Ernest Fontes

Quantitative analysis of highly transient fuel sprays by time-resolved x-radiography

Microsecond time-resolved synchrotron x-radiography has been used to elucidate the structure and dynamics of optically turbid, multiphase, direct-injection gasoline fuel sprays. The combination of an ultrafast x-ray framing detector and tomographic analysis allowed three-dimensional reconstruction of the dynamics of the entire 1-ms-long injection cycle. Striking, detailed features were observed, including complex traveling density waves, and unexpected axially asymmetric flows. These results will facilitate realistic computational fluid dynamic simulations of high-pressure sprays and combustion.

Glass capillary optics for making x-ray beams of 0.1 to 50 microns diameter

We have fabricated a unique computerized glass puller that can make parabolic or elliptically tapered glass capillaries for microbeam x-ray experiments from hollow glass tubing. We have produced optics that work in a single-bounce imaging mode or in a multi-bounce condensing mode. The imaging-mode capillaries have been used to create 20 to 50 micron diameter x-ray beams at 12 keV that are quite useful for imaging diffraction patterns from tiny bundles of carbon and Kevlar fibers. The condensing-mode capillaries are useful for creating submicron diameter beams and show great promise in x-ray fluorescence applications with femtogram sensitivity for patterned Er and Ti dopants diffused into an optically-active lithium niobate wafer.

High-energy Needs and Capabilities to Study Multiscale Phenomena in Crystalline Materials

High-energy synchrotron X-rays are well suited to study engineering (structural) materials due to their small wavelength, adjustable energy and beam size, high flux, and ability to penetrate bulk polycrystalline samples up to centimeters in thickness. Recent advances in the use of high-speed, high-resolution detectors are making it possible to characterize microstructures at both the single grain and ensemble levels and to characterize the micromechanical responses of polycrystalline aggregates in three dimensions. These capabilities open new avenues of “in-situ” research that augments traditional forensic evidence with real-time data on functioning, evolving systems. X-ray scattering data are extremely rich, but taking the best advantage requires a continued refinement of experimental methods and analysis and a closer coupling of material models to detected intensities.

Design and performance of coded aperture optical elements for the CESR-TA x-ray beam size monitor

Abstract We describe the design and performance of optical elements for an x-ray beam size monitor (xBSM), a device measuring e + and e − beam sizes in the CESR-TA storage ring. The device can measure vertical beam sizes of 10 – 100 μ m on a turn-by-turn, bunch-by-bunch basis at e ± beam energies of ~ 2 – 5 GeV . x-rays produced by a hard-bend magnet pass through a single- or multiple-slit (coded aperture) optical element onto a detector. The coded aperture slit pattern and thickness of masking material forming that pattern can both be tuned for optimal resolving power. We describe several such optical elements and show how well predictions of simple models track measured performances.

InSitμ@CHESS, a Resource for Studying Structural Materials

High-energy X-ray diffraction (HEXD) experiments, which include real-time measurements of micromechanical material response using in-situ loading and the non-destructive creation of three-dimensional maps of polycrystalline microstructure, are very rapidly replacing traditional macroscopic mechanical tests and forensic metallurgical characterization methods for structural materials. The center for Integrated Simulation and X-ray Interrogation Tools and Training for Micromechanics at the Cornell High Energy Synchrotron Source (InSitμ@CHESS) was created to facilitate the use of HEXD experiments on structural materials; more notably, metallic alloys such as steel, titanium, aluminum, and nickel. The Office of Naval Research (ONR) has financially supported InSitμ, specifically enabling enhanced industrial user support. This article describes the experimental considerations associated with using HEXD on structural materials and, through a set of examples, illustrates how InSitμ addresses these considerations.

CHESS Facility Update and Upgrade Planning

The year 2013 was an exciting and transformational year for the Cornell High Energy Synchrotron Source (CHESS). While continuing successful scientific and technical initiatives, we added new personnel, reconfigured beamlines, expanded a successful and fun educational program, and have been planning a number of significant upgrades.

Improved High‐Heat‐Load Graphite Filter Design At CHESS Wiggler Beamlines

Conductively cooled highly‐oriented pyrolytic graphite (HOPG) filters have been used at CHESS wiggler beamlines to protect downstream beryllium windows under high heat loads. In the past beam currents above 350 mA have caused excessively high temperatures on the existing HOPG filters, resulting in rapid sublimation of the graphite and drastic shortening of filter lifetimes. A new filter design which eliminates some drawbacks of the existing design is described. The new design utilizes a slotted water jet, which cools a thin, “compliant” graphite‐copper braze joint. Heat‐transfer enhancements should enable an installed filter to survive beam currents of 450 mA. Optimization of design features and analysis results are discussed.

Present and future optics challenges at CHESS and for proposed energy recovery linac source of synchrotron radiation

We present recent test results and discuss design challenges on x-ray optical compo-nents for the wiggler sources at CHESS and for the proposed energy recovery linac (ERL) source at Cornell. For the existing wiggler sources, a new white-beam collimating mirror has been installed and tested at F-line and some preliminary test results are pre-sented. For the proposed ERL, three types of x-ray optical components are identified and considered: (1) high-heat-load capable optics for high-power and high-power-density in-sertion-device sources, (2) brilliance preserving optics that can provide high transverse coherence, and (3) optics used to manipulate, preserve and produce short x-ray pulses.

Improved optics for multiple-wavelength anomalous diffraction crystallography at CHESS

The optics at the F2 station of CHESS have been completely redesigned and rebuilt. The new design consists of a white- beam collimating mirror and a fixed-exit double-crystal monochromator, which are optimized for the growing field of multiple-wavelength anomalous diffraction (MAD) crystallography. The upstream mirror reduces the heat load onto the monochromator by two-thirds and increases the energy resolution of the x-ray beam to its source-size limit. The new single-rotation fixed-exit monochromator employs a slightly- tilted second-crystal translation that allows fast and reliable changes in the energy of the outgoing beam while maintaining its beam position. Two additional angle-segment stages, one for each crystal, are used to fine tune the second-crystal translation tilt so that the translation stage can be always positioned along the tangent of the desired loci of the second crystal for a wide energy range of 7 - 17 keV using Si (111).

Protein crystallography using a multilayer monochromator.

A multilayer monochromator was installed on a bending-magnet beamline at the Cornell High Energy Synchrotron Source (CHESS) and was used to provide an unfocused pseudo-monochromatic X-ray beam for protein crystallography experiments. Datasets were collected from lysozyme at room temperature and human methylthioadenosine phosphorylase at 100 K. The wide energy bandpass of the multilayer allowed short exposure times, typically only a few times longer than on a focused multipole wiggler beamline. The diffraction images were processed using unmodified monochromatic data-processing software to yield datasets of good quality. These first measurements demonstrate that multilayer monochromators can be readily applied to the rapid structure determination of many typical-sized macromolecules.