Photon Factory Advanced Ring Research Articles

SuperKEKB personnel protection system

The Super-KEKB[1] personnel protection system (PPS) takes care of not only Super-KEKB accelerator, but also Photon Factory - Advanced Ring (PF-AR), Positron Damping Ring (PDR)[2] and their beam transport lines (BT)[3]. The logic of the PPS has been changed to adapt the new accelerator operation scheme. The Experimental Physics and Industrial Control System (EPICS) was introduced into the PPS. Many tools developed under EPICS environment are used.

Modification of Beam Transport Line Design for Simultaneous Top-up Injection to PF and PF-AR

The High Energy Accelerator Research Organization (KEK) has two light sources: Photon Factory (PF, 2.5 GeV) and Photon Factory Advanced Ring (PF-AR, 6.5 GeV). In 2017, the operation of a new beam transport line (BT) of PF-AR was started, and the simultaneous top-up injection for both PF and PF-AR was realized. These days, there have been strong demands for the reduction of the operating cost of accelerators, and its importance is greater in PF-AR with higher ring-energy of 6.5 GeV. In 2019, the 5 GeV operation was started in PF-AR. However, the new BT of PF-AR (ARBT) was designed for the energy of 6.5 GeV, then the simultaneous top-up injection is no longer available under the condition of 5 GeV operation of PF-AR and 2.5 GeV operation of PF. In order to mitigate this impact, the pseudo-top-top injection has been employed by fine-tuning the current of a common DC bending magnet placed at the intersection of ARBT and the BT of PF (PFBT) within a given time frame. However, this scheme reduces the flexibility of the operation schedules, and will not be able to respond adequately to low emittance optics of PF-AR that may bring the shorter beam lifetime. In order to realize true-top-up injection, a modification of BTs’ optics design was carried out to add new horizontal steering magnets and a flattened-duct. The beam commissioning succeeded and the application to the user-run will start in this May. This time, details of modification and its extended plan will be presented.

P-V-T equation of state of hydrous phase A up to 10.5 GPa

Abstract Pressure-volume-temperature (P-V-T) data of synthetic Mg7Si2O8(OH)6 phase A were collected under P-T conditions up to ~10.5 GPa and 900 K by energy-dispersive X-ray diffraction using a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory–Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). P-V EoS using only room-temperature data yielded V0 = 511.6(2) Å3, KT0 = 106.8(18) GPa, and pressure derivative KT′ = 3.88(38). These parameters were consistent with the subsequent equation of state (EoS) analysis. The compressibility of phase A was anisotropic, with its a-axis being ~26% more compressible than the c-axis, which is normal to the plane of the distorted close-packed layers. A fit of the present data to the high-temperature Birch-Murnaghan EoS yielded V0 = 511.7(3) Å3, K0 = 104.4(24) GPa, K′ = 4.39(48), (∂KT/∂T)P = –0.027(5) GPa K–1, and thermal expansion α = a + bT with values of a = 2.88(27) × 10–5 K–1 and b = 3.54(68) × 10–8 K–2. The lattice dynamical approach by the Mie-Grüneisen-Debye EoS yielded θ0 = 928(114) K, q = 2.9(10), and γ0 = 1.19(8). The isobaric heat capacity CP of phase A at 1 atm. was calculated based on the Mie-Grüneisen-Debye EoS fit of present P-V-T data. In addition, the density profiles of subducting slabs with different degrees of serpentinization were also calculated along the cold geotherm up to ~13 GPa. The serpentinization of subducting slab will significantly lower the density of slab at shallower depth; however, this effect becomes negligible when antigorite dehydrates to phase A. Because the phase A bearing subducting slab is supposed to be denser than the surrounding mantle, the water can transport into deeper parts of the upper mantle and the transition zone.

Tracking the Local Structure Change during the Photoabsorption Processes of Photocatalysts by the Ultrafast Pump-Probe XAFS Method

The birth of synchrotron radiation (SR) facilities and X-ray free electron lasers (XFELs) has led to the development of new characterization tools that use X-rays and opened frontiers in science and technology. Ultrafast X-ray absorption fine structure (XAFS) spectroscopy for photocatalysts is one such significant research technique. Although carrier behavior in photocatalysts has been discussed in terms of the band theory and their energy levels in reciprocal space (k-space) based on optical spectroscopic results, it has rarely been discussed where photocarriers are located in real-space (r-space) based on direct observation of the excited states. XAFS provides information on the local electronic and geometrical structures around an X-ray-absorbing atom and can address photocarrier dynamics in the r-space observed from the X-ray-absorbing atom. In this article, we discuss the time dependent structure change of tungsten trioxide (WO3) and bismuth vanadate (BiVO4) photocatalysts studied by the ultrafast pump-probe XAFS method in the femtosecond to nanosecond time scale with the Photon Factory Advanced Ring (PF-AR) and the SPring-8 Angstrom Compact free-electron LAser (SACLA). WO3 shows a femtosecond decay process of photoexcited electrons followed by a structural change to a metastable state with a hundred picosecond speed, which is relaxed to the ground-state structure with a nanosecond time constant. The Bi L3 edge of BiVO4 shows little contribution of the Bi 6s electron to the photoabsorption process; however, it is sensitive to the structural change induced by the photoexcited electron. Time-resolved XAFS measurements in a wide range time domain and with varied wavelengths of the excitation pump laser facilitate understanding of the overall details regarding the photocarrier dynamics that have a significant influence on the photocatalytic performance.

In Situ Observation of the Phase Transition Behavior of Shocked Baddeleyite

AbstractBaddeleyite (ZrO2) is used to infer shock pressures and understand the impact history of planetary bodies. Although the high‐pressure phase transition behavior of baddeleyite has been intensively investigated under hydrostatic conditions, there is little information on the dynamic response of phase transitions under shock‐loading conditions. We performed in situ X‐ray diffraction measurements on shock‐loaded baddeleyite using a synchrotron X‐ray pulse at beamline NW14A of the Photon Factory Advanced Ring, High Energy Accelerator Research Organization (KEK), Japan. A phase transition from monoclinic to orthorhombic‐I ZrO2 occurs at 3.3 GPa during shock compression and immediately returns to the monoclinic phase during subsequent release. Orthorhombic‐II ZrO2 is not observed up to 15 GPa. This study refines the phase transition behavior of baddeleyite under shock conditions up to 15 GPa, and the phase transition boundary is determined from direct observations. These findings improve the understanding of the shock history of planetary bodies.

New HMBA lattice for PF-AR

Photon Factory Advanced Ring (PF-AR) has been operated for users about 30 years from 1987. The lattice and optics are almost not changed from the original one as the TRISTAN booster ring constructed in 1984. The lattice employs FODO structure and the horizontal emittance for the 6.5 GeV user run is about 300 nmrad. In order to improve the performance of PF-AR dramatically, the full replacement of the accelerator to the ESRF type HMBA (Hybrid multi bend achromat) lattice is examined. In order to geometrically fit the new lattice to the present PF-AR tunnel, the new ring consists of 12 cells with four long straight sections. The emittance is improved to about 500 pmrad at 3 GeV. With the present user experimental hall at the northern half of the ring, at least eight undulator beam lines can be constructed. The simulated dynamic aperture is about 1.5 cm at the long straight section with reasonable magnetic errors and COD correction. The Touschek lifetime is about 6 hours. The beam injection with conventional injection system is no problem and the beam lifetime is long enough.

Review of the Elementary Particles Physics in the External Electromagnetic Fields Studies at KEK

High Energy Accelerator Research Organization (KEK [1]) is a world class accelerator-based research laboratory. The field of its scientific interests spreads widely from the study of fundamental properties of matter, particle physics, nuclear physics to materials science, life science, technical researches, and industrial applications. Research outcomes from the laboratory achieved making use of high-energy particle beams and synchrotron radiation. Two synchrotron facilities of KEK, the Photon Factory (PF) ring and the Photon Factory Advanced Ring (PF-AR) are the second biggest synchrotron light source in Japan. A very wide range of the radiated light, from visible light to X-ray, is provided for a variety of materials science, biology, and life science [2]. KEK strives to work closely with national and international research institutions, promoting collaborative research activities. Advanced research and facilities provision are key factors to be at the frontier of the accelerator science. In this review I am going to discuss KEK overall accelerator-based science, and to consider light sources research and development. The state of arts of the current projects with respect to the elementary particles physics in the external electromagnetic fields is also stressed here.

Capturing structural dynamics of materials by picosecond X-ray pulses

Picosecond time-resolved X-ray techniques, such as time-resolved X-ray diffraction, scattering, and spectroscopy, utilize the pulsed nature of synchrotron radiation from storage rings, and are becoming general and powerful tools to explore structural dynamics in various materials. This method enables to produce "atomic structural movies" at picosecond temporal resolution. It will be fascinating to apply such capability to capture ultrafast structural dynamics in advanced materials of strongly-correlated electron systems, photochemical catalytic reaction dynamics in liquid or on solid surface, light-induced response of photosensitive proteins, etc. Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK), Tsukuba, Japan is a 6.5-GeV electron storage ring dedicated for single-bunch operation and is suitable for the picosecond time-resolved X-ray studies. An in-vacuum undulator beamline NW14A at the PF-AR was designed and constructed to conduct a wide variety of time-resolved X-ray measurements, such as time-resolved X-ray diffraction, scattering and spectroscopy [1]. Successful examples of time-resolved X-ray studies applied to materials science will be presented in the talk.

Equation of state and phase transition of antigorite under high pressure and high temperature

The equation of state of natural antigorite has been determined up to ∼10GPa and 500°C by in situ X-ray diffraction in a cubic type multi-anvil apparatus, MAX80, located at the Photon Factory-Advanced Ring at the High Energy Accelerator Research Organization (KEK), and the temperature dependence of the bulk modulus was determined for the first time by high pressure and high temperature X-ray diffraction based on a series of direct measurements. No dehydration occurred during the entire experimental process, and no significant deviatoric stress was observed after heating. The room temperature P–V data below 7GPa have been fit to the Birch-Murnaghan equation of state, yielding V0,300K=366.9(7)Å3, K0, 300K=65.2(31)GPa, and the pressure derivative K′ fixed to 6.1. The high pressure phase transition was observed through volume softening behavior at around 7GPa, and the dP/dT slope seems to be flat or slightly positive, which is consistent with the recent report by Bezacier et al. (2013). The high temperature Birch-Murnaghan equation of state was used to fit the P–V–T data below 7GPa. Since the present experimental data was obtained by energy dispersive X-ray diffraction at high pressure and high temperature, the resolution was slightly lower than that obtained by the angle dispersive X-ray method. So the bulk modulus K0, 300K and the pressure derivative K′ were fixed to 62.9GPa and 6.1, respectively, which was obtained by single crystal X-ray diffraction in a diamond anvil cell by means of the angle dispersive method (Nestola et al., 2010) during fitting. From the fitting, we obtained V0, 300K=367.3(2)Å3, dK/dT=−0.0265(41)GPa/K, thermal expansion α0=3.92(50)×10−5/K. The temperature dependence of the bulk modulus was larger than the value calculated empirically (Holland and Powell, 1998). The thermal expansion of antigorite is larger than the results from the previous study. The compression of antigorite is very anisotropic along three axes, with a ratio of 1.15:1.00:3.33 at room temperature. Considering the P–T conditions of the subducting slab, the phase transition of antigorite may occur only in a limited area in the slab.

Laser Pump Diffracted-X-Ray-Tracking (Laser-Pump DXT) for Single Molecule Measurement of Rotational Motion in Reaction with Photodissociated ATP

Laser-pump diffracted-X-ray-tracking measurement system has been developed using nanosecond pulse laser at the beamline NW14A, Photon Factory Advanced Ring, KEK, Japan. Generally, diffracted X-ray tracking (DXT) has elucidated rotational motions of single protein molecule in real time [1]. In this work, single protein molecule labeled with gold nanocrystals in reaction with ATP molecule was irradiated by wide-energy band X-ray and nanosecond UV laser pulse. The motion of diffraction spots from gold nanocrystals were tracked in real time. The laser pulse produced the ATP molecules from photodissociation of caged-ATP in solution. The real-time rotational motion of single protein molecule reacting with ATP molecule can be observed using laser pump DXT.Pulse laser system (Powelite8000, Continuum Inc., USA) was synchronized with the diffracted X-ray tracking system. We took 90-120 diffraction images, and time resolution of DXT was from 5 μs/frame to 36 ms/frame. The wavelength, pulse width and laser intensity of single nanosecond laser pulse was 355 nm of third harmonic generation of the Nd:YAG laser, 10 ns and 20 mJ/cm2, respectively. This beamline gave the wideband-energy X-ray in the energy range 13-18 keV using an undulator at a repetition rate of 794 kHz. Delay time of laser pulse in DXT measurement was controlled by delay generator. Laser pulse can be irradiated sample in the arbitrary frames. We compared the motion of diffraction spots from gold nanocrystals attached protein molecule before laser irradiation with that after laser irradiation. The dynamical structural change of protein molecule in capturing ATP molecule will be revealed using laser-pump DXT. The rotational motion of Chaperonin in the presence of ATP is demonstrated as a typical example.[1] H. Shimizu, et al., Cell, 132, 67 (2008).

Experimental demonstration and visual observation of dust trapping in an electron storage ring

Sudden decreases in the beam lifetime, which are attributed to the dust trappings, sometimes occur at the electron storage ring Photon Factory Advanced Ring (PF-AR). Since these dust events cause difficulties in user operations, we have been carefully observing this phenomenon for many years. Our observations indicated that the dust trappings could be caused by electric discharges in vacuum ducts. In order to demonstrate this hypothesis experimentally, we designed a new vacuum device that intentionally generates electric discharges and installed it in PF-AR. Using this device, we could repeatedly induce sudden decreases in the beam lifetime because of the generated electric discharge. We also detected decreases in the beam lifetime caused by mechanical movement of the electrodes in the device. Moreover, we could visually observe the dust trapping phenomenon; the trapped dust particle was observed by two video cameras and appeared as a luminous body that resembled a shooting star. This was the first direct observation of a luminous dust particle trapped by the electron beam.

Improvement of beam lifetime and vacuum system of the PF-AR

Successive improvements have been performed on the vacuum system for the Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). The main purpose is to prolong electron beam lifetime for stable operation as an intense pulsed X-ray source. In the past three years, a total of 61 sputter ion pumps (SIPs) were additionally installed, and the increased effective pumping speed amounts to 13% of total. Comparison between calculated and observed beam lifetimes indicates that the lifetime is restricted mainly by the residual gas scatterings and that improvement of the vacuum will realize still longer lifetime. Sudden beam lifetime drops caused by dust trappings have been investigated for many years. The frequency of the lifetime drops has decreased as operation time elapsed after a large-scale reconstruction. Effect of distributed ion pumps (DIPs) on the lifetime drops has also been investigated experimentally.

Development of a movable synchrotron-radiation mask for the Photon Factory Advanced Ring (PF-AR)

In order to protect 3.4-m-long rf cavities from impinging intense synchrotron radiation (SR), we developed a unique SR mask for use in the Photon Factory Advanced Ring (PF-AR). To obtain a wide aperture that is required for beam injection, we designed the mask so that the head of the mask can be moved over a horizontal range of 30 mm. To avoid the harmful excitation of resonance modes in this mask structure, a microwave absorber was built into it. Two of the designed masks were installed in the PF-AR, and they showed satisfactory performance during routine single-bunch operations under beam currents of up to 60 mA. We report the design of this movable mask and its performance during operations.

Orbit correction using an eigenvector method with constraints for synchrotron radiation sources

An eigenvector method with constraints (EVC) is proposed as a new orbit correction scheme for synchrotron light sources. EVC efficiently corrects the global orbit in a storage ring, and can simultaneously perform exact correction of local orbits without deterioration of the global orbit. To demonstrate the advantages of EVC over the ordinary eigenvector method (EV), we carried out experimental studies at the Photon Factory storage ring (PF-ring) and the Photon Factory Advanced Ring (PF-AR) at the High Energy Accelerator Research Organization (KEK). The performance of EVC was systematically examined at PF-ring and PF-AR. The experimental results agreed well with the simulated ones. Consequently, we confirmed that EVC easily realized orbit correction for both global and local orbits, and that it was very effective for the beam stabilization of synchrotron radiation (SR) sources.

100 ps time-resolved solution scattering utilizing a wide-bandwidth X-ray beam from multilayer optics

100 ps time-resolved X-ray solution-scattering capabilities have been developed using multilayer optics at the beamline NW14A, Photon Factory Advanced Ring, KEK. X-ray pulses with an energy bandwidth of DeltaE/E = 1-5% are generated by reflecting X-ray pulses (DeltaE/E = 15%) through multilayer optics, made of W/B(4)C or depth-graded Ru/C on silicon substrate. This tailor-made wide-bandwidth X-ray pulse provides high-quality solution-scattering data for obtaining photo-induced molecular reaction dynamics. The time-resolved solution scattering of CH(2)I(2) in methanol is demonstrated as a typical example.

100ps time-resolved X-ray diffraction study on Nd0.5Sr0.5MnO3 thin film

We report the lattice dynamics in the photoinduced phase of Nd0.5Sr0.5MnO3 thin film by means of time-resolved x-ray diffraction measurements at the NW14A beamline in the Photon Factory Advanced Ring. We observed the decrease of intensity after the photoirradiation for a superlattice reflection which is associated with Jahn-Teller distortion.

Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy

An experimental set-up for time-resolved X-ray absorption spectroscopy with 100 ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented.

New injection scheme using a pulsed quadrupole magnet in electron storage rings

We demonstrated a new injection scheme using a single pulsed quadrupole magnet (PQM) with no pulsed local bump at the Photon Factory Advanced Ring (PF-AR) in High Energy Accelerator Research Organization (KEK). The scheme employs the basic property of a quadrupole magnet, that the field at the center is zero, and nonzero elsewhere. The amplitude of coherent betatron oscillation of the injected beam is effectively reduced by the PQM; then, the injected beam is captured into the ring without largely affecting the already stored beam. In order to investigate the performance of the scheme with a real beam, we built the PQM providing a higher field gradient over $3\text{ }\text{ }\mathrm{T}/\mathrm{m}$ and a shorter pulse width of $2.4\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$, which is twice the revolution period of the PF-AR. After the field measurements confirmed the PQM specifications, we installed it into the ring. Then, we conducted the experiment using a real beam and consequently succeeded in storing the beam current of more than 60 mA at the PF-AR. This is the first successful beam injection using a single PQM in electron storage rings.

Developing 100 ps-resolved X-ray structural analysis capabilities on beamline NW14A at the Photon Factory Advanced Ring

NW14A is a newly constructed undulator beamline for 100 ps time-resolved X-ray experiments at the Photon Factory Advanced Ring. This beamline was designed to conduct a wide variety of time-resolved X-ray measurements, such as time-resolved diffraction, scattering and X-ray absorption fine structure. Its versatility is allowed by various instruments, including two undulators, three diffractometers, two pulse laser systems and an X-ray chopper. The potential for the detection of structural changes on the 100 ps time scale at NW14A is demonstrated by two examples of photo-induced structural changes in an organic crystal and photodissociation in solution.

Current status of 50-picosecond resolved x-ray diffraction at Photon Factory Advanced Ring (PF-AR)

Ultra-fast time-resolved x-ray crystallography using electron-accelerator-based x-ray sources has been becoming a general and powerful tool to explore structural dynamics of crystalline state in material and biological sciences. Photon Factory Advanced Ring (PF-AR) is a full-time single-bunch synchrotron radiation source operated for such time-resolved x-ray studies using pulsed x-rays. Here we report instrumentation, feasibility, and applications of time-resolved x-ray diffraction at PF-AR. The time-resolved x-ray diffraction equipment consists of an x-ray pulse selector, an x-ray diffractometer, a femtosecond laser system and their timing modules which provide synchronized x-ray pulses with 50-picosecond duration (rms) and 150-femtosecond laser pulses for laser-pump-x-ray-probe experiment. The current status of the beam lines NW2 and NW14, and their applications are described.