MEC Optical Laser Image
Researchers work in the “MEC hutch” of SLAC’s LCLS Far Experiment Hall. The MEC optical laser system creates extreme temperatures and pressures in materials and the LCLS X-ray laser beam captures the material’s response. (Image by Matt Beardsley/SLAC)

Lawrence Livermore National Laboratory’s expertise in developing high-energy lasers is being tapped to provide a key component of a major upgrade to SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS). Over the next several years, LLNL’s Advanced Photon Technologies (APT) program will design and construct one of the world’s most powerful petawatt (quadrillion-watt) laser systems for installation in an upgraded Matter in Extreme Conditions (MEC) experimental facility at LCLS, funded by the Department of Energy’s Office of Science-Fusion Energy Sciences program.

The new laser will pair with the LCLS X-ray free-electron laser (XFEL) to advance the understanding of high-energy density (HED) physics, plasma physics, fusion energy, laser-plasma interactions, astrophysics, planetary science and other physical phenomena.

The existing MEC facility uses optical lasers coupled to X-ray laser pulses from LCLS to probe the characteristics of matter at extreme temperatures and pressures. MEC experiments have produced groundbreaking science, such as the first observations of “diamond rain” under conditions thought to exist deep inside giant icy planets like Uranus and Neptune.

The MEC-Upgrade (MEC-U) is motivated in part by increasing calls for the United States to re-establish world-class leadership in high-power laser technology. SLAC is partnering with LLNL and the University of Rochester’s Laboratory for Laser Energetics (LLE) to design and construct the MEC-U facility in a new underground cavern. LLNL’s rep-rated laser (RRL), able to fire at up to 10 Hz (10 pulses per second), and a high-energy kilojoule laser developed by LLE will feed into two new experimental areas containing a target chamber and a suite of dedicated diagnostics tailored for HED science.

The LCLS, part of SLAC’s two-mile-long linear particle accelerator in Menlo Park, Calif., is capable of delivering 120 X-ray pulses a second, each one lasting a few femtoseconds (quadrillionths of a second). A concurrent upgrade, dubbed LCLS-II, will deliver a million pulses a second in an almost continuous X-ray beam that, on average, will be 10,000 times brighter and will double the X-ray energy previously attainable.

“Marrying the latest and the best ultrafast laser technologies with the LCLS beamline at the MEC-U facility will give the United States a fundamentally new high-throughput HED capability for discovery science and national security research,” said Vincent Tang, NIF & Photon Science program director for High Energy Density and Photon Systems. “We will be able to rapidly increase our understanding of plasmas and materials at extreme pressures and temperatures, while advancing our ability to operate HED technologies and systems at a repetition rate and scale relevant to important future applications like inertial fusion energy.”

The National Nuclear Security Administration (NNSA) has also expressed interest in developing a high-energy long-pulse laser that could team with LCLS to support NNSA’s core mission areas. Among the goals would be to improve scientists’ ability to predict the performance of next-generation materials in extreme environments, understand how material aging affects material properties, and study the microphysics of inertial confinement fusion.

Tom Spinka, project manager and chief scientist for LLNL’s RRL, said that it will be a simplified and more energetic version of the High-Repetition-Rate Advanced Petawatt Laser System (HAPLS), designed and developed by the APT Program from 2014 to 2018. HAPLS, the world’s first all-diode-pumped petawatt laser, is now a key component of the European Union’s Extreme Light Infrastructure Beamlines facility in the Czech Republic.

“The RRL will build on the groundbreaking work that was done on HAPLS,” Spinka said. “It will pair the direct chirped-pulse amplification technique used in NIF’s flashlamp-pumped neodymium-doped glass Advanced Radiographic Capability with the HAPLS diode-pumped glass pump laser technology in a refined architecture developed through LLNL’s Laboratory Directed Research and Development program. This architecture, originally dubbed the Scalable High-power Advanced Radiographic Capability, or SHARC, eliminates the lossy second (titanium-doped sapphire) stage of the HAPLS laser system, ultimately delivering about five times higher energy than HAPLS at the same peak power and repetition rate.”

LLNL’s RRL for the MEC-U facility will be developed in parallel with performance ramping of the HAPLS (now known as L3-HAPLS) laser at ELI-Beamlines to its full design specifications. It also will leverage additional advanced laser technologies being developed by APT, including a new high-energy Faraday rotator developed under a Cooperative Research and Development Agreement with Electro-Optics Technologies Inc.

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