Generalised analytical method unravels framework-dependent kinetics of adsorption-induced structural transition in flexible metal–organic frameworks

ゲート型吸着剤はガス分子をどう取り込む？ --サブ秒でのX線回折測定が動的過程を紐解く--. 京都大学プレスリリース. 2023-11-08.Flexible metal–organic frameworks (MOFs) exhibiting adsorption-induced structural transition can revolutionise adsorption separation processes, including CO₂ separation, which has become increasingly important in recent years. However, the kinetics of this structural transition remains poorly understood despite being crucial to process design. Here, the CO₂-induced gate opening of ELM-11 ([Cu(BF₄)₂(4, 4’-bipyridine)₂]n) is investigated by time-resolved in situ X-ray powder diffraction, and a theoretical kinetic model of this process is developed to gain atomistic insight into the transition dynamics. The thus-developed model consists of the differential pressure from the gate opening (indicating the ease of structural transition) and reaction model terms (indicating the transition propagation within the crystal). The reaction model of ELM-11 is an autocatalytic reaction with two pathways for CO₂ penetration of the framework. Moreover, gas adsorption analyses of two other flexible MOFs with different flexibilities indicate that the kinetics of the adsorption-induced structural transition is highly dependent on framework structure

Classification of eigenmodes in rf cavities using the group theory

For many damped-accelerating cavities for high-intensity beams, classifications of eigenmodes according to azimuthal indices are generally insufficient due to a lack of their axial symmetry. To classify the eigenmodes in such cavities having general symmetry, the application of group theory is studied. By taking basis functions from a complete set of eigenmodes, one can form a representation of the symmetry group of the cavity. The eigenmodes can then be classified according to irreducible representations of the symmetry group. This method is particularly useful for classifying the eigenmodes in complicated cavities, and for understanding the effects of perturbations on the eigenmodes

Observation of transverse quadrupolar tune shifts in the Photon Factory storage ring

The frequencies (tunes) of transverse quadrupolar oscillations were measured in the 2.5-GeV Photon Factory storage ring at the High Energy Accelerator Research Organization (KEK). As a result, remarkable shifts in the quadrupolar frequencies with the bunch current were found; they were both positive and negative in the horizontal and vertical directions, respectively. This result can be explained by a focusing effect due to short-range wakefields containing a quadrupolar component

Reduction and compensation of the transient beam loading effect in a double rf system of synchrotron light sources

Double rf systems are used to lengthen the beam bunches in synchrotron light sources. In such a system, the performance of the bunch lengthening is limited by the transient beam-loading effect, which is induced by gaps in the fill pattern. To improve its performance, we investigate an application of a normal-conducting harmonic cavity, which is based on the TM020 resonant mode. By using the TM020 mode with low R/Q and high Q, fluctuation of the rf voltage due to the transient beam loading can be reduced significantly. The remaining small fluctuation of the rf voltage can be compensated by using an active feedforward technique. Using these measures, we expect to realize a bunch-lengthening performance that is comparable to that obtained with superconducting cavities under realistic operational parameters of a proposed 3-GeV next-generation light source. We estimate the bunch-lengthening performances using macroparticle tracking simulations together with semianalytical calculations

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

High-throughput gas separation by flexible metal–organic frameworks with fast gating and thermal management capabilities

ゲート型吸着剤を活用した二酸化炭素の高効率分離システムを提案 --二酸化炭素の分離回収技術の開発に貢献--. 京都大学プレスリリース. 2020-08-04.Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. Herein, we show that ELM-11 ([Cu(BF4)2(4, 4′-bipyridine)2]n), a member of flexible metal–organic frameworks (MOFs), exhibits rapid responsiveness to a gas feed and an ‘intrinsic thermal management’ capability originating from a structural deformation upon gas adsorption (gate-opening). These two characteristics are suitable for developing a pressure vacuum swing adsorption (PVSA) system with rapid operations. A combined experimental and theoretical study reveals that ELM-11 enables the high-throughput separation of CO2 from a CO2/CH4 gas mixture through adiabatic operations, which are extreme conditions in rapid pressure vacuum swing adsorption. We also propose an operational solution to the ‘slipping-off’ problem, which is that the flexible MOFs cannot adsorb target molecules when the partial pressure of the target gas decreases below the gate-opening pressure. Furthermore, the superiority of our proposed system over conventional systems is demonstrated

Improvement in the beam lifetime by means of an rf phase modulation at the KEK Photon Factory storage ring

In the 2.5-GeV Photon Factory storage ring at KEK, we have found that the beam lifetime can be improved by modulating the phase of an rf accelerating voltage at a frequency of 2 times the synchrotron oscillation frequency. By applying this phase modulation with a peak-to-peak amplitude of 3.2°, the beam lifetime could be improved, typically, from 22 to 36 h under a beam current of about 360 mA. At the same time, the longitudinal coupled-bunch instability could be considerably suppressed. The improvement in the beam lifetime can be explained as an improved Touschek lifetime, which was caused by a quadrupole-mode longitudinal oscillation of the stored bunches

Systematic study on the static Robinson instability in an electron storage ring

The static Robinson instability and associated coherent synchrotron frequencies were systematically studied at the Photon Factory (PF) 2.5-GeV storage ring at KEK. Under machine parameters close to an anticipated Robinson limit, we observed beam dumps at which the beam and related signals were recorded. The evolution of the beam phase and the threshold condition at the beam dumps were consistent with theoretical values calculated based on the uniformly filled point-bunch model. However, we found remarkable discrepancies from theoretical predictions with additional coherent-frequency measurements. Under conditions close to the Robinson limit, we observed an unpredicted sharp peak at a frequency of approximately 5.2 kHz, together with discrepancies in both the frequency and damping rate of the coherent oscillation. These results indicate the importance of further experimental and theoretical studies on the static Robinson instability