An X-ray beam profile monitoring system at a beamline front-end combining a single-crystal diamond film and energy discrimination using droplet analysis
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-04-20 |
| Journal | Journal of Synchrotron Radiation |
| Authors | Togo Kudo, Mutsumi Sano, Takahiro Matsumoto, Toshiro Itoga, Shunji Goto |
| Institutions | SPring-8, Japan Synchrotron Radiation Research Institute |
| Citations | 5 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates a novel X-ray beam profile monitoring system critical for next-generation Diffraction-Limited Storage Rings (DLSRs).
- Core Value Proposition: The system provides energy-resolved spatial profiles of pink-beam X-rays directly at the beamline front-end, enabling accurate detection of the beam centroid for stabilization purposes.
- Material Innovation: Switching from polycrystalline to single-crystal Chemical Vapor Deposition (CVD) diamond film eliminated image degradation caused by crystal grain diffraction, yielding high-quality, diffraction-spot-free images.
- Methodology: The system combines the single-crystal diamond scatterer with pinhole optics and a direct-detection CMOS sensor (SOPHIAS-L).
- Energy Resolution: Photon energy discrimination is achieved using a sophisticated âdroplet analysisâ algorithm applied to single-photon events, successfully resolving the fundamental radiation peak (12.4 keV) from higher harmonics.
- Performance Achievement: Energy discrimination significantly sharpened the beam profile, particularly in the horizontal direction, allowing the beam centroid to be accurately determined, consistent with theoretical SPECTRA calculations.
- Practical Impact: The results confirm that a small FE slit aperture (1 mm x 1 mm) is sufficient for centroid detection when using energy discrimination, crucial for minimizing heat load on downstream optical components during high-current operation (100 mA).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Required Beam Stability | 10 | nrad | DLSR requirement |
| Fundamental Photon Energy | 12.4 | keV | Experimental setting (ID gap 17.26 mm) |
| Diamond Film Material | Single-crystal CVD | N/A | Used as scattering screen |
| Diamond Film Thickness | 70 | ”m | High transparency |
| Diamond Transmittance | 97 | % | At 12.4 keV |
| Pinhole Diameter | 10 | ”m | Tungsten, 500 ”m thick |
| Scattering Angle | 30 | ° | Angle of observation above horizontal |
| Detector Type | SOPHIAS-L | CMOS | Direct detection image sensor |
| Pixel Size | 30 | ”m | Square pixels |
| Detector Noise | 67 | e (r.m.s.) | Low noise characteristic |
| Detection Efficiency | 86 | % | At 12.4 keV |
| Frame Rate | 30 | frames s-1 | Detector operation speed |
| Exposure Time (Chopped) | 0.7 | ms | Per shot (using 30 Hz chopper) |
| Droplet Analysis Threshold 1 (TH1) | 80 | ADU | Higher threshold for charge reconstruction |
| Droplet Analysis Threshold 2 (TH2) | 40 | ADU | Lower threshold for charge reconstruction |
| PSF FWHM | ~20 | ”m | Point Spread Function Full Width at Half-Maximum |
| FE Slit Aperture (Required for Centroid) | 1 x 1 | mm | Sufficient size based on energy discrimination |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized the SPring-8 BL05XU beamline to monitor pink-beam X-rays using a specialized pinhole camera system and advanced data processing.
- Beam Preparation and Scattering: Undulator pink-beam X-rays (12.4 keV fundamental) were shaped by the Front-End (FE) slit. The beam then irradiated a 70 ”m thick single-crystal CVD diamond film, which served as a scattering medium, positioned 35.5 m from the source point in a high-vacuum environment (10-6 Pa).
- Image Formation: Forward-scattered X-rays, observed at a 30° angle, passed through a 10 ”m diameter tungsten pinhole, projecting a cross-sectional image of the beam.
- Single-Photon Condition: A rotating attenuation disk (chopper) operating at 30 Hz was placed near the pinhole. This reduced the effective exposure time to 0.7 ms per shot, ensuring that the detector operated under the necessary one-photon condition for accurate energy measurement.
- Detection and Digitization: Images were captured by the SOPHIAS-L direct-detection CMOS detector (30 ”m pixels) at 30 frames s-1. Raw data underwent flat-field and dark correction.
- Energy Discrimination (Droplet Analysis): A computational algorithm was applied to 10,000 images to reconstruct the energy of individual photons. This âdroplet analysisâ matched the detected charge spread patterns (due to the detectorâs ~20 ”m PSF) across adjacent pixels.
- Thresholding and Spectrum Generation: Optimized thresholds (TH1 = 80 ADU and TH2 = 40 ADU) were used to sum the charge, recovering the photon energy. This allowed the generation of an energy spectrum and the isolation of specific energy bands (e.g., 14 keV to 16 keV) corresponding to the fundamental radiation.
- Centroid Visualization: By filtering the images to show only the fundamental energy component, the system successfully visualized the true beam centroid, demonstrating a clear profile sharpening compared to simple integrated images.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed for high-stability X-ray beam monitoring is directly applicable to facilities and industries requiring ultra-precise control over high-flux, high-energy radiation sources.
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Advanced Light Source Facilities:
- DLSR Diagnostics: Essential for monitoring and stabilizing the photon beam position and angle in next-generation Diffraction-Limited Storage Rings (e.g., SPring-8-II, ESRF-EBS) where stability requirements are extremely strict (10 nrad).
- X-ray Free-Electron Lasers (XFELs): Providing high-quality, diffraction-free beam profile monitoring using single-crystal diamond films, critical for maintaining beam coherence.
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High-Power Optics and Component Protection:
- Heat Load Management: Real-time monitoring of the beam profile and centroid upstream of sensitive optics (like monochromators) allows for dynamic adjustment of FE slits, ensuring components remain within safe thermal limits during high-current (100 mA) operation.
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Scientific Instrumentation and Detector Technology:
- High-Resolution Spectroscopy: The combination of single-photon counting and energy discrimination techniques is valuable for developing advanced X-ray detectors used in materials science and structural biology experiments.
- Beamline Commissioning: Serving as a powerful diagnostic tool during the commissioning and alignment of new undulators and beamline optics.
View Original Abstract
This work has successfully demonstrated a system for monitoring pink-beam X-rays exiting from a beamline front-end, which has a specific spatial distribution based on each energy component. In this study, the X-rays scattered from a single-crystal chemical-vapor-deposited diamond film were converted into a cross-sectional image using pinhole optics, followed by digitization with a direct detection complementary metal-oxide-semiconductor 2D detector. By using single crystals instead of poly-crystals, good quality images were obtained with no diffraction bright spots. As a result of applying photon energy discrimination using the droplet analysis to the image information, the spatial distribution of each energy component of the undulator radiation was successfully visualized. The result was found to be in good agreement with the theoretically calculated result obtained using the synchrotron radiation calculation code SPECTRA . The new synchrotron radiation beam monitor proposed in this paper can serve as a powerful beam diagnostic tool for diffraction-limited rings that require strict light source stability.