Mogno Beamline

MOGNO was designed to be a world-leading high-brilliance micro- and nano-imaging beamline using quasi-monochromatic (ΔE/E approx. 10-2) tender (22 and 39 keV) and hard (67.5 keV) X-rays, in a cone-beam geometry. This design is optimized for continuous zoom tomography (i.e. continuous magnification of the image), where the same specimen can be studied at low and high-resolution. The field of view also varies, from hundreds of micrometers, for the high resolution, up to dozens of milimeters for the low resolution. MOGNO will also be dedicated to 4D (time-resolved) imaging through in-situ experiments. The beamline will potentially attend different areas, such as geological, biological, material, earth/planetary, agriculture, and food sciences, as well as civil engineering, bioengineering, paper and wood research, chemistry, paleontology, archeology, and cultural heritage.

The advantages of X-ray tomography using a high brightness synchrotron light source are better image contrast and greater spatial and temporal resolution. In addition, the small beam bandwidth (< 1 keV, for all energies) reduces undesirable effects, such as beam hardening, and improves the quality of the data for some quantitative analysis, such as the density determination. The detection of micrometer scale characteristics in millimeter-sized samples has been somewhat routine in many X-ray tomography beamlines around the world. Notwithstanding, Mogno beamline shifted to higher energies and a nanofocus, making possible the study of high density and/or large samples with nanometric resolution (local tomography) and low dose.

The optical system of this beamline was optimized for high flux in high energies, with a small bandwidth. After the front-end, the first optical element is an horizontal elliptical mirror designed to collect the radiation from the BC, which is collimated by its sagittal curvature. The second optical system consists of Kirkpatrick–Baez (KB) mirror system coated with a ML, which selects the energies and focalizes the beam in a 100 x 100 nm2 spot. Position of both sample and detector can be adjusted to measure in a chosen magnification and image regime required by the experiment. Various detector systems based either on direct detection, such as Medipix, or indirect detection such as CCDs will be available, covering FOVs from 0.08 x 0.08 to 85 x 85 mm2, and resolutions of the order of 0.13 x 0.13 to 52 x 52 μm2.

## CONTACT & STAFF

Coordination: Nathaly L. Archilha
Tel.: +55 19 3512 1281
E-mail: nathaly.archilha@lnls.br

## Layout & Optical Elements

Figure 1 presents the optical design of MOGNO beamline. The primary source of MOGNO is a 3.2 T superbend, a permanent dipole that generates hard X-rays with critical energy of 19.15 keV and beam size of 22.1 x 8.5 mm2 (HxV, rms). MOGNO optical concept is based on a set of elliptical mirrors, the first one being a total reflection horizontal focusing mirror, which demagnifies the X-ray beam and counterbalance the horizontal inhomogeneity caused by the KB system, the second optical elements of MOGNO beamline. The KB system is composed by two multilayer mirrors, which focus the X-ray beam on both directions, down to a nanometric spot size of ~100 x 100 nm2, and also delivers three different energies: 22, 39 and 67.5 keV – simulated photon flux and energy resolution are presented in Table 1. Such high demagnification implies in a divergent beam (~3.1 mrad in both directions), and so, MOGNO beamline will operate in a cone beam geometry.

Figure 2 shows (a) an overview of the optical and experimental hutch of MOGNO beamline. The optical hutch is located on the ground represented in red, followed by the experimental hutch (approx. 30 m long), from the KB chamber to the PiMega detector stage. All mirror supports and the nanostation are based on a set of wedge shaped granite tables, designed to have three degrees of freedom (x, y and z) and all the movements are based on air bearings. The nanostation is shown in brown and three detectors serve this station: Mobipix (high-Z CdTe sensor), PiMega (Si sensor) and the PCO.edge 4.2 (sCMOS + scintillator). Next, the microstation is represented by the external gray rail. This station is composed by a set of conventional X-ray tomography stages and only the PiMega serves this experimental station. Note that there is an overlap between the two experimental stations, which covers FOVs between 3 and 18.4 mm. The side view of the front end and optical hutch is presented in (b), the nanostation in (c) and the microstaion in (d).

Figure 2. MOGNO beamline layout. a) Overview of the optical and experimental hutch; b) Side view of the front-end and the optical hutch. The experimental hutch has two stations: c) the nanostation, and d) the microstation. BVS: beam visualization system; PB: pink beam; WB: white beam; BC: magnet dipole BC.

Table 1 presents the elements that comprehends the front end and optical hutch and their respective functions.

Element Type Position [m] Description
Source BM Bending Magnet
Slit Front-end Slit 17.200 Limits Beamline Acceptance
Slit Pink Slit 21.133 Defines Angular Aperture
MOG-1-ME Mirror 22.500 Horizontal Focusing
Focused beam Secondary Source 22.875 First Mirror Horizontal Focus
MOG-2-KB-HFM Mirror 25.175 KB – Horizontal Focusing
MOG-3-KB-VFM Mirror 25.445 KB – Vertical Focusing
Focused beam MOGNO Source 25.735 MOGNO nanofocus

Table 1 presents the elements that comprehends the front end and optical hutch and their respective functions.

## Parameters

Table 2 shows detailed information regarding the available energies at MOGNO beamline. All the three energies are selected by the ML, as a result of the high intensity diffraction outcome of first, second and third harmonics.

Table 2. Energy resolution, beam size and divergence on focal position and total flux for MOGNO beamline.

Parameter Value 1 Value 2 Value 3
Central Energy [keV] 22 39 67.5
Stripe (Harmonic) 1(1) 1(2) 2(1)
Source Spectral Flux
[ph/s/0.1%b.w./100mA]
7.4×109 5.0×109 1.8×109
Energy Bandwidth [eV] 2840 940 720
Sample Flux [ph/s/100mA] 8.9×1011 9.3×1010 1.8×1010
Flux Density* [ph/s/px/100mA] 3.8×105 3.9×104 2.6×104
Beam Size [nm] 94×90 89×87 86×87
Beam Divergence [mrad] 3.0×3.2  3.0×3.2  3.0×3.2

*Detector:  Pimega

Table 3 presents the available detection system at MOGNO beamline.

Table 3. Available detection system at MOGNO beamline. FOV: Field of View

Instrument Type Model | Manufacturer Specifications
Detector sCMOS – based PCO Edge 4.2 2048 x 2048 pixels
Pixel size = 6.5 x 6.5 µm2
Microscope White beam Microscope with multiple lenses Optique Peter 2x: Pixel size = 3.612µm2, FOV= 7.402mm2
*5x: Pixel size = 1.44²µm2, FOV= 2.962mm2
*10x: Pixel size = 0.72²µm2, FOV= 1.482mm2
Scintillator LuAg:Ce Crytur Thickness = 5, 20, 100 µm
Detector Direct detection Mobpix (CdTe) LNLS/PiTec 512 x 512 pixels
Pixel size = 55 x 55 µm2
FOV = 28 mm x 28 mm
Detector Direct detection Pimega (Si)** LNLS/PiTec 1536 x 1536 pixels
Pixel size = 55 x 55 µm2, FOV = 80 mm x 80 mm

* The objectives 5x and 10x are also available, but there is no significant gain in terms of resolution and the FOV is significantly decreased.

** The ideal sensor for MOGNO’s energies is a CdTe-based detector (project in progress).

## Experimental Techniques

Table 3 presents some of the most relevant experimental parameters for planning future experiments at MOGNO.

Table 3. MOGNO Main Experiments

Requirement​ Nano-tomography​ Micro-tomography​ 4D micro-tomography
Use case​ Dry samples, < 0.5 kg under contactless furnace or cryo stream cooling from the top​ Dry samples, or live animals (in-vivo tomog.) with air and anesthetic supply (< 0.5 kg) Special condition samples (flow cell) 5 mm wide, with oil flow (100-200 psi)​
Maximum Resolution​ 100 nm​ 500 nm ​ > 0.5 µm @ 1 Hz,
> 1 µm @ 10 Hz
Beam size at sample​ 50 µm (min)​ 500 µm (min)​ 1 mm (min)​
Average scan time​ 5 seconds/tomo​ 500 milliseconds/tomo​ 30 milliseconds/tomo​
Average throughput***​ 30 tomographies/hour​ 60 tomographies/hour​ 20 tomographies/seconds
Max sample load​ 0.5 kg​ 2 kg​ 2 kg​
Sample width**​ < 80 mm​ < 80 mm​ < 8 mm​

* Same sample, under in-situ experimental conditions.
** Special samples, i.e. cryogenic samples, have limited size < 16 mm.

### Zoom tomography - Micro and nanotomography in local and panoramic modes

At MOGNO beamline, the sample can move along the Z axis from the X-ray secondary source (KB system’s focus) up to the detector (Pimega) position, which will be fixed 27.5 m downstream (Fig. 3). In a cone-beam system like MOGNO’s, the resulting geometrical resolution (σR) is a function of the source size (σs), the pixel size of the detector (σD), and local magnification (m) which, in turn, depends on the source-to-sample (Z1) and sample-to-detector (Z2) distances (Table 3, Fig. 3), according to the following relations (Bartels, 2013; Krenkel et al., 2015):

$$\sigma_R = \sqrt{\left( 1-\frac{1}{2}\right)^2 \sigma_S^2 + \frac{1}{m^2}\sigma_D^2}$$

where m = 1 + Z2/Z1,  and  σD/m  is the effective pixel size (σeff).

In addition to σR and m, the field of view at sample (FOVS) also varies depending on the sample position in Z axis (FOVS= σeff * number of pixels) (Fig. 4). The continuous magnification of the image allowed by this design – from dozens of micrometers to hundreds of nanometers – will be exploited to image samples in different resolutions, in a true non-destructive way (no need of resizing the samples), and this is known as zoom-tomography. The beamline will count on a microstation, devoted to more complex setups that might cause a certain level of vibration, and a nanostation dedicated to simpler setups due to more rigorous requirements of stability to achieve the higher image resolutions. Besides acquiring a single local tomography, with high image resolution (e.g. FOVS = 77 um and σR = 130 nm), from a volume of interest of a sample that is larger than the FOVS, it will also be possible to acquire multiple neighboring local tomographies with the same σR, aiming to generate a final panoramic tomography (e.g., three neighboring local tomographies making a total FOVS = 225 µm with no significative impact on image resolution). The zoom-tomography capability of MOGNO will be especially important for studies of hierarchical materials that often present properties varying across scales and, thus, require investigations focused on the upscaling of findings and solutions.

Figure 3. Optical magnification layout. Micro and nanostation magnification limits. Notes: Z1: distance source-sample; σR: geometrical resolution; FOVS: field of view at sample.

Figure 4. Relationship between the field of view at sample (FOVS), the geometrical resolution (σR), and the source-to-sample distance (Z1), along the experimental stations. The numbers are related to the PiMega detector.

### Absorption and phase contrast imaging

MOGNO’s flexible design will allow different contrast imaging. The absorption contrast imaging is based on differences in the X-ray absorption by different materials in a given sample and will be predominant in micrometric resolutions. On the other hand, increasing the spatial resolution and lowering the energy leads to the phase-contrast imaging, based on the X-ray wave refraction followed by free-space propagation. The absorption and phase-contrast imaging occur in the so-called contact and far to near field image regimes, respectively (Bartels, 2013). Phase-contrast imaging will benefit measurements of biological samples (Cloetens et al., 1999; Momose et al., 1996) or biological structures inside an inorganic matrix (Carrel et al., 2017), which present low X-ray attenuation particularly at high energies.

### Time Resolved (4D) tomography

The high X-ray flux at MOGNO will allow to perform an experiment (i.e. collect data to reconstruct a 3D image of the sample) in a short time frame, around a few seconds [3]. Due to this characteristic, 3D imaging competences can be extended to 4D (time-resolved) imaging through in-situ/in-vivo experiments. Particularly, the combination of high X-ray flux and high energy at MOGNO enables 4D measurements of hierarchical samples, such as rocks and soils. Fast imaging provides more detailed fundamental understanding of several dynamical processes, such as fluid flow in porous media (Pak et al., 2020), material responses during mechanical, thermal, or chemical loadings (Kudrna Prašek et al., 2018; Yoshinaka et al., 2019), and in in-vivo condition for small rodents (Bayat et al., 2020). In porous media related investigations, such rigorous studies open the way for upscaling the results from the pore to field scale (Archilha et al., 2016; Lucas et al., 2020). In parallel, in vivo measurements of small animals (e.g. mouse) can help in the evaluation of the effects of biomaterials implantation on bone structure, growth, osteointegration and degradation/resorption of these materials. To tackle the broad applications of 4D measurements, specific environmental cells that mimic real conditions, e.g. controlled pressure, temperature and flow rates, are required. These cells and all the necessary structure are under development to ensure the system’s compatibility with the beamline and users can count on the MOGNO team to help developing new environmental cells.

## References

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• Bartels, M., 2013. Cone-beam x-ray phase contrast tomography of biological samples. Optimization of contrast, resolution and field of view, V.13. ed. Gottingen series in x-ray physics.
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• Yoshinaka, F., Nakamura, T., Takeuchi, A., Uesugi, M., Uesugi, K., 2019. Initiation and growth behaviour of small internal fatigue cracks in Ti‐6Al‐4V via synchrotron radiation microcomputed tomography. Fatigue Fract. Eng. Mater. Struct. 42, 2093–2105. DOI: 10.1111/ffe.13085