X-ray beam diagnostics at the MID instrument of the European X-ray Free-Electron Laser Facility

At a Glance

Metadata	Details
Publication Date	2024-04-08
Journal	Journal of Synchrotron Radiation
Authors	Ulrike Boesenberg, G. Ansaldi, Alexander Bartmann, L E Batchelor, Felix Brauße
Institutions	European X-Ray Free-Electron Laser
Citations	4
Analysis	Full AI Review Included

Diamond Solutions for X-ray Free-Electron Laser Diagnostics: An Analysis of EuXFEL MID Instrument Requirements

This technical documentation analyzes the material requirements for advanced X-ray beam diagnostics at the European X-ray Free-Electron Laser (EuXFEL) Materials Imaging and Dynamics (MID) instrument, focusing on the critical role of MPCVD diamond.

Executive Summary

The research confirms that high-purity, high-thermal-conductivity diamond is indispensable for beam diagnostics in extreme XFEL environments characterized by high repetition rates (up to 4.5 MHz) and intense photon flux.

Heat Load Mitigation: Diamond is the material of choice for devices inserted directly into the beam due to its exceptional radiation hardness and thermal properties, crucial for handling the unprecedented heat load at EuXFEL.
Pulse-Resolved Intensity Monitoring: Diamond solid-state ionization chambers (40 µm thick) successfully resolve individual X-ray pulses at the full 4.5 MHz repetition rate, providing essential intensity normalization data.
High-Resolution Spectroscopy: Bent Single Crystal Diamond (SCD) spectrometers (using C(220) reflection, R ≈ 90 mm) enable pulse-resolved spectral characterization of SASE and HXRSS modes.
Spectral Performance: The SCD spectrometer achieved a high geometric energy resolution of 0.35 eV at approximately 9 keV incident photon energy.
Imaging Capability: Low-resolution imaging utilizes a 20 µm thick Boron-Doped Diamond (BDD) screen, demonstrating stability for continuous beam insertion.
Future Requirements: Ongoing efforts require the insertion of ultra-thin SCD crystals upstream to generate diffraction extinction notches for absolute energy calibration, a key 6CCVD capability.

Technical Specifications

The following hard data points were extracted regarding the diamond components and operational parameters of the Diagnostic End-Station (DES) at the MID instrument:

Parameter	Value	Unit	Context
Maximum Repetition Rate	4.5	MHz	EuXFEL pulse train operation
Photon Energy Range (Tested)	5 to 25	keV	Beamstop transmission calculations
Intensity Monitor Material	Diamond	SCD	Solid-state ionization chamber
Intensity Monitor Thickness	40	µm	Diamond plate thickness
Electrode Coating Thickness	250	nm	Beryllium (Be) coating on diamond
Spectrometer Crystal Material	Single Crystal Diamond	SCD	Used for C(220) and C(440) reflections
Spectrometer Bending Radius (R)	≈ 90	mm	Used for C(220) reflection
Experimental Energy Resolution (δE)	0.35	eV	Measured at ≈9 keV incident energy
Imager Screen Material	Boron-Doped Diamond	BDD	Low-resolution imaging screen
Imager Screen Thickness	20	µm	B-doped diamond screen
Imager Screen Angle	45	°	Angle relative to the direct beam
Minimum Pulse Duration Estimated	0.73	fs	Derived from short pulse spectral width (2.48 eV)
Crystal Alignment Precision	0.5	µrad	High-precision piezo stage accuracy

Key Methodologies

The successful implementation of XFEL beam diagnostics relies on the precise fabrication and integration of MPCVD diamond components:

Intensity Monitoring: Diamond solid-state ionization chambers were fabricated using 40 µm thick diamond plates coated with 250 nm Be electrodes. These detectors operate under a moderate bias voltage (< 100 V) and are fast enough to resolve individual X-ray pulses at 4.5 MHz.
Spectrometer Setup: A bent Single Crystal Diamond (SCD) crystal was mounted on a high-precision piezo stage, providing 0.5 µrad rotational accuracy for fine alignment. The crystal disperses the beam spectrum onto a 1D linear detector (Gotthard-I) or a 2D YAG imager.
Spectral Measurement: The spectrometer utilized the C(220) reflection of the bent SCD crystal, covering an angular range of 45° to 110° to collect spectra in the 6 keV to 25 keV range.
Imaging Implementation: Low-resolution imaging was achieved using a 20 µm thick Boron-Doped Diamond (BDD) screen, positioned at a 45° angle to the beam to minimize damage while remaining continuously inserted.
Heat Load Management: The primary beamstop was designed as a layered sandwich of 40 mm Boron Carbide (B₄C) and 10 mm Aluminum (Al), chosen for their low-Z properties and high ablation resistance under focused, high-intensity beams (up to 10¹² photons per pulse).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate, upgrade, and extend the capabilities demonstrated at the EuXFEL MID instrument. Our expertise in custom dimensions, thickness control, and specialized doping ensures optimal performance for next-generation XFEL diagnostics.

Applicable Materials

EuXFEL Requirement	6CCVD Material Recommendation	Rationale and Capability Match
Bent Crystal Spectrometer	Optical Grade Single Crystal Diamond (SCD)	We provide high-purity SCD substrates up to 500 µm thick, ideal for precise mechanical bending (R ≈ 90 mm) and achieving the required C(220) diffraction quality and sub-eV energy resolution. Polishing to Ra < 1nm is available.
Intensity Monitors & Thin Films	Custom Thickness SCD/PCD	We supply ultra-thin SCD and PCD films ranging from 0.1 µm to 500 µm, perfectly matching the 40 µm monitor and 20 µm imager screen specifications with excellent thickness uniformity.
Radiation-Hard Imaging Screens	Boron-Doped Diamond (BDD)	We offer custom BDD material, essential for high-stability imaging screens that must withstand continuous, high-intensity XFEL exposure without suffering beam damage.
High-Power Beamstops	Polycrystalline Diamond (PCD) Plates	For large-area, high-power applications, 6CCVD offers PCD plates up to 125mm in diameter, providing superior thermal management compared to traditional B₄C or metal beamstops.

Customization Potential

The EuXFEL research highlights the need for highly customized components, which is a core strength of 6CCVD:

Custom Dimensions: We can supply plates and wafers up to 125mm (PCD) and custom-sized SCD, allowing researchers to design large-area detectors or optical elements.
Precision Polishing: To maintain beam quality and minimize scattering losses, 6CCVD offers precision polishing services, achieving surface roughness of Ra < 1nm for SCD and Ra < 5nm for inch-size PCD.
Custom Metalization: The paper noted the use of 250 nm Be electrodes. 6CCVD offers in-house metalization using high-Z materials (Au, Pt, Pd, Ti, W, Cu) for optimized charge collection and electrode design in diamond detectors.
Laser Cutting and Shaping: We provide advanced laser cutting services to achieve the precise geometries and mounting features required for complex vacuum chamber integration, such as the DES unit.

Engineering Support

6CCVD’s in-house PhD team specializes in the physics and engineering of MPCVD diamond for extreme environments. We offer comprehensive support for similar XFEL Beam Diagnostics projects, including:

Material selection consultation to optimize thermal conductivity versus cost (SCD vs. PCD).
Guidance on doping levels (BDD) for specific detector sensitivity and response speed.
Design assistance for integrating thin diamond films into high-vacuum systems and custom metalization schemes.

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

View Original Abstract

The Materials Imaging and Dynamics (MID) instrument at the European X-ray Free-Electron Laser Facility (EuXFEL) is equipped with a multipurpose diagnostic end-station (DES) at the end of the instrument. The imager unit in DES is a key tool for aligning the beam to a standard trajectory and for adjusting optical elements such as focusing lenses or the split-and-delay line. Furthermore, the DES features a bent-diamond-crystal spectrometer to disperse the spectrum of the direct beam to a line detector. This enables pulse-resolved characterization of the EuXFEL spectrum to provide X-ray energy calibration, and the spectrometer is particularly useful in commissioning special modes of the accelerator. Together with diamond-based intensity monitors, the imager and spectrometer form the DES unit which also contains a heavy-duty beamstop at the end of the MID instrument. Here, we describe the setup in detail and provide exemplary beam diagnostic results.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s1600577524001279