Single-bunch Mode Research Articles

Energy resolution of pulsed neutron beam provided by the ANNRI beamline at the J-PARC/MLF

We studied the energy resolution of the pulsed neutron beam of the Accurate Neutron–Nucleus Reaction Measurement Instrument (ANNRI) at the Japan Proton Accelerator Research Complex/Materials and Life Science Experimental Facility (J-PARC/MLF). A simulation in the energy region from 0.7meV to 1MeV was performed and measurements were made at thermal (0.76−62meV) and epithermal energies (4.8−410eV). The neutron energy resolution of ANNRI determined by the time-of-flight technique depends on the time structure of the neutron pulse. We obtained the neutron energy resolution as a function of the neutron energy by the simulation in the two operation modes of the neutron source: double- and single-bunch modes. In double-bunch mode, the resolution deteriorates above about 10eV because the time structure of the neutron pulse splits into two peaks. The time structures at 13 energy points from measurements in the thermal energy region agree with those of the simulation. In the epithermal energy region, the time structures at 17 energy points were obtained from measurements and agree with those of the simulation. The FWHM values of the time structures by the simulation and measurements were found to be almost consistent. In the single-bunch mode, the energy resolution is better than about 1% between 1meV and 10keV at a neutron source operation of 17.5kW. These results confirm the energy resolution of the pulsed neutron beam produced by the ANNRI beamline.

Time-resolved X-ray excited optical luminescence using an optical streak camera

We report the development of a time-resolved XEOL (TR-XEOL) system that employs an optical streak camera. We have conducted TR-XEOL experiments at the Canadian Light Source (CLS) operating in single bunch mode with a 570 ns dark gap and 35 ps electron bunch pulse, and at the Advanced Photon Source (APS) operating in top-up mode with a 153 ns dark gap and 33.5 ps electron bunch pulse. To illustrate the power of this technique we measured the TR-XEOL of solid-solution nanopowders of gallium nitride - zinc oxide, and for the first time have been able to resolve near-band-gap (NBG) optical luminescence emission from these materials. Herein we will discuss the development of the streak camera TR-XEOL technique and its application to the study of these novel materials.

Angle-resolved time-of-flight spectroscopy applied to multi-bunch operation at MAX-lab: a design study

Angle-resolved time-of-flight (ARTOF) spectrometers have found use in a number of applications, including ARPES. However, the fundamental requirement of an external start trigger matching the read-out time of the instrument limits its usability at many storage rings. Hitherto all reported experiments have been performed at storage rings capable of running in single-bunch mode. To eliminate this restriction, we propose a method where a pulsed electronic gate is introduced to allow for ARTOF usage at normal multi-bunch operation of the MAX II storage ring. This paper will show the working principle and outline the design for this technique.

Operational Status of PF-Ring and PF-AR after the Earthquake

In 2011, two SR sources of KEK, PF-ring and PF-AR, needed to change the operation schedule because of the unprecedented earthquake on March 11. Though the injector linac and the storage rings suffered a serious damage, temporary recovery was accomplished quickly and the trial operation started in May. The regular user operation could be resumed in October 2011. In the restoration work after the earthquake, some old vacuum components were removed from PF-ring. This work fortunately brought an effect of settling the quadrupole-mode longitudinal instability. For the top-up injection of PF-ring, the pulsed sextupole magnet has been used instead of the conventional kicker magnets since 2011. The hybrid-fill mode in place of the single-bunch mode has become available. Recently, the 10-Hz orbit switching for the tandem circularly polarized undulators has been developed for the user operation.

Site-selective photofragmentation of chlorinated polymeric films observed around the chlorine K-edge

Photon stimulated ion desorption (PSID) and Near-edge X-ray absorption fine structure (NEXAFS) studies have been performed on poly(vinyl chloride) (PVC) and poly(vinyl dichloride) (PVDC) around the chlorine 1s-edge. Experiments were performed using a synchrotron source operating in the single-bunch mode and a time-of-flight mass spectrometry for ion analysis. Cl+ ion yields, as a function of the photon energy, reproduce the photoabsorption spectrum, showing significant increase at the 1s-resonance. Edge-jump ratios, defined as the ratio between edge-jumps (intensity ratio of the yields between above and below the absorption edge) of two different transitions, for Cl+ ion yields were much higher than the equivalent electron yields, indicating site-selectivity in C–Cl bond breaking for both polymers, as a result of efficient spectator Auger decay. The expected isotope ratio of 3:1 for chlorine was measured for PVC. The interpretation of the NEXAFS spectrum was assisted by quantum mechanical calculations at a multireference perturbation theory level.

Ionization, dissociation and desorption of pyrimidine ice due to X-ray interaction

The photoionization and the photodissociation of pyrimidine in condensed phase due to soft X-ray interaction were experimentally investigated. The measurements were performed at the Brazilian Synchrotron Light Source (LNLS), operated in the single-bunch mode, employing X-ray photons at energies around the C1s (288 eV) and N1s (400 eV) resonances. Mass spectra of ionic fragments desorbed from pyrimidine ice were obtained using the time-of-flight mass spectrometry (TOF-MS). The photodesorption yields (ions photons−1) and ion yields (cm−3 s−1) were determined, providing data to astrochemistry models.

X-ray excited optical luminescence of Ce-doped BaAl2O4

The luminescence properties of Ce3+ in BaAl2O4 are reported. The results of simultaneous measurements of XEOL and XAS in the X-ray energy range that includes the Ba LII,III-edges and Ce LIII edge are shown. The XEOL yield increases as the energy of the photons increases. The radioluminescence spectra, taken from 200 to 1100nm, showed broad emission bands corresponding to 5d1→2F5/2, 2F7/2 transitions of Ce3+ when incorporated into two nonequivalent Ba sites. The lifetime of the light emission was also measured using the single bunch operation mode at the Brazilian National Synchrotron Laboratory (LNLS), and BaAl2O4:Ce3+ showed single exponential decay time component of about 44.3ns.

Fluorescence lifetime measurement from a designated single-bunch in the BEPC II colliding mode

Fluorescence lifetime measurement in the time domain requires excitation from a well separated single bunch using synchrotron light sources. In the colliding mode of the Beijing Electron Positron Collider II (BEPCII), a hybrid filling pattern was realized such that a single bunch was placed in the middle of a large gap between two multi-bunch groups. Detection of fluorescence lifetime, based on the excitation of the light pulse from this designated single-bunch, was established at Beamline 4B8 of the Beijing Synchrotron Radiation Facility (BSRF). The timing signal of the BEPCII was utilized as a trigger to gate this fluorescence event. L-Tryptophan amino acid, a known lifetime standard, was selected to assess the lifetime measurement performance. The measured lifetime was consistent in both colliding and single-bunch mode with the time resolution down to 450 ps. Moreover, both the bunch purity and the fine structure of the hybrid filling pattern were characterized.

Development of a bunch-by-bunch longitudinal feedback system with a wide dynamic range for the HIGS facility

Electron beam coupled-bunch instabilities can limit and degrade the performance of storage ring based light sources. A longitudinal feedback system has been developed for the Duke storage ring to suppress multi-bunch beam instabilities which prevent stable, high-current operation of the storage ring based free-electron lasers (FELs) and an FEL driven Compton gamma source, the high intensity gamma-ray source (HIGS) at Duke University. In this work, we report the development of a state-of-the-art second generation longitudinal feedback system which employs a field programmable gate array (FPGA) based processor, and a broadband, high shunt-impedance kicker cavity. With two inputs and two outputs, the kicker cavity was designed with a resonant frequency of 937 MHz, a bandwidth of 97 MHz, and a shunt impedance of 1530 Ω . We also developed an S-matrix based technique to fully characterize the performance of the kicker cavity in the cold test. This longitudinal feedback system has been commissioned and optimized to stabilize high-current electron beams with a wide range of electron beam energies (250 MeV to 1.15 GeV) and a number of electron beam bunch modes, including the single-bunch mode and all possible symmetric bunch modes. This feedback system has become a critical instrument to ensure stable, high-flux operation of HIGS to produce nearly monochromatic, highly polarized Compton gamma-ray beams.

Positive and negative ionic desorption from condensed formic acid photoexcited around the O 1s-edge: Relevance to cometary and planetary surfaces

Photon stimulated ion desorption (PSID) studies have been performed in condensed formic acid using oxygen 1s-edge synchrotron radiation from the Brazilian synchrotron light source (LNLS), operating in a single-bunch mode. Ion formation was discussed in terms of the Auger stimulated ion desorption (ASID) and X-ray induced electron stimulated desorption (XESD) mechanisms. It is found that O 1s(C–OH) → π*(C O) and O 1s(C O) → 3s/σ*(HCO) transitions favored the production of C +, CH +, O +, O − and H − ions. The hydroxyl anion has not been observed while the hydroxyl cation showed low intensity or was absent. Some anion formation routes from dissociative reactions are suggested taking into account the positive ion yields.

Ionic desorption from intrinsically conducting polymer films based on polypyrrole induced by high energy electrons and soft X-ray synchrotron radiation

Ionic desorption from polypyrrole films doped with dodecylsulfate as counter anion (PPyDS) deposited onto fluorine tin oxide glass (FTO) was studied through electron (ESID) and photon (PSID) stimulated ion desorption techniques, employing time-of-flight mass spectrometry (TOF-MS) for ion analysis. ESID results suggested strong contribution from DS fragments to the mass spectra. In the 650–1500 eV energy range the relative desorption ion yield curves show maxima at about 700, 1200 and 1400 eV, which may be related to carbon, nitrogen and oxygen containing fragments, respectively, and interpreted in terms of the Auger stimulated ion desorption (ASID) mechanism. For energies greater than 1500 eV, the secondary electrons play an important role in the ion formation. PSID studies were performed at the Brazilian Synchrotron Light Source (LNLS) covering the sulphur K-shell photoexcitation during a single-bunch operation mode of the storage ring. Ionic desorption of atomic and molecular fragments were also observed. Relative desorption ion yield curves have been determined as a function of the photon energy, indicating that at the photon energy region covered by the PSID studies the indirect XESD (X-ray induced electron stimulated desorption) process plays an important role in the ionic desorption of PPyDS irradiated by soft X-rays.

X-band rf structure with integrated alignment monitors

We present the electrical design for an $X$-band traveling wave accelerator structure with integrated alignment monitors to measure the transverse wake, which will be used as part of the PSI-XFEL project and in the CLIC structure testing program. At PSI, it will compensate nonlinearities in the longitudinal phase space at the injector prototype of the PSI-XFEL. At CLIC it will be tested for breakdown limits and rates in the high gradient regime. The prolonged operation of such a structure in the PSI-XFEL injector, albeit not for the CLIC parameter regime, will constitute a good quality test of the manufacturing procedures employed. The operation in the PSI-XFEL injector will be at a relatively modest beam energy of 250 MeV, at which transverse wakes can easily destroy the beam emittance. For this reason, the layout chosen employs a large iris, $5\ensuremath{\pi}/6$ phase advance geometry, which minimizes transverse wakefield effects while still retaining a good efficiency. As a second important feature, the design includes two wakefield monitors coupling to the transverse higher order modes, which allow steering the beam to the structure axis, potentially facilitating a higher precision than mechanical alignment strategies. Of special interest is the time domain envelope of these monitor signals. Local offsets due to bends or tilts have individual signatures in the frequency spectrum, which in turn are correlated with different delays in the signal envelope. By taking advantage of this combined with the single bunch mode at the PSI-XFEL, the use of a relatively simple detector-type rf front end should be possible, which will not only show beam offsets but also higher order misalignments such as tilts in the structure. The resolution of these monitors is determined by the tolerance of the random cell-to-cell misalignment leading to a spurious signal in the monitors.

The Nonplanar Secretory IgA2 and Near Planar Secretory IgA1 Solution Structures Rationalize Their Different Mucosal Immune Responses

Secretory IgA (SIgA) is the most prevalent human antibody and is central to mucosal immunity. It exists as two subclasses, SIgA1 and SIgA2, where SIgA2 has a shorter hinge joining the Fab and Fc regions. Both forms of SIgA are predominantly dimeric and contain an additional protein called the secretory component (SC) that is attached during the secretory process and is believed to protect SIgA in harsh mucosal conditions. Here we locate the five SC domains relative to dimeric IgA2 within SIgA2 using constrained scattering modeling. The x-ray and sedimentation parameters showed that SIgA2 has an extended solution structure. The constrained modeling of SIgA2 was initiated using two IgA2 monomers that were positioned according to our best fit solution structure for dimeric IgA1. SC was best located along the convex edge of the Fc-Fc region. The best fit models showed that SIgA2 is significantly nonplanar in its structure, in distinction to our previous near planar SIgA1 structure. Both the shorter IgA2 hinges and the presence of SC appear to displace the four Fab regions out of the Fc plane in SIgA2. This may explain the noncovalent binding of SC in some SIgA2 molecules. This nonplanar structure is predicted to result in specific immune properties for SIgA2 and SIgA1. It may explain differences observed between the SIgA1 and SIgA2 subclasses in terms of their interactions with antigens, susceptibility to proteases, effects on receptors, and distribution in different tissues. The different structures account for the prevalence of both forms in mucosal secretions.

Photoabsorption and desorption studies on poly-3-hexylthiophene/multi-walled carbon nanotube composite films

Photon stimulated ion desorption (PSID) and Near-edge X-ray absorption fine structure (NEXAFS) studies have been performed on poly-3-hexylthiophene and nanocomposites thin films made of poly-3-hexylthiophene/multi-walled carbon nanotubes (MWNT) filled with iron/iron-oxide. The experiments were performed at the Brazilian Synchrotron Light Source (LNLS) operating in a single-bunch mode following sulphur K-shell photoexcitation and using time-of-flight mass spectrometry for ion analysis. Both PSID mass spectra show great similarity and exhibit desorption of the polymer fragments only. This result seems to be in accordance with previous morphological studies on these materials, which suggested that the nanotubes are highly dispersed and involved by the polymer. Although similar, the spectra present shifts in the direction of greater time-of-flights in the case of the poly-3-hexylthiophene/multi-walled carbon nanotube composite. This behavior may be related to the donation of electronic charge between the polymer matrix and the carbon nanotubes. In both cases, S + desorption seems to be suppressed, which may be due to the hexyl side-chains. Relative desorption ion yield curves have been determined as a function of the photon energy, which reproduced the photoabsorption spectrum. These results are discussed in terms of the indirect XESD (X-ray induced electron stimulated desorption) process.

Characterization of the anion-ordering transition in(TMTTF)2ReO4by x-ray absorption and photoemission spectroscopies

We have characterized the electronic structure of single crystals of the organic quasi-one-dimensional salt $(\mathrm{TMTTF}{)}_{2}{\mathrm{ReO}}_{4}$ $(\mathrm{TMTTF}=\mathrm{tetramethyl}\text{\ensuremath{-}}\mathrm{tetrathiafulvalene})$ by x-ray-absorption near-edge spectroscopy and x-ray photoemission spectroscopy using synchrotron radiation under low-intensity conditions (single-bunch ring operation mode) in order to strongly reduce detrimental beam-induced damage. The observed differences in spectra taken at $T=116\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $T=207\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ are ascribed to the anion-ordering transition, which takes place at $155\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. It is proposed that the ordering transition driven by the anions perturbs the structural organization of the organic stacks, increasing the overlap of the $\ensuremath{\pi}$-type orbitals through dimerization.

AZ-1518 Photoresist analysis with synchrotron radiation using high-resolution time-of-flight mass spectrometry

With the aim of identifying molecular modifications among photoresists unexposed and previously exposed to the ultraviolet light the photon stimulated ion desorption (PSID) technique was employed in the study of the AZ-1518 photoresist. Data acquisition was performed at the Brazilian Synchrotron Light Source (LNLS), during a single-bunch operation mode of the storage ring and using high-resolution time-of-flight mass spectrometry (TOF-MS) for ion analysis. PSID mass spectra on both photoresists (unexposed and exposed) were obtained following the S K-shell photoexcitation and desorption ion yield curves have been determined for the main fragments as a function of the photon energy. The AZ-1518 photoresists presented different PSID spectra, showing characteristic fragments. Most of the analyzed ions showed larger relative yields for the exposed photoresist. Fragments related to the photochemical decomposition of the photoresist could be clearly identified. These results showed that the PSID technique is adequate to investigate structural changes in molecular level in unexposed and exposed photoresists.

シングルバンチ放射光とミニチュア円筒鏡型分析器（ＣＭＡ）を用いた脱離イオンの質量と運動エネルギー分布の同時測定―凝縮ＮＨ３の内殻励起誘起Ｈ｀＋´脱離研究への応用―

We measured mass and kinetic-energy distribution of desorbed ions using a miniature cylindrical mirror analyzer (CMA) and synchrotron radiation under the single-bunch mode operation. We have applied it for the measurements of kinetic energy distribution of ions desorbed by N 1s transitions of condensed NH3.

Photon stimulated ion desorption from intrinsically conducting polymer films based on polypyrrole doped with [Ni(dmit) 2] 2−

Photon stimulated ion desorption and near-edge X-ray absorption fine structure studies have been performed on polypyrrole (PPy) films doped with [Ni(dmit) 2] 2− as counter ion. The experiments were taken at the Brazilian synchrotron light source (LNLS) operating in a single-bunch mode following sulphur K-shell photoexcitation and using time-of-flight mass spectrometry for ion analysis. At the sulphur 1s-edge ionic desorption of atomic and molecular fragments can be observed. Desorption ion yield curves have been determined as a function of the photon energy. The results showed that while the S + ion yield reproduces the photoabsorption spectrum, the S 2+ desorption is enhanced at higher energy excitations. These results are discussed in terms of the Auger stimulated ion desorption (ASID) mechanism, since these ions are not observed below the sulphur K-shell excitation region. Furthermore, for the other ionic species the indirect XESD (X-ray induced electron stimulated desorption) and the ASID processes seem to play an important role.

Photon stimulated ion desorption from condensed chloroform on Si(100) at the Cl and Si K-edges

Photon stimulated ion desorption (PSID) studies have been performed in chloroform condensed on Si(100) at ∼85 K using synchrotron radiation at the chlorine and silicon 1s-edges. Data acquisition was performed at the Brazilian synchrotron light source (LNLS), during a single-bunch operation mode of the storage ring. It was found that hydrogen ion is the main ionic species to desorb after photon excitation followed by other fragments with lower intensities. Desorption ion yields for H + and Cl + were obtained as a function of the photon energy. A pronounced enhancement of the Cl + yield was observed at the first Cl 1s resonance, which may be related to a spectator Auger process. In order to verify the influence of the substrate in the ionic desorption of condensed chloroform, PSID spectra were also measured at the silicon 1s-edge. The indirect X-ray induced electron stimulated desorption (XESD) mechanism seems to dominate.

Photon stimulated ion desorption studies from poly(sulphone) using synchrotron radiation in a single-bunch mode

Photon stimulated ion desorption (PSID) studies from poly(sulphone) (PS) have been carried out by using high-resolution time-of-flight mass spectrometry. Synchrotron radiation at the Brazilian Synchrotron Light Source (LNLS) operating in a single-bunch mode was used as excitation source. PS was excited at the sulphur 1s-edge and the desorption of small and large fragments has been observed. The results are discussed in terms of the X-ray induced electron stimulated desorption mechanism. The present results contrast with previous ones reported for poly(3-methylthiophene) (PMeT), in which the observation of S + and S 2+ was interpreted solely in terms of an Auger-stimulated ion desorption mechanism.