Performance Evaluation of GAGG+ and Tungsten CarbideBlades in an X-ray Pinhole Camera
S. Burholt, N. Vitoratou, L. Bobb, Diamond Light Source, Oxfordshire, UKABSTRACT
At Diamond Light Source two X-ray pinhole cameras are used to measure the transverse profile of the 3 GeV electron beam [1]. The current pinhole assembly is formed usingtungsten blades with chemically etched shims to produce a 25 µm x 25 µm aperture and the imager incorporates a 0.2 mm LuAG:Ce scintillator. Tungsten carbide is a machinablehigh-Z material which at millimetre thicknesses is opaque to X-rays. With a slight change in pinhole design, similar to that already in place at the ESRF [2], tungsten carbide blades
could offer a well-controlled aperture size for the pinhole camera with simpler assembly. Further to this, improvements to the photon yield of scintillators mean that the newscintillator GAGG+ has an almost two-fold increase in yield compared to the current LuAG:Ce scintillator [3]. An evaluation of the tungsten carbide blades and GAGG+ scintillator ispresented.
X-RAY PINHOLE CAMERAS AT DIAMONDPINHOLE BLADES AND DESIGNS TO FORM REQUIRED APERATURES

Table 1: X-ray pinhole camera systems at Diamond.
PINHOLE CAMERADESCRIPTION

1
2

Used in the vertical emittance feedbacksystem.

3

Used for research and development.

Figure 2: Schematic of the traditional tungsten blade – shim – tungsten blade design(light grey and blue) and the tungsten carbide C-D design (dark grey) [2].

Figure 1: Schematic of the monochromatic X-ray pinhole camera system [1,4].

The tungsten carbide blades were manufactured by Midland Carbides, UK [5].
Microscope images measurements of these new tungsten carbide C-D apertures
have found them to be larger at around 35 µm, when they should be 25 µm.

TUNGSTEN AND TUNGSTEN CARBIDE APERTURE SCANS USING X-RAY FAN

Figure 3: Horizontal aperture scan with fitted beam
size (σx,σY), peak intensity, and normalised error oftungsten and tungsten carbide aperture.

Figure 4: Vertical aperture scan with fitted beam size
(σx,σY), peak intensity, and normalised error oftungsten and tungsten carbide aperture.

PHOTON YIELD COMPARISON BETWEEN LUAG:CE AND GAGG+LuAG:Ce VS GAGG+ MODULATION TRANSFERFUNCTIONS

Figure 5: A comparison of the knife edge experimentsof LuAG:Ce and GAGG+ scintillators.
MTF

LuAG:CeGAGG+

MTF50 (lp/mm)

27.8

32.0

MTF10 (lp/mm)

70.7

78.6

Table 2: MTF values for LuAG:Ce and GAGG+CONCLUSIONSIt has been demonstrated that the new tungsten carbide
blades are larger by around 10 µm, which was confirmed by
microscope images. The blade scans have shown they still
produce good attenuation of the beam, though the vertical scanshows an increase in vertical beam size, attituded to its larger size.
GAGG+ has been demonstrated to have around an 78% increasein photon yield and produce similar MTF values. This means
replacement of LuAG:Ce with GAGG+ would improve the photon
yield of the pinhole cameras without any loss of spatial resolution,even at low currents.

Figure 6: LuAG:Ce (Left) and GAGG+ (Right) knife edge images captured using the same
pinhole camera setup. ROIs shown for knife-edge MTF (dashed orange) and photon yieldmeasurements (solid blue).
For a beam only section (solid blue ROI), the average intensity per pixel for LuAG:Ce was 88
a.u/pixel and GAGG+ was 157 a.u/pixel which is an increase of 78%. This improvement can help
provide reliable vertical emittance measurements, even with the synchrotron at lower currents. This canalso help reduce jitter by allowing for shorter exposure times.

Further investigations are planned to record the PSF valuesof these pinhole cameras with the new tungsten carbide blades
and GAGG+ scintillator using the Touschek calibration method.

ACKNOWLEDGEMENTS
The authors would like to thank the Diamond operations team forthe shift time to complete these experiments. Our thanks also goes toMidland Carbides for their effort in producing these blades.

REFERENCES[1] C. Thomas et al., “X-ray pinhole camera resolution and emittance measurement, Phys. Rev. Spec. Top. Accel Beams., vol. 13, no. 2, 2010.
[2] F. Ewald, "Emittance diagnostics at ESRF-EBS using the X-ray Pinhole Camera," presented at the ELETTRA 2.0 Workshop on Optical Diagnostics for LowEmittance Storage Rings, Mar. 24, 2022
[3] Crytur Company Website, Specific GAGG+ and other materials, Accessed: Aug. 29, 2023. [Online.] Available: https://www.crytur.cz/materials/gagg/[4] L.M. Bobb et al., "Performance Evaluation of Molybdenum Blades in an X-ray Pinhole Camera,“ Proc. of IBIC2016, Barcelona, Spain, pp. 795-798, 2016.
[5] Midland Carbides Company Website, Accessed: Aug. 29, 2023. [Online.] Available: https://www.midlandcarbides.co.uk/