The Matter in Extreme Conditions Instrument at LCLS

The Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS) has significantly advanced laser-shock compression research. By leveraging ultrafast, high-brightness x-ray pulses, x-ray diffraction enables the precise characterization of materials under high-pressure conditions with unparalleled temporal and spatial resolution.

A key feature of the MEC instrument is its standard configuration for x-ray diffraction. It combines two optical laser beams with a total energy of 100 J in 3–35 ns, generating pressures as high as ~300 GPa. The LCLS beam delivers ~50 fs x-ray pulses with tunable photon energies ranging from ~6 to 25 keV. Diffraction data are collected using four ePix10k detectors arranged around the interaction point. These detectors provide a high dynamic range and low noise, making them ideal for capturing diffraction patterns from materials undergoing dynamic compression. Their strategic placement ensures comprehensive angular coverage, facilitating detailed structural analysis of materials under high-pressure conditions.

In addition to the ePix10k detectors, MEC has recently commissioned new detectors with large-area sensors (VAREX XRD 4343CT). These scintillator-based detectors feature a sensitive area of 43 × 43 cm and a pixel pitch of 150 µm. Operating at a rate of 10 Hz, they are positioned around the interaction point, offering an angular coverage of approximately 2θ ~ [10°–85°] and φ ~ [-70°–250°], with an azimuthal gap of about 30°–60° between the two detectors. These detectors have been tested at photon energies of 17 keV and above.

The integration of these advanced detectors with MEC's long-pulse laser system provides the laser-shock compression community with a powerful platform for investigating the behavior of materials under extreme conditions. The combination of the high temporal resolution of LCLS x-ray pulses and the extensive detection capabilities of the ePix10k detectors enables detailed studies of phase transitions, structural dynamics, and other critical phenomena essential to understanding material properties at high pressures and temperatures.