Insertion Device Beamline Research Articles

Measurement of absorbed dose by 7-GeV bremsstrahlung in a PMMA phantom

High-energy electron storage rings generate energetic bremsstrahlung photons through radiative interaction of the particle beam with the residual gas molecules and other components inside the storage ring. At synchrotron radiation facilities, where beamlines are channeled out of the storage ring, a continuous bremsstrahlung spectrum, with a maximum energy of the stored particle beam, will be present. At the advanced photon source (APS), where the stored beam energy is 7 GeV, bremsstrahlung generated in the straight sections of the insertion device beamlines, which are a total of 15.38 m in length, can be significant. The contribution from each bremsstrahlung interaction adds up to produce a narrow mono-directional bremsstrahlung beam that comes down through the insertion device beamlines. The resulting absorbed dose distributions by this radiation in a 300 mm×300 mm×300 mm tissue substitute cube phantom were measured with LiF:Mg,Ti (TLD-700) thermoluminescent dosemeters. The normalized absorbed dose, in a cross-sectional area of 100 mm 2 at a depth of 150 mm of the PMMA phantom, was measured as 3.3×10 6 mGy h −1W −1 for 7-GeV bremsstrahlung spectrum.

Dose measurements of bremsstrahlung-produced neutrons from thick targets

Photons of sufficiently high energies ( E γ ≥5–15 MeV) can produce neutrons by means of photonuclear interactions. Bremsstrahlung from high energy electron storage rings, which have an energy range of zero to the maximum energy of the particle beam, can interact with beamline components like beam stops and collimators generating photoneutrons of varying energies. This paper presents the results of simultaneous measurements of bremsstrahlung power and corresponding photoneutron dose equivalent rate at the insertion device beamlines of the Advanced Photon Source, using a lead-glass calorimeter and an Andersson–Braun remmeter. Targets made of Fe, Cu, W, and Pb are placed in the bremsstrahlung beam inside the first optics enclosure of the insertion device beamlines. The photoneutron dose equivalent rates, normalized to bremsstrahlung power, beam current, and storage ring pressure, are measured for the four targets. The photoneutron dose equivalent rates, normalized to the bremsstrahlung power and corrected for systematic variations, are given as 2.2±0.5 rem/h/W for Fe,3.0±0.5 rem/h/W for Cu, 3.8±0.5 rem/h/W for W, and 3.7±0.8 rem/h/W for Pb targets, at a distance of 0.8 m perpendicular from the target center.

Optical design of the U7 undulator beamline at the Pohang Light Source.

The first insertion-device beamline at the Pohang Light Source is designed for high-resolution spectroscopy and spectromicroscopy. The beamline will contain a variable-included-angle plane-grating monochromator (VIA-PGM) using a grating substrate which has seven different grooves with different depths. The advantages of this scheme will be the fixed exit-slit position and the mechanical stability of the grating scan mechanism while changing the photon energy range. The beamline is designed to cover the photon energy range 20-2000 eV. The estimated spectral resolution, E/DeltaE, is above 8000 in the photon energy range below 500 eV, and above 4000 for the remaining photon energy range. The estimated flux at the end-station is of the order of 10(12) photons s(-1) (0.1% bandwidth)(-1).

Smart X-ray beam position monitor system using artificial-intelligence methods for the Advanced Photon Source insertion-device beamlines.

At the Advanced Photon Source (APS), each insertion-device (ID) beamline front end has two X-ray beam position monitors (XBPMs) to monitor the X-ray beam position for both vertical and horizontal directions. Performance challenges for a conventional photoemission-type XBPM during operations are contamination of the signal from the neighbouring bending-magnet sources and the sensitivity of the XBPM to the insertion-device gap variations. Problems are exacerbated because users change the ID gap during their operations, and hence the percentage level of the contamination in the front-end XBPM signals varies. A smart XBPM system with a high-speed digital signal processor has been built at the Advanced Photon Source for the ID beamline front ends. The new version of the software, which uses an artificial-intelligence method, provides a self-learning and self-calibration capability to the smart XBPM system. The structure of and recent test results with the system are presented in this paper.

Inelastic scattering energy loss in CaF2 observed with soft X-ray fluorescence spectroscopy

Abstract The advent of third-generation synchrotron radiation sources has stimulated interest in the study of X-ray emission using photon excitation. Soft X-ray fluorescence (SXF) provides a means of measuring the element and angular momentum selective valence band density of states in complex materials. Tenability of the excitation source allows a detailed investigation of the dynamical behavior of the relaxation channels and the coupling between the excitation and emission process that occurs near a resonance or an absorption edge. As an example of resonant inelastic scattering studies in solid systems by SXF spectroscopy at the insertion device beam line BL 8.0 at ALS, results from CaF 2 will be presented. When the energy of exciting photons is tuned to the Ca 2p–3d threshold absorption peak in CaF 2 , the SXF produced by recombination of the excited electrons with core holes exhibits remarkable resonances for both the 2p 3/2 and 2p 1/2 levels. When the resonant 2p–3d SXF peaks are excited, additional broad peaks appear in the spectra below the normal valence band spectrum, which are displaced from the resonant peaks by about 17 eV and track the changes in excitation energy. We identify this as evidence of a coherent, inelastic scattering process, analogous to resonant Raman scattering, in which incident photons excite a localized electronic transition and are re-radiated at an energy reduced by the energy of the excitation. Evidence is also presented which indicates that the 2p–3d absorption transitions lie about 1 eV above a weak Ca 4s absorption threshold.

Electronics for SPring-8 X-ray beam monitors.

A sensitive current-measuring system is required to construct a highly sensitive X-ray beam-position monitor (XBPM). A current-voltage converter (I/V) which can measure currents between 0.1 nA and 10 mA was designed, and the signal processing system of the XBPM was constucted using this I/V. This system was used in beamline commissioning. Beam-position data standard deviations of sigma approximately 3 micro m for the bending-magnet beamline, and sigma(x) approximately 3 micro m and sigma(y) approximately 1 micro m for the insertion-device beamline were obtained during the beamline commissioning.

Charge-coupled device/fiber optic taper array x-ray detector for protein crystallography

A large area charge-coupled device (CCD) based fiber optic taper array detector (APS-1) is installed at the insertion-device beamline of the Structural Biology Center at the Argonne Advanced Photon Source x-ray synchrotron. The detector is used in protein crystallography diffraction experiments, where the objective is to measure the position and intensity of x-ray Bragg peaks in diffraction images. Large imaging area, very high spatial resolution, high x-ray sensitivity, good detective quantum efficiency, low noise, wide dynamic range, excellent stability and short readout time are all fundamental requirements in this application. The APS-1 detector converts the 2-D x-ray patterns to visible light images by a thin layer of x-ray sensitive phosphor. The phosphor coating is directly deposited on the large ends of nine fiber optic tapers arranged in a 3{times}3 array. Nine, thermoelectrically cooled 1024{times}1024pixel CCDs image the patterns, demagnified by the tapers. After geometrical and uniformity corrections, the nine areas give a continuous image of the detector face with virtually no gaps between the individual tapers. The 18 parallel analog signal-processing channels and analog-to-digital converters ensure short readout time and low readout noise. We discuss the design and measured performance of the detector. {copyright} {ital 1998 Society of Photo-Optical Instrumentationmore » Engineers.}{ital Key words:} charge-coupled device; fiber optic taper; x-ray diffraction; crystallography; imaging detector. {copyright} {ital 1998} {ital Society of Photo-Optical Instrumentation Engineers}« less

A Multi-Anvil, High-Pressure Facility for Synchrotron Radiation Research at GeoSoilEnviroCARS at the Advanced Photon Source.

This paper describes the multi-anvil, large-volume, high-pressure facility that is being constructed at the GeoSoilEnviroCARS at the Advanced Photon Source, Argonne National Laboratory. The facility consists of multi-anvil high pressure systems at the end stations of the bending magnet and the insertion device beamline at Sector 13. Various pressure apparatus will be used to cover pressure and temperature conditions up to 40 GPa and 3000°C, with millimeter sized samples at high pressure end and centimeter sized samples at low pressure end. This national facility is open to all users and a variety of high pressure, high temperature experiments will be carried out.

Semiconductor Material Processes in Synchrotron Radiation SPring-8.

Material processes related to semiconductor device manufacturing in research project in synchrotron radiationfacility, SPring-8, have been discussed. SPring-8 has 61 beamlines including 23 bending magnet beamlinesand 38 insertion device beamlines. Soft X-ray beamline in SPring-8 will be available for the materialprocessing near future and has 8-figure undulator which radiates strong polarized soft X-ray in energy range of 0.5-5 keV. Possibilities of the SR research are discussed showing the reported results. Research plans such as SR-CVD, SR-etching, surface modification, SR-ablation and their analyses have been proposed as effectivesubjects.

Measurement of gas bremsstrahlung from electron storage rings

Bremsstrahlung is produced in electron storage rings when the particle beam interacts with the storage ring components or with the residual gas molecules in the storage ring vacuum. The interaction of the particle beam with the gas molecules occurs continuously during storage ring operation. At straight sections of a storage ring, the gas bremsstrahlung contribution from each interaction adds up to produce a narrow monodirectional photon beam that travels down the beamlines. At the Advanced Photon Source (APS), where the stored electron beam energy is 7 GeV, gas bremsstrahlung generated in the straight sections of the insertion device beamlines, which is a total of 15.38 m in effective length, can be significant. This paper presents the results of the bremsstrahlung spectrum and energy measurements from the insertion device beamlines of the APS using a hermetic lead glass calorimeter. The calorimeter consists of 25 lead glass blocks, each 6.3 cm × 6.3 cm × 35 cm, stacked into a 5 × 5 array. Phototubes connected to the lead glass blocks collected the signals. The calorimeter is calibrated using the maximum energy of the observed bremsstrahlung spectrum. The total energy radiated and the bremsstrahlung spectrum were measured as a function of the storage ring beam current for both electrons and positrons of 7 GeV energy. Vacuum in the straight section was continuously monitored, and measurements to determine the nature of the residual gas inside the storage ring were performed. The measured bremsstrahlung spectra are fitted to a function that shows an approximate 1 E behavior. The gas bremsstrahlung rate from the APS undulator beamline straight path of 15.38 m is measured as 60.0 ± 2.0 GeV/s/nT/mA. Significant contribution of bremsstrahlung from sources other than the residual gas molecules is observed. The maximum bremsstrahlung energy measured in a beamline during the experiment is 369.0 ± 22.0 GeV/s/nT/mA.

Diamond Beam-Position Monitor for Undulator Radiation and Tests at the Tristan Super Light Facility

A photon beam-position monitor using a diamond foil as a position-sensitive device has been developed for use on insertion-device beamlines of third-generation synchrotron radiation facilities such as SPring-8, and was tested on the undulator beamline of the Tristan Super Light Facility at KEK. The beam test results show that the diamond monitor can be operated in a photoconductive mode like a semiconductor detector. It has a linear working range of about +/-1 mm and a position sensitivity of less than 3 mum. The stability of the monitor was confirmed by continuous operation under low photon beam intensity conditions.

X-ray welding of metal-matrix composites

We present the first results of use of the high power x-rays from an insertion device beamline at the Advanced Photon Source for welding. X-rays with energies between 3 and 200 keV and power densities greater than 10 000 W/cm2 can penetrate deeply into most materials and thus can be used as volumetric heating sources. In this article we show results of bead-on-plate welds of a 3.3-mm-thick Al/Al2O3 metal-matrix composite and discuss results obtained for other materials. The potential of x-rays for welding is also discussed.

Earth, soil and environmental science research facility at sector 13 of the Advanced Photon Source. I. Sector layout and optical design (abstract)

The earth, soil and environmental science component (GSECARS) of the Consortium of Advanced Radiation Sources (CARS), is designing a national research facility to be built at sector 13 of the Advanced Photon Source. The bending magnet beam will be split to allow simultaneous operation of two stations, a monochromatic (8–15 keV) side station and a multipurpose, white beam/monochromatic end station. The undulator beamline will have two white beam stations, which may operate simultaneously using a double-crystal monochromator (cryogenic Si) with a thin first crystal. In this mode, the upstream station will accept the monochromatized (4.5–22 keV) beam deflected horizontally by a third (bendable) Ge crystal, while the end station accepts the high energy component (blue beam) transmitted by the first crystal. The need for small x-ray beams and broad spectral range have led us to base the focusing aspects of the optic design on grazing incidence mirrors. Both our bending magnet and insertion device beamlines will have long (∼1 m), bendable mirrors (demagnification <11, E(cut-off) ≳70 keV; beam sizes ≳tens of micrometers). For smaller focal spots, we will use small, dynamically bent Kirpatrick-Baez mirrors (demagnification 100–400; E(cut-off) <70 keV; beam sizes ∼1 micrometer). A unique aspect of our insertion device beamline is the ability to deliver focused white beam to the sample, through the incorporation of a power management pinhole in the first optics enclosure.

Secondary bremsstrahlung dose rates from glancing incidence target

Several collaborative access teams at the Advanced Photon Source (APS) are planning to use a vertically or horizontally reflecting mirror as the first optical element in the insertion device beamlines. The scattering of the bremsstrahlung from the glancing incidence mirrors is significantly different than that from normal incidence targets. The Electron Gamma Shower program (EGS4) was used to calculate the angular distribution of the scattered secondary bremsstrahlung from copper and silicon glancing incidence mirrors. These calculations were done for an incident angle of 0.15°. Pair production, positron annihilation at rest and in flight, Moliere multiple scattering, Moller and Bhabha scattering, delta ray production, Compton scattering, the photoelectric effect, and the continuous energy loss by Bethe-Bloch formalism were the processes simulated in this calculation. The dose at one meter away from the mirror, due to the scattered secondary bremsstrahlung, was calculated from the energy deposited in the standard ICRU tissue placed at that location. Since the EGS4 result is expressed as the dose per photon, the dose rate was obtained by multiplying the dose per photon by the total number of photons produced in unit time in the insertion device vacuum chamber. The dose rate results and its implication for the design of the first optical enclosures are presented in this paper.

Performance analysis of a novel monochromator design for the APS SRI-CAT beamline 2-ID-E

Third-generation synchrotron x-ray facilities, such as the Advanced Photon Source, produce x-ray beams that generate a very high heat flux in a very small area. In order to preserve the brilliance of the source, optical components have to be designed to undergo very small thermal deformation (or a change of slope of a flat surface). When an optical component is subjected to a heat load, there will be thermal deformation caused by a temperature increase from the initial state. For a plate-like structure, the temperature difference over the thickness causes bending, and the average temperature increment causes axial deformation. For an optical element, the slope change due to bending is the main reason for the degradation of the performance of the optical component. The change of slope should be limited to a few microradians. There are many ways to control the thermal deformation, such as cryogenic cooling, inclined geometry, liquid-metal cooling, pin-posts or microchannels, using a high-heat-conductivity material, such as diamond, etc. In an accompanying conference paper, an adaptive design technique has been proposed to make use of a novel self-adapted smart structure. Its performance is essentially independent of the heat-load intensity. When such a device is exposed to a heat load, the flat surface remains flat in the area of interest. Therefore this technique can potentially be used to achieve a high precision optical component. Application of the proposed design technique to the monochromator for the SRI-CAT Sector 2 insertion device beamline (Sector 2-ID-E) is explained, and initial analytical results are presented on its performance.

The PNC-CAT insertion device beamline at the Advanced Photon Source

The PNC-CAT is a consortium of Pacific Northwest institutions formed to instrument a sector (number 20) at the Advanced Photon Source (APS). Research is planned in a variety of areas, with an emphasis on environmentally based problems. The insertion device beamline is based on the APS undulator A and will be optimized for producing microbeams as well as for applications requiring energy scanning capabilities. This paper describes the basic layout and some special features of the beamline. Two experimental stations are planned: one general purpose and one dedicated to MBE and surface science problems. Both tapered capillaries and Kirkpatrick-Baez optics will be used for producing microbeams, and a large optical bench is planned for the main station to allow for easy accommodation of new optics developments. Design calculations and initial capillary tests indicate that flux densities exceeding 1011 photons/sec/mm2 should be achievable. All major components are under construction or in procurement, and initial testing is planned for late 1996.

Performance analysis of the commissioning filter and window assembly for insertion device beamlines at the Advanced Photon Source

Although the Advanced Photon Source (APS) undulator beamlines are designed for windowless operation, a special window assembly will be used during the commissioning phase of the beamlines until sufficient operational experience is gained with the powerful undulator A photon beam. This assembly is called a ‘‘commissioning window.’’ The commissioning window assembly as designed consists of a 300-μm-thick filter (made of graphite), a fixed mask (made of Glidcop), a multipurpose transmitting filter/BPM disk (made of 127-μm-thick CVD diamond), and set of a double windows (made of 250-μm-thick beryllium). Due to the high total power and power density, the filter/window assembly must be carefully designed to guarantee longevity and satisfactory performance throughout its service. Hence extensive analytical work has been conducted on various thermal and structural aspects of the commissioning window assembly. This paper summarizes the analytical results and presents the expected performance characteristics of the as-designed commissioning window.

White beam transport design for insertion device beamlines at the Advanced Photon Source

To evaluate the feasibility of designing an economic beamline transport system for insertion device beamlines at the Advanced Photon Source, two sample cases have been designed and analyzed, one for an undulator source and the other for a wiggler source. The results show that it is possible to build a 70-meter-long beamline transport system for an undulator source with less than four lead/tungsten-alloy bremsstrahlung collimators. Six or fewer collimators are needed to construct a 70-meter-long white-beam transport system for a wiggler source. To prevent damage from any missteered powerful white beam, a water-cooled fixed mask is placed in front of each collimator. Ray tracing for both bremsstrahlung and synchrotron radiation have been conducted for the sample transports. Modular mask/collimator assembly designs and ray-tracing results are presented.

Design of a dedicated beamline for x-ray microfocusing- and coherence-based techniques at the Advanced Photon Source

A dedicated insertion-device beamline has been designed and is being constructed at the Advanced Photon Source (APS) for development of x-ray microfocusing- and coherence-based techniques and applications. Important parameters considered in this design include preservation of source brilliance and coherence, selectable transverse coherence length and energy bandwidth, high beam angular stability, high order harmonic suppression, quick x-ray energy scan, and accurate and stable x-ray energy. The overall design of this beamline layout and the major beamline components are described. The use of a horizontally deflecting mirror as the first optical component is one of the main features of this beamline design, and the resulting advantages are briefly discussed.

Monte Carlo simulations of the vacuum performance of differential pumps at the Advanced Photon Source

Monte Carlo computer simulations have been successfully applied in the design of vacuum systems. These simulations allow the user to check the vacuum performance without the need of making a prototype of the vacuum system. In this paper we demonstrate the effectiveness and aptitude of these simulations in the design of differential pumps for synchrotron radiation beamlines. Eventually a good number of the beamline front ends at the Advanced Photon Source (APS) will use differential pumps to protect the synchrotron storage ring vacuum. A Monte Carlo computer program is used to calculate the molecular flow transmission and pressure distribution across the differential pump. A differential pump system, which consists of two 170 l/s ion pumps with three conductance-limiting apertures, was previously tested on an APS insertion-device beamline front end. Pressure distribution measurements using controlled leaks demonstrated a pressure difference of over two decades across the differential pump. A new differential pump utilizes a fixed mask between two 170 l/s ion pumps. The fixed mask, which has a conical channel with a small cross section of 4.5×4.5 mm2 in the far end, is used in the beamline to confine the photon beam. Monte Carlo simulations indicate that this configuration with the fixed mask significantly improves the pressure reduction capability of the differential pump, to ∼3×10−5, within the operational range from ∼10−4 to 10−10 Torr. The lower end of pressure is limited by outgassing from front-end components and the higher end by the pumping ability of the ion pump.