Storage Ring Facility Research Articles

Nuclear magnetic dipole moment effect on the angular distribution of the Kα lines

We present a theoretical analysis of the fine-structure transitions for helium-like heavy ions with non-zero nuclear spin. The angular distribution of these transitions is studied for its sensitivity with regard to the nuclear magnetic dipole moment . Detailed calculations, performed for the helium-like , and ions with nuclear spin , indicate that the emission pattern of the fine-structure resolved photons is significantly affected by and that this effect can be addressed experimentally at present storage ring facilities.

Present status of Rare-RI Ring facility at RIBF

A new storage ring facility called the Rare-RI Ring is currently under preparation at the RI Beam Factory (RIBF) in RIKEN. The storage ring is dedicated to the single-ion precision mass spectrometry of neutron-rich exotic nuclei. The masses are essential to elucidate the evolution of the nuclear shell structure far from the β stability and to determine the pathway of astrophysical nucleosynthesis. Such exotic nuclei are provided by the large-acceptance superconducting fragment separator, BigRIPS, at the RIBF accelerator complex. The experimental principle of the Rare-RI Ring mass measurements is based on isochronous mass spectrometry combined with the individual injection technique. This novel technique enables exotic species of interest to be produced randomly, in time to be sequentially stored in the storage ring. The Rare-RI Ring facility realizes the most efficient measurements for rare isotopes. An overview of the project is presented, along with its present status.

An ion-beam injection line for the ELASR storage ring at KACST

A versatile ion injector beam-line has been developed for the specific use in the multi-purpose low-energy, storage ring facility at the King Abdulaziz City for Sciences and Technology (KACST) in Riyadh, Saudi Arabia. It incorporates a purpose-developed, high-resolution mass analyzing magnet and it is thereby dedicated to provide the ELASR storage ring with beams of ions of specific mass. It is also intended to operate independently as a single-pass experiment. This versatile ion-injection line was constructed in a staged approach, in which an axial injection version was built first, commissioned and is currently operating. The injection line in its final design is now being assembled and commissioned at KACST.

Photon-in photon-out hard X-ray spectroscopy at the Linac Coherent Light Source.

X-ray free-electron lasers (FELs) have opened unprecedented possibilities to study the structure and dynamics of matter at an atomic level and ultra-fast timescale. Many of the techniques routinely used at storage ring facilities are being adapted for experiments conducted at FELs. In order to take full advantage of these new sources several challenges have to be overcome. They are related to the very different source characteristics and its resulting impact on sample delivery, X-ray optics, X-ray detection and data acquisition. Here it is described how photon-in photon-out hard X-ray spectroscopy techniques can be applied to study the electronic structure and its dynamics of transition metal systems with ultra-bright and ultra-short FEL X-ray pulses. In particular, some of the experimental details that are different compared with synchrotron-based setups are discussed and illustrated by recent measurements performed at the Linac Coherent Light Source.

Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses.

Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution as compared with storage ring facilities, these measurements constitute the first X-ray-based visualization of a non-equilibrated intramolecular electron transfer process over large interatomic distances. Experimental and theoretical results establish that mediation through electronically excited molecular states is a key mechanistic feature. The present study demonstrates the extensive potential of femtosecond X-ray techniques as diagnostics of non-adiabatic electron transfer processes in synthetic and biological systems, and some directions for future studies, are outlined.

Beam loss distribution calculation and collimation efficiency simulation of a cooler storage ring in a heavy ion research facility

The Heavy Ion Research Facility in Lanzhou is an ion cooler storage ring facility in China's Institute of Modern Physics. The beams are accumulated, electron cooled, accelerated, and extracted from the main cooler storage ring (CSRm) to the experimental ring or different terminals. The heavy ion beams are easily lost at the vacuum chamber along the CSRm when it is used to accumulate intermediate charge state particles. The vacuum pressure bump due to the ion-induced desorption in turn leads to an increase in beam loss rate. In order to avoid the complete beam loss, the collimation system is investigated and planned to be installed in the CSRm. First, the beam loss distribution is simulated considering the particle charge exchanged process. Then the collimation efficiency of the lost particles is calculated and optimized under different position and geometry of the collimators and beam emittance and so on. Furthermore, the beam orbit distortion that is caused by different types of errors in the ring will affect the collimation efficiency. The linearized and inhomogeneous equations of particle motion with these errors are derived and solved by an extended transfer matrix method. Actual magnet alignment errors are adopted to investigate the collimation efficiency of the lost particles in the CSRm. Estimation of the beam loss positions and optimization of the collimation system is completed by a newly developed simulation program.

Opportunities and challenges for time-resolved studies of protein structural dynamics at X-ray free-electron lasers.

X-ray free-electron lasers (XFELs) are revolutionary X-ray sources. Their time structure, providing X-ray pulses of a few tens of femtoseconds in duration; and their extreme peak brilliance, delivering approximately 1012 X-ray photons per pulse and facilitating sub-micrometre focusing, distinguish XFEL sources from synchrotron radiation. In this opinion piece, I argue that these properties of XFEL radiation will facilitate new discoveries in life science. I reason that time-resolved serial femtosecond crystallography and time-resolved wide angle X-ray scattering are promising areas of scientific investigation that will be advanced by XFEL capabilities, allowing new scientific questions to be addressed that are not accessible using established methods at storage ring facilities. These questions include visualizing ultrafast protein structural dynamics on the femtosecond to picosecond time-scale, as well as time-resolved diffraction studies of non-cyclic reactions. I argue that these emerging opportunities will stimulate a renaissance of interest in time-resolved structural biochemistry.

ALS-II, a Potential Soft X-ray, Diffraction Limited Upgrade of the Advanced Light Source

The Advanced Light Source (ALS) at Berkeley Lab has seen many upgrades over the years, keeping it one of the brightest sources for soft x-rays worldwide. Recent developments in magnet technology and lattice design appear to open the door for very large further increases in brightness [1], particularly by reducing the horizontal emittance, even within the space constraints of the existing tunnel. Initial studies for possible lattices will be presented that could approach the soft x-ray diffraction limit around 2 keV in both planes within the ALS footprint.Emerging scientific applications and experimental methods that would greatly benefit from ring based sources having much higher brightness and transverse coherence than present or near future storage ring facilities include nanometer imaging applications, X-ray correlation spectroscopy, diffraction microscopy, holography, ptychography, and resonant inelastic soft X-ray scattering at high resolution.

SPARC collaboration: new strategy for storage ring physics at FAIR

SPARC collaboration at FAIR pursues the worldwide unique research program by utilizing storage ring and trapping facilities for highly-charged heavy ions. The main focus is laid on the exploration of the physics at strong, ultra-short electromagnetic fields including the fundamental interactions between electrons and heavy nuclei as well as on the experiments at the border between nuclear and atomic physics. Very recently SPARC worked out a realization scheme for experiments with highly-charged heavy-ions at relativistic energies in the High-Energy Storage Ring HESR and at very low-energies at the CRYRING coupled to the present ESR. Both facilities provide unprecedented physics opportunities already at the very early stage of FAIR operation. The installation of CRYRING, dedicated Low-energy Storage Ring (LSR) for FLAIR, may even enable a much earlier realisation of the physics program of FLAIR with slow anti-protons.

Preparations for laser cooling of relativistic heavy-ion beams at the CSRe

Laser cooling is one of the most promising techniques to reach high phase-space densities for relativistic heavy-ion beams. Preparations for laser cooling of relativistic lithium-like ions, such as C3+ and N4+, are being made at the experimental cooler storage ring (CSRe) in Lanzhou, China. In December 2011, a new buncher was installed and tested with a 70 MeV u−1 22Ne10+ ion beam by electron cooling at the CSRe. The longitudinal momentum spread of the bunched ion beam was measured by the new resonant Schottky pick-up. As a result, Δp/p ≈ 2 × 10−5 has been reached at ion numbers less than 107. According to this test result, the RF-buncher is suitable for the upcoming experiment of laser cooling at the CSRe. Laser cooling of heavy-ion beams will also be applied at future storage ring facilities, e.g. FAIR in Darmstadt, and HIAF in Lanzhou.

Time-resolved magnetic imaging in an aberration-corrected, energy-filtered photoemission electron microscope

We report on the implementation and usage of a synchrotron-based time-resolving operation mode in an aberration-corrected, energy-filtered photoemission electron microscope. The setup consists of a new type of sample holder, which enables fast magnetization reversal of the sample by sub-ns pulses of up to 10 mT. Within the sample holder current pulses are generated by a fast avalanche photo diode and transformed into magnetic fields by means of a microstrip line. For more efficient use of the synchrotron time structure, we developed an electrostatic deflection gating mechanism capable of beam blanking within a few nanoseconds. This allows us to operate the setup in the hybrid bunch mode of the storage ring facility, selecting one or several bright singular light pulses which are temporally well-separated from the normal high-intensity multibunch pulse pattern.

Polarization properties of Mo/Si multilayers in the EUV range

We investigate polarization properties of two novel reflective Mo/Si multilayers (ML) in the EUV range using polarized synchrotron radiation at the BESSY-II storage ring facility. One of the Mo/Si ML is used as a retarder, the other one as an analyzer within the experimental setup of the BESSY soft-x-ray polarimeter. The analyzer multilayer is characterized by performing reflectivity measurements with s- and p-polarized light as a function of the incidence angle for different wavelengths. The characterization of the retarder multilayer consists of reflectivity measurements with s- and p-polarized light as a function of the wavelength for three different angles near normal incidence. In addition the phase retardance on reflection was determined for one angle of incidence as function of wavelength. Uncertainties of the phase retardance are estimated via the block bootstrap method. As an additional by-product of the ML characterization the Stokes parameters of the beamline could be determined. With the 8-axis BESSY polarimeter we have measured the complex reflection coefficients for the first time and established this ellipsometry technique as an additional probe to characterize multilayer optical elements.

Storage ring measurements of the dissociative recombination of H 3 +

The dissociative recombination (DR) of H(3)(+) is a key process in interstellar chemistry. More than 30 experimental studies of the DR process have been published in the literature. The H(3)(+) DR rate coefficient results obtained from these measurements, however, have not always been consistent. The outcome seems to depend on the experimental method, on the exact measurement procedure and sometimes even on the interpretation of the experimental data. In the past two decades, heavy-ion storage rings have become the working horse for DR measurements, as they provide a direct measurement of the DR products. Furthermore, storage ring measurements yield energy-resolved rate coefficients with unprecedented resolution that allow for detailed comparison with theory. DR results from different storage ring facilities have shown a remarkable consistency throughout the years and they provide additional information on break-up dynamics and internal excitation. In this study, we will review the storage ring DR measurements that have been carried out for H(3)(+).

Probing buried layers by photoelectron spectromicroscopy with hard x-ray excitation

We report about a proof-of-principle experiment which explores the perspectives of performing hard x-ray photoemission spectromicroscopy with high lateral resolution. Our results obtained with an energy-filtered photoemission microscope at the PETRA III storage ring facility using hard x-ray excitation up to 6.5 keV photon energy demonstrate that it is possible to obtain selected-area x-ray photoemission spectra from regions less than 500 nm in diameter.

Fast-beam fragmentation experiments on dissociative recombination

An overview of recent developments is given for storage ring experiments on dissociative recombination using fast merged ion and electron beams. Dynamical aspects of the process are outlined, demonstrating that fast-beam reaction studies can advance the understanding of basic mechanisms holding generally for the fragmentation of electronically excited molecular systems. Experiments yield the collision energy dependence of the process, including rich resonant structure, product branching ratios of the fragmentation, and fragment momenta which also reveal the internal excitation of the fragments. Using cold electron beams and imaging detectors capable of fragment mass recognition at high readout speed, recent detailed fast-beam fragmentation experiments address the dissociative recombination of multielectron diatomic and polyatomic ions. Some of their results are presented together with an outlook on experiments at upcoming storage ring facilities.

Polarization and anisotropic emission of K-shell radiation from heavy few electron ions1This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

The population of magnetic sublevels in hydrogen-like uranium ions has been investigated in relativistic ion–atom collisions by observing the subsequent X-ray emission. Using the gas target at the experimental storage ring facility we observed the angular emission of Lyman-α radiation from hydrogen-like uranium ions. The alignment parameter for three different interaction energies was measured and found to agree well with theory. In addition, the use of different gas targets allowed for the electron-impact excitation process to be observed.

Direct Mass Measurements of Short-Lived Nuclides at the Storage Ring Facility in Lanzhou

Properties of unstable nuclei are indispensable for our understanding of nuclear structure and of nucleosynthesis processes in stars. Today, accurate data for nuclides lying far from the valley of beta-stability are required. However, these nuclides can generally be characterized by short half-lives and very small production rates, which makes their experimental investigation extremely difficult. Very fast and efficient methods are therefore needed.

Dynamic impact of Diamond Light Source foot bridge

The main foot bridge provides access to linac, booster and storage ring facilities in the synchrotron of Diamond Light Source. The impact of the passage of pedestrian traffic and equipment across the bridge structure was noticeable to the site of beamlines below. One of them, I20, is the most sensitive beamline to such impact. The bridge obviously oscillated with even light traffic, and it was also assumed that this would couple to the storage ring structure where the bridge is mounted. The optics for beamline I20, for stability, stands directly on the slab within the I20 experimental area; this was however subject to excessive vibration transmitted by foot traffic from the overhead footbridge producing a vibration on the experimental floor of 86 nm whereas elsewhere in the experimental hall experiences only about 20 nm, demonstrating a four times increase in vibration caused by the pedestrian bridge. Vibration measurements on the ground underneath the bridge and finite element analyses clearly show that frequencies of 2 and 5 Hz were caused by the bridge and traffic on it. Several remedies were proposed. However, dampers will only damp out vibrations of around 5–6 Hz but not to damp out 2 Hz, which is caused directly by human foot steps. After investigation of cost and effectiveness and several vibration tests conducted, a compromise with extra propping at the mid-span of the bridge was eventually selected. Such reinforcement has been now implemented. The 5 Hz frequency has been successfully removed and a amplitude of 2 Hz also considerably reduced.

FLASH—from accelerator test facility to the first single-pass soft x-ray free-electron laser

The development from a test facility for the TESLA project of a linear collider with an integrated x-ray free-electron laser (FEL) to the world's first soft x-ray FEL user facility is described. In the wavelength range from 6.5 to 60 nm, FLASH (Free-Electron Laser in Hamburg) provides short pulses (∼25 fs) containing ∼1012 photons in laterally coherent beams with brilliance of about nine orders of magnitude higher than achieved at the best synchrotron radiation storage ring facilities today. FLASH has opened up a new area in photon science where matter in non-equilibrium states is studied with atomic resolution in space and time.

Energy-sensitive imaging detector applied to the dissociative recombination ofD2H+

We report on an energy-sensitive imaging detector for studying the fragmentation of polyatomic molecules in the dissociative recombination of fast molecular ions with electrons. The system is based on a large area (10 cm x 10 cm) position-sensitive, double-sided Si-strip detector with 128 horizontal and 128 vertical strips, whose pulse height information is read out individually. The setup allows to uniquely identify fragment masses and is thus capable of measuring branching ratios between different fragmentation channels, kinetic energy releases, as well as breakup geometries, as a function of the relative ion-electron energy. The properties of the detection system, which has been installed at the TSR storage ring facility of the Max-Planck Institute for Nuclear Physics in Heidelberg, is illustrated by an investigation of the dissociative recombination of the deuterated triatomic hydrogen cation D2H+. A huge isotope effect is observed when comparing the relative branching ratio between the D2+H and the HD+D channel; the ratio 2B(D2+H)/B(HD+D), which is measured to be 1.27 +/- 0.05 at relative electron-ion energies around 0 eV, is found to increase to 3.7 +/- 0.5 at ~5 eV.