Hikaru Kishimoto

Outline of soft X-ray photochemistry beamline BL27SU of SPring-8

Abstract BL27SU of SPring-8 was constructed for soft X-ray photochemistry. To perform different types of experiments, BL27SU has three branches. In a branch for spectroscopic experiments, a monochromator of very high energy resolving power was required. The other branches were built for experiments in need of high flux rather than energy resolution. In this report the optics and some apparatuses for photochemistry installed in BL27SU are presented.

Performance of a Highly Stabilized and High-resolution Beamline BL17SU for Advanced Soft X-ray Spectroscopy at SPring-8

A new soft x‐ray beamline BL17SU (RIKEN) has been constructed at SPring‐8. The beamline consists of two branches with each varied‐line‐spacing‐plane‐grating‐monochromator. Both monochromators perform high energy resolution (E/ΔE > 10,000) between 0.2 and 1 keV. One of the monochromator achieves high energy stability of 10 meV over a period of half a day.

Fundamental Techniques for High Photon Energy Stability of a Modern Soft X‐ray Beamline

High energy resolution and high energy stability are required for modern soft x‐ray beamlines. Attempts at improving the energy stability are presented in this paper. Some measures have been adopted to avoid energy instability. It is clearly observed that the unstable temperature of the support frame of the optical elements results in photon energy instability. A photon energy stability of 10 meV for half a day is achieved by controlling the temperature with an accuracy of 0.01°C.

Upgrade of beamline BL25SU for soft x-ray imaging and spectroscopy of solid using nano- and micro-focused beams at SPring-8

Substantial upgrades have been made to the beamline BL25SU at SPring-8 for soft X-ray imaging and spectroscopy of solid-state materials. The upgraded beamline consists of two branches: a micro-beam branch with high energy resolution, and a nano-beam branch with small angular divergence. The beamline has been available for use since October 2014, following a half year commissioning period. We present here the beamline performance parameters, including resolving power, photon flux, and focused beam size, which are consistent with designed specifications.

Upgrade status of hard x-ray 100-nm probe beamlines BL37XU and BL39XU at SPring-8

BL37XU (trace element analysis beamline) and BL39XU (magnetic materials beamline) at SPring-8 have been upgraded to provide nano-probe analysis. We designed and installed Kirkpatrick-Baez (KB) mirrors and corresponding manipulators, which have an X-ray focusing beam as small as 100 nm. To realize a high-flux 100-nm focusing beam, a high-demagnification optical design was used, and new experimental hutches were constructed that are located about 80 m from the light source. By taking advantage of extended beamline, focusing photon flux density of over 1 x 109(photons/sec/100x100nm2) is possible with a working distance of 100 mm at X-ray energy of around 10 keV. The current status of these beamlines is reported.

Improvement in Stability of SPring‐8 Standard X‐Ray Monochromators with Water‐Cooled Crystals

SPring‐8 standard double‐crystal monochromators containing water‐cooled crystals were stabilized to a sufficient level to function as a part of optics components to supply stable microfocused x‐ray beams, by determining causes of the instability and then removing them. The instability was caused by two factors—thermal deformation of fine stepper stages in the monochromator, which resulted in reduction in beam intensity with time, and vibrations of coolant supply units and vacuum pumps, which resulted in fluctuation in beam intensity. We remodeled the crystal holders to maintain the stage temperatures constant with water, attached x‐ray and electron shields to the stages in order to prevent their warming up, introduced accumulators in the water circuits to absorb pressure pulsation, used polyurethane tubes to stabilize water flow, and placed rubber cushions un der scroll vacuum pumps. As a result, the intensity reduction rate of the beam decreased from 26% to 1% per hour and the intensity fluctuation from 13% to 1%. The monochromators were also modified to prevent radiation damage to the crystals, materials used as a water seal, and motor cables.

Lightweight-compact variable-gap undulator with force cancellation system based on multipole monolithic magnets

A lightweight-compact variable-gap undulator (LCVGU) having the force-cancellation system based on the multipole monolithic magnets (MMMs) has been developed. The LCVGU is free from the heavy mechanical frames, which is a fundamental element specific to conventional variable-gap undulators (VGUs) because of a strong attractive force, and thus the cost and time for construction and installation are expected to be significantly reduced; the MMMs counteract the strong attractive force in a cost-effective manner. Results of mechanical tests and magnetic-field measurements of two prototype LCVGUs equipped with the proposed force cancellation system have revealed the comparable performance with the conventional VGUs.

Development of contamination-free x-ray optics for next-generation light sources

We studied typical forms of contamination on X-ray mirrors that cause degradation of beam quality, investigated techniques to remove the contaminants, and propose methods to eliminate the sources of the contamination. The total amount of carbon-containing substances on various materials in the vicinity of a mirror was measured by thermal desorption-gas chromatography/mass spectrometry and thermal desorption spectroscopy. It was found that cleanliness and ultra-high vacuum techniques are required to produce the contamination-free surfaces that are essential for the propagation of high-quality X-ray beams. The reduction of carbonaceous residue adsorbed on the surfaces, and absorbed into the bulk, of the materials in the vicinity of the mirrors is a key step toward achieving contamination-free X-ray optics.

Upgrade of surface profiler for x-ray mirror at SPring-8

In beamlines at third-generation synchrotron radiation and X-ray free-electron-laser (XFEL) facilities, various mirrors are used as deflection, focusing, and collimating optics. The required specifications for the mirrors depend on their purpose. In recent years, high-precision aspheric mirrors and flat mirrors, with a figure error less than 10 nm are used as diffraction-limited focusing optics and deflection optics, respectively. The origins of the figure error are fabrication error, gravitational deformation, and clamping deformation. In the case of the bend mirror, figure error is also induced by the bender mechanism. The fabrication error is measured by a long trace profiler (LTP) [1] or by relative-angle determinable stitching interferometry (RADSI) [2] with special high frequency of 0.1–1/mm. Deformation caused by gravity, clamping, and bending should be measured under actual operating conditions because these deformations depend on the direction of the mirror surface and the direction of clamping and bending, respectively. In recent years, in-situ and atwavelength metrology techniques such as the Hartmann sensor, pencil beam, grating base and the speckle-effect-based technique, have been reported [3-6]. These methods are able to investigate the profile of the mirror under real conditions, including the effects of thermal bump; however, these techniques require X-rays and a long optical length to the detector. We attempted to upgrade the LTP at SPring-8 using autocollimators for the precise measurement of height profiles under conditions of both upward and horizontal reflection geometries. A portable Fizeau interferometer was installed for onsite measurement.

Measurement of groove density variation of varied-line-space grating for high-resolution soft x-ray monochromator

A varied-line-space grating is used in modern soft X-ray monochromators with a high resolving power. The grating parameters require high accuracy because errors of the parameters lead to the degradation of the resolving power. The parameter tolerances required to maintain a high resolving power were estimated by analytical calculation. The groove density variations of three gratings were measured with a long trace profiler. The measured errors in the parameters were found to be sufficiently small.