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The undulator is a magnetic device usually consisting of a series of rare-earth permanent magnets (REPMs) arranged to generate a sinusoidal magnetic field, and is installed in synchrotron radiation and free electron laser facilities to periodically deflect high-energy electrons. Because the undulator is operated under a high-radiation environment, it is important to take possible measures to avoid the quality degradation, in particular the radiation damage of REPMs. We present a simple scheme to enhance the radiation resistance of REPMs in undulators, in which the easy axis of each REPM is tilted by 45\ifmmode^\circ\else\textdegree\fi{}. Experimental studies have revealed that the radiation resistance of REPMs in this configuration is enhanced by an order of magnitude compared to that in the conventional undulator.

This paper describes the development of a phase shifter that can be used in cross undulators for fast polarization switching. The phase shifter is composed of a pair of cut-core coils and a thin-walled stainless steel duct. Evaluation of the magnetic fields of the phase shifter indicates that the switching frequency of this simple and low-cost device can exceed 30 Hz.

The BL28XU beamline, dedicated to rechargeable battery analysis, is described., The newly installed BL28XU beamline at SPring-8 is dedicated to in situ structural and electronic analysis of rechargeable batteries. It supports the time range (1 ms to 100 s) and spatial range (1 µm to 1 mm) needed for battery analysis. Electrochemical apparatus for battery charging and discharging are available in experimental hutches and in a preparation room. Battery analysis can be carried out efficiently and effectively using X-ray diffraction, X-ray absorption fine-structure analysis and hard X-ray photoelectron spectroscopy. Here, the design and performance of the beamline are described, and preliminary results are presented.

We report an unexpectedly large flux loss observed in permanent magnets in one of the undulators operated in SACLA, the x-ray free electron laser facility in Japan. Characterizations of individual magnets extracted from the relevant undulator have revealed that the flux loss was caused by a homogeneous magnetization reversal extending over a wide area, but not by demagnetization of individual magnets damaged by radiation. We show that the estimated flux-loss rate is much higher than what is reported in previous papers, and its distribution is much more localized to the upstream side. Results of numerical and experimental studies carried out to validate the magnetization reversal and quantify the flux loss are presented, together with possible countermeasures against rapid degradation of the undulator performance.

Researchers report sub-angstrom fundamental-wavelength lasing at the SPring-8 Angstrom Compact Free-Electron Laser in Japan. The output has a maximum power of more than 10 GW, a pulse duration of 10−14 s and a lasing wavelength of 0.634 A.

Demagnetization owing to high-energy electron irradiation has been analyzed for permanent magnets used in insertion devices of synchrotron radiation sources, using the Monte Carlo code FLUKA. The experimental data of a thermally treated Nd(2)Fe(14)B permanent magnet with a copper or a tantalum block at electron energies ranging from 2 to 8 GeV were compared with the calculation data of the absorbed doses, photoneutron production distributions and star densities. The results indicate that low-energy photoneutrons and bremsstrahlung photons are not involved in the demagnetization process, and suggest that the star density owing to the photoneutrons is strongly correlated with the demagnetization process.

Single-pass free-electron lasers based on self-amplified spontaneous emission1,2,3,4 are enabling the generation of laser light at ever shorter wavelengths, including extreme ultraviolet5, soft X-rays and even hard X-rays6,7,8. A typical X-ray free-electron laser is a few kilometres in length and requires an electron-beam energy higher than 10 GeV (refs 6, 8). If such light sources are to become accessible to more researchers, a significant reduction in scale is desirable Here, we report observations of brilliant extreme-ultraviolet radiation from a 55-m-long compact self-amplified spontaneous-emission source, which combines short-period undulators with a high-quality electron source operating at a low acceleration energy of 250 MeV. The radiation power reaches saturation at wavelengths ranging from 51 to 61 nm with a maximum pulse energy of 30 µJ. The ultralow emittance (0.6π mm mrad) of the electron beam from a CeB6 thermionic cathode9 is barely degraded by a multiple-stage bunch compression system that dramatically enhances the beam current from 1 to 300 A. This achievement expands the potential for generating X-ray free-electron laser radiation with a compact 2-GeV machine. Free-electron lasers can produce powerful pulses of radiation at very short wavelengths, even in the hard-X-ray region. In general, however, they comprise facilities several kilometres in length. A 55-m-long laser could open up the technology to a broader range of researchers.

Permanent magnets Nd2Fe14B are the main component of the insertion devices of the synchrotron radiation facilities and used at other accelerators. The radiation induced demagnetization of permanent magnets, becomes one of the most important issues of the next generation light sources. To investigate the radiation damage the magnetic field change of Nd2Fe14B magnet exposed to a 2.5 GeV electron beam has been measured. The radiation field near the magnet and the distribution of energy deposition in the magnet are studied with Monte Carlo code FLUKA. The radiation induced demagnetization is analyzed and a fitted formula is proposed to estimate the relative reduction of remanence.

Rare-earth permanent magnets such as Nd 2 Fe 14 B and Sm 2 Co 17 are the main components of the insertion devices of synchrotron radiation facilities and are used at other particle accelerators. Due to radiation safety concern the induced radioactivity in permanent magnets at a 2.5 GeV electron accelerator were studied with Monte Carlo simulations and experiments. The saturated activity of each radioactive isotope was estimated with FLUKA code (2005 version) and compared with measurement results. Three models of NEOMAX Nd 2 Fe 14 B magnets and one trivial Sm 2 Co 17 magnet were chosen as the test magnets. The remnant dose rate at 1 m from the magnet and its cooling time dependence are calculated with the induced activities from the view of radiation protection. These are investigated under unique radiation environments due to different target conditions. The transverse distributions of induced radioactivities of several representative isotopes, which were measured at different target conditions, agree well with the electromagnetic shower characteristics at different target conditions as well as the spatial distributions of photon and neutron fluences.

High-energy electron-beam bombardment of Nd 2 Fe 14 B-type permanent magnets induces radiation damage characterized by a drop in the magnetic field. Experiments carried out at the SPring-8 booster synchrotron, with 4, 6, and 8 GeV electrons, show that the drop in magnetic field is energy dependent. Electromagnetic shower simulations suggest that most of the radiation damage happens in a small region around the irradiation axis, and that the contribution of neutrons with large scattering angles or with low energies to the magnetic field change is small.

Sintered Nd 2 Fe 14 B permanent magnets are damaged (demagnetized) by strong radiation, though some techniques of the magnets can reduce the sensitivity to radiation. High coercivity magnets show strong resistance to radiation, while they have a manufacturing dependence. Using magnets at very low temperature is effective. Stabilization under the appropriate annealing conditions enhances the radiation resistance successfully. Stabilizing by reverse field also increases the resistance. Combination of these techniques is much more effective, for example, annealed high coercivity magnets indicate very strong resistance.

A new application of high-temperature superconducting (HTS) bulk magnets to synchrotron radiation (SR) sources, i.e., magnetic devices that generate a periodic field to produce highly brilliant SR, is presented. Utilization of HTS bulk magnets brings two advantages over the existing SR sources: much stronger field than that of conventional SR sources with rare-earth permanent magnets (REPMs) and higher feasibility than existing superconducting SR sources with low-temperature superconducting coils. Two schemes for the application of HTS bulk magnets to SR sources are presented. In the first scheme, HTS bulk rings are mounted on REPMs to enhance the magnetic field. In the second one, HTS bulk magnets are arranged in line instead of REPMs. Principles and recent demonstration experiments are described.

Synchrotron X-ray diffraction measurements on a spin–Peierls material CuGeO 3 in applied magnetic fields, H , up to 15 T are made. We find that the temperature, T , dependence of the incommensurate Bragg peak at a lower H is quite different from that at a higher H . At sufficiently high fields, we find that the lattice incommensurability, δ l , is almost independent of T , while at H slightly above the critical field = 12.25 T for the commensurate to incommensurate transition, δ l decreases with increasing T . We interpret that this finding is due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations.

A long undulator is a direct way to create a brilliant synchrotron radiation source. However, the length of undulators has been bounded by technical limitations and available space in accelerators. The first long undulator was developed at SPring-8, which is a third-generation synchrotron radiation facility equipped with four 30-m-long straight sections, making it the most brilliant x-ray source in the world. The magnets are placed inside a vacuum chamber and this makes it possible to arrange 780 periods continuously for 25 m. The absolute flux and spectrum of the output radiation were measured and compared with theory. The observed spectrum is in a good agreement with theory once the electron beam orbit was corrected for geomagnetic fields.

This article presents the first operation of the magnetic circular dichroism (MCD) measurement system with periodic photon-helicity switching. The measurements were performed at the newly constructed soft x-ray beamline—BL23SU— at the third-generation synchrotron radiation facility, SPring-8. The monochromator control system was synchronized to the movement of the magnetic row (phase shift) of an APPLE-2 (Sasaki) type variably polarizing undulator. The periodic phase shift of the undulator provided the switching of helicity polarizing soft x rays up to 0.1 Hz. The closed-orbit distortion of the storage ring was controlled to avoid optical axis disturbances at this beamline as well as at other beamlines. The circular dichroism spectra with helicity switching by APPLE-2 show the possibility of high-sensitivity MCD measurements. This method promotes precise MCD measurements and can be a powerful technique to study magnetism as well as dichroism.

The construction of the 25-m long undulator of in-vacuum type was finished successfully and installed into the 30-m straight section of the SPring-8 storage ring. The period length is 32 mm and the number of periods is 780. The maximum field is obtained as 0.59 T at the minimum gap of 12 mm. Although this device is composed of five segments, it works as a one-piece undulator without any phasing system. Following this long device, the in-vacuum revolver undulator of mini-gap type will soon be completed. This device has four undulators with different period length.

We have developed and installed a revolver type undulator for a contract beamline (BL15XU) at SPring-8. Since wide energy range photons (0.5–60 keV) are used for the research in advanced materials at BL15XU, the revolver undulator has two pairs of undulator magnet arrays; one is a planar undulator for X-ray radiation and the other is a helical undulator for soft X-ray radiation. The two undulators are mounted on the same top and bottom rotatable magnet beams by 90°, and the beamline users can switch the undulators at anytime without any observable effect on the electron beam orbit and the photon beam position.

An in-vacuum X-ray helical undulator has been developed for a high flux beamline (BL40XU) of SPring-8. Since BL40XU is not equipped with a monochromator in order to provide high photon flux, on-axis fundamental radiation from the helical undulator is directly used for user experiments after being focused by horizontal and vertical mirrors. The energy resolution available at the beamline is determined by the undulator spectrum and the front end physical aperture. Compared to a conventional beamline of SPring-8 with a crystal monochromator, the available photon flux is higher by two orders. Since a specific polarization state is not requested from the user experiments, there is no phasing mechanics on the undulator. The magnet structure is newly designed to obtain better magnetic field performance. The measured spectral bandwidth shows a good agreement with the expected one.

The magnetic field change of undulator magnets when exposed to a 2.0 GeV electron beam has been measured. We study the effect of (1) stacking magnets, of (2) magnet shape, of (3) magnetized direction, of (4) target materials, of (5) magnet materials, and of (6) manufacturers. Two undulator models adopting the actual magnet array dimensions of the in-vacuum undulators in SPring-8 were also irradiated.

A 25 m long undulator has been constructed in order to be installed in one of the long straight sections at the Super Photon Ring-8GeV (SPring-8). An in-vacuum structure has been adopted to avoid phasing difficulties encountered in the case of an out-of-vacuum structure. The undulator is divided into five segments, each of which is similar to a standard in-vacuum undulator at the SPring-8. Field measurements and corrections have been carried out first for each segment and second for junctions between segments. After final corrections, it has been confirmed that both multipole components and phase errors are small at various gap values, showing that the long undulator can be operated without any problem.

A key feature of the SPring-8 storage ring is the presence of four 30 m long straight sections for the installation of very long insertion devices. Two characteristics of very long undulators are presented here: first, the problems brought by the necessity to phase the individual segments, which in turn, imposed the use of the in-vacuum technology; next, the near-field effects which appear on-axis as these undulators length is comparable to the distance between the observation point and the source.

In the following we present a new analysis of the data obtained after an irradiation of magnets with a 2 GeV electron beam under various conditions (with or without a target placed in front of the magnets). This analysis, based on the measured magnetic field, indicates the importance of a precise determination of the three components of the magnetization for a better understanding of the demagnetization process.

An electron beam halo monitor using diamond-based detectors, which are operated in the ionization mode, has been developed for the SPring-8 Angstrom compact free-electron laser (SACLA) to protect its undulator magnets from radiation damage. Diamond-based detectors are inserted in a beam duct to measure the intensity of the beam halo directly. To suppress the degradation of the electron beam due to the installation of the beam halo monitor, rf fingers with aluminum windows are newly employed. We evaluated the effect of radiation from the Al windows on the output signal both experimentally and by simulation. The operational results of the beam halo monitor employed in SACLA are presented.

A tapered undulator beamline BL36XU was constructed at SPring-8 to conduct structural and electronic analysis of dynamic events on polymer electrolyte fuel cell (PEFC) cathode catalysts for the development of next-generation PEFCs. BL36XU provides various time and spatially resolved XAFS techniques in an energy range from 4.5 to 35 keV for investigating PEFCs under the operating conditions. In addition, we developed in-situ complementary measurement systems, such as in-situ time-resolved XAFS/XRD and ambient pressure HAXPES systems. This report describes the performance and present status of the BL36XU.

The effect of thermal stabilization (pre-baking at 142°C) on the sensitivity of neodymium–iron–boron (Nd 2 Fe 14 B) magnets to irradiation was studied. Thermally stabilized magnets showed higher resistance to irradiation with 2.0 GeV electrons: their demagnetization curves decrease linearly with respect to the number of electrons, and with a demagnetization rate remarkably smaller than that of the unbaked magnets.

Using a diamond-based detector, the electron beam halo in a high-energy accelerator can be measured with a lower detection limit than that using other instruments, such as a core monitor, a dose meter, or an optical fiber. We have successfully measured an electron beam halo using diamond-based detectors operating in the ionization mode, which were installed in the beam duct to measure the intensity of the beam halo directly. Pulse-by-pulse measurements were adopted to suppress the background noise efficiently. Feasibility tests on the diamond-based detector and beam halo monitor were performed in the beam dump area of the 8 GeV SPring-8 synchrotron booster and at the 250 MeV SPring-8 Compact SASE Source test accelerator for the SPring-8 Angstrom Compact free electron LAser (SACLA), respectively. We achieved a lower detection limit of $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }\mathrm{electrons}/\mathrm{pulse}$ for single-shot measurement, which corresponds to a ratio of about ${10}^{\ensuremath{-}6}$ relative to the typical charge of the beam core of 0.3 pC. We also confirmed the feasibility of the electron beam halo monitor for use as an interlock sensor to protect undulator permanent magnets used in SACLA from radiation damage.

A wiggler dedicated to material research has been designed for SPring-8 to provide high brilliance hard X-rays in the 20–200 keV range. The originality of this device is not so much in its magnetic arrangement (a simple conventional hybrid design), but in the fact that it is of the in vacuum type. The first magnetic measurements are presented here, as well as some unusual characteristics of this wiggler (low total power, narrow emission angle).

We achieved stable operation of a free-electron laser (FEL) based on the self-amplified spontaneous-emission (SASE) scheme at the SPring-8 Compact SASE Source (SCSS) test accelerator in the extremely ultraviolet region. Saturation of the SASE FEL power has been achieved at wavelengths ranging from 50 to 60 nm. The pulse energy has reached $\ensuremath{\sim}30\text{ }\text{ }\ensuremath{\mu}\mathrm{J}$ at 60 nm. The observed fluctuation of the pulse energy is about 10% (standard deviation) for several hours, which agrees with the expectation from the SASE theory showing the stable operation of the accelerator. The SASE FEL has been routinely operated to provide photon beams for user experiments over a period of a few weeks. Analysis on the experimental data gave the normalized-slice emittance at the lasing part is around $0.7\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$. This result indicates that the normalized-slice emittance of the initial electron beam, $0.6\ensuremath{\pi}\text{ }\mathrm{mm}\text{ }\mathrm{mrad}$ in a 90% core part, is kept almost unchanged after the bunch compression process with a compression factor of approximately 300. The success of the SCSS test accelerator strongly encourages the realization of a compact XFEL source.

The measurements of high-energy and high dose mixed radiation from high-energy electron accelerator are carried out using a radiation damage monitor. It consists of two Radiation-Sensing Field-Effect Transistors (RADFETs) for total absorbed dose from mainly gamma ray and other charged particles and a Si PIN diode for neutron fluence. This is a part of the demagnetization study of rare earth permanent magnet irradiated by 2.5-GeV electron beam. The sensitivities of damage detectors are measured using 65-MeV quasi-monoenergic neutron, 14-MeV D-T neutron, (252)Cf neutron for Si PIN diode and (60)Co and (137)Cs gamma ray for RADFETs. Measured sensitivities are in acceptable range in the comparison of producer's proposed values. The dose and fluence measurements are carried out for the same target condition, Cu and Ta, as that for the demagnetization study. The 5 x 5 cm(2) cross-sectional and 5.5-cm-thick Pb target is also used for the general comparison with photoneutron yields. All measured dose and fluence are compared with the calculated results using the FLUKA code and agree well each other. The application of this kind of radiation damage monitor to high-level dosimetry at high-energy electron accelerator has been discussed.

Most of radiation damages in materials are structural changes (radiation‐induced defects), but the origins of radiation‐induced demagnetization of permanent magnets can be explained by a magnetization reversal caused by a thermal process. We propose a model for the mechanism of radiation‐induced demagnetization and suggest some protections strategies.

A simple scheme for field enhancement in synchrotron radiation sources such as undulators and wigglers is proposed, which is based on the fundamental nature of the superconducting loop where the magnetic flux is preserved. A superconductor ring placed to enclose the magnetic pole works as a kind of permanent magnet. The magnetization is performed by electromagnetic induction brought by the opening movement of the magnetic gap. Since neither additional external power supplies nor current leads are necessary, high-temperature bulk superconductors can easily be implemented in this scheme. Calculations to check the effectiveness of the new concept show that the critical current density of the superconductor is crucial to the performance of the synchrotron radiation sources based on this concept. Experiments were performed to verify the principle of the proposed scheme, which gave promising results to strongly support it.

SCSS: SPring-8 Compact SASE Source (Soft X-ray FEL project) was started in 2002 in order to establish the technology required for the X-ray Free Electron Laser at 1 Angstrom region. Three key technologies: the short-period in-vacuum undulator, the high-gradient C-band accelerator and the low emittance electron source using CeB/sub 6/ single crystal thermionic-cathode enable to design the SCSS machine size within 100 m facility. The C-band RF system R&D was originally started at KEK to establish linear-accelerator technology for the e/sup +/e/sup -/ Linear Collider project, and transferred to SCSS project at SPring-8/RIKEN. In SCSS, 8 klystrons and modulators, 16 accelerating structures will be used to accelerate the beam up to 1 GeV. Construction and operation of SCSS machine will provide realistic information on reliability, maintainability and cost of the C-band RF system, which will be very useful to judge the reality of Linear Collider project based on C-band technology.

In‐vacuum type revolver undulator has been developed. This device has four undulators with different period length. The exotic in‐vacuum technologies were used in this device.

One of the neodymium‐iron‐boron (Nd2Fe14B) magnet with high coercivity was found to show very high resistance to irradiation. The sample was irradiated with 2.0 GeV electrons. The radiation‐induced demagnetization of this Nd2Fe14B magnet was as small as that of the samarium‐cobalt (Sm2Co17) magnets, known as to show high radiation resistance, irradiated under same experimental conditions for comparison.

We are currently constructing a new X-ray absorption fine structure (XAFS) beamline BL36XU at SPring-8 dedicated for the structural and electronic analysis of the dynamic events on polymer electrolyte fuel cell (PEFC) cathode catalysts for the development of next-generation PEFCs. To investigate the cathode catalyst nanoparticles in PEFCs under the operating conditions, the beamline is designed to provide time- and spatially resolved XAFS techniques having a time resolution of 100 μs, spatial resolution of 200 nm, and depth resolution of 1 μm. We report the outline and design of the new beamline.

The cryogenic permanent magnet undulator (CPMU) is an insertion device in which permanent magnets (PMs) are cooled to a cryogenic temperature to improve magnetic performances in terms of remanence and coercivity. Operation of CPMUs is expected to be much easier than that of existing superconductive undulators (SCUs) with low-temperature superconducting coils, since the operating temperature can be much higher than that of liquid helium. In addition to pure PMs, high-permeability pole pieces and/or high-temperature superconductors (HTSCs) can be exploited to enhance the magnetic field of the CPMU. Towards realization of this concept, a number of R&Ds are in progress at SPring-8: field measurement under a cryogenic environment and reinforcement of HTSC samples. Encouraging results have been obtained from preliminary studies.