- **1990**: The confirmation of the [quark](/Quark) structure inside [protons](/Proton) and [neutrons](/Neutron).
- **1995**: The discovery of the [tau lepton](/Tau_lepton).
In 1984, the laboratory was designated an [ASME National Historic Engineering Landmark](/List_of_Historic_Mechanical_Engineering_Landmarks) and an [IEEE Milestone](/List_of_IEEE_milestones).
SLAC developed and, in December 1991, began hosting the first [World Wide Web](/World_Wide_Web) server outside of Europe.
In the early-to-mid 1990s, the **Stanford Linear Collider (SLC)** investigated the properties of the [Z boson](/Z_boson) using the Stanford Large Detector.
By 2005, SLAC employed over 1,000 people, including approximately 150 physicists with doctorate degrees, and served over 3,000 visiting researchers annually. The laboratory operated particle accelerators for high-energy physics and the [Stanford Synchrotron Radiation Laboratory (SSRL)](/Stanford_Synchrotron_Radiation_Laboratory) for synchrotron light radiation research, which was instrumental in the research leading to the 2006 [Nobel Prize in Chemistry](/Nobel_Prize_in_Chemistry) awarded to Stanford Professor [Roger D. Kornberg](/Roger_D._Kornberg).
In October 2008, the Department of Energy announced that the center's name would be changed to **SLAC National Accelerator Laboratory**. The reasons cited included better representation of the new direction of the lab and the ability to trademark the laboratory's name, as Stanford University had legally opposed the Department of Energy's attempt to trademark "Stanford Linear Accelerator Center".
In March 2009, SLAC received $68.3 million in Recovery Act Funding to be disbursed by the Department of Energy's Office of Science.
In October 2016, **Bits and Watts** launched as a collaboration between SLAC and Stanford University to design "better, greener electric grids". SLAC later withdrew from the project over concerns about an industry partner, the state-owned Chinese electric utility.
In April 2024, SLAC completed two decades of work constructing the world's largest digital camera for the **Legacy Survey of Space and Time (LSST)** project at the [Vera C. Rubin Observatory](/Vera_C._Rubin_Observatory) in Chile. The camera became operational in 2025.
## Components
### Accelerator
The main accelerator was an [RF linear accelerator](/Linear_particle_accelerator) that accelerated [electrons](/Electron) and [positrons](/Positron) up to 50 GeV. At 3.2 km (2 mi) long, the accelerator was the longest linear accelerator in the world until 2017 when the [European X-ray Free Electron Laser](/European_x-ray_free_electron_laser) opened. The main accelerator is buried 9 m (30 ft) below ground and passes underneath [Interstate Highway 280](/Interstate_280_(California)). The above-ground [klystron](/Klystron) gallery atop the beamline was the longest building in the United States until the [LIGO](/LIGO) project's twin interferometers were completed in 1999. It is easily distinguishable from the air and is marked as a visual waypoint on aeronautical charts.
A portion of the original linear accelerator is now part of the **Linac Coherent Light Source (LCLS)**.
### Stanford Linear Collider
The **Stanford Linear Collider (SLC)** was a linear accelerator that collided electrons and positrons at SLAC. The center-of-mass energy was about 90 GeV, equal to the mass of the [Z boson](/W_and_Z_bosons), which the accelerator was designed to study. Graduate student Barrett D. Milliken discovered the first Z event on April 12, 1989, while analyzing data from the Mark II detector. The bulk of the data was collected by the **SLAC Large Detector (SLD)**, which came online in 1991. Although largely overshadowed by the [Large Electron–Positron Collider (LEP)](/Large_Electron%E2%80%93Positron_Collider) at [CERN](/CERN), which began running in 1989, the highly polarized electron beam at SLC (close to 80%) made certain unique measurements possible, such as parity violation in Z boson-b quark coupling.
### SLAC Large Detector
The **SLAC Large Detector (SLD)** was the main detector for the Stanford Linear Collider. It was designed primarily to detect Z bosons produced by the accelerator's electron-positron collisions. Built in 1991, the SLD operated from 1992 to 1998.
### PEP and PEP-II
**PEP (Positron-Electron Project)** began operation in 1980, with center-of-mass energies up to 29 GeV. At its peak, PEP had five large particle detectors in operation, as well as a sixth smaller detector. About 300 researchers utilized PEP. PEP stopped operating in 1990, and **PEP-II** began construction in 1994.
From 1999 to 2008, the main purpose of the linear accelerator was to inject electrons and positrons into the **PEP-II** accelerator, an electron-positron collider with a pair of storage rings 2.2 km (1.4 mi) in circumference. PEP-II was host to the [BaBar experiment](/BaBar_experiment), one of the so-called [B-Factory](/B-Factory) experiments studying [charge-parity symmetry (CP symmetry)](/CP-symmetry).
### Stanford Synchrotron Radiation Lightsource
The **Stanford Synchrotron Radiation Lightsource (SSRL)** is a synchrotron light user facility located on the SLAC campus. Originally built for particle physics, it was used in experiments where the [J/ψ meson](/J/psi_meson) was discovered. It is now used exclusively for materials science and biology experiments that take advantage of the high-intensity synchrotron radiation emitted by the stored electron beam to study the structure of molecules. In the early 1990s, an independent electron injector was built for this storage ring, allowing it to operate independently of the main linear accelerator.
### Fermi Gamma-ray Space Telescope
SLAC plays a primary role in the mission and operation of the **Fermi Gamma-ray Space Telescope**, launched in August 2008. The principal scientific objectives of this mission are:
- To understand the mechanisms of particle acceleration in [active galactic nuclei (AGNs)](/Active_galactic_nucleus), pulsars, and [supernova remnants (SNRs)](/Supernova_remnant).
- To resolve the gamma-ray sky: unidentified sources and diffuse emission.
- To determine the high-energy behavior of gamma-ray bursts and transients.
- To probe dark matter and fundamental physics.
### Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)
The **Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)** is partially housed on the grounds of SLAC, in addition to its presence on the main Stanford campus.
### Stanford PULSE Institute
The **Stanford PULSE Institute (PULSE)** is a Stanford Independent Laboratory located in the Central Laboratory at SLAC. PULSE was created by Stanford in 2005 to help Stanford faculty and SLAC scientists develop ultrafast X-ray research at the **Linac Coherent Light Source (LCLS)**.
### Linac Coherent Light Source (LCLS)
The **Linac Coherent Light Source (LCLS)** is a free electron laser facility located at SLAC. The LCLS is partially a reconstruction of the last 1/3 of the original linear accelerator at SLAC and can deliver extremely intense X-ray radiation for research in a number of areas. It achieved first lasing in April 2009.
The laser produces hard X-rays, 10^9 times the relative brightness of traditional synchrotron sources, and is the most powerful X-ray source in the world. LCLS enables a variety of new experiments and provides enhancements for existing experimental methods. Often, X-rays are used to take "snapshots" of objects at the atomic level before obliterating samples. The laser's wavelength, ranging from 6.2 to 0.13 nm (200 to 9500 electron volts (eV)), is similar to the width of an atom, providing extremely detailed information that was previously unattainable. Additionally, the laser is capable of capturing images with a "shutter speed" measured in femtoseconds, or million-billionths of a second, necessary because the intensity of the beam is often high enough so that the sample explodes on the femtosecond timescale.
### LCLS-II
The **LCLS-II** project aims to provide a major upgrade to LCLS by adding two new X-ray laser beams. The new system will utilize the 500 m (1,600 ft) of existing tunnel to add a new superconducting accelerator at 4 GeV and two new sets of undulators that will increase the available energy range of LCLS. The advancements from the discoveries using this new capability may include new drugs, next-generation computers, and new materials.
### Facility for Advanced Accelerator Experimental Tests (FACET)
In 2012, the first two-thirds (~2 km) of the original SLAC LINAC were recommissioned for a new user facility, the **Facility for Advanced Accelerator Experimental Tests (FACET)**. This facility was capable of delivering 20 GeV, 3 nC electron (and positron) beams with short bunch lengths and small spot sizes, ideal for beam-driven [plasma acceleration](/Plasma_acceleration) studies. The facility ended operations in 2016 for the construction of LCLS-II, which will occupy the first third of the SLAC LINAC. The **FACET-II** project will re-establish electron and positron beams in the middle third of the LINAC for the continuation of beam-driven plasma acceleration studies in 2019.
### Next Linear Collider Test Accelerator (NLCTA)
The **Next Linear Collider Test Accelerator (NLCTA)** is a 60–120 MeV high-brightness electron beam linear accelerator used for experiments on advanced beam manipulation and acceleration techniques. It is located at SLAC's end station B.
### Theoretical Physics
SLAC also performs theoretical research in elementary particle physics, including in areas of [quantum field theory](/Quantum_field_theory), collider physics, [astroparticle physics](/Astroparticle_physics), and particle phenomenology.
## Other Discoveries
- SLAC has been instrumental in the development of the [klystron](/Klystron), a high-power [microwave](/Microwave) amplification tube.
- There is active research on [plasma acceleration](/Plasma_acceleration) with recent successes such as the doubling of the energy of 42 GeV electrons in a meter-scale accelerator.
- A [Paleoparadoxia](/Paleoparadoxia) fossil was found at the SLAC site, and its skeleton can be seen at a small museum in the breezeway.
- The SSRL facility was used to reveal hidden text in the [Archimedes Palimpsest](/Archimedes_Palimpsest). X-rays from the synchrotron radiation light source caused the iron in the original ink to glow, allowing the researchers to photograph the original document that a Christian monk had scrubbed off.
## Directors
The following persons have served as director of SLAC:
| No. | Image | Director | Term Start | Term End | Refs. |
|-----|-------|----------|------------|----------|-------|
| 1 | | [Wolfgang Panofsky](/Wolfgang_Panofsky) | 1961 | 1984 | |
| 2 | | [Burton Richter](/Burton_Richter) | 1984 | August 31, 1999 | |
| 3 | | [Jonathan Dorfan](/Jonathan_Dorfan) | September 1, 1999 | December 12, 2007 | |
| - | | [Persis Drell](/Persis_Drell) (acting) | September 9, 2007 | December 12, 2007 | |
| 4 | | [Persis Drell](/Persis_Drell) | December 12, 2007 | October 31, 2012 | |
| 5 | | Chi-Chang Kao | November 1, 2012 | February 3, 2023 | |
| - | | [Stephen Streiffer](/Stephen_Streiffer) (interim) | February 4, 2023 | October 1, 2023 | |
| 6 | | [John Sarrao](/John_Sarrao) | October 2, 2023 | present | |
## See Also
- [San Francisco Bay Area portal](/Portal:San_Francisco_Bay_Area)
- [Cyclotron](/Cyclotron) – Type of particle accelerator
- [Dipole magnet](/Dipole_magnet) – Simplest type of magnet
- [Electromagnetism](/Electromagnetism) – Fundamental interaction between charged particles
- [List of particles](/List_of_particles)
- [List of United States college laboratories conducting basic defense research](/List_of_United_States_college_laboratories_conducting_basic_defense_research)
- [Particle beam](/Particle_beam) – Stream of charged, or less frequently neutral particles
- [Quadrupole magnet](/Quadrupole_magnet) – Group of four magnets
- [Spallation Neutron Source](/Spallation_Neutron_Source) – Accelerator-based neutron source in Oak Ridge, Tennessee, US
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