Mohan Ramanathan

A dedicated powder diffraction beamline at the Advanced Photon Source: Commissioning and early operational results

A new dedicated high-resolution high-throughput powder diffraction beamline has been built, fully commissioned, and opened to general users at the Advanced Photon Source. The optical design and commissioning results are presented. Beamline performance was examined using a mixture of the NIST Si and Al(2)O(3) standard reference materials, as well as the LaB6 line-shape standard. Instrumental resolution as high as 1.7 x 10(-4) (DeltaQQ) was observed.

A twelve-analyzer detector system for high-resolution powder diffraction.

A dedicated high-resolution high-throughput X-ray powder diffraction beamline has been constructed at the Advanced Photon Source (APS). In order to achieve the goals of both high resolution and high throughput in a powder instrument, a multi-analyzer detector system is required. The design and performance of the 12-analyzer detector system installed on the powder diffractometer at the 11-BM beamline of APS are presented.

An energy dispersive x-ray absorption spectroscopy beamline, X6A, at NSLS

An energy dispersive x‐ray absorption spectroscopy instrument has been built at the X6A beam port of the x‐ray ring at the National Synchrotron Light Source (NSLS). This instrument allows the collection of extended x‐ray‐absorption fine structure and/or x‐ray absorption near‐edge structure spectra for many elements on the millisecond time scale. The beamline employs a four‐point crystal bender and a rectangular Si 220 crystal to access incident energies between 6.5 and 21 keV. Because the polychromator focuses the synchrotron beam to a narrow 100‐μm line, this experimental apparatus is ideal for x‐ray absorption spectroscopy experiments in special environments such as at high pressures, for in situ experiments, and/or for very small samples. In this manuscript we will describe the instrument design and present data with which to evaluate the instrument. This beamline is available through the NSLS user proposal system.

Avalanche photodiodes as large dynamic range detectors for synchrotron radiation

Abstract We investigated silicon-based avalanche photodiodes (APDs) as X-ray detectors in terms of their linearity, maximum counting rates, and dynamic range with 8.4 keV synchrotron radiation. Measurements resulted in counting rates that extend from the APDs noise level of 10−2 Hz to saturation counting rates in excess of 108 Hz. In addition, by monitoring the APDs noise level and photon counting efficiency between synchrotron bursts, we demonstrate nine orders of magnitude dynamic range.

ELLIPTICAL MULTIPOLE WIGGLER FACILITY AT THE ADVANCED PHOTON SOURCE

The use of circularly polarized radiation is advantageous for the study of magnetic materials using x‐ray scattering techniques. The APS is an ideal source of x‐ray radiation for such studies. We present a description of the elliptical multipole wiggler (EMW) [S. Yamamoto, H. Kawata, H. Kitamura, and M. Ando, Phys. Rev. Lett. 62, 2672 (1989)] to be constructed at the APS. This device has been chosen for reasons of tunability and special polarization properties. This insertion device is capable of producing circularly polarized x rays on axis. The EMW period will be λu=16 cm, the number of full strength poles in the hybrid structure is 31, and the device length is 2.8 m. The hybrid magnetic structure produces a peak vertical magnetic field with Ky=14 and the electromagnet provides horizontal magnetic field with Kx=1–2. The frequency of the horizontal field change is up to 10 Hz. The beamline will consist of three stations operating in tandem with only one station receiving x rays at any one time. The three...

A simple sagittal focusing crystal which utilizes a bimetallic strip

A sagittal focusing monochromator which utilizes a bimetallic strip as its active focusing member has been designed and has undergone preliminary testing. The crystal bender is very easy to use as only setting the temperature of the bimetallic strip is necessary to adjust the focus. The mechanism utilizes bending rods mounted on live centers which prevent twisting of the crystal. A finite element analysis has been done on a new ribbed crystal which, based on the analysis, would have very small aberrations.

Versatile double‐crystal fixed exit monochromator for x‐ray synchrotron radiation

We describe a new monochromator that was designed and constructed for applications in x‐ray scattering and extended x‐ray‐absorption fine structure experiments. The monochromator consists of two separate crystals of the same type. The monochromator covers a wide angular range from 58° to 5.1° which is equivalent to an energy range of 2.3–22 keV using Si 111 crystals. A constant offset of 1 in. is maintained between the incident white radiation and the exiting monochromatic radiation. The monochromator employs a simple mechanism to achieve this result. The monochromator is housed inside a stainless steel vacuum chamber and is currently operating in a high vacuum environment. The first monochromator crystal is water cooled in order to avoid temperature drifts due to the high heat load synchrotron radiation. This article presents the design details, characteristics, and data collected with this monochromator.

Insertion device operating experience at the Advanced Photon Source.

The Advanced Photon Source has 29 insertion devices (IDs) installed in the 7 GeV electron storage ring; 28 of these devices, most of which are 3.3 cm period undulators, use two horizontal permanent magnet structures positioned over a straight vacuum chamber. A support and drive mechanism allows the vertical gap between the magnet structures to be varied, thus changing the x-ray energy produced by the ID [J. Viccaro, Proc. SPIE 1345, 28 (1990); E. Gluskin, J. Synchrotron Radiat. 5, 189 (1998)]. Most of these IDs use a drive scheme with two stepper motors, one driving each end through a mechanism synchronizing the upper and lower magnet structures. Our experience in almost 5 yr of operating this system will be discussed. All of the IDs are in continuous operation for approximately 10 weeks at a time. Reliability of operation is of paramount importance, as access to the storage ring for servicing of a single ID inhibits operation for all users. Our experience in achieving highly reliable ID operation is reviewed. Accuracy of operation and repeatability over time are also vital. To this end, these devices use absolute optical linear encoders with submicron resolution for primary position feedback. Absolute rotary encoders are used as a backup to the linear encoders. The benefits and limitations of each type of encoder, and our experience dealing with radiation and electrical noise are reviewed. The insertion devices operate down to gaps as small as 8.5 mm, with clearance over the vacuum chamber as small as 200 μm. The vacuum chamber has a minimum wall thickness of only 1 mm. A number of levels of safeguards are used to prevent contact between the magnet structure and the vacuum chamber. These safeguards and their evolution after gaining operational experience are presented.

Progress of the APS high heat load x-ray beam position monitor development

Several novel design developments have been established for the Advanced Photon Source (APS) insertion device (ID) X-ray beam position monitor (XBPM) to improve its performance: --- optimized geometric configuration of the monitor’s sensory blades; --- smart XBPM system with an intelligent digital signal processor, which provides a self-learning and calibration function; and --- Transmitting XBPM with prefiltering in the commissioning windows for the front end. In this write-up, we summarize the recent progress on the XBPM development for the APS ID front ends.

Argonne National Laboratory X6B beamline at NSLS: A versatile facility

With high‐intensity, high‐energy resolution, energy tunability, and flexibility of operation, the Argonne National Laboratory X6B beamline at the National Synchrotron Light Source (NSLS) has become a versatile facility for a variety of x‐ray diffraction, scattering, and spectroscopy experiments. The beamline can be operated in either focused or unfocused beam mode, depending on the requirement of specific experiments. We describe the x‐ray optics and beamline performance, and present selected experimental results to demonstrate the main features of the X6B beamline.