LCLS-II

LCLS-II is a major upgrade to the original Linac Coherent Light Source at the SLAC National Accelerator Laboratory, transforming it into a world-leading, high-repetition-rate X-ray free-electron laser. This superconducting accelerator enables scientists to conduct experiments at unprecedented speeds and resolutions, capturing the behavior of atoms and molecules in extreme detail. The facility represents a cornerstone of the United States Department of Energy's portfolio for materials science, chemistry, and biology.

Overview

LCLS-II is designed to produce X-ray pulses up to a million times per second, a dramatic increase from its predecessor, which operated at 120 pulses per second. This leap in capability is enabled by a state-of-the-art superconducting radio-frequency accelerator, a technology also used in facilities like the European XFEL and the planned SHINE (accelerator). The project is a collaborative effort involving SLAC National Accelerator Laboratory, the DOE Office of Science, and numerous international partners, including contributions from Fermilab and Thomas Jefferson National Accelerator Facility. Its primary mission is to probe matter at the atomic scale with extraordinary temporal resolution, opening new frontiers in understanding fundamental processes.

Technical specifications

The heart of the facility is a continuous-wave superconducting linear accelerator capable of accelerating electrons to energies of up to 4 GeV. This linac is cooled by a powerful cryogenic plant operating at 2 Kelvin, a temperature colder than outer space, to maintain superconductivity. The accelerated electron beam is then sent through a series of undulator magnets, where it generates coherent, ultra-bright X-rays via the SASE (physics) process. The machine can tune the photon energy of these pulses from the soft X-ray to the hard X-ray regime, specifically from 250 eV to 5,000 eV, with peak brightness exceeding 10³⁴ photons per second per square millimeter.

Scientific capabilities

The high repetition rate allows for the collection of statistically significant data in minutes rather than days, enabling new classes of experiments. Key capabilities include performing ultrafast spectroscopy to track electron dynamics in chemical reactions and studying the structure of fragile biomolecules, like proteins and viruses, before they are damaged by the intense beam. It can also create and probe exotic states of matter, such as warm dense matter, relevant to understanding planetary interiors. These tools are critical for research in quantum materials, catalysis, and the dynamics of complex systems studied at institutions like the Max Planck Institute.

Development and construction

The project was formally initiated in 2013, with major construction beginning in 2015 following the completion of the original Linac Coherent Light Source. A significant milestone was the successful installation and commissioning of the superconducting accelerator cryomodules, a feat achieved through collaboration with Fermilab and expertise from the International Linear Collider community. The construction involved major upgrades to the existing SLAC infrastructure, including a new cryoplant and a second undulator hall. The first electron beam was achieved in 2022, marking the transition to commissioning and early experiments.

Research and applications

Research at the facility spans multiple disciplines, with experiments conducted by teams from universities, national laboratories, and industry worldwide. In chemistry, it is used to film the making and breaking of chemical bonds. In biology, it aids in determining the structures of complex biomolecules to inform drug discovery for diseases like COVID-19. For energy research, it probes the atomic-scale processes in next-generation batteries and solar cells. The data generated also feeds into large-scale computational studies, leveraging resources from the National Energy Research Scientific Computing Center and informing projects at the Advanced Photon Source and the Spallation Neutron Source.

Category:SLAC National Accelerator Laboratory Category:Linear particle accelerators Category:Synchrotron radiation facilities Category:Research facilities in California