Kirkpatrick-Baez Research Articles

Exploring Degradation in PEM Water Electrolysis Cells Due to Metal Migration: Insights from X-Ray Fluorescence Analysis

Green hydrogen production through proton exchange membrane (PEM) water electrolysis offers a viable renewable energy storage and transport solution. The Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER) are central to this technology, with the latter’s slow kinetics posing a significant bottleneck. Despite research efforts, iridium (Ir) is the only element which currently meets the stability and activity needs of OER, challenging the search for alternatives and shifting focus towards enhancing catalyst stability [1]. Recent studies have identified metal migration, particularly of Ir, as a critical factor in the degradation of PEM water electrolyzers [2]. This finding has highlighted the importance of understanding metal migration mechanisms and the need to investigate the contribution or interaction of less studied elements such as platinum (Pt), titanium (Ti), and iron (Fe) to the degradation process.This study investigates the migration of both catalytically active (Ir, Pt) and inactive (e.g., Ti, Fe, Ca) metals within PEM water electrolysis membranes, using ex-situ 2D X-ray fluorescence (XRF) mapping (s. Fig. 1). Tests were conducted on PEM water electrolysis single cells (active area: 4 cm2) with a NafionTM 115 catalyst-coated membrane, with anode and cathode loadings of 2.0 mgIr/cm2 and 1.0 mgPt/cm2, respectively. The study entailed varying operating times (10 h, 100 h, 500 h, 1500 h) under constant load, different load profiles (e.g., open-circuit voltage (OCV) and accelerates stress test (AST) phases) for 500 h, and the introduction of specific impurities like iron (Fe) and calcium (Ca) through the anodic feed water. Complementary ICP-MS analysis of the anode and cathode waters was also performed. Selected segments of the catalyst-coated membranes (CCMs) were investigated using synchrotron radiation-based XRF at microXAS beamline (X05LA) of the Swiss Light Source (Paul Scherrer Institute, Villigen, Switzerland) at 11.0, 11.4, and 11.7 keV (below and above the Ir L3- and Pt L3-edges, for IrO2, see e.g. ref. [3]). The beam was focused using a Kirkpatrick-Baez (KB) mirror system. The spatial resolution of the measurements was approx. 1 μm, allowing selective identification and relative concentration of elements to be mapped within the entire cell cross-section (electrodes and polymer layer).Through our XRF analysis, it is possible to detect migration of the catalytically active materials (Ir, Pt) through the Nafion membrane depending on the degradation time. Interestingly, while impurity tests with Ca led to its accumulation in the membrane, Fe impurities introduced similarly did not show significant accumulation. These results, demonstrating the intricate details of metal migration and their varying behaviors under different operational conditions, underscore the value of high-resolution XRF mapping with synchrotron radiation in providing critical insights. This understanding is vital to unraveling the complex degradation mechanisms of PEM water electrolyzers. Further experiments may in principle allow for precise quantification of metal migration, with measurement of appropriate elemental standards. Figure 1. Schematic overview of the study: Catalyst-coated membranes (CCMs) at various stages of degradation are investigated using synchrotron radiation-based X-ray fluorescence (XRF) mapping. This method provides a 2D elemental distribution map, as demonstrated with Iridium (Ir) in this example. Analysis of the cross-sectional distribution of the element within the membrane allows for inferences regarding its migration. We thank the SLS for providing beam-time through an accepted proposal (20221749) and appreciate the micro-XAS beamline team’s help during measurements and data processing.

Hot spot localization in the field of view of the Kirkpatrick–Baez microscope

The Kirkpatrick–Baez (KB) microscope is an effective instrument for x-ray imaging of hot spot. However, the non-uniform distribution of response efficiency in the field of view is a drawback of the KB microscope. A more accurate hot spot image requires the correction of the measured image by combining the hot spot position and the response efficiency distribution. Here, we describe a method to locate the position of the hot spot in the field of view during hot spot imaging with a KB microscope. The position of the hot spot in the field of view can be obtained by measuring the grazing incidence angle change during hot spot imaging. In the experiment of hot spot self-emission imaging with a four-channel KB microscope, the location of the hot spot with an accuracy of 15 μm was realized, and the intensity corrected hot spot image was obtained. This will solve the problem of the non-uniform distribution of the response efficiency of the KB microscope and enable quantitative measurement of hot spot radiation intensity.

Soft-X-ray nanobeams formed by aberration-reduced elliptical mirrors with large numerical aperture.

X-ray focusing mirrors often employ the Kirkpatrick-Baez (KB) geometry, which sequentially crosses two elliptic-cylindrical mirrors in grazing-incidence configurations. However, KB mirrors do not satisfy the Abbe sine condition and thus potentially expand the focus size with severe coma aberration. Satisfying the Abbe sine condition complicates mirror shapes or increases the number of ultraprecision mirrors required. The present study shows that the focal length and mirror length of KB mirrors have to be shortened to simultaneously achieve a large numerical aperture and reduced aberration. Such ultracompact KB (ucKB) mirrors are examined using a simulation that combines ray tracing and wave propagation. The focus intensity distributions show that ucKB mirrors suppress the aberration produced by their rotation errors and that they robustly achieve diffraction-limited focusing. The simulation results are confirmed in a synchrotron radiation experiment. ucKB mirrors can be advantageous for soft-X-ray nanoprobes, which require focusing devices to achieve a large numerical aperture.

Residual stress measurement system of the general purpose powder diffractometer at CSNS

Neutron diffraction has become a well-established technique for the determination of residual stresses in various structural materials and bulk industrial products because of the unique deep penetration, three-dimensional mapping capability, and volume averaged bulk measurements characteristic of the scattering neutron beam. To conduct experiments in this research area, a residual stress measurement system was established on the general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS), which diffractometer now combines both powder diffraction and residual stress measurement conditions. The best d-space resolution of the diffractometer of medium-angle detector bank is Δd/d ≈ 0.33%. The gauge volume is precisely controlled by the four-blade slits, neutron Kirkpatrick–Baez (KB) mirror and radial collimators, and the general gauge volume is φ2*2 mm 3. The intelligent scanning positioning system established by GPPD achieves high-precision sample positioning, with an accuracy of up to 100μm. Until now, it has completed measurements on standard cycle samples of VAMAS shrink fit rings and plugs with known residual stress distributions, the results confirming the diffractometer’s high sensitivity and high accuracy to stress/strain gradients in materials or components. A large number of beam times are dedicated to user researches including residual stress studies of superalloys, high-entropy alloys, engineering steels, welds, and more. This demonstrates that the GPPD’s residual stress test system and the established test methods are feasible and effective.

Ion Beam Figuring System for Synchrotron X-Ray Mirrors Achieving Sub-0.2-µrad and Sub-0.5-nm Root Mean Square

Optics with high-precision height and slope are increasingly desired in numerous industrial fields. For instance, Kirkpatrick–Baez (KB) mirrors play an important role in synchrotron X-ray applications. A KB system is composed of two aspherical, grazing-incidence mirrors used to focus an X-ray beam. The fabrication of KB mirrors is challenging due to the aspherical departure of the mirror surfaces from base geometries and the high-quality requirements for slope and height residuals. In this paper, we present the process of manufacturing an elliptical cylinder KB mirror using our in-house-developed ion beam figuring (IBF) and metrology technologies. First, the key aspects of figuring and finishing processes with IBF are illustrated in detail. The effect of positioning error on the convergence of the residual slope error is highlighted and compensated. Finally, inspection and cross-validation using different metrology instruments are performed and used as the final validation of the mirror. Results confirm that relative to the requested off-axis ellipse, the mirror has achieved 0.15-µrad root mean square (RMS) and 0.36-nm RMS residual slope and height errors, respectively, while maintaining the initial 0.3-nm RMS microroughness.

Study on full-aperture intensity response measurement for x-ray Kirkpatrick–Baez microscope

The diagnostic demand of hot-spot intensity distribution in laser inertial confinement fusion experiment has motivated quantitative measurement experiment to give the response efficiency of grazing incidence system to improve the accuracy of the diagnosis. In our study, a full-aperture intensity response measurement method is proposed, which is based on pinhole-scanning field of view (FOV) to obtain the response efficiency of grazing incidence system. The method is highly repeatable and enables response efficiency measurements over the full FOV with acceptable accuracy. A silicon positive-intrinsic-negative detector with an energy response range of 1.5 to 30 keV is used to directly detect the input and output spectrum. The response efficiency of a single-channel aspheric Kirkpatrick–Baez (KB) microscope coated with W/Si is obtained under the FOV of ±150 μm. The response efficiency of center FOV of the KB system is measured to be 2.52E-7 sr. The value is promising, as it shows a 6.6% maximum deviation from the theoretical value at center FOV, with a global uncertainty of 7.4%.

An innovative optical element for X-ray beam aperture, monitoring, and diagnostic at the CARNAÚBA beamline at SIRIUS/LNLS

The CARNAÚBA beamline is the tender-to-hard X-ray nanoprobe under commissioning for the new source Sirius at the Brazilian Synchrotron Light Laboratory (LNLS). The all-achromatic optics relies on horizontal deflection mirrors, a horizontal secondary source aperture (SSA), and Kirkpatrick–Baez (KB) mirrors to reach beam size down to ~30x30 nm2 at the sample position. To handle the highly focused power density of the pink beam and reach the desired stability for the horizontal secondary source, essential for the desired focusing and coherent properties at the sample position, we present here an SSA device based on a cryogenically cooled Si crystal in a channel-cut geometry. The crystal slabs define the channel aperture, which is controlled by a fine rotation. Simultaneously to the aperture function, the device plays the key role of beam position monitor and beam diagnostic. The scattered signal from the slabs is used to monitor the horizontal beam position during experiments and serves as a feedback input for the pitch control system of the upstream focusing mirror to stabilize the beam intensity and wavefront. The Bragg magnifier geometry of the device spreads the beam over the slabs, allowing the diffracted image of the beam to be collected by an area detector. The beam spread on the slabs also reduces the power density reaching the device, keeping it stable and under controlled temperatures.

Commissioning of the cryogenic sample environment for the TARUMÃ station at the CARNAÚBA beamline at Sirius/LNLS

TARUMÃ is a multi-technique station at CARNAÚBA (Coherent X-Ray Nanoprobe Beamline) at the 4th-generation light source Sirius at the Brazilian Synchrotron Light Laboratory (LNLS). With a tender-to-hard energy range from 2.05 to 15 keV and a fully coherent nanoprobe focused via an all-achromatic KB (Kirkpatrick-Baez) optics, it can be used for simultaneous multiple nanoscale X-ray techniques in 2D and 3D. This includes ptychography coherent diffraction imaging (ptycho-CDI), absorption spectroscopy (XAS), diffraction (XRD), fluorescence (XRF) and luminescence (XEOL). In particular, the tender energies can be used to study light elements that are commonly present in soft biological samples, ensuring the unique position of the station in the Life and Environmental Sciences program at LNLS. Still, enabling this range of experiments is sometimes only possible with cryogenically cooled samples as the high beam dose can result in both chemical and structural damage at ambient temperature conditions. At TARUMÃ, to comply with the heavily occupied volume around the sample and the sample positioning architecture, this is enabled by an open-atmosphere cryogenic system based on a commercial cryojet and a custom-designed sample holder. Following a predictive engineering approach, the system is capable of conditioning the sample down to 155K, whilst avoiding icing and condensation in nearby instrumentation and preserving the nanometer-level positioning requirements of the scanning station. Here we present the commissioning results of the referred system along with the first beamline measurements.

Complete alignment of a KB-mirror system guided by ptychography.

We demonstrate how the individual mirrors of a high-quality Kirkpatrick-Baez (KB) mirror system can be aligned to each other to create an optimally focused beam, through minimizing aberrations in the phase of the ptychographically reconstructed pupil function. Different sources of misalignment and the distinctive phase artifacts they create are presented via experimental results from the alignment of the KB mirrors at the NanoMAX diffraction endstation. The catalog of aberration artifacts can be used to easily identify which parameter requires further tuning in the alignment of any KB mirror system.

Kirkpatrick-Baez mirrors commissioning for coherent scattering and imaging endstation at SXFEL

Shanghai Soft X-ray Free-Electron Laser (SXFEL) is the first X-ray free-electron laser facility in China. The initial commissioning of the beamline was carried out in May 2021. Herein, we present a status report and the first experimental results obtained during the early commissioning of Kirkpatrick-Baez (KB) mirrors for the Coherent Scattering and Imaging (CSI) endstation, including three types of diagnostics. A bright X-ray focal spot of less than 3 μm was achieved by using edge-scan and silicon ablation imprint measurements. In order to confirm the spot size, the attenuated beam and full beam are used respectively for the two measurement methods.

Real-time spatial characterization of micrometer-sized X-ray free-electron laser beams focused by bendable mirrors.

A real-time and accurate characterization of the X-ray beam size is essential to enable a large variety of different experiments at free-electron laser facilities. Typically, ablative imprints are employed to determine shape and size of µm-focused X-ray beams. The high accuracy of this state-of-the-art method comes at the expense of the time required to perform an ex-situ image analysis. In contrast, diffraction at a curved grating with suitably varying period and orientation forms a magnified image of the X-ray beam, which can be recorded by a 2D pixelated detector providing beam size and pointing jitter in real time. In this manuscript, we compare results obtained with both techniques, address their advantages and limitations, and demonstrate their excellent agreement. We present an extensive characterization of the FEL beam focused to ≈1 µm by two Kirkpatrick-Baez (KB) mirrors, along with optical metrology slope profiles demonstrating their exceptionally high quality. This work provides a systematic and comprehensive study of the accuracy provided by curved gratings in real-time imaging of X-ray beams at a free-electron laser facility. It is applied here to soft X-rays and can be extended to the hard X-ray range. Furthermore, curved gratings, in combination with a suitable detector, can provide spatial properties of µm-focused X-ray beams at MHz repetition rate.

High-resolution dual-energy sixteen-channel Kirkpatrick–Baez microscope for ultrafast laser plasma diagnostics

High-resolution x-ray imaging diagnostics play a crucial role in fundamental research, such as inertial confinement fusion (ICF) and high-energy density physics (HEDP). Plasma signals are typically characterized by small scales, rapid evolution, and spectral complexity. These characteristics make it essential to develop x-ray diagnostics optics with high spatial resolution, collection efficiency, and spectral resolution. These requirements can be met using a combination of a high-resolution multi-channel Kirkpatrick–Baez (KB) microscope with spectrum-resolved multilayers and a time-resolved framing camera. This study describes the optical and multilayer design of a dual-energy sixteen-channel KB microscope. The calibrated results of online and offline imaging are shown. By utilizing a dual-energy multi-channel KB microscope, high-resolution backlighting and self-emission x-ray imaging can be realized and detailed information related to plasma density and temperature can be simultaneously obtained.

Optical design and performance of the biological small-angle X-ray scattering beamline at the Taiwan Photon Source.

The optical design and performance of the recently opened 13A biological small-angle X-ray scattering (SAXS) beamline at the 3.0 GeV Taiwan Photon Source of the National Synchrotron Radiation Research Center are reported. The beamline is designed for studies of biological structures and kinetics in a wide range of length and time scales, from angstrom to micrometre and from microsecond to minutes. A 4 m IU24 undulator of the beamline provides high-flux X-rays in the energy range 4.0-23.0 keV. MoB4C double-multilayer and Si(111) double-crystal monochromators (DMM/DCM) are combined on the same rotating platform for a smooth rotation transition from a high-flux beam of ∼4 × 1014 photons s-1 to a high-energy-resolution beam of ΔE/E ≃ 1.5 × 10-4; both modes share a constant beam exit. With a set of Kirkpatrick-Baez (KB) mirrors, the X-ray beam is focused to the farthest SAXS detector position, 52 m from the source. A downstream four-bounce crystal collimator, comprising two sets of Si(311) double crystals arranged in a dispersive configuration, optionally collimate the DCM (vertically diffracted) beam in the horizontal direction for ultra-SAXS with a minimum scattering vector q down to 0.0004 Å-1, which allows resolving ordered d-spacing up to 1 µm. A microbeam, of 10-50 µm beam size, is tailored by a combined set of high-heat-load slits followed by micrometre-precision slits situated at the front-end 15.5 m position. The second set of KB mirrors then focus the beam to the 40 m sample position, with a demagnification ratio of ∼1.5. A detecting system comprising two in-vacuum X-ray pixel detectors is installed to perform synchronized small- and wide-angle X-ray scattering data collections. The observed beamline performance proves the feasibility of having compound features of high flux, microbeam and ultra-SAXS in one beamline.

Development of scanning X-ray fluorescence microscope using KB mirror and white synchrotron radiation at SAGA Light Source

A scanning X-ray fluorescence microscope that uses a Kirkpatrick-Baez (KB) mirror and white synchrotron radiation (SR) was developed for obtaining detailed elemental maps within a micro-meter order. The KB mirror is a total reflection mirror, and the white X-rays are focused at a focus point without chromatic aberration. Therefore, the proposed microscope can use strong white and/or pink SR and enable elemental mapping within a practical measurement time at small synchrotron facilities. A feasibility study on the developed microscope was performed by using white SR at the SAGA Light Source in Tosu, Japan. By using the developed microscope, an X-ray microbeam 1 μm in diameter was successfully formed, and a fine elemental map of a Cu mesh and a seed of eustoma were obtained.

Monochromatic Kirkpatrick–Baez microscope combining a spherically bent crystal and a multilayer mirror

Most Kirkpatrick–Baez (KB) microscopes for imaging monochromatic laser-produced plasma are composed of two concave multilayer mirrors; their energy resolution (ΔE/E) is approximately 1×10−1. In this study, a new type of monochromatic KB microscope combining a spherically bent crystal and a multilayer mirror was developed. As the spherically bent crystal features a narrow spectral bandwidth, it can attain a high energy resolution. In addition, the grazing incidence angle on the crystal is significantly larger than that on a multilayer mirror; therefore, a large collection solid angle and a high spatial resolution can be achieved. A prototype consisting of a spherically bent mica crystal and a mirror coated with Ni/C multilayers was constructed to demonstrate the feasibility and performance of the proposed KB microscope. In the backlight imaging experiment performed, the microscope achieved a spatial resolution of approximately 10μm throughout a 200μm field of view at 4.51 keV, with ΔE/E = 4.9 ×10−3. The proposed KB microscope featuring a high energy and spatial resolution is expected to be a novel experimental tool for inertial confinement fusion (ICF) diagnostics.

Generation of an X-ray nanobeam of a free-electron laser using reflective optics with speckle interferometry.

Ultimate focusing of an X-ray free-electron laser (XFEL) enables the generation of ultrahigh-intensity X-ray pulses. Although sub-10 nm focusing has already been achieved using synchrotron light sources, the sub-10 nm focusing of XFEL beams remains difficult mainly because the insufficient stability of the light source hinders the evaluation of a focused beam profile. This problem is specifically disadvantageous for the Kirkpatrick-Baez (KB) mirror focusing system, in which a slight misalignment of ∼300 nrad can degrade thefocused beam. In this work, an X-ray nanobeam of a free-electron laser wasgenerated using reflective KB focusing optics combined with speckle interferometry. The speckle profiles generated by 2 nm platinum particles were systematically investigated on a single-shot basis by changing the alignment of the multilayer KB mirror system installed at the SPring-8 Angstrom Compact Free-Electron Laser, in combination with computer simulations. It was verified that the KB mirror alignments were optimized with the required accuracy, and a focused vertical beam of 5.8 nm (±1.2 nm) was achieved after optimization. The speckle interferometry reported in this study is expected to be an effective tool for optimizing the alignment of nano-focusing systems and for generating an unprecedented intensity of up to 1022 W cm-2 using XFEL sources.

Nondestructive Differentiation of Polyester Single White Fibers Using Synchrotron Radiation Microbeam X-ray Fluorescence Spectrometry with Vertical Focusing.

In this study, the nondestructive differentiation of individual white polyester clothing fibers was accomplished via synchrotron radiation microbeam X-ray fluorescence (SR-μ-XRF) analysis. SR-μ-XRF with vertical focusing is a useful nondestructive method for the analysis of a single polyester clothing fiber. Kirkpatrick-Baez (KB) mirror was used to vertically focus 20 keV X-rays for the analysis of 22 individual white polyester fibers taken from clothing commonly sold in Japan. SR-μ-XRF with a vertical focused 2 μm (V) × 300 μm (H) beam was approximately 12.8 times more sensitive than SR-XRF with an unfocused 300 μm (V) × 300 μm (H) beam for the detection of elements in single fibers. The minimum detection limits (MDLs) of the SR-μ-XRF method were 8.15 ppm for Cl and 0.06 ppm for Br. In addition to Ti in TiO2 delustering agents, Zr and Nb impurities in the delustering agents were detected in individual fibers. Sb from a polymerization catalyst and Co from a transesterification catalyst were also detected in individual fibers. Comparing the Ti Kβ /Sb Lα,β and Zr Kα /Nb Kα X-ray intensity ratios was a useful way to distinguish individual clothing fibers, and 98% of the fibers were differentiated when additional trace elements were used as discrimination indicators.

Kirkpatrick-Baez active optics system at FERMI: system performance analysis.

FERMI is the first and only seeded EUV-SXR free-electron laser (FEL) facility available to users; it operates at Elettra - Sincrotrone Trieste (Italy) and it presents five operating endstations. Three of them, namely LDM (Low Density Matter), DiProI (Diffraction and Projection Imaging) and MagneDyn (Magneto-Dynamical studies), use a Kirkpatrick-Baez (KB) active X-ray optics system to focus the FEL pulses into the experimental chambers. The present work reports on the final results of the upgraded KB Active Optics Systems (KAOS), which have been mechanically modified in order to improve stability and repeatability with respect to the original design. The results have been obtained on both the FERMI FEL lines, FEL1 and FEL2, and are particularly relevant for the latter as it is the low-wavelength line recently opened to users. After a thorough description of the new mechanical layout of the system and the aspects that have been improved after the refurbishment, a set of simulations of the optical performances are presented. The code used to simulate the behavior of KAOS is WISEr, a physical-optics-based tool, which is freely accessible, and integrated into the Oasys platform, that takes into account the specific surface metrology characterization of the beamline mirrors, including figure errors and microroughness power spectral density. The results of WISEr are then used as a reference for the actual optimization of the optical system. This procedure relies heavily on a wavefront sensor (WFS) mounted out of focus to optimize the refocusing mirrors alignment as well as their curvature bending (by minimization of the coefficients of the Zernike wavefront expansion). Moreover, the WFS data are used to reconstruct the focal spot parameters by means of a back-propagation of the electric field. Finally, these results are compared with those obtained after the FEL ablation of a PMMA layer positioned on the focal plane, and analyzed ex situ in a post-mortem fashion. The mechanically refurbished optical system and the multi-technique alignment approach, aimed at optimizing the mirrors' curvature, pitch and roll angles, allowed a focal spot of 1.8 µm × 2.4 µm at 4.14 nm wavelength (FEL2) to be inferred, confirmed by the PMMA ablation imprints.

Practical, corrected Kirkpatrick-Baez telescope for x-ray astronomy.

Kirkpatrick-Baez (K-B) optics offer a means of imaging soft x-rays with modest resolution and a multi-arc-minute field of view at a cost far below the conventional Wolter design. Such a low-cost system could be useful for dedicated, long-time-line observation of astronomical x-ray sources from orbit. A K-B telescope consists of crossed arrays of parabolic mirrors at grazing incidence. The classic K-B telescope is subject to significant aberration arising from the interplay between the focusing of the fore and aft mirror arrays. We demonstrate here a corrected K-B prescription with aberrations reduced by an order of magnitude. We show, furthermore, that it is possible to construct such a system by constraining flat "slats" of commercially available glass in precision-milled grooves. The slats deform into shapes that adequately approximate the optimal figures, thereby yielding focusing better than the best version of the classic K-B telescope. The result is a new approach that greatly simplifies the task of achieving both useful resolution and high effective area for x-ray astronomy applications.

Development of an adjustable Kirkpatrick-Baez microscope for laser driven x-ray sources.

A prototype of a highly adjustable Kirkpatrick-Baez (KB) microscope has been designed, built, and tested in a number of laser driven x-ray experiments using the high power (200 TW) VEGA-2 laser system of the Spanish Centre for Pulsed Lasers (CLPU). The presented KB version consists of two, perpendicularly mounted, 500 μm thick silicon wafers, coated with a layer of platinum, a few tens of nanometers thick. Unlike the usual millimeter thick glass substrate, this design allows for a larger bending flexibility and large adjustment range. According to simulations, this KB microscope offers broadband multikiloelectron volt reflection spectra (1 eV-20 keV), allowing more spectral tunability than conventional Bragg crystals. In addition to be vacuum compatible, this prototype is characterized by a relatively small size (21 cm × 31 cm × 27 cm) and permits remote control and modification both of the radii of curvature (down to 10 m) and of the grazing incidence angle (up to 60 mrad). A few examples of focusing performance tests and experimental results are discussed.