White beam diagnostics using X-ray back-scattering from a CVD diamond vacuum window

At a Glance

Metadata	Details
Publication Date	2019-12-10
Journal	Journal of Synchrotron Radiation
Authors	Roelof van Silfhout, D. Pothin, Thierry Martin
Institutions	University of Manchester, European Synchrotron Radiation Facility
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: CVD Diamond for High-Power X-ray Beam Diagnostics

Executive Summary

This research validates the use of Chemical Vapor Deposition (CVD) diamond windows as robust, non-invasive components for high-resolution white X-ray beam diagnostics in high-brilliance synchrotron environments.

High Power Handling: CVD Polycrystalline Diamond (PCD) windows successfully managed extreme power densities up to 500 W mm^-2, a critical requirement where traditional materials (like Beryllium or thin metal foils) would fail or melt.
Non-Invasive Monitoring: The technique utilizes back-scattered X-rays from the standard vacuum window itself, eliminating the need to place additional, potentially distorting, components in the beam path.
Sub-Micrometre Precision: The setup achieved high-precision beam position monitoring, demonstrating root-mean-square (RMS) noise figures as low as 150 nm (horizontal) and 350 nm (vertical).
Material Superiority: Diamond’s superior thermal conductivity and surface flatness minimize X-ray wavefront distortions, making it the material of choice for next-generation synchrotron optics.
6CCVD Relevance: 6CCVD specializes in the custom, high-purity PCD and SCD wafers required for replicating and advancing this critical diagnostic technology, offering precise thickness control and large-area capabilities.
Thermal Stability Requirement: Beam position stability was directly linked to cooler temperature precision, requiring regulation of ±0.1 °C to eliminate micrometre-scale beam oscillations.

Technical Specifications

The following hard data points were extracted from the experimental results, demonstrating the performance envelope of the CVD diamond diagnostic system.

Parameter	Value	Unit	Context
Maximum Power Density Handled	500	W mm^-2	Reached when both undulators (CPMU18 & U32) were used jointly
Diamond Window Material	CVD Polycrystalline Diamond	N/A	Used as the vacuum window and scattering source
Diamond Window Thickness	50	µm	Used for the proof-of-principle experiment
Diamond Window Diameter	12	mm	Overall size of the disc
Beam Aperture Diameter	8	mm	Clear aperture provided by the water-cooled copper support
RMS Noise Figure (Horizontal)	150	nm	Achieved beam position stability
RMS Noise Figure (Vertical)	350	nm	Achieved beam position stability
Pinhole Camera Tilt Angle	36 (±2)	°	Angle used to position the camera outside the beam path
Magnification Factor (Measured)	1.967 (±0.018)	N/A	Calibration factor for vertical displacement
Required Cooler Precision	±0.1	°C	Necessary to eliminate beam position oscillations
Camera Read Noise	1.7	ADU	Arbitrary Digital Units

Key Methodologies

The experiment successfully demonstrated high-power white beam diagnostics using a specialized geometry leveraging the properties of the CVD diamond vacuum window.

Material Selection and Mounting: A 50 µm thick CVD diamond window (PCD) was selected for its high thermal conductivity and mounted on a water-cooled copper support, defining an 8 mm beam aperture.
High Power Density Generation: Experiments were conducted at ESRF beamline ID6 using two undulators (CPMU18 and U32). Power density was varied by changing the undulator gap, reaching a maximum of almost 500 W mm^-2.
Back-Scattering Geometry: The setup utilized a pinhole camera arrangement tilted at 36° (±2)° out of the horizontal plane to collect X-rays back-scattered from the diamond window surface.
Pinhole Configuration: Pinhole apertures (e.g., 25 µm, 70 µm) were laser-cut into thin tungsten (50 µm) or lead (1 mm) foils to define the image resolution.
Detection System: The camera consisted of a CMOS sensor (1280 x 1024 pixels, 7 µm x 7 µm) fibre-optically coupled to a Gadox (Gd₂O₂S:Tb) scintillator, covered with a thin aluminum layer for visible light insensitivity.
Position Determination: Beam center position was determined by fitting a Gaussian distribution to the summed pixel intensities (row- and column-wise), a method shown to provide superior signal-to-noise ratio and sub-pixel precision.
Thermal Stability Validation: Beam position stability was confirmed to be dependent on the precision of the recirculating cooler system, demonstrating that high-precision temperature control (±0.1 °C) is essential for achieving nanometre-scale stability.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced CVD diamond materials necessary to replicate, optimize, and extend the high-power X-ray diagnostic research presented in this paper.

Applicable Materials

The success of this diagnostic method relies entirely on the thermal and mechanical stability of the diamond window. 6CCVD offers materials tailored for this extreme environment:

Optical Grade Polycrystalline Diamond (PCD): Ideal for high-power vacuum windows and beam scatterers. We provide PCD wafers up to 125 mm in diameter, ensuring high thermal conductivity (essential for handling >500 W mm^-2 loads) and superior mechanical robustness.
Single Crystal Diamond (SCD): For applications requiring the absolute lowest wavefront distortion or highest purity, 6CCVD offers high-quality SCD plates with thicknesses ranging from 0.1 µm to 500 µm.
Custom Thickness Control: The paper utilized 50 µm thick windows. 6CCVD provides precise thickness control for both SCD and PCD materials in the critical 0.1 µm to 500 µm range, allowing researchers to optimize scattering yield and transmission characteristics.

Customization Potential

To meet the specific geometric and functional requirements of synchrotron beamlines, 6CCVD offers comprehensive customization services:

Requirement from Paper/Application	6CCVD Customization Service	Benefit to Researcher
Custom Dimensions (e.g., 12 mm diameter disc)	Custom laser cutting and shaping of plates/wafers up to 125 mm (PCD).	Rapid prototyping and integration into existing vacuum mounts.
High Surface Quality (Ra < 1 nm for SCD)	Precision polishing services achieving Ra < 1 nm (SCD) and Ra < 5 nm (PCD).	Minimizes X-ray wavefront distortion and improves scattering uniformity.
Alternative Diagnostics (Quad Diodes)	Internal metalization capabilities (Au, Pt, Pd, Ti, W, Cu).	Enables fabrication of transmission-mode devices (quad diodes, multi-pixel arrays) mentioned in the literature review, despite potential wavefront issues.
Substrate Support	Supply of thick diamond substrates (up to 10 mm) for robust mounting or heat spreading layers.	Ensures maximum thermal contact and structural integrity under high vacuum and high heat flux.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers provides expert consultation to optimize material selection for high-power X-ray diagnostics projects. We assist clients globally with:

Thermal Modeling: Selecting the optimal PCD grade and thickness to manage specific heat loads (e.g., up to 500 W mm^-2 and beyond).
Interface Design: Advising on material preparation and metalization schemes for robust, high-vacuum compatible bonding to water-cooled copper mounts.
Global Logistics: Ensuring reliable, DDU or DDP global shipping of sensitive diamond components directly to synchrotron facilities worldwide.

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

View Original Abstract

Collecting back-scattered X-rays from vacuum windows using a pinhole X-ray camera provides an efficient and reliable method of measuring the beam shape and position of the white synchrotron beam. In this paper, measurements are presented that were conducted at ESRF beamline ID6 which uses an in-vacuum cryogenically cooled permanent-magnet undulator (CPMU18) and a traditional U32 undulator as its radiation sources, allowing tests to be performed at very high power density levels that were adjusted by changing the gap of the undulators. These measurements show that it is possible to record beam shape and beam position using a simple geometry without having to place any further items in the beam path. With this simple test setup it was possible to record the beam position with a root-mean-square noise figure of 150 nm.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s1600577519015340