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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.

The X-ray source based on parametric X-ray radiation (PXR) has been regularly providing a coherent X-ray beam for application studies at Nihon University. Recently, three dimensional (3D) computed tomography (CT) has become one of the most important applications of the PXR source. The methodology referred to as K-edge subtraction (KES) imaging is a particularly successful application utilizing the energy selectivity of PXR. In order to demonstrate the applicability of PXR-KES, a simultaneous KES experiment for a specimen containing strontium was performed using a PXR beam having an energy near the Sr K-edge of 16.1 keV. As a result, the 3D distribution of Sr was obtained by subtraction between the two simultaneously acquired tomographic images.

Development of THz wave source has been underway at Nihon University in collaboration with National Institute of Advanced Industrial Science and Technology. The THz wave transport lines have been constructed on the same axis as the X-ray and FEL beam line. The average intensity of the backward THz CTR wave obtained at the output port of the Parametric Xray Radiation beam line in the accelerator room has been 1 mJ/macro-pulse. The superposition transport system of the THz waves to the X-ray beam-line was installed in a vacuum chamber. Additionally, the energy of the CER as high as 0.2 mJ/macro-pulse were achieved with the experimental room.

Nihon University and National Institute of Advanced Industrial Science and Technology have planned to develop an intense terahertz-wave (THz-wave) source based on coherent Cherenkov radiation (CCR) at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. By passing an electron beam through a hollow conical dielectric with apex facing the incident electron beam, the wave front of CCR generated on the inner surface of the hollow conical dielectric is matched to the basal plane. The CCR matched to a circle plane wave is more powerful than conventional THz-wave sources based on electron accelerators. A hollow conical high-resistance silicon with a diameter of the basal plane of 40 mm and an inner diameter of 6 mm will emit the THz-wave beam with a macropulse energy of 14 mJ at LEBRA.

We propose a high-peak-power terahertz-wave source based on an electron accelerator. By passing an electron beam through a hollow conical dielectric with apex facing the incident electron beam, the wave front of coherent Cherenkov radiation generated on the inner surface of the hollow conical dielectric matches the basal plane. Using the electron beam generated at the Laboratory for Electron Beam Research and Application at Nihon University, the calculated power of coherent Cherenkov radiation that matched the circular plane (CCR-MCP) was above 1 MW per micropulse with a short interval of 350 ps, for wavelengths ranging from 0.5 to 5 mm. The electron beam is not lost for generating the CCR-MCP beam by using the hollow conical dielectric. It is possible to combine the CCR-MCP beams with other light sources based on an accelerator.

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

A novel X-ray source based on parametric X-ray radiation (PXR) has been put into practical use at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, Japan. The PXR beam has been generated from a Si single crystal irradiated by a 100-MeV electron beam from a linac at the LEBRA. In this study, phase-contrast imaging experiments using a diffraction-enhanced imaging (DEI) method have been carried out by using the parametric X-rays at an energy of 17.5 keV. The successful images obtained by the DEI method have shown detailed inner structures of soft biological tissues more clearly as compared with those by conventional absorption radiography. Given the significant properties of the LEBRA PXR source, i.e., compact system, large X-ray beam irradiation field of approximately 80 mm in diameter and quasi-monochromaticity, the result suggests a possible construction of a compact linac-driven PXR-DEI device and application to medical diagnoses. Copyright © 2012 John Wiley & Sons, Ltd.

Parametric X-ray (PXR) is a new type of radiography with variable monochrome wavelength and high coherent characteristics. The Laboratory for Electron Beam Research and Application (LEBRA) at Quantum Science Institute, Nihon University generated LEBRA-PXR, a system that irradiates Si crystal with electron accelerated by linear accelerator (LINAC). LEBRA-PXR is uniquely developed for world-wide application experiment. X-ray images of tooth samples were taken with flat panel detector using LEBRA-PXR. As a result, images were captured as short as 1 sec. LEBRA-PXR uses LINAC with micro-macro pulse electron beam structure. Imaging time of 1 sec is equivalent to about 0.025 msec when x-ray is converted to actual radiation exposure. The effective dose point estimates of x-rays were about 1 μ Sv/5 sec. Results show that LEBRA-PXR can be used to generate low dose x-ray imaging advocating the possibility of its application in biological studies and medical treatment.

The parametric X-ray radiation (PXR) generator system at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University is a monochromatic and coherent X-ray source with horizontal wavelength dispersion. The energy definition of the X-rays, which depends on the horizontal size of the incident electron beam on the generator target crystal, has been investigated experimentally by measuring the X-ray absorption near edge structure (XANES) spectra on Cu and CuO associated with conventional X-ray absorption imaging technique. The result demonstrated the controllability of the spectrum resolution of XANES by adjusting of the horizontal electron beam size on the target crystal. The XANES spectra were obtained with energy resolution of several eV at the narrowest case, which is in qualitative agreement with the energy definition of the PXR X-rays evaluated from geometrical consideration. The result also suggested that the wavelength dispersive X-ray absorption fine structure measurement associated with imaging technique is one of the promising applications of PXR.

Advanced applications of parametric X-ray radiation (PXR) such as energy-dispersive X-ray absorption fine structure (DXAFS) analysis and phase-contrast imaging have been developed at the Laboratory for Electron Beam Research and Application (LEBRA) of Nihon University. To improve the electron beam quality and geometrical stability of the target crystal, the cooling-water system for the linac and the PXR target was replaced with a new one capable of more precise control. As a result, the reliability of the experimental data in PXR applications, especially in X-ray imaging, has improved. The effect of the electron beam focusing on the target crystal was also investigated. The results of X-ray imaging with a long propagation distance and measurement of the time-structure of the PXR intensity suggest that the correlation between the electron beam profile and the X-ray coherence is rather complicated. It is possible that incident electrons cause some deformation of the target crystal, becoming the dominant factor restricting the quality of intense PXR.

A parametric X-ray radiation (PXR) generator system was constructed in 2001 in a dedicated beamline connected to the 125 MeV electron linac of the Laboratory for Electron Beam Research and Application at Nihon University. This generator system consists of two perfect-silicon-crystal plates mounted on precisely moving mechanical setup to achieve a wide tunability. The experimental operation of the PXR generator started early in 2004; X-rays were first observed through this device in April 2004. Application studies using the PXR beam from a 100 MeV electron beam have been conducted since July 2004. Preliminary results suggest the possibility of applying the PXR to advanced X-ray imaging and to the measurement of X-ray absorption fine structure.

We developed an intense coherent transition radiation (CTR) at the Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University. A rectangular titanium screen with dimensions of 80 × 60 mm2 was used as the target, and the backward CTR generated on the screen was extracted through a crystal quartz window to air. We observed an intense terahertz (THz) radiation and confirmed it to be the CTR by measuring the spatial distribution and the dependence of the power on the electron charge. The CTR spectrum measured using a Martin–Puplett-type interferometer showed a maximum at a frequency of 0.3 THz and was emitted up to 1.6 THz. The CTR energy and peak power of a micropulse were approximately 80 nJ and 100 kW, respectively. The CTR energy during a 4.5 µs macropulse was approximately 1 mJ, indicating that this broadband THz light source is one of the most powerful coherent radiation sources in normal conducting linac facilities.

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.

A novel X‐ray source based on Parametric X‐ray radiation (PXR) has been employed for phase‐contrast imaging at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, Japan. The PXR X‐rays were generated by the 100 MeV electron beam passing through a Si single crystal. The X‐rays in the 16∼34 keV range were chosen for imaging of biological samples. The quasi‐monochromatic, tunable, and coherent X‐ray source is appropriate for this application. In addition, the large X‐ray beam irradiation field of approximately 100 mm in diameter, which was achieved without special optics, suggests that the PXR is applicable to imaging for medical diagnostics.

The monochromatic X-ray source based on parametric X-ray radiation (PXR) was developed by using Si(111) perfect crystals and the electron beam from the 125-MeV linac at Nihon University. Since the X-ray beam from the PXR system has a large exposure area with uniform flux density, the PXR-based source is suited for X-ray radiography. In addition to ordinary radiography, X-ray absorption spectroscopy and phase-contrast imaging have been developed as advanced applications of PXR. The absorption spectra of several samples were obtained using the energy dispersion of PXR, and the X-ray absorption fine structures (XAFS) were actually found in the spectra. With respect to phase-contrast imaging, refraction-contrast images have been obtained by using the X-ray diffraction in the (+, −, +) arrangement of perfect crystals. The high-contrast and the phase-reversal of the images taken in the experiment suggest that LEBRA-PXR has a high spatial coherence sufficient for phase-contrast imaging.

A novel X-ray source based on parametric X-ray radiation (PXR) has been employed for X-ray imaging at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University. Notable features of PXR are tunable energy, monochromaticity with spatial chirp, narrow local bandwidth and spatial coherence. Since the X-ray beam from the PXR system has a large irradiation area with uniform flux density, the PXR-based source is suited for X-ray imaging, especially for application to phase-contrast imaging. Despite the cone-like X-ray beam, diffraction-enhanced imaging (DEI) can be employed as a phase contrast imaging technique. DEI experiments were performed using 14- to 34-keV X-rays and the phase-gradient images were obtained. The results demonstrated the capability of PXR as an X-ray source for phase-contrast imaging with a large irradiation field attributed to the cone-beam effect. Given the significant properties of the LEBRA-PXR source, the result suggests the possible construction of a compact linac-driven PXR-Imaging instrument and its application to medical diagnoses.

We observed intense coherent synchrotron radiation (CSR) in the terahertz region using an S-band linac at the Laboratory for Electron Beam Research and Application at Nihon University. The evolution of the CSR power was measured, and the CSR reflected in the vacuum chamber of the bending magnet could be extracted through the quartz window for a few tens of picoseconds. The long wave packet of the delayed CSR in the autocorrelation suggests that the delayed CSR was the non-resonant ring-down of the vacuum chamber of the bending magnet. To design a high-energy accelerator, it is necessary to decrease high-energy photons resulting from Compton backscattering with intense CSR.