Synchrotron Radiation Storage Ring Research Articles

Modeling of intrinsic photon-stimulated desorption yields under readsorption effect

In synchrotron radiation and electron storage rings, photon-stimulated gas desorption is a major contributor to gas load, leading to vacuum degradation and compromising the stability and quality of the beamline. Therefore, it is imperative to investigate the underlying mechanisms of photon-stimulated gas desorption to enhance the reliability of the experiments. In this paper, a theoretical model for analyzing the process of photon-stimulated desorption is presented, and the equations are solved numerically by considering the evacuation, bulk diffusion, thermal outgassing, adsorption, and desorption of surface gas molecules. The modified model can predict the yield of H2 gas desorption induced by photon stimulation when synchrotron radiation is directed vertically onto various sample surfaces, utilizing the coupled multi-physics solution. The calculated results are consistent with the experimental measurements obtained from the Shanghai Synchrotron Radiation Facility. The results show that the photodesorption yield is related to the amount of surface-adsorbed molecules, which explains the observed decrease in the photodesorption yield with increasing accumulated photon dose. Furthermore, the study provides a theoretical approach to predicting the pressure evolution of photon-stimulated desorption.

Dynamics of the H2 levels lying between the third and fourth dissociation thresholds (132 500 – 139 000 cm− 1)

The absorption spectrum of H2 at room temperature, was recorded at high resolution at the BESSY II synchrotron radiation storage ring in the 132500 – 139000 cm−1 energy range, allowing the study of the dynamics of the excited levels (npσ 1Σu+ and npπ 1Πu±) located between the H(n = 3) + H(n = 1) and H(n = 4) + H(n = 1) thresholds. Ionization anddissociation were found to compete for levels with n ≤ 8. In most cases, for the levels with n > 8, ionization is the only decay channel. The relative importance of the direct ionization, direct dissociation, autoionization and predissociation processes was evaluated for the whole energy range. From the different detected channels, and from the comparison with theoretical approaches, the main continua responsible for the predissociations were assigned to the V and to the B"B¯ states and the H(3p)/H(n = 3) ratios of the dissociation fragments from the 4pπ and 5pπ 1Πu- levels were measured. Molecular fluorescence was observed for few 1Πu- levels and the importance of its contribution is discussed.

L-Shell Photoionization of Magnesium-like Ions with New Results for Cl5+

This study reports on the absolute photoionization cross sections for the magnesium-like Cl5+ ion over the 190–370 eV photon energy range, corresponding to the L-shell (2s and 2p subshells) excitation regime. The experiments were performed using the Multi-Analysis Ion Apparatus (MAIA) on the PLéIADES beamline at the SOLEIL synchrotron radiation storage ring facility. Single and double ionization ion yields, produced by photoionization of the 2p subshell of the Cl5+ ion from the 2p63s2 1S0 ground state and the 2p63s3p 3P0,1,2 metastable levels, were observed, as well as 2s excitations. Theoretical calculations of the photoionization cross sections using the Multi-Configuration Dirac-Fock and R-matrix approaches were carried out, and the results were compared with the experimental data. The Cl5+ results were examined within the overall evolution of L-shell excitation for the early members of the Mg-like isoelectronic sequence (Mg, Al+, Si2+, S4+, Cl5+). Characteristic photon energies for P3+ were estimated by interpolation.

Commissioning of a multi-beamline femtoslicing facility at SOLEIL.

The investigation of ultrafast dynamics, taking place on the few to sub-picosecond time scale, is today a very active research area pursued in a variety of scientific domains. With the recent advent of X-ray free-electron lasers (XFELs), providing very intense X-ray pulses of duration as short as a few femtoseconds, this research field has gained further momentum. As a consequence, the demand for access strongly exceeds the capacity of the very few XFEL facilities existing worldwide. This situation motivates the development of alternative sub-picosecond pulsed X-ray sources among which femtoslicing facilities at synchrotron radiation storage rings are standing out due to their tunability over an extended photon energy range and their high stability. Following the success of the femtoslicing installations at ALS, BESSY-II, SLS and UVSOR, SOLEIL decided to implement a femtoslicing facility. Several challenges were faced, including operation at the highest electron beam energy ever, and achievement of slice separation exclusively with the natural dispersion function of the storage ring. SOLEIL's setup also enables, for the first time, delivering sub-picosecond pulses simultaneously to several beamlines. This last feature enlarges the experimental capabilities of the facility, which covers the soft and hard X-ray photon energy range. In this paper, the commissioning of this original femtoslicing facility is reported. Furthermore, it is shown that the slicing-induced THz signal can be used to derive a quantitative estimate for the degree of energy exchange between the femtosecond infrared laser pulse and the circulating electron bunch.

Advanced environmental control as a key component in the development of ultrahigh accuracyex situmetrology for x-ray optics

The advent of fully coherent free-electron laser and diffraction-limited synchrotron radiation storage ring sources of x-rays is catalyzing the development of new ultrahigh accuracy metrology methods. To fully exploit these sources, metrology needs to be capable of determining the figure of an optical element with subnanometer height accuracy. The major limiting factors of the current absolute accuracy of ex situ metrology are drift errors due to temporal instabilities of the lab’s environmental conditions and systematic errors inherent to the metrology instruments. Here, we discuss in detail work at the Advanced Light Source X-Ray Optics Laboratory on building of advanced environmental control that is a key component in the development of ultrahigh accuracy ex situ metrology for x-ray optics. By a few examples, we show how the improvement of the environmental conditions in the lab allows us to significantly gain efficiency in performing ex situ metrology with high-quality x-ray mirrors. The developed concepts and approaches, included in the design of the new X-Ray Optics Laboratory, are described in detail. These data are essential for construction and successful operation of a modern metrology facility for x-ray optics, as well as high-precision measurements in many fields of experimental physics.

Ultrashort x-ray pulse generation by electron beam slicing in storage rings

We propose a new method to generate ultrashort x-ray pulses using focused short low energy ($\ensuremath{\sim}20\text{ }\mathrm{MeV}$) electron bunches to create short slices of electrons from the circulating electron bunches in a synchrotron radiation storage ring. When a low energy electron bunch crosses from the top of a high energy storage ring electron bunch, its Coulomb force will kick a short slice from the core of the storage ring electron bunch. The separated slices, when passing through an undulator, will radiate ultrashort x-ray pulses at about 160 fs. We discuss the advantages, challenges, and provide data which confirm the feasibility of this new method.

X-Ray Beam Position Monitor Based on a Single Crystal Diamond Performing Bunch by Bunch Detection

Diamond is a promising material for the production of semitransparent in situ photon beam monitors which can withstand the high dose rates occurring in new generation synchrotron radiation storage rings and in free electron lasers. We report on the development of a 500 μm thick freestanding, single crystal chemical vapor deposited diamond detector with segmented electrodes. Performances in both low and radio frequency beam monitoring are presented as well. By using charge integration techniques at a frame rate of 6.5 kHz in combination with a needle synchrotron radiation beam and mesh scans, the inhomogeneity of the sensor was found to be of the order of 2%; with a measured electronics noise of 2 pA / a 0.05% relative precision in the intensity measurements (at 1 μA) and a 0.1 μm resolution in the position encoding have been estimated. Moreover, the high electron-hole mobility of diamond compared with other active materials enables very fast charge collection characterized by rise-times below 1 ns; this allowed us to utilize single pulse integration to simultaneously detect the intensity and the position of each synchrotron radiation photon bunch generated by a bending magnet.

The history of X-ray free-electron lasers

The successful lasing at the SLAC National Accelerator Laboratory of the Linear Coherent Light Source (LCLS), the first X-ray free-electron laser (X-ray FEL), in the wavelength range 1.5 to 15 Å, pulse duration of 60 to few femtoseconds, number of coherent photons per pulse from 1013 to 1011, is a landmark event in the development of coherent electromagnetic radiation sources. Until now electrons traversing an undulator magnet in a synchrotron radiation storage ring provided the best X-ray sources. The LCLS has set a new standard, with a peak X-ray brightness higher by ten orders of magnitudes and pulse duration shorter by three orders of magnitudes. LCLS opens a new window in the exploration of matter at the atomic and molecular scales of length and time. Taking a motion picture of chemical processes in a few femtoseconds or less, unraveling the structure and dynamics of complex molecular systems, like proteins, are some of the exciting experiments made possible by LCLS and the other X-ray FELs now being built in Europe and Asia. In this paper, we describe the history of the many theoretical, experimental and technological discoveries and innovations, starting from the 1960s and 1970s, leading to the development of LCLS.

Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region

A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of ~8 to ~120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.

Efficient cascaded parameter scan approach for studying top-off safety in storage rings

We introduce a new algorithm, which we call the cascaded parameter scan method, to efficiently carry out the scan over magnet parameters in the safety analysis for top-off injection in synchrotron radiation storage rings. In top-off safety analysis, one must track particles populating phase space through a beam line containing magnets and apertures and clearly demonstrate that, for all possible magnet settings and errors, all particles are lost on scrapers within the properly shielded region. In the usual approach, if one considers $m$ magnets and scans each magnet through $n$ setpoints, then one must carry out ${n}^{m}$ tracking runs. In the cascaded parameter scan method, the number of tracking runs is reduced to $n\ifmmode\times\else\texttimes\fi{}m$. This reduction of exponential to linear dependence on the number of setpoints $n$ greatly reduces the required computation time and allows one to more densely populate phase space and to increase the number $n$ of setpoints scanned for each magnet.

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.

Nonlinear optimization of the modern synchrotron radiation storage ring based on frequency map analysis

In this paper, we present a rule to improve the nonlinear solution with frequency map analysis (FMA), and without frequently revisiting the optimization algorithm. Two aspects of FMA are emphasized. The first one is the tune shift with amplitude, which can be used to improve the solution of harmonic sextupoles, and thus obtain a large dynamic aperture. The second one is the tune diffusion rate, which can be used to select a quiet tune. Application of these ideas is carried out in the storage ring of the Shanghai Synchrotron Radiation Facility (SSRF), and the detailed processes, as well as better solutions, are presented in this paper. Discussions about the nonlinear behaviors of off-momentum particles are also presented.

Coincidence technique using synchrotron radiation for triple photoionization: Results on rare gas atoms

Final-state trication spectra and electron distributions produced by soft x-ray single-photon triple ionization of rare gas atoms have been obtained by a multiple-coincidence technique using storage-ring synchrotron radiation. The technique uses electron time of flight with ion detection to overcome the problem of high repetition rates in single-bunch operation. A correction needed to the triple-ionization energy of Kr currently listed in standard tables is confirmed, and the method's ability to examine the three-electron distributions, characterizing the ionization mechanisms and post-collision interactions, is illustrated.

The High Energy Materials Science Beamline at PETRA III

The future High Energy Materials Science Beamline HEMS at the new German high brilliance synchrotron radiation storage ring PETRA III [1] will have a main energy of 120 keV, will be fully tunable in the range of 50 to 300 keV, and will be optimized for sub-micrometer focusing with Compound Refractive Lenses and Kirkpatrick-Baez Multilayer mirrors. Design and construction is the responsibility of the Research Center Geesthacht, GKSS, with approximately 70 % of the beamtime being dedicated to Materials Research, the rest reserved for “general physics” experiments covered by DESY, Hamburg. Fundamental research will encompass metallurgy, physics and chemistry. For first experiments in investigating grain-grain-interactions a dedicated 3D-microstructure-mapper will be designed. Applied research for manufacturing process optimization will benefit from the high flux in combination with ultra-fast detector systems allowing complex and highly dynamic in-situ studies of microstructural transformations. The beamline infrastructure will allow easy accommodation of large user provided equipment. Experiments targeting the industrial user community will be based on well established techniques with standardised evaluation, allowing "full service" measurements. Environments for strain mapping [2] on large structural components up to 1 t will be provided as well as automated investigations of large numbers of samples, e.g. for tomography and texture determination. The current design for the beamline (P07 in sector 5 of the future experimental hall) consists of a nearly five meter in-vacuum undulator source (U19-5) optimized for high energies, a general optics hutch, an in-house test facility and three independent experimental hutches working alternately, plus additional set-up and storage space for long-term experiments. HEMS should be operational in spring 2009 as one of the first beamlines running at PETRA III.

Observation of Nuclear Excitation of 19F by Synchrotron Radiation

Fluorine (F) has the lowest atomic number and atomic weight of the members of the halogen family. Only the isotope with atomic weight 19 is stable. Fluorine is the most electronegative element and the most chemically energetic of the nonmetallic elements. The reactivity of the element fluorine is so high that chemical processes take place at about 500 C; a good sample is the reaction of fluorine and uranium dioxide leading to the production of uranium hexafluoride. F nuclei with a nuclear spin of 1/2 and a 100% natural abundance presents favourable nuclear magnetic resonance (NMR) characteristics. The application of the F NMR to metabolic studies of fluoropyrimidine drugs in clinical use; such as the anticancer drug 5-fluorouracil in human biofluids, have emphasized the usefulness of the technique for the quantitative detection of novel and unexpected metabolites. The use of synchrotron radiation as a source for nuclear resonant scattering experiments has led to many new studies of physical problems such as nuclear Bragg scattering, nuclear forward scattering, and nuclear inelastic scattering that can not be investigated satisfactorily with radioactive sources in the conventional Mossbauer spectroscopy. The unique characteristics of synchrotron radiation are the collimation, the polarization, the pulsed nature, and the high brilliance. The discrimination between the scattering from electrons and the scattering from nuclei has been solved by taking advantage of the instantaneous character of the atomic prompt nonresonant scattering compared with the relatively long lifetime of the nuclear excited states. Avalanche photodiodes allow the observation of delayed events after a few nanoseconds, even in the presence of a huge prompt background. High-resolution monochromators allow us to select energy and tune by energy bands of the order of 1meV width. The third generation synchrotron radiation storage rings, ESRF, APS, and SPring-8, were constructed and equipped with beamlines dedicated to nuclear resonance scattering experiments. The nuclear resonance scattering of synchrotron radiation has been experimentally observed in various nuclei, i.e., Ta (6.21 keV), Tm (8.41 keV), Kr (9.4 keV), Fe (14.41 keV), Eu (21.54 keV), Sm (22.49 keV), Sn (23.88 keV), Dy (25.65 keV), K (29.83 keV), and Sb (37.13 keV). The use of parentless Mossbauer isotopes, e.g., K, has become a reality. Other isotopes such Ni (67.41 keV), Au (77.35 keV), and Gd (79.51 keV) with high-transition energies above 50 keV have been excited and their fluorescence decay has been detected. Excitation energies above 100 keV of nuclei have not yet been reported. In this paper, we report the observation of the F nuclear excitation (109.89 keV) by the use of synchrotron radiation. The experiment was performed at the undulator beamline (BL09XU) at SPring-8. The undulator gap was tuned such that the seventeenth harmonic of the undulator radiation corresponds to the F resonance energy for the transition from the 1=2þ ground state to the 109.89 keV 1=2 excited state. Figure 1 shows our optics and detecting system for the F nuclear excitation and deexcitation. The double-crystal monochromator operates with diamond (333) reflection, while the X-rays from diamond (111) reflection were eliminated using a Ge(111) crystal. X-ray pulses with a time width of 50 ps [full width of half maximum (FWHM)] excited the F nuclei, using a several-bunch operation of the storage ring. The system with a silicon avalanche photodiode (APD) recorded the time spectra of -rays emitted from the 109.89 keV 1=2 state of the F nuclei. The details of the fast counting system with the APD detector were reported by Kishimoto. The APD has a 4 2 array of 3 5 0:15mm pixels and a depletion layer 150 mm thick. An efficiency of 0.6% at 100 keV was estimated, corresponding to absorption in 150-mm-thick silicon. The time resolution is 1.3 ns (FWHM). The APD was mounted under the sample. We used a fast amplifier to obtain fast negative pulses of the APD outputs, which were processed with a constant fraction discriminator (CFD). The outputs from the CFD were used as the start signals into a time-toamplitude converter (TAC). The veto signals into the CFD and the stop signals into the TAC were supplied through some divider and delay modules by 508.58MHz signals from the accelerator. The time spectra were recorded by the TAC and a multichannel analyzer. The prompt radiation outputs were inhibited during the first 5 ns by veto signals. Delayed signals started to be detected after the first 5 ns of the prompt radiation. For the study of the first excited level of the F nuclei, a lithium fluoride sample (LiF, 20 20 10mm) was used as a scattering sample. Figure 2 shows the time dependences of

The radiation measurement applied to beam lifetime study on the synchrotron radiation facilities

To collect beam loss information from an accelerator radiation field is helpful to machine study and operation. For a synchrotron radiation storage ring, shower electrons give a distinct clue to loss location and a BLM-XS model detector is suitable to detect them. Recently, we set up a new beam loss monitoring system by this method for National Synchrotron Radiation Laboratory (NSRL) storage ring. It does not interfere with the vacuum chamber and machine operation. Different from other systems, the detectors are used in pairs, fixed on opposite sides of the chamber separately. Some interesting phenomena about beam lifetime were observed. We located exactly where an excessive beam loss took place during ramping process and solved the problem. It was proved that gas accumulated at the front ends of photo-beam lines strongly impacted the electron beam and led to beam lifetime decreases. The cause of beam lifetime decrease because of superconducting wiggler is discussed.

Storage ring synchrotron radiation sources both planned and operating (october 1999)

Storage ring synchrotron radiation sources both planned and operating (october 1999)

Ultrahigh-Vacuum Reaction Apparatus to Study Synchrotron-Radiation-Stimulated Processes

An ultrahigh-vacuum reaction apparatus to study synchrotron-radiation-stimulated processes has been constructed and placed on beamline 4B of the synchrotron radiation storage ring (UVSOR) at the Institute for Molecular Science. The apparatus is designed so that multiple synchrotron radiation processes such as etching and chemical vapour deposition can be carried out successively without breaking the high vacuum. It is equipped with IR reflection absorption spectroscopy (IRRAS) apparatus and reflective high-energy electron diffraction (RHEED) apparatus for in situ observations. The basic parameters of the apparatus including etching and deposition rates have been measured. IRRAS using buried metal layer substrates has been confirmed to be a very useful method of analyzing the reaction mechanisms of the synchrotron-radiation-stimulated processes.

Development of synchrotron radiation storage rings.

Many third-generation light sources have been commissioned over the past ten years, and the soundness of the principal design concepts has been well recognized through experiences at these facilities. Also, technological developments concerning third-generation light sources have been remarkable. With the emittance and current of the beams far exceeding the previous levels, stability requirements of the beams have become much more stringent. In this report the present status of light sources, operational and projected, is summarized, and developments and future prospects of synchrotron radiation storage rings in view of accelerator physics and technology are reviewed.

Microscopic X-ray fluorescence analysis and related methods with laboratory and synchrotron radiation sources

The present status of microprobe versions of XRF analysis with tube excitation and with synchrotron radiation sources is reviewed with respect to analytical parameters such as lateral resolution and imaging capability, and achievable detection limits, precision and accuracy. The main characteristics of the method are contrasted with those of other microanalytical techniques. For laboratory source µ-XRF, results with a rotating anode tube equipped with capillary X-ray optics are discussed in terms of sensitivity and achievable lateral resolution. The possibilities of the new third generation synchrotron radiation storage rings, especially those of the European Synchrotron Radiation Facility (ESRF) and its X-ray micro-fluorescence, imaging and diffraction beamline (ID 22) are discussed and related to second generation storage rings. Some characteristic applications are given to illustrate the recent possibilities of the methodologies, in particular for the characterization of atmospheric particles, and in an analytical problem related to archaeology.