ID03 Coherent X-ray Diffraction (CoXRD)

1. Introduction

2. Scientific Objective

The coherent X-ray diffraction beamline is one of the most active beamlines utilizing the coherence characteristics of the 4GSR light source. This beamline focuses on supporting coherent X-ray diffraction imaging and microbeam diffraction research by highly focusing light sources with excellent coherence. Additionally, we plan to support real-time X-ray diffraction research using a diffractometer.

This beamline will provide a spatial resolution of less than 10 nm for coherent X-ray diffraction imaging. In Korea, Bragg CDI, one of the advanced techniques in coherent X-ray diffraction imaging, is actively used in research on secondary battery, catalyst, and semiconductor materials. This imaging technique enables the study of dynamic processes such as complex structures, defect formation and growth, and material changes. Furthermore, it greatly contributes to understanding the properties of various materials by vhgkddirectly observing microscopic physical phenomena at the nanoscale. These observations can be applied to various fields, including industrial applications and the development and application of next-generation materials. This beamline aims to increase the utilization of coherent X-ray diffraction imaging and microbeam X-ray diffraction.

3. Beamline Requirements for the Insertion Devices

ID03 will be installed in-vacuum undulator with a period of 22 mm of 3 m length.

The ID of the ID03 beamline is available in a continuous energy range and from 3 keV.

Table 1. ID03 Coherent X-ray Diffraction Source Parameters

Beamline	Und ulator	** Period** (mm)	** Length** (m)	Max Power (kW)	Max K value
Coherent X-ray D iffraction	I n-vacuum	22	3	15.165	2.315

4. Beamline Requirements for the Front End

The FE of this beamline is designed for all optical component under the following conditions. (Reference the 4GSR beamline FE section)

• Structural stress due to heat load should not exceed the yield strength.

• The temperature rise due to heat load should not exceed the softening temperature of the materials.

• The LCW temperature of the wall should not exceed the boiling point of water.

The maximum power drawn from the IVU22 is 15.165 kW, and the overall power is gradually removed in the FE. The power of the beam ultimately emitted from the FE is 120 W. The FE Movable Mask is located right in front of the photon shutter at the end of the FE, where it roughly conditions the beam to FWHM before it is incident on the PTL.

5. Beamline Layout

Table 2. Coherent X-ray Diffraction Beamline Component Table

Di stance (m)	Component	Description
22.5	Movable mask	4-way slit, UHV, Water cooling
23.8	Safety shutter
28	White beam filter	Graphite : 0.5 mm, 1 mm, 2 mm Diamond : 0.1 mm, 0.2 mm, 0.5 mm
29	White beam screen	Diamond window, Fluorescent metal screen, current signal output
29.5	White beam PBPM	4-Blade-type
56.5	ID Photon shutter
57.9	White beam slits	4-way slit, UHV, Water cooling
58.6	White beam screen	Diamond window Fluorescent metal screen, current signal output
60	HDCM	Si (111), fixed exit
61.7	White beam screen	Diamond window Fluorescent metal screen, current signal output
62.1	Mono beam screen	YAG window Fluorescent metal screen, current signal output
62.5	FCS
64.1	Mono beam slits	4-way slit, UHV
64.5	Mono beam screen	YAG window Fluorescent metal screen, current signal output
66	High harmonics rejection mirror	2-stripe coating (Pt, Rh)
67	Mono beam slits	4-way slit, UHV
67.6	Mono beam screen	YAG window Fluorescent metal screen, current signal output
68	Beam position monitor	UHV QBPM, Ti foil : 500 nm / Ni foil : 500 nm
68.8	Hutch shutter
70.3	Slits	4-way slit, UHV
71	KB mirror	2-stripe coating (Pt, Rh), Vertical/Horizontal focusing, Pair
	Be window	Double-side polished, 127-um-thick
	Slits	4-way slit, HV
	Beam position monitor	HV QBPM, Ti foil : 500 nm / Ni foil : 500 nm
	Attenuator	8-channel (Al, Mn + block)
73.5	Kappa diffractometer	LM-guide or Air-bearing base plate

6. Optics Overview

This beamline should be designed to maintain the wavefront to the sample. Therefore, the optics are designed to minimize vibration(<100 nrad) and mirror surface slope errors(<0.1 urad).

6.1 Optics Specifications

Rejection Mirror)

	DCM	M1
Distance (m)	60	66
Incidence Angle (mrad)		2.5 – 4.1
Shape	Plane	Flat
Surface Normal direction	Horizontal	Horizontal
Substrate	Si (111)	Si
Coating Materials (Thickness, nm)		Rh (50), Pt (50)
Substrate size (L × W) (mm × mm)	1st : 50 2nd : 150	800 × 50
Roughness (nm, RMS)	< 0.5	< 0.2
Slope error (urad, RMS)	< 1	< 0.1

The monochromator will be used as the DCM(Double Crystal Monochromator), which has high energy resolution, and the crystal is Si(111), covering the energy range of 3-30 keV. Recently manufactured DCM, made with Si(111), can cover high energy, and optics designed with Si(111) is mechanically more stable compared to those using Si(111) and Si(311) pairs.

Table 4. DCM Mechanical specifications

Energy range	3 ~ 30 keV
Crystal	Si (111)
Bragg angle	41.234°~ 3.779°
Angel resolution	< 0.25 μrad
Offset	25 mm
Motion axis	Bragg, gap, roll, pitch, piezo roll and pitch for feedback

The high harmonics rejection mirror is located behind the monochromator serves to suppress the high harmonics energy of the beam coming out of the monochromator. Silicon crystal is FCC (Diamond structure). According to the diffraction selection rule, if h, k, and l are all odd or all even, and h+k+l is a multiple of 4, then n times the corresponding energy. High energy has a high transmittance, so even if it is slightly reflected, it affects the diffraction data. Therefore, a mirror coated with bare Si, Rh, and Pt is used and usually the incidence angle is 2.5 mrad. The reflectivity according to energy is shown in figure 2. The available energy range for each coating material is 5 to 12 keV for Si (reflectivity greater than 90%), 11 to 23 keV for Rh (reflectivity greater than 90%), and 15 to 30 keV for Pt (reflectivity greater than 80%). The incidence angle of 2.5 mrad is basically an angle calculated to enable use up to 30 keV, which is the target energy of this beamline. When using tender energy, the incidence angle must be changed up to 4.07 mrad to reduce the reflectivity of the harmonic energy corresponding to the tender energy by 10%. When using a bare-Si Mirror, the incidence angle-reflectivity result according to energy is shown in figure 3.

	KB (VFM)	KB (HFM)
Distance (m)	70.62	71
Incident Angle	2.5 mrad	2.5 mrad
Shape	Elliptical cylinder	Elliptical cylinder
Semi-major axis (mm)	36750	36750
Semi-minor axis (mm)	35.6533	33.3072
Surface Normal direction	Vertical	Horizontal
Substrate	Si	Si
Coating Materials (Thickness, nm)	Rh (50), Pt (50)	Rh (50), Pt (50)
Substrate size(L × W) (mm × mm)	330	330
Focus distance (m)	2.88	2.5
Roughness (nm)	< 0.2	< 0.2
Slope error (μrad, RMS)	< 0.1	< 0.1

The KB mirror system for the this beamline

6.2 Optical Simulation and Tolerances