The High Energy Density Scientific Instrument at the European XFEL

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	Deutsches Elektronen-Synchrotron DESY, European X-Ray Free-Electron Laser
Citations	80
Analysis	Full AI Review Included

Technical Documentation: MPCVD Diamond Solutions for High Energy Density (HED) XFEL Instrumentation

6CCVD specializes in providing high-purity, custom-engineered MPCVD diamond materials essential for extreme environment scientific instruments, such as the High Energy Density (HED) facility at the European XFEL. The following analysis connects the critical material requirements identified in the research paper (Zastrau et al., 2021) directly to 6CCVD’s core capabilities.

Executive Summary

Core Application: The European XFEL HED instrument enables groundbreaking experiments in warm dense matter (WDM), high-pressure physics (DACs), and ultrafast dynamics using hard X-rays (5-25 keV).
Extreme Conditions: The facility operates with ultra-high repetition rates (up to 4.5 MHz) and femtosecond pulses (≤50 fs), achieving extreme power densities exceeding 10¹⁷ W cm^-2.
Diamond Criticality: High-purity CVD diamond is indispensable for components requiring extreme radiation hardness, high thermal conductivity, and low X-ray absorption.
Key Diamond Components: Diamond is used for highly transmissive X-ray monitors (BDD screens, 22 µm to 100 µm), high-power attenuators (up to 2.4 mm thick), and vacuum windows (100 µm thick, 10 mm diameter).
Precision Optics: SCD crystals are utilized in bent crystal spectrometers, demanding ultra-low surface roughness (Ra < 1 nm) for high spectral resolution (down to 0.13 eV).
6CCVD Value Proposition: 6CCVD provides custom Single Crystal Diamond (SCD) and Boron-Doped Diamond (BDD) materials, tailored dimensions, and specialized metalization services necessary to meet the stringent requirements of next-generation HED diagnostics and sample environments.

Technical Specifications

The following table summarizes key operational parameters and material requirements derived from the HED instrument design:

Parameter	Value	Unit	Context
X-ray Photon Energy Range	5 - 25	keV	SASE2 Undulator Source
X-ray Pulse Duration	≤50	fs	Ultrashort pulses for ultrafast dynamics
Maximum Repetition Rate	4.51	MHz	Intra-burst rate (222 ns pulse spacing)
Peak Intensity (Focused)	>10¹⁷	W cm^-2	Focused to 5 µm FWHM
Tight Focus Spot Size (CRL3)	1 - 2	µm	Achievable at Target Chamber Center (TCC)
Nanofocus Spot Size (CRL4)	~220	nm	FWHM demonstrated at 9 keV
BDD Monitor Screen Thicknesses	22, 50, 100	µm	X-ray Intensity and Position Monitors (IPMs)
CVD Diamond Attenuator Range	0.075 - 2.4	mm	High-power X-ray attenuation
DAC/IC Window Thickness	100	µm	10 mm diameter, high X-ray transmission
Monochromator Bandwidth (Si(111))	~1.2 x 10^-4	∆E/E	High-resolution X-ray optics
HED-flex Spectrometer Resolution	0.13	eV	Using Si(111) crystal, 78 mm bending radius

Key Methodologies

The HED instrument relies on specialized techniques that demand high-performance materials, particularly CVD diamond, for operation under extreme conditions:

High-Pressure Generation: Static pressures up to several 100 GPa are generated using Diamond Anvil Cells (DACs). Dynamic compression is achieved using piezo-driven dDACs on millisecond timescales.
Extreme Heating Methods: Samples are heated to 1000-10000 K either via double-sided pulsed laser heating or through X-ray heating by varying the repetition rate or intensity of the MHz X-ray pulse train within the DAC platform (IC1/IC2).
Laser Compression Drivers: High-energy lasers (DiPOLE 100-X, up to 100 J, 2-15 ns pulse duration) are used for laser-driven shock and ramp compression, generating transient pressures up to 1 TPa.
Ultrafast Pump-Probe: Femtosecond optical lasers (ReLaX, 25 fs) are synchronized with XFEL pulses to study transient, non-equilibrium states (e.g., electron-ion thermalization) on ultrafast timescales.
X-ray Focusing and Diagnostics: Compound Refractive Lenses (CRLs) achieve tight focusing (micron to sub-micron). Highly transmissive Boron-Doped Diamond (BDD) screens are used for active beam stabilization and timing (PAM) due to their radiation tolerance and low absorption.
High-Resolution Spectroscopy: Bent crystal spectrometers utilize Si and CVD diamond crystals (e.g., HED-flex) to achieve pulse-resolved spectral analysis with resolutions down to 0.13 eV, critical for diagnosing plasma and electronic states.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced CVD diamond components required to replicate, enhance, and extend the capabilities of the European XFEL HED instrument and similar facilities globally.

Applicable Materials

Research Requirement	6CCVD Material Solution	Technical Advantage
Highly Transmissive Monitors	Heavy Boron-Doped Diamond (BDD)	Ideal for non-invasive X-ray Intensity and Position Monitors (IPMs/PAMs). BDD screens (22 µm to 100 µm) offer high radiation tolerance and stable signal response at 4.5 MHz rates.
High-Power Attenuators/Windows	Optical Grade Single Crystal Diamond (SCD)	SCD offers the highest thermal conductivity and lowest absorption for high-fluence X-ray beams. Available in custom thicknesses (0.1 µm - 500 µm) and substrate sizes (up to 10 mm).
Bent Crystal Spectrometers	High-Purity SCD Plates	Required for high-resolution optics (e.g., HED-flex). Our SCD achieves Ra < 1 nm polishing, minimizing scattering and ensuring the necessary spectral purity for meV resolution IXS/XES experiments.
High-Pressure DAC Windows	SCD Substrates (up to 10 mm thick)	Provides robust, high-transmission windows for DAC platforms operating at gigapascal pressures and high temperatures (X-ray heated).

Customization Potential

The HED instrument utilizes components with highly specific geometries and surface treatments. 6CCVD’s in-house engineering capabilities ensure these requirements are met precisely:

Custom Dimensions: We offer custom plates and wafers up to 125 mm (PCD), suitable for large-area detectors or specialized optics. We can provide the exact 10 mm diameter, 100 µm thick SCD windows required for the IC vacuum chambers.
Precision Polishing: Our standard SCD polishing achieves Ra < 1 nm, and inch-size PCD achieves Ra < 5 nm. This ultra-smooth finish is critical for minimizing beam jitter and diffraction effects from monitor screens and optical components.
Metalization Services: 6CCVD provides internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu). This is essential for creating electrical contacts on BDD sensors for signal readout or applying custom coatings to diagnostic optics.
Laser Cutting and Shaping: We provide precise laser cutting services for complex geometries, such as the B₄C/Densimet sandwich used in the pulse picker unit, ensuring high mechanical accuracy (sub-µm positioning accuracy is required for slits).

Engineering Support

6CCVD’s in-house PhD material science team specializes in optimizing diamond properties (doping, thickness, surface finish) for extreme environments. We can assist researchers in selecting the optimal SCD or BDD material to replicate or extend high-pressure DAC and ultrafast X-ray pump-probe experiments. Our expertise ensures that material selection maximizes X-ray transmission, minimizes thermal load, and guarantees long-term stability under MHz repetition rates.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s1600577521007335