Showing papers on "Synchrotron radiation published in 2021"

Discovery of magnetic fields along stacked cosmic filaments as revealed by radio and X-ray emission

Abstract: Diffuse filaments connect galaxy clusters to form the cosmic web. Detecting these filaments could yield information on the magnetic field strength, cosmic ray population and temperature of intercluster gas, yet, the faint and large-scale nature of these bridges makes direct detections very challenging. Using multiple independent all-sky radio and X-ray maps we stack pairs of luminous red galaxies as tracers for cluster pairs. For the first time, we detect an average surface brightness between the clusters from synchrotron (radio) and thermal (X-ray) emission with $\gtrsim 5\sigma$ significance, on physical scales larger than observed to date ($\geq 3\,$Mpc). We obtain a synchrotron spectral index of $\alpha \simeq -1.0$ and estimates of the average magnetic field strength of $ 30 \leq B \leq 60 \,$nG, derived from both equipartition and Inverse Compton arguments, implying a 5 to 15$\,$per cent degree of field regularity when compared with Faraday rotation measure estimates. While the X-ray detection is inline with predictions, the average radio signal comes out higher than predicted by cosmological simulations and dark matter annihilation and decay models. This discovery demonstrates that there are connective structures between mass concentrations that are significantly magnetised, and the presence of sufficient cosmic rays to produce detectable synchrotron radiation.

Comparison of the ion-to-electron temperature ratio prescription: GRMHD simulations with electron thermodynamics

Abstract: The Event Horizon Telescope (EHT) collaboration, an Earth-size sub-millimetre radio interferometer, recently captured the first images of the central supermassive black hole in M87. These images were interpreted as gravitationally-lensed synchrotron emission from hot plasma orbiting around the black hole. In the accretion flows around low-luminosity active galactic nuclei such as M87, electrons and ions are not in thermal equilibrium. Therefore, the electron temperature, which is important for the thermal synchrotron radiation at EHT frequencies of 230 GHz, is not independently determined. In this work, we investigate the commonly used parameterised ion-to-electron temperature ratio prescription, the so-called R-$\beta$ model, considering images at 230 GHz by comparing with electron-heating prescriptions obtained from general-relativistic magnetohydrodynamical (GRMHD) simulations of magnetised accretion flows in a Magnetically Arrested Disc (MAD) regime with different recipes for the electron thermodynamics. When comparing images at 230 GHz, we find a very good match between images produced with the R-$\beta$ prescription and those produced with the turbulent- and magnetic reconnection- heating prescriptions. Indeed, this match is on average even better than that obtained when comparing the set of images built with the R-$\beta$ prescription with either a randomly chosen image or with a time-averaged one. From this comparative study of different physical aspects, which include the image, visibilities, broadband spectra, and light curves, we conclude that, within the context of images at 230 GHz relative to MAD accretion flows around supermassive black holes, the commonly-used and simple R-$\beta$ model is able to reproduce well the various and more complex electron-heating prescriptions considered here.

Experimental demonstration of the mechanism of steady-state microbunching.

Abstract: The use of particle accelerators as photon sources has enabled advances in science and technology1. Currently the workhorses of such sources are storage-ring-based synchrotron radiation facilities2–4 and linear-accelerator-based free-electron lasers5–14. Synchrotron radiation facilities deliver photons with high repetition rates but relatively low power, owing to their temporally incoherent nature. Free-electron lasers produce radiation with high peak brightness, but their repetition rate is limited by the driving sources. The steady-state microbunching15–22 (SSMB) mechanism has been proposed to generate high-repetition, high-power radiation at wavelengths ranging from the terahertz scale to the extreme ultraviolet. This is accomplished by using microbunching-enabled multiparticle coherent enhancement of the radiation in an electron storage ring on a steady-state turn-by-turn basis. A crucial step in unveiling the potential of SSMB as a future photon source is the demonstration of its mechanism in a real machine. Here we report an experimental demonstration of the SSMB mechanism. We show that electron bunches stored in a quasi-isochronous ring can yield sub-micrometre microbunching and coherent radiation, one complete revolution after energy modulation induced by a 1,064-nanometre-wavelength laser. Our results verify that the optical phases of electrons can be correlated turn by turn at a precision of sub-laser wavelengths. On the basis of this phase correlation, we expect that SSMB will be realized by applying a phase-locked laser that interacts with the electrons turn by turn. This demonstration represents a milestone towards the implementation of an SSMB-based high-repetition, high-power photon source. The mechanism of steady-state electron microbunching is demonstrated, providing a basis that will enable its full implementation in electron storage rings to generate high-repetition, high-power coherent radiation.

The new X-ray absorption fine-structure beamline with sub-second time resolution at the Taiwan Photon Source

Abstract: The new TPS 44A beamline at the Taiwan Photon Source, located at the National Synchrotron Radiation Research Center, is presented. This beamline is equipped with a new quick-scanning monochromator (Q-Mono), which can provide both conventional step-by-step scans (s-scans) and on-the-fly scans (q-scans) for X-ray absorption fine-structure (XAFS) spectroscopy experiments, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectral measurements. Ti and Te K-edge XAFS spectra were used to demonstrate the capability of collecting spectra at the limits of the working energy range. The Ni and Cu K-edge XAFS spectra for a Cu-doped Pt/Ni nanocomposite were acquired to test the performance of the newly commissioned beamline. Pt L3- and Ru K-edge quick-scanning XAFS (QXAFS) spectra for standard Pt and Ru foils, respectively, revealed the stability of the q-scan technique. The results also demonstrated the beamline's ability to collect XAFS spectra on a sub-second timescale. Furthermore, a Zn(s)|Zn2+(aq)|Cu(s) system was tested to indicate that the states of the Zn electrode could be observed in real time for charging and discharging conditions using an in situ/operando setup combined with QXAFS measurements.

New era of synchrotron radiation: fourth-generation storage ring

Abstract: There had been remarkable progress in developing third-generation electron storage rings as the main sources of very bright photon beams. Fourth-generation storage rings based on the multi-bend achromat lattice concept may be able to surpass the brightness and coherence that are attained using present third-generation storage rings. In this paper, we survey ongoing work around the world to develop concepts and designs for fourth-generation electron storage rings.

Coherent inverse Compton scattering by bunches in fast radio bursts

Abstract: The extremely high brightness temperature of fast radio bursts (FRBs) requires that their emission mechanism must be "coherent", either through concerted particle emission by bunches or through an exponential growth of a plasma wave mode or radiation amplitude via certain maser mechanisms. The bunching mechanism has been mostly discussed within the context of curvature radiation or cyclotron/synchrotron radiation. Here we propose a family of model invoking coherent inverse Compton scattering (ICS) of bunched particles that may operate within or just outside of the magnetosphere of a flaring magnetar. Crustal oscillations during the flaring event may excite low-frequency electromagnetic waves near the magnetar surface. The X-mode of these waves could penetrate through the magnetosphere. Bunched relativistic particles in the charge starved region inside the magnetosphere or in the current sheet outside of the magnetosphere would upscatter these low-frequency waves to produce GHz emission to power FRBs. The ICS mechanism has a much larger emission power for individual electrons than curvature radiation. This greatly reduces the required degree of coherence in bunches, alleviating several criticisms to the bunching mechanism raised in the context of curvature radiation. The emission is $\sim 100\%$ linearly polarized (with the possibility of developing circular polarization) with a constant or varying polarization angle across each burst. The mechanism can account for a narrow-band spectrum and a frequency downdrifting pattern, as commonly observed in repeating FRBs.

Protein Dynamics and Time Resolved Protein Crystallography at Synchrotron Radiation Sources: Past, Present and Future

Abstract: The ultrabright and ultrashort pulses produced at X-ray free electron lasers (XFELs) has enabled studies of crystallized molecular machines at work under ‘native’ conditions at room temperature by the so-called time-resolved serial femtosecond crystallography (TR-SFX) technique. Since early TR-SFX experiments were conducted at XFELs, it has been largely reported in the literature that time-resolved X-ray experiments at synchrotrons are no longer feasible or are impractical due to the severe technical limitations of these radiation sources. The transfer of the serial crystallography approach to newest synchrotrons upgraded for higher flux density and with beamlines using sophisticated focusing optics, submicron beam diameters and fast low-noise photon-counting detectors offers a way to overcome these difficulties opening new and exciting possibilities. In fact, there is an increasing amount of publications reporting new findings in structural dynamics of protein macromolecules by using time resolved crystallography from microcrystals at synchrotron sources. This review gathers information to provide an overview of the recent work and the advances made in this filed in the past years, as well as outlines future perspectives at the next generation of synchrotron sources and the upcoming compact pulsed X-ray sources.

Spatiotemporal analysis of the runaway distribution function from synchrotron images in an ASDEX Upgrade disruption

Abstract: Synchrotron radiation images from runaway electrons (REs) in an ASDEX Upgrade discharge disrupted by argon injection are analysed using the synchrotron diagnostic tool Soft and coupled fluid-kinetic simulations. We show that the evolution of the runaway distribution is well described by an initial hot-tail seed population, which is accelerated to energies between 25-50 MeV during the current quench, together with an avalanche runaway tail which has an exponentially decreasing energy spectrum. We find that, although the avalanche component carries the vast majority of the current, it is the high-energy seed remnant that dominates synchrotron emission. With insights from the fluid-kinetic simulations, an analytic model for the evolution of the runaway seed component is developed and used to reconstruct the radial density profile of the RE beam. The analysis shows that the observed change of the synchrotron pattern from circular to crescent shape is caused by a rapid redistribution of the radial profile of the runaway density.

Modelling synchrotron and synchrotron self-Compton emission of gamma-ray burst afterglows from radio to very-high energies

Abstract: Synchrotron radiation from a decelerating blastwave is a widely accepted model of radio to X-ray afterglow emission from gamma-ray bursts (GRBs). GeV gamma-ray emission detected by the Fermi Large Area Telescope (LAT) and the duration of which extends beyond the prompt gamma-ray emission phase, is also compatible with broad features of afterglow emission. We revisit the synchrotron self-Compton (SSC) emission model from a decelerating blastwave to fit multiwavelength data from three bright GRBs, namely GRB~190114C, GRB~130427A and GRB~090510. We constrain the afterglow model parameters using the simultaneous fit of the spectral energy distributions at different times and light curves at different frequencies for these bursts. We find that a constant density interstellar medium is favored for the short GRB~090510, while a wind-type environment is favored for the long GRB~130427A and GRB~190114C. The sub-TeV component in GRB~190114C detected by MAGIC is the SSC emission in our modelling. Furthermore we find that the SSC emission in the Thomson regime is adequate to fit the spectra and light curves of GRB~190114C. For the other two GRBs, lacking sub-TeV detection, the SSC emissions are also modeled in the Thomson regime. For the model parameters we have used, the $\gamma\gamma$ attenuation in the blastwave is negligible in the sub-TeV range compared to the redshift-dependent $\gamma\gamma$ attenuation in the extragalactic background light.

Transverse Beam Emittance Measurement by Undulator Radiation Power Noise

Abstract: Generally, turn-to-turn power fluctuations of incoherent spontaneous synchrotron radiation in a storage ring depend on the 6D phase-space distribution of the electron bunch. In some cases, if only one parameter of the distribution is unknown, this parameter can be determined from the measured magnitude of these power fluctuations. In this Letter, we report an absolute measurement (no free parameters or calibration) of a small vertical emittance (5-15 nm rms) of a flat beam by this method, under conditions, when it is unresolvable by a conventional synchrotron light beam size monitor.

Disentangling x-ray dichroism and birefringence via high-purity polarimetry

Abstract: High-brilliance synchrotron radiation sources have opened new avenues for x-ray polarization analysis that go far beyond conventional polarimetry in the optical domain. With linear x-ray polarizers in a crossed setting, polarization extinction ratios down to 10−10 can be achieved. This renders the method sensitive to probe the tiniest optical anisotropies that would occur, for example, in strong-field quantum electrodynamics due to vacuum birefringence and dichroism. Here we show that high-purity polarimetry can be employed to reveal electronic anisotropies in condensed matter systems with utmost sensitivity and spectral resolution. Taking CuO and La2CuO4 as benchmark systems, we present a full characterization of the polarization changes across the Cu K-absorption edge and their separation into dichroic and birefringent contributions. At diffraction-limited synchrotron radiation sources and x-ray lasers, where polarization extinction ratios of 10−12 can be achieved, our method has the potential to assess birefringence and dichroism of the quantum vacuum in extreme electromagnetic fields.

Intense monochromatic photons above 100 keV from an inverse Compton source

Abstract: Quasimonochromatic x rays are difficult to produce above 100 keV, but have a number of uses in x-ray and nuclear science, particularly in the analysis of transuranic species. Inverse Compton scattering (ICS) is capable of fulfilling this need, producing photon beams with properties and energies well beyond the limits of typical synchrotron radiation facilities. We present the design and predicted output of such an ICS source at CBETA, a multiturn energy-recovery linac with a top energy of 150 MeV, which we anticipate producing x rays with energies above 400 keV and a collimated flux greater than 108 photons per second within a 0.5% bandwidth. At this energy, the anticipated flux exceeds that attainable from storage ring sources of synchrotron radiation, even though CBETA is a significantly smaller accelerator system. We also consider the consequences of extending the CBETA ICS source performance to higher electron energies, exploring achievable parameters and applications for MeV-scale photons. We foresee that future energy-recovery linacs may serve as ICS sources, capable of providing high energy photons unavailable at synchrotron radiation facilities or photon beams above approximately 300 keV which outperform sources at synchrotron radiation facilities in both flux and average brilliance.

Commissioning of the hybrid multibend achromat lattice at the European Synchrotron Radiation Facility

Abstract: Successful commissioning of a hybrid multibend achromat lattice at the European Synchrotron Radiation Facility demonstrates that ultralow emittance can be achieved with excellent lifetime and large dynamic aperture for high energy storage rings.

High quantum efficiency GaAs photocathodes activated with Cs, O2, and Te

Abstract: GaAs photocathodes are the primary choice for generating spin-polarized electron beam with high brightness, high polarization, and fast polarization reversal However, it suffers from short lifetime due to the highly reactive nature of the emission surface, resulting in substantial operational difficulties Activating GaAs with a more robust material, such as Cs2Te, shows comparable polarization to that of Cs–O activation and increases the lifetime due to the robustness of the Cs2Te layer However, previously reported photocathodes based on Cs–Te activation on GaAs suffer from 10× lower quantum efficiency (QE) compared to that activated with conventional Cs–O activation Herein, we report activation recipes for GaAs photocathodes using Cs, O2, and Te For Cs–Te activation, the QE was 66% at 532 nm For Cs–O–Te activation, the QE was 88% at 532 nm and 45% at 780 nm The negative electron affinity of the activated GaAs was directly measured and confirmed by low energy electron microscopy We also report the activation layer chemical states and stoichiometry using in situ micro-spot synchrotron radiation x-ray photoelectron spectroscopy

The newborn black hole in GRB 191014C proves that it is alive

Abstract: A multi-decade theoretical effort has been devoted to finding an efficient mechanism to use the rotational and electrodynamical extractable energy of a Kerr-Newman black hole (BH), to power the most energetic astrophysical sources such as gamma-ray bursts (GRBs) and active galactic nuclei. We show an efficient general relativistic electrodynamical process which occurs in the “inner engine” of a binary driven hypernova. The inner engine is composed of a rotating Kerr BH of mass M and dimensionless spin parameter α , a magnetic field of strength B 0 aligned and parallel to the rotation axis, and a very low-density ionized plasma. Here, we show that the gravitomagnetic interaction between the BH and the magnetic field induces an electric field that accelerates electrons and protons from the environment to ultrarelativistic energies emitting synchrotron radiation. We show that in GRB 190114C the BH of mass M = 4.4 M ⊙ , α = 0.4, and B 0 ≈ 4 × 1010 G can lead to a high-energy (≳GeV) luminosity of 1051 erg s−1 . The inner engine parameters are determined by requiring (1) that the BH extractable energy explains the GeV and ultrahigh-energy emission energetics, (2) that the emitted photons are not subjected to magnetic-pair production, and (3) that the synchrotron radiation timescale agrees with the observed high-energy timescale. We find for GRB 190114C a clear jetted emission of GeV energies with a semi-aperture angle of approximately 60° with respect to the BH rotation axis.

When x-rays alter the course of your experiments.

Abstract: The continuing increase in the brilliance of synchrotron radiation beamlines allows for many new and exciting experiments that were impossible before the present generation of synchrotron radiation sources came on line. However, the exposure to such intense beams also tests the limits of what samples can endure. Whilst the effects of radiation induced damage in a static experiment often can easily be recognized by changes in the diffraction or spectroscopy curves, the influence of radiation on chemical or physical processes, where one expects curves to change, is less often recognized and can be misinterpreted as a 'real' result instead of as a 'radiation influenced result'. This is especially a concern in time-resolved materials science experiments using techniques as powder diffraction, small angle scattering and x-ray absorption spectroscopy. Here, the effects of radiation (5-50 keV) on some time-resolved processes in different types of materials and in different physical states are discussed. We show that such effects are not limited to soft matter and biology but rather can be found across the whole spectrum of materials research, over a large range of radiation doses and is not limited to very high brilliance beamlines.

A practical design and field errors analysis of a merged APPLE–Knot undulator for High Energy Photon Source

Abstract: Users of HEPS require polarization adjustable and high-flux synchrotron radiation with energy of 100–2000 eV. To achieve 100 eV photon energy at HEPS, a 6 GeV storage ring, the problem of on-axis heat load becomes a significant challenge for users. A new type of four-row merged APPLE–Knot undulator recently proposed seems to be the most effective solution to reduce on-axis power density. However, as an undulator with such complex magnetization orientation distribution of magnetic blocks, its field integrals correction and the effect of field errors on the radiation performance are different from that of conventional EPU. Whether it can realize its field integrals correction and perform as well as in theory with field errors has become a concern. Here, a set of field integrals correction schemes is reported and field errors analysis has been done. A general method for evaluating the effect of magnetization orientation deviation of the magnetic block on radiation performance is proposed. It can be used for any insertion device containing permanent magnetic magnets if necessary.

The Interaction Region of the Electron-Ion Collider EIC

Abstract: This paper presents an overview of the Interaction Region (IR) design for the planned Electron Ion Collider (EIC) at Brookhaven National Laboratory. The IR is designed to meet the requirements of the nuclear physics community as outlined in [1]. The IR design features a ±4.5 m free space for the detector; a forward spectrometer magnet is used for the detection of hadrons scattered under small angles. The hadrons are separated from the neutrons allowing detection of neutrons up to ±4 mrad. On the rear side the electrons are separated from photons using a weak dipole magnet for the luminosity monitor and to detect scattered electrons (e-tagger). To avoid synchrotron radiation backgrounds in the detector no strong electron bending magnet is placed within 40 m upstream of the IP. The magnet apertures on the rear side are large enough to allow synchrotron radiation to pass through the magnets. The beam pipe has been optimized to reduce the impedance; the total power loss in the central vacuum chamber is expected to be less than 90 W. To reduce risk and cost the IR is designed to employ standard NbTi superconducting magnets, which are described in a separate paper.

Propagation of partially coherent radiation using Wigner functions

Abstract: Undulator radiation from synchrotron light sources must be transported down a beam line from the source to the sample. A partially coherent photon beam may be represented in phase space using a Wigner function, and its transport may use some similar techniques that are familiar in particle beam transport. We describe this process in the case that the beam line is composed of linear focusing and defocusing sections as well as apertures. We present a compact representation of the beam line map involving linear transformations and convolutions. We create a $1\ensuremath{\mathbin:}1$ imaging system with a single slit on the image plane and observe the radiation downstream to it. We propagate a Gaussian beam and undulator radiation down this sample beam line, drawing parameters from current and future ultra low emittance light sources. We derive an analytic expression for the partially coherent Gaussian case including passage through a single slit aperture. We benchmark the Wigner function calculation against the analytical expression and a partially coherent calculation in the synchrotron radiation workshop (SRW) code.

Exploring Frontiers of 4D X-ray Tomography

Abstract: In the 4D world of three-dimensional (3D) space plus time that we live in, there is a vast blue ocean in the spatio-temporal domain of micrometers and milliseconds that has never been accessed even with the most advanced measurement technology, and it is expected to be full of various non-equilibrium phenomena. In this paper, we review recent advances in synchrotron hard X-ray tomography we have made that can be used to explore the 4D frontier.

Time-of-flight photoelectron momentum microscopy with 80–500 MHz photon sources: electron-optical pulse picker or bandpass pre-filter

Abstract: The small time gaps of synchrotron radiation in conventional multi-bunch mode (100–500 MHz) or laser-based sources with high pulse rate (∼80 MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100 ps range yield only 20–100 resolved time slices within the small time gap. Here we present two techniques of implementing efficient ToF recording at sources with high repetition rate. A fast electron-optical beam blanking unit with GHz bandwidth, integrated in a photoelectron momentum microscope, allows electron-optical `pulse-picking' with any desired repetition period. Aberration-free momentum distributions have been recorded at reduced pulse periods of 5 MHz (at MAX II) and 1.25 MHz (at BESSY II). The approach is compared with two alternative solutions: a bandpass pre-filter (here a hemispherical analyzer) or a parasitic four-bunch island-orbit pulse train, coexisting with the multi-bunch pattern on the main orbit. Chopping in the time domain or bandpass pre-selection in the energy domain can both enable efficient ToF spectroscopy and photoelectron momentum microscopy at 100–500 MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80 MHz, <1 meV bandwidth) facilitates momentum microscopy with an energy resolution of 4.2 meV and an analyzed region-of-interest (ROI) down to <800 nm. In this novel approach to `sub-µm-ARPES' the ROI is defined by a small field aperture in an intermediate Gaussian image, regardless of the size of the photon spot.

Temporal evolution of prompt GRB polarization

Abstract: The dominant radiation mechanism that produces the prompt emission in gamma-ray bursts (GRBs) remains a major open question. Spectral information alone has proven insufficient in elucidating its nature. Time-resolved linear polarization has the potential to distinguish between popular emission mechanisms, e.g., synchrotron radiation from electrons with a power-law energy distribution or inverse Compton scattering of soft seed thermal photons, which can yield the typical GRB spectrum but produce different levels of polarization. Furthermore, it can be used to learn about the outflow's composition (i.e. whether it is kinetic-energy-dominated or Poynting-flux-dominated) and angular structure. For synchrotron emission it is a powerful probe of the magnetic field geometry. Here we consider synchrotron emission from a thin ultrarelativistic outflow, with bulk Lorentz factor $\Gamma(R)=\Gamma_0(R/R_0)^{-m/2}\gg1$, that radiates a Band-function spectrum in a single (multiple) pulse(s) over a range of radii, $R_0\leq R\leq R_0+\Delta R$. Pulse profiles and polarization evolution at a given energy are presented for a coasting ($m=0$) and accelerating ($m=-2/3$) thin spherical shell and for an off-axis top-hat jet with sharp as well as smooth edges in emissivity. Four different magnetic field configurations are considered, such as a locally ordered field coherent over angular scales $\theta_B\gtrsim1/\Gamma$, a tangled field ($B_\perp$) in the plane transverse to the radial direction, an ordered field ($B_\parallel$) aligned in the radial direction, and a globally ordered toroidal field ($B_{\rm tor}$). All field configurations produce distinct polarization evolution with single (for $B_\perp$ and $B_\parallel$) and double (for $B_{\rm tor}$) $90^\circ$ changes in the polarization position angle.

Advanced X-ray imaging at beamline 07 of the SAGA Light Source.

Abstract: The SAGA Light Source provides X-ray imaging resources based on high-intensity synchrotron radiation (SR) emitted from the superconducting wiggler at beamline 07 (BL07). By combining quasi-monochromatic SR obtained by the newly installed water-cooled metal filter and monochromatic SR selected by a Ge double-crystal monochromator (DCM) with high-resolution lens-coupled X-ray imagers, fast and low-dose micro-computed tomography (CT), fast phase-contrast CT using grating-based X-ray interferometry, and 2D micro-X-ray absorption fine structure analysis can be performed. In addition, by combining monochromatic SR obtained by a Si DCM with large-area fiber-coupled X-ray imagers, high-sensitivity phase-contrast CT using crystal-based X-ray interferometry can be performed. Low-temperature CT can be performed using the newly installed cryogenic system, and time-resolved analysis of the crystallinity of semiconductor devices in operation can be performed using a time-resolved topography system. The details of each instrument and imaging method, together with exemplary measurements, are presented.

In situ synchrotron X-ray analysis: Application of high-pressure sliding process to Ti allotropic transformation

Abstract: 1Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan 2Magnesium Research Center, Kumamoto University, Kumamoto 860-8555, Japan 3Synchrotron Light Application Center, Saga University, Saga 840-8502, Japan 4Department of Materials Science and Engineering, Kyushu University, Fukuoka 819-0395, Japan 5Department of Mechanical Engineering and Materials Science, Yokohama National University, Yokohama 240-8501, Japan 6Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan