The LCLS-II project, supported by the US Department of Energy Basic Energy Sciences, will provide a major upgrade to the functionality of the existing Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Laboratory (SLAC), taking up 500 meters of the existing two-mile tunnel. A baseline design has been established, incorporating a 4 GeV superconducting accelerator and two undulators capable of delivering femtosecond-scale X-ray pulses at up to 1 MHz repetition rate for photon energies between 250 eV and 5 keV. These upgrades will also enable photon energies as high as 25 keV in the fundamental beam at 120 Hz repetition rate using the existing accelerator.
LCLS-II will add two new X-ray laser beams and provide room for additional new instruments, greatly increasing the number of experiments carried out there each year.
Tom Peterson, cryogenic engineer, gave an overview of the project, which involves Fermilab and Thomas Jefferson National Accelerator Facility (Jefferson Lab) (both CSA CSMs) in the design and fabrication of the cryomodules. The accelerator will consist of 35 ILC-style 1.3 Ghz cryomodules, each containing eight superconducting radio frequency (SRF) cavities. The design builds on work being done at DESY in Hamburg for the X-ray Free Electron Laser (XFEL). Peterson said that DESY is being very cooperative in sharing information on their project with Fermilab.
LCLS-II is now in the design phase. They are buying parts for the first prototypes and plan to begin first production of the cryomodules in 2016. The procurement is divided, with both Jefferson Lab and Fermilab each producing a prototype cryomodule, and finally 17 more being built by Jefferson Lab and 16 by Fermilab. The design is being led by Fermilab and they are taking advantage of Jefferson Lab’s experience in building the cryomodules for their recent 12 Gev upgrade as well as providing cryomodules for the Spallation Neutron Source at Oak Ridge National Laboratory (CSA CSM). Fermilab will also fabricate and test two 3.9 GHz cryomodules.
Other groups collaborating on the LCLS-II include Cornell and Argonne National Laboratory (ANL) (CSA CSM), working on studies, analyses and tests; Lawrence Berkeley National Laboratory (LBNL) providing the electron source; and ANL and LBNL working on the undulating magnets at the high energy end of the linac.
Peterson explained that Jefferson Lab is providing the cryogenic plant—the big cryogenic refrigerator—and Fermilab will provide the cryogenic distribution system. At Fermilab, Rich Stanek is the senior team leader on LCLS-II and Camille Ginsburg is deputy. John Galayda is the project director at SLAC and Marc Ross is the cryogenic systems manager there. Leadership at Jefferson Lab is in transition with the retirement of George Neil; Joe Preble is acting LCLS-II project senior team leader. Work on the cryogenic distribution system at Fermilab is being led by Arkadiy Klebaner in the Cryogenics Department. Working with industry to manufacture the distribution system are Alexander Martinez, Andrew Dalesandro and Jerry Makara. Leading the building of the cryomodule test facility are Benjamin Hansen and Michael White.During a visit with Tom Nicol, mechanical engineer and group leader, we toured the manufacturing area and got a look at SRF cavities, cryomodules under construction and other state-of-the art hardware.
The scientific advancements made possible by LCLS have brought worldwide attention. It creates X-ray pulses a billion times brighter than was previously available at synchrotrons, fired at 120 pulses per second, each lasting quadrillionths of a second (femtoseconds). In this time scale the motion of atoms can be seen and tracked. Scientists can study important proteins at room temperature, in some cases even while they are active.
LCLS has enabled scientists to uncover the 3-D molecular structure of an enzyme involved in transmitting African sleeping sickness, to study the action of a new type of painkiller, to see live snapshots during the water-splitting reaction in photosynthesis and to study microscopic components of air pollution at the nanoscale. LCLS has provided the first glimpse of the structure of supercooled water, which remains liquid well below its normal freezing temperature, and opened a new window into tiny quantum tornadoes which form in fast-spinning droplets of supercooled liquid helium. The unprecedented brightness of LCLS X-rays has enabled completely new areas of science and opened frontiers in imaging and in understating chemistry. LCLS can measure the ultrafast biochemical processes at the scale of atoms and molecules.
The new capabilities provided by LCLS-II’s increased repetition rate and energy range will allow scientists to study how light triggers chemical reactions in gases and physical changes in materials. The upgrade will also foster study of the high-resolution structure of matter under such extreme conditions as high pressures and high temperatures. Scientific advancements springing from this project could lead to new and more effective drugs, components for next-generation computers, new aircraft materials that are more damage-resistant and highly customized chemical reactions that produce clean and renewable energy sources.