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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Demonstration of a diamond anvil cell platform at the Linac Coherent Light Source: capabilities and outlook

A novel X-ray free electron laser (XFEL) diffraction setup for use with diamond anvil cells (DACs) at the Linac Coherent Light Source (LCLS) is described. The new diamond window at the Matter at Extreme Conditions (MEC) instrument allows hard X-ray experiments on DACs to be performed in air. The platform is described along with alignment and calibration procedures, and details of the X-ray beam and diagnostics. Example data are presented, including a reversible XFEL-induced phase transition in CsPbI 3 . The DAC setup was commissioned at MEC, but is applicable to most LCLS instruments where the unique pulse structures available at LCLS offer access to new ultrafast experimental techniques at high pressure.

Linac Coherent Light Source (LCLS)↗
DOE OSTI2024

Improving equations of state calibrations in the toroidal DAC—The case study of molybdenum

We report an updated isothermal equation of state (EoS) of molybdenum (Mo) obtained by compression in beveled and toroidal diamond-anvil cells (DACs). For an improved compression environment, we developed a copper (Cu) pressure-transmitting medium (PTM) for the toroidal diamond-anvil cell samples, as it is a soft metal compared to Mo with a well calibrated EoS. A Ne PTM was used for the conventional beveled DAC samples. The unit-cell volumes of Mo were measured to 336(1) GPa in the Cu PTM and 231.2(6) GPa in the Ne PTM at room temperature. We additionally calculated elastic stiffness and compliance constants and evaluated the uniaxial stress of Mo and Cu with pressure. A new EoS for Mo is presented from data collected in all sample environments and compared to our theoretical predictions as well as previous compression studies of Mo. The (200) lattice plane of Mo produced the lowest volumes across the pressure range of this study for all compression environments, suggesting that it is less affected by nonhydrostatic stresses in the DAC compared to the other observed diffraction planes. The presented Mo EoS is compatible with extrapolations of EoS fits of Mo in helium (He) within ~1% at 330 GPa. Results from this work demonstrate that compressing a sample in a softer metal in the toroidal DAC can improve the compression environment and result in measured sample volumes comparable to those collected in noble-gas media at multi-megabar conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2026

Demonstration of a diamond anvil cell platform at the Linac Coherent Light Source: Capabilities and Outlook

A novel x-ray free electron laser (XFEL) diffraction setup for use with diamond anvil cells (DACs) at the Linac Coherent Light Source (LCLS) is described. Using the new diamond window at the Matter at Extreme Conditions (MEC) instrument, it allows hard x-ray experiments on DACs to be performed in air. The platform is described along with alignment and calibration procedures and details of the x-ray beam and diagnostics. Example data are presented, including a reversible XFEL induced phase transition in CsPbI3. The DAC setup was commissioned at MEC, but is applicable to most LCLS instruments where the unique pulse structures available at LCLS offer access to new ultrafast experimental techniques at high pressure.

Diamond Anvil Cells, LCLS, XFEL, High-Pressure↗
DOE OSTI2024

A miniature multi-anvil apparatus using diamond as anvils—MDAC: Multi-axis diamond anvil cell

The diamond anvil cell (DAC) has been widely used in high-pressure research. Despite significant progress over the past five decades, the opposed anvil geometry in the DAC inevitably leads to a disk-shaped sample configuration at high pressure. This intrinsic limitation is largely responsible for the large pressure and temperature gradients in the DAC, which often compromise precise experiments and their characterizations. Here, we designed and fabricated a multi-axis diamond anvil cell (MDAC) by adopting the concept of a multi-anvil apparatus but using single crystal diamonds as the anvil material. Preliminary data show that the MDAC can generate extreme pressure conditions above 100 GPa. The advantages of the MDAC over a traditional opposed anvil DAC include thicker, voluminous samples, quasi-hydrostatic, or designed deviatoric stress conditions, and multidirectional access windows for optical applications and x-ray probes. In this article, we present the design and performance of a prototype MDAC, as well as the application prospects in high-pressure research.

47 OTHER INSTRUMENTATION↗
DOE OSTI2026

The MuFusE large-volume diamond anvil cell for exploring muon-catalyzed fusion at higher pressures and temperatures

A new large-volume diamond anvil cell (DAC) has been developed for the Muon-catalyzed Fusion (μCF) Experiment (MuFusE), enabling the compression and heating of deuterium–tritium (d–t) mixtures to pressures and temperatures needed to advance μCF research. The MuFusE DAC achieves the large sample volumes necessary for high-precision fusion measurements while integrating cryogenic loading, all-metal sealing, and flexible bellows to maintain a secure environment during cell compression. Combined with remote pneumatic actuation and secondary containment, the DAC safely managed a 25 Ci tritium inventory while providing a clear optical path for in situ measurements of sample pressure and composition via laser spectroscopy. Utilizing 5 mm diameter diamond anvils oriented in the path of a high-intensity muon beam, the apparatus achieved a stable sample volume of 19.2 mm 3 at liquid density, pressures up to 933 MPa and temperatures up to 400 K—benchmarks that significantly exceed previously reported limits for static d–t targets.

Kalow, J. D. [Acceleron Fusion, Inc., Cambridge, M↗
DOE OSTI2025

Raman scattering of rhenium for secondary pressure calibration

With the increasing number of 100 s GPa experiments in the diamond anvil cell (DAC), improved accuracy in secondary pressure calibrations to extreme pressures is essential. The rhenium equation of state has been proposed as a pressure calibrant via x-ray diffraction with potentially broad applications as it is commonly used as a gasket material in DAC experiments. In this work, we conducted Raman spectroscopy experiments on rhenium in the DAC and report the pressure shift of the E2g mode, a refined high-pressure C44 and mode-Grüneisen parameter above 200 GPa. We used flat, beveled, and toroidal diamond anvils under quasi-hydrostatic and non-hydrostatic conditions. By measuring the E2g mode from the culet edge to the center, we analyzed pressure distribution based on culet type and distance from the anvil center. The shift in the E2g mode can be expressed as a function of pressure, and diamond edge measurements appear reliable across all anvil types. Comparing the center and edge pressures reveals anvil cupping, offering insights into predicting or preventing anvil failure during materials properties measurements at extreme conditions.

Diamond anvil cells↗
DOE OSTI2024

Magnetometry in a diamond anvil cell using nitrogen vacancy centers in a nanodiamond ensemble

The emerging field of optical magnetometry utilizing negative-charged nitrogen vacancy (NV – ) centers provides a highly sensitive lab bench technique for spatially resolved physical property measurements. Their implementation in high pressure diamond anvil cell (DAC) environments will become common as other techniques are often limited due to the spatial constraints of the sample chamber. Apparatus and techniques are described here permitting for more general use of magnetic field measurements inside a DAC using continuous wave optical detected magnetic resonance in NV – centers in a layer of nanodiamonds. A microstrip antenna delivers a uniform microwave field to the DAC and is compatible with simple metal gaskets, and the sensor layer of deposited nanodiamonds allows for simple determination of the magnetic field magnitude for B in the 1–100 G range. The ferromagnetic transition in iron at 18 GPa is measured with the apparatus, along with its hysteretic response.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Anomalous lattice expansion of bcc Ta in helium-loaded diamond anvil cells

Anomalous lattice expansion of bcc Ta is observed in helium-loaded diamond anvil cell (DAC) experiments near 6 GPa and above 400 K, while co-loaded W, Mo, and Au exhibit normal thermal expansion. The Ta volume expansion increases with temperature, reaching ~14% near 650 K before plateauing, and is largely retained after recovery to ambient conditions. Time-resolved measurements at 500 K reveal progressive expansion over several hours, consistent with gradual, thermally activated He incorporation. The largely retained expansion during subsequent cooling and holding at 400 K indicates that the incorporated He is predominantly kinetically trapped. The data reveal two distinct regimes: below ~550 K, modest and spatially uniform expansion consistent with interstitial He trapping at isolated, randomly distributed vacancies; above ~550 K, He-vacancy cluster growth producing dramatically larger expansion, peak broadening, and a core–shell microstructure revealed by micron-resolution X-ray diffraction mapping. These results demonstrate that He is not always a passive pressure medium in DAC experiments and reveal a previously unrecognized regime of He-mediated lattice modification in Ta, complementing conventional ion-implantation studies relevant to nuclear and fusion structural materials.

Diamond anvil cell↗
DOE OSTI2025

Investigation of warm dense matter by combining static and dynamic compression

Shock-compressing material samples that are precompressed with diamond-anvil cells (DACs) enables benchmarking equation of state measurements over a wide range of high-pressure conditions, in particular, warm dense matter relevant to planetary science, astrophysics, and inertial confinement fusion. These targets provide optical access to the shocked sample, so optical velocity interferometry and pyrometry are typical diagnostics. We present a scaling for the coupling of the laser drive to the shock pressure in DACs based on over 150 prior experiments that can be used to design future experiments. For initial static pressures ≤ 5 GPa, using a sapphire window mitigates the effect of photoionization compared to diamond windows and allows the measurement of shock pressures up to 1 TPa with optical diagnostics.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Experimental and theoretical investigation into the high pressure deflagration products of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105)

Diamond anvil cell (DAC) laser ignition experiments and reactive ab initio molecular dynamics (AIMD) simulations were performed on the high explosive (HE) LLM-105 to investigate its high pressure (HP) deflagration chemistry. Raman and optical spectroscopy measurements reveal LLM-105 reacts into an opaque carbonaceous product at 4–25 GPa. At pressures >~ 27 GPa, the reaction product consists of an amorphous optically transparent solid and nitrogen (N 2 ) in the solid phase. While not a one-to-one comparison due to the small time and length scales, the HP AIMD simulations show that some of the product is molecular N 2 , in qualitative agreement with experiment, while above 20 GPa most of the product consists of large amorphous C x H y N z O k clusters. Clustering is enhanced with pressure and reduces with temperature. In the experiments with initial sample pressure >~ 25 GPa, the pressure within the DAC decreases with minimal change in DAC cavity area. At initial sample pressures of 43.9 GPa, when quenched to 0 K, simulations predict a product experiencing a lower pressure consistent with the experimental measurement at lower load pressures. In conclusion, the results are important for understanding the HP deflagration chemistry of LLM-105.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Design and Commissioning of a Deuterium-Tritium Gas Delivery System for Muon Catalyzed Fusion in a Diamond Anvil Cell

We report the design, commissioning, and operation of deuterium-deuterium (DD) and deuterium-tritium (DT) gas delivery systems developed to load a diamond anvil cell (DAC) beam target for muon-catalyzed fusion (muCF). The DAC approach enables DT fuel to be compressed to GPa pressures at more than twice the liquid density and heated from cryogenic temperatures through 500 K, opening access to a substantially expanded parameter range for muCF kinetics and yield measurements. In this approach, DT is cryo-condensed to a liquid in a minichamber and then compressed in the DAC using a helium-driven pneumatic membrane, achieving high pressures in a millimeter-scale DT sample volume. A DD gas delivery system was designed and used to validate the experimental apparatus, measure the gas quantities needed for filling, develop operational experience, and collect kinetics and yield data with DD targets. The DT gas delivery system adds tritium-specific capabilities for inventory minimization, secondary containment, and activity monitoring. The DT system integrates depleted uranium storage beds and a liquid helium cryogenic condenser used for pressure building and cryopumping. High-purity delivery is provided by a rapid-response palladium permeator. The system is housed in a helium-atmosphere glovebox held at negative pressure with continuous cleanup. We present the process and instrumentation design, a failure modes and effects analysis (FMEA), and data from the experiment's in situ Raman spectrometer, which provides direct confirmation of target loading and composition through the optically clear diamond anvils. The 2024 and 2025 DT campaigns achieved repeatable target fills and operation with no measurable tritium releases to the stack, demonstrating safe, high-purity DT loading at novel density-temperature conditions for muCF studies.

Koukina, Elena [Acceleron Fusion]↗
DOE OSTI2026

Hyperspectral radiance mapping and chromatic correction for temperature measurement in laser-heated diamond anvil cells

In laser-heated diamond anvil cell (DAC) experiments, the effective heated region typically decreases in size with increasing pressure, leading to steeper thermal gradients. Under these conditions, chromatic aberration in the optical path from sample to detector can significantly create bias in spectro-radiometric temperature measurement. We present a radiance-mapping approach using a hyperspectral camera that records 25 spectral channels spanning 605–875 nm at each pixel in a single exposure, providing spatially and spectrally resolved radiance in each frame. This enables chromatic effects to be recorded and corrected in data processing. We developed a procedure for hyperspectral mapping, involving per-camera calibration, crosstalk removal, measured spectral throughput functions, and optional sub-pixel co-registration to minimize chromatic distortion. The calibrated radiance maps are then used to derive temperature maps of the laser-heated hotspots. For smaller heating spots, the radiance mapping approach reveals chromatic shifts that conventional spectro-radiometric methods cannot quantify. Ambient-pressure heating experiments confirm accurate temperature retrieval. At high pressure, application of the hyperspectral system to a platinum-heating experiment at 12 GPa demonstrates stable temperature reconstruction under steep thermal gradients. Beyond mitigating chromatic aberrations, the ability to diagnose optical artifacts separately from emissivity variations during controlled test experiments or in situ suggests a path toward more rigorous spectral emissivity analysis and improved modeling of thermal transport in laser-heated DAC experiments.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Rules for the crystallite size and dislocation density evolution in phases during α-ω transformation in Zr under high-pressure and severe plastic flow

The first in-situ X-ray diffraction (XRD) study of the evolution of the crystallite size and dislocation density in phases during plastic strain-induced phase transformation (PT) is performed utilizing α-ω PT in strongly pre-deformed commercially pure Zr as an important example. Rough diamond anvils (rough-DA) are introduced to intensify all occurring processes during heterogeneous compression of Zr in a diamond anvil cell (DAC). The main rule is found that during α-ω PT the crystallite size and dislocation density in ω-Zr depend solely on the volume fraction of ω-Zr and are independent of pressure, plastic strain tensor, its path, and initial nanostructure. Crystallite size in ω-Zr increases from 10 to 60 nm during the PT, while dislocation density reduces from 1.83×10 15 /m 2 to 0.6×10 15 /m 2 . Rough-DA produce a steady nanostructure in α-Zr before PT with smaller crystallite size and larger dislocation density than smooth-DA, leading to a reduction of the minimum pressure for α-ω PT to a record value 0.67 GPa, 9 times smaller than under hydrostatic loading and 5.1 times lower than the phase equilibrium pressure. In addition to strain, the kinetics of strain-induced PT unexpectedly depends on time. Also, strain-controlled part of kinetics is zero order, in contrast to the first-order kinetics with smooth-DA. The obtained results open a new window for understanding the mutual effects of nanostructure evolution and PT during severe plastic flow in various technological and natural processes. In conclusion, they may bring up economic strategies of producing nanocomposites and single-phase nanostructured materials with optimal properties.

Crystalline size↗
DOE OSTI2024

Quantitative kinetic rules for plastic strain-induced α - ω phase transformation in Zr under high pressure

Plastic strain-induced phase transformations (PTs) and chemical reactions under high pressure are broadly spread in modern technologies, friction and wear, geophysics, and astrogeology. However, because of very heterogeneous fields of plastic strain $E$ p and stress σ tensors and volume fraction c of phases in a sample compressed in a diamond anvil cell (DAC) and impossibility of measurements of σ and $E$ p , there are no strict kinetic equations for them. Here, we develop a kinetic model, finite element method (FEM) approach, and combined FEM-experimental approaches to determine all fields in strongly plastically predeformed Zr compressed in DAC, and specific kinetic equation for α-ω PT consistent with experimental data for the entire sample. Since all fields in the sample are very heterogeneous, data are obtained for numerous complex 7D paths in the space of 3 components of the plastic strain tensor and 4 components of the stress tensor. Kinetic equation depends on accumulated plastic strain (instead of time) and pressure and is independent of plastic strain and deviatoric stress tensors, i.e., it can be applied for various above processes. Our results initiate kinetic studies of strain-induced PTs and provide efforts toward more comprehensive understanding of material behavior in extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exploring toroidal anvil profiles for larger sample volumes above 4 Mbar

Abstract With the advent of toroidal and double-stage diamond anvil cells (DACs), pressures between 4 and 10 Mbar can be achieved under static compression, however, the ability to explore diverse sample assemblies is limited on these micron-scale anvils. Adapting the toroidal DAC to support larger sample volumes offers expanded capabilities in physics, chemistry, and planetary science: including, characterizing materials in soft pressure media to multi-megabar pressures, synthesizing novel phases, and probing planetary assemblages at the interior pressures and temperatures of super-Earths and sub-Neptunes. Here we have continued the exploration of larger toroidal DAC profiles by iteratively testing various torus and shoulder depths with central culet diameters in the 30–50 µm range. We present a 30 µm culet profile that reached a maximum pressure of 414(1) GPa based on a Pt scale. The 300 K equations of state fit to our P–V data collected on gold and rhenium are compatible with extrapolated hydrostatic equations of state within 1% up to 4 Mbar. This work validates the performance of these large-culet toroidal anvils to > 4 Mbar and provides a promising foundation to develop toroidal DACs for diverse sample loading and laser heating.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

A study of silver acetate under extreme conditions

With the aim of exploring chemical systems that may undergo metallization when irradiated with hard X-rays, we selected silver acetate (AgC 2 H 3 O 2 ) for the subject of this study. X-ray-induced decomposition of silver acetate under ambient and high-pressure conditions was observed in a diamond anvil cell (DAC), leading to the formation of metallic nanograins of silver at ambient pressure and 1.65 GPa. At 4 GPa, no decomposition was observed. The Avrami kinetics equation also provides information about novel structural formation at ambient pressure and 1.65 GPa. By modeling of the XRD data, it was found that the size of the silver nanocrystallites formed at 1.65 GPa pressure steadily increased to ∼5 nm after 600 min of X-ray irradiation as determined by applying the Scherrer equation to the diffraction peak widths. Time-resolved X-ray diffraction (XRD) revealed pressure-dependent kinetics, demonstrating that coupling pressure with irradiation enables controlled photochemical pathways in this model system. Concurrent with previous studies, the application of high pressure (HP) can be considered as a means of controlling X-ray synthetic photochemistry.

36 MATERIALS SCIENCE↗
DOE OSTI2026

PIPS-2025: an updated practical pressure scale for the large-volume presses

In 1997, AIRAPT recommended a set of room-temperature pressure reference points (PRPs) for the large-volume press (LVP) community, known as the Practical International Pressure Scale (PIPS-97). With recent AIRAPT-recommended ruby scale Ruby2020 for diamond-anvil cell (DAC) experiments, it is now necessary to re-examine PIPS-97 for consistency with the DAC pressure scale. Here, we reconstruct equations of state (EOSs) for NaCl and Au that are explicitly tied to Ruby2020 and recalculate the PRPs using these EOSs. The revised PRP values are given. GaAs is removed from the PRP list because of the complexity of its phase transitions. The ZnS value, although retained, requires further investigation. Overall, the revised pressures are systematically higher than PIPS-97 by up to 4% at 35 GPa. We propose that this updated set of PRPs, referred to as PIPS-2025, be adopted for LVP experiments to improve pressure consistency between the LVP and DAC communities.

Large volume press↗
DOE OSTI2026

Isostructural electronic transition in MoS 2 probed by solid-state high-harmonic generation spectroscopy

Studying materials under extreme pressure in diamond anvil cells (DACs) is key to discovering emergent states of matter, yet no method currently allows the direct measurement of the electronic structure in this environment. Solid-state high-harmonic generation (sHHG) offers a unique all-optical window into the electronic structure of materials. We demonstrate sHHG spectroscopy inside a DAC by probing 2H-MoS 2 , up to 30 GPa, revealing a pressure-induced crossover of the lowest direct bandgap from the K-point to the Γ-point. This transition manifests as a sharp minimum in harmonic intensity and a 30° rotation of the sHHG polarization anisotropy, despite the absence of a structural phase change. First-principles simulations attribute these features to interference between competing excitation pathways at distinct points in the Brillouin zone. Our results establish sHHG as a sensitive probe of electronic transitions at high pressure, enabling access to quantum phenomena that evade detection by conventional techniques.

Nebgen, Bailey R. [University of California, Berke↗