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A coupling device, which can extract coherent edge radiation (CER) from an optical cavity for a free-electron laser (FEL) without damaging the FEL due to diffraction loss, was developed at Nihon University. We successfully observed the CER beam with a power of 1 mW or more in the terahertz range during FEL oscillation. It is revealed that the CER power changed with the detuning of the optical cavity and the dependence of the CER power on the detuning length differs from that of the FEL power. The measured CER spectra indicate that the longitudinal electron distribution in a bunch is modulated by the FEL oscillation with a period corresponding to the FEL slippage length. We herein report the characteristics of the CER with FEL oscillation in detail. These results demonstrate that the CER is excellent tool to reveal the overall effect of FEL interaction on electron distribution in a bunch.

Light perception is an intriguing subject, and it has been demonstrated that some animals can perceive wavelengths beyond human vision. However, it is still controversial whether animals can see mid-infrared radiation. A combination of two free-electron laser (FEL) facilities, LEBRA-FEL (Nihon University) and KU-FEL (Kyoto University), can provide light sources with high peak power and spatially coherent monochromatic wavelengths that are continuously tuneable from 400 nm to 20 μm. We show that the crayfish (Procambarus clarkii) compound eye responds to pulsed mid-infrared FELs (1 Hz for KU-FEL; 2 Hz for LEBRA-FEL) from 3 to 17 μm. Our finding provides insight into the animal’s visual sensing of mid-infrared radiation, and that the sensing does not depend on thermal effects. Although the behavioural reason for vision in this wavelength range and the mechanism are still under investigation, understanding this type of visual sensing may lead to applications other than photophysical applications.

We developed a novel method for element detection utilizing an x-ray source based on parametric x-ray radiation (PXR), an accelerator-based light source at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University. The method is a type of $K$-edge subtraction (KES) imaging that uses the drastic change of x-ray absorption around the $K$-shell absorption edge of the target element. Using the properties of PXR, simultaneous KES imaging is possible, and can easily be applied to 3-dimensional (3D) computed tomography (CT). We demonstrated the feasibility of simultaneous KES-CT in our previous work. In this study, we investigate the quantitative performance of simultaneous KES imaging for a sample containing the element strontium (Sr) for which the $K$-edge energy is 16.1 keV. Results of a simultaneous KES-CT experiment employing the LEBRA-PXR source confirm that the imaging method can provide a 3D distribution of the element with a value proportional to the Sr concentration. Concerning sensitivity to element concentration, at least in the region of 0.5%-concentration, the sample was successfully distinguished from the region without Sr in the 3D tomographic image obtained using the element-imaging technique.

We study the effect of a combination of velocity bunchings and its application to THz coherent undulator radiation at LEBRA, Nihon U. by simulations. The velocity bunching is a technique that is commonly used to make the bunch length shorter at lower energies. However, since one velocity bunching has a correlation between bunch energy and length, we may not have so much room to change energies to obtain different coherent radiation wavelengths. Hence we propose a combination of velocity bunchings, that relaxes the restrictive correlation. We have three 4m traveling-wave accelerator tubes at LEBRA, Nihon U. The undulator is installed after the acceleration tubes and 2 x 45 degree bending magnets. Since the design of current undulator requires less than 25 MeV beam energy to obtain the radiation at THz region, the velocity bunching is reasonable for coherent radiation. We show the simulation results of a combination of velocity bunchings of the three tubes and the magnetic bunching at bending magnets, suitable for the coherent undulator radiation., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

This paper describes a proposal for a compact x-ray source based on parametric x-ray radiation (PXR). The PXR, which is produced when a single crystal is bombarded with relativistic electrons, has good monochromaticity and spatial coherence, and is expected to be well suited for imaging of low-Z materials and medical application. The proposed system employs a pair of copper accelerating structures which are operated at a cryogenic temperature of 20 K and arranged to form a resonant ring configuration. The electron beam is once accelerated up to 75 MeV in one of the structures, being decelerated down to lower than 7 MeV in the other structure after generating PXR at a single crystal, and then dumped. The expected x-ray yield is $1{0}^{9}\text{ }\text{ }\mathrm{photons}/\mathrm{s}$ at a center energy of 15 keV or higher.

Tooth enamel is composed of nano-scale, needle-like biological apatite crystallites. These crystallites constitute the enamel prisms. The generally accepted Meckel's model of arrangement of crystallites in enamel prism might be slightly revised according to the variations in tooth enamel chemical composition and structures. An x-ray diffraction method was proposed to survey the three-dimensional crystallite orientation instead of electron microscopy. Preliminary results showed clear difference in the convergence and broadening of enamel crystallite orientations of human tooth enamel. This method has high potential in analyzing partial deviation in crystallite orientation as well as easy sample preparation and operation.

Wavelength-tunable monochromatic Parametric x-ray (PXR) was generated at the Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University. Using the LEBRA-PXR, phase contrast imaging was carried out. Phase contrast images of a kitten deciduous tooth were taken by diffraction enhanced imaging (DEI) method. The results showed that LEBRA-PXR is a high coherent x-ray and is suitable for phase contrast imaging.

Parametric X-rays (PXR) are a new type of X-ray that are generated by crystal-electron interactions. The Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University generates PXR using a double-crystal system generating electrons from a 100-MeV class LINAC. LEBRA-PXR has potential for use as a wavelength tunable, ultra-high bright X-ray source with a macro-/micro-pulse structure. LEBRA-PXR has an energy-dispersion in the horizontal axis, assumed to be 0.2% in the experimental window, but can be used as monochromatic X-ray source for diffraction using a simple slit-system. A diffraction experiment was successfully carried out by applying an 11 keV, or 1.1273 A, LEBRA-PXR. Near-perfect crystals, such as graphite used for a monochromator showed sharp diffraction peaks. Clear, transparent mineral quartz and fluorapatite crystals also showed sharp diffraction peaks, while the diffraction peaks from clear calcite and silicon powder were not detected. Possible reasons for the lack of diffraction peaks from these materials are discussed. LEBRA-PXR has potential for use in studies on the diffraction of other materials, and is therefore, expected to be a useful tool for crystallographic analysis.

A cryogenic C-band 2.6-cell photocathode RF electron gun has been studied at Nihon University in collaboration with KEK for future use in a compact electron-accelerator based monochromatic X-ray source. The cold model cavity with an input coupler was fabricated at KEK in 2016 by ultraprecision machining and diffusion bonding techniques. The RF characteristics of the cavity obtained at cryogenic measurements have been in agreement with the result of the CST Studio simulation. The unloaded quality factor of ~73000 has been obtained at the cavity temperature of 20 K, which is 5.5 times higher than that at room temperature and consistent with the simulation taking into account the anomalous skin effect of the cavity surface resistance. The input coupling coefficient of approximately 20 at 20 K has well reproduced the design value. The shift in the accelerating n-mode resonant frequency due to the cavity temperature change from 296.65 to 20 K has been 19.02 MHz, being 0.12 MHz greater than the value based on the linear expansion coefficients for copper by NIST.

A new project to develop a terahertz (THz)-wave light source is in progress at the parametric X-ray (PXR) beamline of the Laboratory for Electron Beam Research and Application (LEBRA) at Nihon University. The THz-wave source is based on coherent transition radiation (CTR) emitted from a metal foil inserted downstream from a crystal target that is the PXR radiator. Beryllium or titanium foil is the most promising candidate for a THz-wave radiator. Since the electron linac of LEBRA was developed for a free electron laser (FEL), electron beam with bunch length of 1 ps (rms) can be provided by magnetic bunching at the bending magnet section. Thus, very intense coherent transition radiation (CTR) can be obtained in the frequency region around 1 THz. The results of preliminary experiments for CTR production suggested that sufficiently intense THz-CTR can be obtained using the LEBRA linac. In order to realize a THz-wave source for practical application studies, we have a plan to add the extraction feature for THz waves to the PXR beamline.

We have developed an initial-beam-loading compensation system by a new compensation method, where the system modulates the phase and amplitude of a low-level rf signal simultaneously, thereby optimizing a high-power rf waveform fed to an accelerating structure to compensate the beam energy spread. This compensation system is very compact and can easily be installed in and removed from a klystron system. This system was used in a beam test performed in the 125 MeV electron linac of the Laboratory for Electron Beam Research and Application in Nihon University. Experimental results demonstrate that this system effectively corrects the beam energy spread due to the initial-beam-loading effect. The new compensation method is expected to be effective in the compensation of energy spread in high-intensity and long-pulse beams in electron linacs.

X-ray imaging based on small-angle X-ray scattering (SAXS) was carried out using the parametric X-ray radiation (PXR) source at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. The experimental setup employed in this novel imaging approach is the same as that employed in diffraction-enhanced imaging (DEI), a kind of X-ray phase-contrast imaging method. In SAXS-based imaging, the image contrast is correlated with the broadening of the rocking curve peak due to the scattering from micron- or sub-micron-sized grains in the sample material. An experiment using the 25.5-keV PXR beam demonstrated that SAXS-based imaging with PXR provides a substantially strong contrast for granular materials despite the extremely low density of the material.

Wavelength tunable Free Electron Laser, FEL, was irradiated onto the polished surfaces of human tooth enamel and dentin using the FEL system at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. LEBRA-FEL system was so powerful that only 2 mJ/pulse shot resulted in an apparent pit on the surfaces. The pit showed neither marked scorch nor formation of secondary crystalline phase revealed by micro-XRD and micro-FTIR. Optimum wavelength for pit formation on the dental hard tissues was about 3.0 mm. However, the optimum wavelengths for enamel and dentin should be at 3.2 mm, 3.0 mm, respectively. The results strongly suggested that the ablation mechanism by laser irradiation for dental hard tissues might be not the simple interaction of laser beams with water, but complex phenomena, which could not be neglected of the hard tissue components and structure.

An in-line ionization chamber has been developed for the real-time measurement of the absolute intensity of the pulsed parametric X-ray (PXR) beam during irradiation experiments. The quasi-monochromatic PXR generating system was developed at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. In contrast to typical narrow X-ray beams in synchrotron radiation facilities, the PXR beam profile is as large as approximately 100 mm in diameter with rather uniform flux distribution at the X-ray output port in the experimental hall. The energy of the PXR beam ranges from 5 to 34 keV, which is specified by the PXR target crystal plane and its geometrical condition. The ionization chamber is of a plane parallel type employing 6-μm thick double-sided aluminum vapor-deposited polyester films for the plane electrodes through which the X-ray beam passes. The plane bias electrode has been placed at an equal distance of 25 mm from the two plane earth electrodes that act as the beam windows with an aperture diameter of 120 mm. Due to the pulsed property of the PXR beam and the geometrical configuration of the ionization chamber, the charge-sensitive preamplifier output pulse height represents an integral of the fast electron current, corresponding to a half of the total ionization charge produced by the beam. The intensity of the PXR beam has been measured for various X-ray energies by using nitrogen and argon, respectively, as the filling gas.

The construction and the development of an UV free electron laser at Narashino Campus, Nihon U. have been started under the cooperation of Nihon U., KEK 1 , PNC 2 , ETL 3 and Tohoku U. The project requires a 125 MeV S-band electron linear accelerator to expand the oscillation of FEL to the UV region using fundamental mode. The injection system consists of a thermionic RF-gun with a LaB 6 cathode and a magnet for magnetic bunching. We are studying to reduce the back-bombarding electrons to realize the macropulse length of 20 μs. Electron beams, up to the energy of 125 MeV, are injected into the optical cavity. Changing the accelerating energy and/or undulator parameters, this system will cover the range from infrared to ultraviolet for the applications in the various fields.

The steady-state kinetics of alcohol dehydrogenases (alcohol:NAD + oxidoreductase, EC 1.1.1.1 and alcohol:NADP + oxidoreductase, EC 1.1.1.2), lactate dehydrogenases ( l -lactate:NAD + oxidoreductase, EC 1.1.1.27 and d -lactate:NAD + oxidoreductase, EC 1.1.1.28), malate dehydrogenase ( l -malate:NAD + oxidoreductase, EC 1.1.1.37), and glyceraldehyde-3-phosphate dehydrogenases [ d -glyceraldehyde-3-phosphate:NAD + oxidoreductase (phosphorylating), EC 1.2.1.12] from different sources (prokaryote and eukaryote, mesophilic and thermophilic organisms) have been studied using NAD(H), N 6 -(2-carboxyethyl)-NAD(H), and poly(ethylene glycol)-bound NAD(H) as coenzymes. The kinetic constants for NAD(H) were changed by carboxyethylation of the 6-amino group of the adenine ring and by conversion to macromolecular form. Enzymes from thermophilic bacteria showed especially high activities for the derivatives. The relative values of the maximum velocity ( NAD = 1) of Thermus thermophilus malate dehydrogenase for N 6 -(2-carboxyethyl)-NAD and poly(ethylene glycol)-bound NAD were 5.7 and 1.9, respectively, and that of Bacillus stearothermophilus glyceraldehyde-3-phosphate dehydrogenase for poly(ethylene glycol)-bound NAD was 1.9.