LCLS-II: A World-Class Discovery Machine

LCLS-II Overview

Responding to a call to build a revolutionary new X-ray laser, SLAC is developing an upgrade of its Linac Coherent Light Source (LCLS) that will be at the forefront of X-ray science.


Funded by the U.S. Department of Energy (DOE), the LCLS is the world’s first hard X-ray free-electron laser. Its strobe-like pulses are just a few millionths of a billionth of a second long, and a billion times brighter than previous X-ray sources. Scientists use LCLS to take crisp pictures of atomic motions, watch chemical reactions unfold, probe the properties of materials and explore fundamental processes in living things.

Its performance to date, over the first few years of operation, has already provided a breathtaking array of world-leading results, published in the most prestigious academic journals and has inspired other XFEL facilities to be commissioned around the world.

Taking the Next Step

LCLS-II Aerial

LCLS-II will build from the success of LCLS to ensure that the U.S. maintains a world-leading capability for advanced research in chemistry, materials, biology and energy.

LCLS-II will provide a major jump in capability – moving from 120 pulses per second to 1 million pulses per second. This will enable researchers to perform experiments in a wide range of fields that are now impossible. The unique capabilities of LCLS-II will yield a host of discoveries to advance technology, new energy solutions and our quality of life.

LCLS-II first-light is expected in the fall of 2020, followed by the LCLS-II early science program (see LCLS-II Instruments for projected commissioning schedules). The LCLS Cu-linac is expected to resume 120 Hz operation in early 2020.

Superconducting Technology

The new X-ray laser will work in parallel with the existing one. Both LCLS and LCLS-II will use electrons accelerated to nearly the speed of light to generate beams of extremely bright X-ray laser light. The electrons fly through a series of magnets, called an undulator, which forces them to travel a zigzag path and give off energy in the form of X-rays. But the way those electrons are accelerated will be quite different and give LCLS-II much different capabilities. At present, electrons are accelerated down a copper pipe that operates at room temperature and allows the generation of 120 X-ray laser pulses per second.

Cryoplant rendering

Image: Artist’s rendering of the planned cryoplant building that will house the refrigeration system for LCLS-II.

LCLS-II will add a superconducting accelerator, occupying one-third of SLAC’s original 2-mile-long linear accelerator tunnel, which will generate an almost continuous X-ray laser beam. In addition to the new accelerator, LCLS-II requires a number of other cutting-edge components, including a new electron source, a powerful cooling plant that produces refrigerant for the accelerator, and two new undulators to generate X-rays.

Read more in the SLAC press release, Major Upgrade Will Boost Power of World’s Brightest X-ray Laser.

Addressing Grand Challenges

The potential for truly transformational fundamental research aimed at understanding matter and energy at the electronic, atomic and molecular level was captured by the DOE's Office of Basic Energy Sciences in a set of five interrelated grand challenges for science and the imagination:


  1. How do we control material processes at the level of electrons?

  2. How do we design and perfect atom- and energy-efficient synthesis of revolutionary new forms of matter with tailored properties?

  3. How do remarkable properties of matter emerge from complex correlations of the atomic or electronic constituents and how can we control these properties?

  4. How can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living things?

  5. How do we characterize and control matter away—especially very far away—from equilibrium?

The breadth of science enabled by LCLS-II will be essential for advancing these original grand challenges, and will address many critical knowledge gaps at the frontiers of matter and energy. Their ultimate goal is to provide the foundations for new energy technologies and to support DOE missions in energy, environment and national security.

The scientific community has identified six areas among the research topics where the unique capabilities of LCLS-II will be essential for further scientific progress.