Hitoshi Tanaka

X-ray diffractometry for the structure determination of a submicrometre single powder grain.

A high-precision diffractometer with a synchrotron radiation microfocusing technique has been developed to investigate the crystal structure of a submicrometre-scale single grain of powder sample. The structure of a BaTiO3 single powder grain, of dimensions ∼600 × 600 × 300u2005nm, was determined.

Time-Resolved Investigation of Nanosecond Crystal Growth in Rapid-Phase-Change Materials: Correlation with the Recording Speed of Digital Versatile Disc Media

The crystallization process in digital versatile disc (DVD) media was investigated using a time-resolved X-ray diffraction apparatus coupled with in situ photoreflectivity measurement. The time profiles of crystallization were found to be consistent with the changes in photoreflectivity. The phase changes were characterized by the start and end time; 90±1 and 273±1 ns for Ge2Sb2Te5, and 85±1 and 206±1 ns for Ag3.5In3.8Sb75.0Te17.7, respectively. The faster crystallization time in Ag3.5In3.8Sb75.0Te17.7 is ascribed to its characteristic crystallization process; its X-ray diffraction profile shows a significant sharpening during the crystallization process, whereas the peak width of Ge2Sb2Te5 remained unchanged. The present findings suggest that crystal growth control is another key for designing faster phase-change materials.

First operation of circular dichroism measurements with periodic photon-helicity switching by a variably polarizing undulator at BL23SU at SPring-8

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.

Ultra-high-precision time control system over any long time delay for laser pump and synchrotron x-ray probe experiment

An ultra-high-precision clock system for long time delay has been developed for picosecond time-resolved x-ray diffraction measurements using synchrotron radiation (SR) pulses and synchronized femtosecond laser pulses. The time delay control between pump laser pulse and the probe SR pulse was achieved by combining an in-phase quadrature modulator and a synchronous counter. This method allowed us to change the delay time by a nearly infinite amount while maintaining the precision of +/-8.40 ps. Time-resolved diffraction measurements using the delay control system were demonstrated for precise measurement of an acoustic velocity in a single crystal of gallium arsenide.

Scheme for precise correction of orbit variation caused by dipole error field of insertion device

We developed a scheme for precisely correcting the orbit variation caused by a dipole error field of an insertion device (ID) in a storage ring and investigated its performance. The key point for achieving the precise correction is to extract the variation of the beam orbit caused by the change of the ID error field from the observed variation. We periodically change parameters such as the gap and phase of the specified ID with a mirror-symmetric pattern over the measurement period to modulate the variation. The orbit variation is measured using conventional wide-frequency-band detectors and then the induced variation is extracted precisely through averaging and filtering procedures. Furthermore, the mirror-symmetric pattern enables us to independently extract the orbit variations caused by a static error field and by a dynamic one, e.g., an error field induced by the dynamical change of the ID gap or phase parameter. We built a time synchronization measurement system with a sampling rate of 100Hz and app...

High‐Precision Time Delay Control with Continuous Phase Shifter for Pump‐Probe Experiments Using Synchrotron Radiation Pulses

Brilliant pulsed x‐ray synchrotron radiation (SR) is useful for pump‐probe experiment such as time‐resolved x‐ray diffraction, x‐ray absorption fine structure, and x‐ray spectroscopy. For laser pump‐SR x‐ray probe experiments, short pulsed lasers are generally synchronized to the SR master oscillator controlling the voltage for acceleration of electron bunches in an accelerator, and the interval between the laser and the SR pulses is changed around the time scale of target phenomenon. Ideal delay control produces any time delay as keeping the time‐precision and pointing‐stability of optical pulses at a sample position. We constructed the time delay control module using a continuous phase shifter of radio frequency signal and a frequency divider, which can produce the delayed trigger pulses to the laser without degradation of the time precision and the pointing stability. A picoseconds time‐resolved x‐ray diffraction experiment was demonstrated at SPring‐8 storage ring for fast lattice response by femtosec...

Simulation Studies of Beam Commissioning and Expected Performance of the SPring-8-II Storage Ring

In the SPring-8 upgrade project, the 5-bend achromat lattice is adopted for achieving a very low emittance of 157 pm.rad at 6 GeV. Since the dynamic aperture (DA) and the beam performance become sensitive against errors, we carried out tracking simulations to evaluate the tolerance of machine imperfections. It is found that the first-turn-steering (FTS) with the use of single-pass BPMs is indispensable for accumulating the beam and by performing the orbit and optics corrections, we can finally achieve an emittance value of 160 ~ 180 pm.rad, being close to the design value. We also found that a naive application of the SVD algorithm to orbit corrections yields unwanted local bumps between BPMs and this deteriorates the vertical emittance. A possible scheme to avoid such local bumps by effectively interpolating the measured orbit is also discussed.

Pulse-by-Pulse Multi-XFEL Beamline Operation with Ultra-Short Laser Pulses

The parallel operation of multiple beamlines is an important issue to expand the opportunity of user experiments for linear accelerator based FELs. At SACLA, the parallel operation of three beamlines, BL1~3, has been open to user experiments since September 2017. BL1 is a soft x-ray beamline driven by a dedicated accelerator, which is a former SCSS test accelerator, and BL2 and BL3 are XFEL beamlines sharing the electron beam from the SACLA main accelerator. In the parallel operation, a kicker magnet with 10 ppm stability (peak-to-peak) switches the two XFEL beamlines pulse by pulse at 60 Hz. To ensure wide spectral tunability and optimize the laser performance, the beam energy and the electron bunch length are independently adjusted for the two XFEL beamlines according to user experiments. Since the electron bunch of SACLA has typically 15 fs (FWHM) in length and its peak current exceeds 10 kA, CSR effect at a dogleg beam transport to BL2 is quite significant. In order to suppress the CSR effect, an isochronous and achromatic beam optics based on two DBA structures was introduced. The parallel operation of the three FEL beamlines substantially increases user time at SACLA.

Current status and future plan of the soft x-ray beamline at SACLA (Conference Presentation)

SACLA was inaugurated in March 2012 with two beamlines: BL3 for hard X-ray FEL and BL1 for wide range spontaneous emission. To enhance the research opportunities in soft X-ray region, the SCSS test accelerator, which was a prototype linac of SACLA and decommissioned in 2013, was upgraded, relocated to the SACLA undulator hall, and connected to BL1. The commissioning of this upgraded BL1 had been started from September in 2015, and user operation was started from June 2016. Currently, SASE-FEL pulses in the photon energy range of 20 to 150 eV are available and average pulse energy is about 70 μJ at 100 eV. We are developing beam diagnostic systems such as an arrival timing diagnostics between the SXFEL and the synchronized optical laser. We have further upgrade plans of the accelerator and the beamline. In this presentation, I will report the latest status and future upgrade plans of this beamline.

Commissioning Status of the Extreme-Ultraviolet FEL Facility at SACLA

To equip SACLA with wide ability to provide laser beams in EUV and soft X-ray regions to experimental users, we have constructed a new free electron laser facility for the SACLA beamline-1. Injector components, such as a thermionic electron gun, two buncher cavities, and their RF sources, were relocated from the SCSS test accelerator. At the downstream of a bunch compressor chicane, 3 C-band acceleration units were newly installed to effectively boost a beam energy up to 500 MeV. 3 invacuum undulators with a larger K-value of 2.1 were remodelled for increasing SASE intensity. Beam commissioning was started in autumn 2015. We carefully tuned an electron beam orbit and bunch compression processes to obtain 240 A at the peak along the injector and 2 bunch compressors. The bunch length was successfully compressed from 1 ns to 1 ps. After the tuning, the lasing of the EUV-FEL was realized. So far the FEL radiation with energy of about 25 uf06dJ and a 30 nm wavelength driven by a 500 MeV electron beams was observed. In this summer, we will install additional 2 C-band accelerator units to raise the maximum beam energy to 750 MeV for providing a laser at 13 nm.