The High Energy Density Scientific Instrument at the European XFEL
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-08-23 |
| Journal | Journal of Synchrotron Radiation |
| Authors | U. Zastrau, Karen Appel, Carsten Baehtz, Oliver Baehr, L E Batchelor |
| Institutions | Helmholtz-Zentrum Dresden-Rossendorf, The University of Tokyo |
| Citations | 80 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- Core Capability: The High Energy Density (HED) instrument at the European XFEL combines hard X-ray Free-Electron Laser (FEL) pulses (5-25 keV, ≤50 fs) with high-power drivers to study matter under extreme conditions (pressure >1 Mbar, magnetic fields up to 500 T).
- Unique XFEL Feature: The facility exploits the unique pulse structure, delivering up to 27,000 pulses per second at a 4.5 MHz intra-train repetition rate, enabling the study of sub-millisecond dynamics.
- Primary Drivers: Experiments are driven by two high-power optical lasers (ReLaX: 300 TW, femtosecond; DiPOLE 100-X: 100 J, nanosecond/picosecond) for shock compression and relativistic laser-matter interaction, alongside Diamond Anvil Cells (DACs) and pulsed magnets (up to 60 T).
- High-Resolution Probing: The instrument supports volumetric X-ray diffraction (XRD), X-ray emission spectroscopy (XES), and inelastic X-ray scattering (IXS), with nanofocusing optics achieving spot sizes down to 64 nm (theoretical diffraction limit).
- Ultrafast Synchronization: An online Photon Arrival Monitor (PAM) synchronizes the optical pump-probe laser with the X-ray pulses, achieving a timing jitter of 20-30 fs RMS.
- Key Scientific Achievements: Demonstrated ultrafast synthesis of iron nitride (e-Fe3N1+x) in a DAC using MHz X-ray heating and observation of spin cross-over in Fe-bearing compounds under pressure.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| XFEL Photon Energy Range | 5 to 25 | keV | SASE2 Undulator operation |
| XFEL Pulse Duration | ≤50 | fs | Ultrashort X-ray pulses |
| XFEL Repetition Rate (Intra-train) | 4.51 | MHz | Minimum pulse spacing: 222 ns |
| XFEL Peak Intensity (CRL3 Focus) | >1017 | W cm-2 | Focused to 5 µm FWHM |
| ReLaX Laser Peak Power | 300 | TW | 5 Hz repetition rate, 25 fs pulse |
| ReLaX Laser Wavelength | 800 ± 40 | nm | Nominal operation mode |
| DiPOLE 100-X Laser Energy | 100 | J | 10 ns pulse duration (10 Hz operation) |
| DiPOLE 100-X Wavelength | 1030 | nm | Fundamental wavelength |
| Pump-Probe Laser Jitter (RMS) | 20-30 | fs | Relative arrival time (X-ray vs. PP laser) |
| DAC Static Pressure Capability | Several 100 | GPa | High-pressure experiments |
| Dynamic Compression Pressure | Up to 1 | TPa | Using laser ablation pressure |
| Pulsed Magnet Peak Field | Up to 60 | T | Horizontal bi-conical solenoid |
| Si(111) Monochromator Resolution (ΔE/E) | 1.2 x 10-4 | N/A | At 6055 eV photon energy |
| HIREX-II Spectrometer Resolution | ≤0.2 | eV | Covers 5-25 keV range |
| CRL3 Tight Focus Spot Size (Measured) | 4-5 | µm (FWHM) | At 6 keV (SASE beam) |
| Nanofocus (CRL4) Diffraction Limit | 64 | nm | 50 CRLs, 9 keV, monochromatic beam |
| AGIPD Detector Dynamic Range | Up to 104 | photons/pixel | Single photon sensitivity at 12 keV |
Key Methodologies
Section titled “Key Methodologies”The HED instrument supports several combined pump-probe techniques:
-
DAC High-Pressure/Temperature Studies:
- Pressure Generation: Static compression (DACs) or dynamic compression (dDACs) up to several 100 GPa.
- Heating: Achieved via X-ray pulse train absorption (MHz rate) or double-sided pulsed infrared laser heating (1000-10000 K).
- Probing: MHz X-ray diffraction (XRD) in IC2 using AGIPD/Varex detectors for time-resolved structural analysis, or X-ray Emission Spectroscopy (XES) in IC1.
-
Dynamic Laser Shock Compression:
- Driver: DiPOLE 100-X laser (100 J, 10 ns/2 ns) generates transient pressures up to 1 TPa.
- Diagnosis: Velocity Interferometer System for Any Reflector (VISAR) and Streaked Optical Pyrometry (SOP) measure pressure and temperature evolution over 50 ns windows.
- Probing: Time-resolved XRD using the hard X-ray FEL beam to capture density and crystal structure during compression.
-
Ultrafast Femtosecond Pump-Probe:
- Driver: ReLaX (300 TW, 25 fs) or PP (15-300 fs) lasers excite solid-density matter.
- Synchronization: Photon Arrival Monitor (PAM) ensures 20-30 fs RMS timing precision between optical pump and X-ray probe.
- Application: Study of electron-ion thermalization, non-thermal melting, and associated transport properties in Warm Dense Matter (WDM).
-
Pulsed High Magnetic Field Experiments:
- Driver: Pulsed magnets generating fields up to 60 T.
- Environment: Cryogenic sample environment (4 K to 600 K).
- Probing: X-ray diffraction and resonant magnetic X-ray diffraction (RMXD) to investigate correlated electron systems and quantum criticality.
-
High-Resolution Spectroscopy and Scattering:
- Techniques: XES and Inelastic X-ray Scattering (IXS) using HAPG mosaic crystals (resolving power up to 2800) or diced analyzer crystals (40 meV resolution at 7495 eV).
- Application: Resolving inelastic scattering from phonons in solids or ion-acoustic waves in plasmas.
Commercial Applications
Section titled “Commercial Applications”The HED instrument’s capabilities in generating and diagnosing extreme states of matter are relevant to several high-technology sectors:
- Inertial Confinement Fusion (ICF) and Energy Research: Investigation of Warm Dense Matter (WDM) and high-pressure physics relevant to fusion fuel compression and material behavior in extreme plasma environments.
- Advanced Materials Processing: Understanding material ablation, phase transitions, and transport properties under high-intensity laser and X-ray irradiation, critical for optimizing laser-based manufacturing and surface modification.
- High-Pressure Industrial Synthesis: Development and monitoring of novel material synthesis routes (e.g., high-pressure nitrides, superhard materials) using DACs combined with controlled X-ray heating and MHz diagnostics.
- Aerospace and Ballistics: Characterizing the Equation of State (EOS) and dynamic response of materials (metals, ceramics) under ultrahigh strain rates and TPa pressures, essential for impact modeling and protective structures.
- Quantum Materials and Electronics: Study of correlated electron systems, high-Tc superconductors, and topological materials under extreme magnetic fields (up to 60 T) to inform the design of next-generation electronic components.
- High-Power Optics and Diagnostics: Development and testing of radiation-hardened X-ray optics, detectors (e.g., AGIPD), and timing systems required for high-repetition-rate, high-fluence facilities.
View Original Abstract
The European XFEL delivers up to 27000 intense (>10 12 photons) pulses per second, of ultrashort (≤50 fs) and transversely coherent X-ray radiation, at a maximum repetition rate of 4.5 MHz. Its unique X-ray beam parameters enable groundbreaking experiments in matter at extreme conditions at the High Energy Density (HED) scientific instrument. The performance of the HED instrument during its first two years of operation, its scientific remit, as well as ongoing installations towards full operation are presented. Scientific goals of HED include the investigation of extreme states of matter created by intense laser pulses, diamond anvil cells, or pulsed magnets, and ultrafast X-ray methods that allow their diagnosis using self-amplified spontaneous emission between 5 and 25 keV, coupled with X-ray monochromators and optional seeded beam operation. The HED instrument provides two target chambers, X-ray spectrometers for emission and scattering, X-ray detectors, and a timing tool to correct for residual timing jitter between laser and X-ray pulses.