bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-normalization behavior of crystal glitches in an EXAFS spectrum: Is it possible to remove crystal glitches?
Authors: Dobson B.R. , Hasnain S. S. , Morrell C. , Konigsberger D. C. , Pandya K. , Kampers F. , van Zuylen P. , van der Hoek M. J.
Published: July 2002

The existence of crystal glitches in EXAFS data is widely recognized and is usually dealt with during data analysis. However, in many cases, especially as samples become more dilute, the disruption of the data can become irretrievable. The advent of new, high output, double-crystal x-ray monochromators has made it necessary to investigate the cause of such glitches with a view to reducing them in the original data. The occurrence of multiple reflections within the crystal gives rise to the glitches seen in EXAFS data when the two crystals in a double-crystal monochromator are not accurately aligned. The results of a simple alignment of such a double-crystal monochromator are presented and show a reduction of the glitches in the recorded data. A purpose-built monochromator for further investigation of this problem is described and some results towards the further reduction of glitches are presented. It is shown that the removal of crystal glitches from EXAFS data is possible
Measurements of x-ray diffraction for liquid metals under high pressure
Authors: Tsuji Kazuhiko , Yaoita Kenichi , Imai Motoharu , Shimomura Osamu , Kikegawa Takumi
Published: July 2002

By using synchrotron radiation with high brightness, high energy, and continuous spectrum in energy, x-ray diffraction for liquid metals has been measured at pressures to 9 GPa and temperatures to 800 °C by a transmitting and energy-dispersive method. A cubic-type apparatus for high-pressure and high-temperature experiments was used. A thick specimen could be used as the absorption coefficient was small for high energy x rays (40–120 keV). A sharp slit system eliminated the background intensity from the pressure-transmitting medium and the sample container. This method has been applied to the investigation of pressure-induced structural changes in liquid selenium, gallium, and bismuth.
H° temperature and density measurements in a Penning surface-plasma H− ion source. I.
Authors: Smith H. Vernon , Allison Paul , Pitcher E. J. , Stevens R. R. , Worth G. T. , Stutzin G. C. , Young A. T. , Schlachter A. S. , Leung K. N. , Kunkel W. B.
Published: July 2002

Using vacuum ultraviolet laser-absorption spectroscopy, the H° density and temperature are measured as a function of discharge current and H2-gas flow in both the plasma column and the drift region between the plasma column and the emitter in the 4X source. For typical source operating parameters, the atom temperature is 1.5 eV in the plasma column and 0.6 eV in the drift region; the atom density 7×1014 cm−3 in the plasma column and 4×1014 cm−3 in the drift region. Separate measurements give 2% for the ratio of H2 molecules in the first vibrational level to the total H2 density.
A reflection electron microscope for imaging of fast phase transitions on surfaces
Authors: Bostanjoglo O. , Heinricht F.
Published: July 2002

A reflection electron microscope for ultrashort-time imaging of laser-induced processes on surfaces was developed. The instrument is based on a conventional transmission electron microscope modified for high-energy electron reflection, and, in addition, equipped with a laser-pulsed high-brightness electron gun, an interaction chamber, and a tilting unit. Images with exposure times of ≤20 ns of transient surface processes can be obtained. The spatial resolution depends on the exposure time and is limited by a compromise between shot noise in the electron image, chromatic aberration of the objective lens, and radiation damage due to the illuminating electron beam. The performance of the microscope is demonstrated by short exposure time images of laser pulse treated bulk GaAs and Au films on Si showing evaporation, flow, and capillary waves, proceeding within 10–500 ns.
The Synchrotron Radiation Center of the University of Wisconsin–Madison
Authors: Green Michael A. , Huber David L. , Rowe Ednor M. , Tonner Brian
Published: July 2002

This article presents a brief introduction to the Synchrotron Radiation Center, a description of its present capabilities, and an overview of current improvement programs.
Recent advances in soft x-ray scattering instrumentation at the National Synchrotron Light Source
Authors: Johnson Erik D. , Kao Chi-Chang , Hastings J. B.
Published: July 2002

For the study of condensed-matter systems x-ray scattering experiments are often the best choice as they have several desirable features including complete conservation of momentum in the incident and detected particles, well characterized initial and final electronic states, and insensitivity of photon transport to external electric and magnetic fields (as compared to photoelectrons, for example). To extend these techniques to soft x-ray region (ℏν<1 keV) the lack of suitable detectors, and the difficulties associated with performing scattering experiments in vacuum must be overcome. In this article we provide details of our instrumental development program, and show some representative examples of experiments we have performed to date.
The combined use of a singly charged ion beam and undulator radiation for photoelectron spectrometry studies on atomic ions
Authors: Bizau J. M. , Cubaynes D. , Richter M. , Wuilleumier F. , Obert J. , Putaux J. C.
Published: July 2002

We present the first photoelectron spectrometry experiment on a singly charged ion beam. Taking advantage of the high photon flux emitted in the undulator SU6 of Super-ACO, we have measured photoelectron spectra produced in the resonant photoionization of Ca+ ions at 33.2-eV photon energy. The success of this experiment depended strongly on the photon flux available. We demonstrate the capability of photoelectron spectrometry to precisely calibrate the photon spectrum emitted in the undulator.
Open-loop fiber optic gyroscope with wide dynamic range
Authors: Chien Pie-Yau
Published: July 2002

An open-loop, wide dynamic range, fiber optic gyroscope has been demonstrated by using the PLL phase tracking technique. This technique provides a linear output of an open-loop gyroscope with the Sagnac phase shift up to 2Nπ rad, N=2n, is where n an integer number.
A low-light television system for visible and infrared videoangiography
Authors: Longobardi G. , Poggi P.
Published: July 2002

Fluorescence angiography has become a very important diagnostic aid in modern clinical ophthalmology. The design and performance of a high-sensibility TV system incorporated into a standard fundus camera for the fundus eye analysis are described. Compared to the usual angiographic procedure, the new equipment has allowed the reduction of both eye exposure and dose of fluorescent dye injected intravenously to the patient. Examples of some choroidal angiograms obtained using this apparatus are presented.
A simple dynamic piezoelectric X-Y translation stage suitable for scanning probe microscopes
Authors: Tapson J. , Greene J. R.
Published: July 2002

We describe a novel XY micropositioning stage which operates using a single piezoelectric actuator to produce slip-stick motion. The stage can be moved in steps as small as 20 nm over an area of 9 mm×9 mm, at translation speeds of up to 0.5 mm/s. Cross coupling between axes is negligible, and the threshold voltage for movement is typically 10 V or less. The device is simple in construction and requires no precision components. The stage is small and robust, requires no mechanical connections, and offers the unique advantage in scanning tunneling microscopy and atomic force microscopy applications of being able to provide a Z displacement of some microns.
Stabilizing a laser beam’s focal point inside a liquid-helium cryostat
Authors: Jaffe S. M. , Yen W. M. , Grill W.
Published: July 2002

The focal point of a laser beam inside a liquid-helium cryostat has been spatially stabilized. Both passive and active stabilization techniques are employed. The position of the focal point is maintained to submicrometer dimensions in the plane transverse to the beam path. The instabilities along the beam propagation direction are reduced to the order of 10 μm.
A fast spectroscopic diagnostic for the measurement of plasma impurity ion dynamics
Authors: Den Hartog D. J. , Fonck R. J.
Published: July 2002

A high-resolution spectrometer has been developed and used to measure simultaneously impurity ion temperatures and flow velocities in high temperature plasmas with 10 μs temporal resolution (limited by digitization rate). This device is actually a duo-spectrometer: measurements from two different chordal views of the plasma can be made simultaneously via two separate quartz input fiber optic bundles coupled to the entrance slits which are tilted to compensate for line curvature. The dispersed spectra on the exit plane of the duo-spectrometer are coupled via quartz fiber optics to two arrays of 16 photomultiplier tubes each. Measurements made by recording the Doppler broadened and shifted 227.091 nm emission from the C v impurity ions in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) plasma have achieved precisions of <6 eV for temperatures of 150 eV and <0.7 km/s for flow velocities of 6 km/s. Representative results from the MST RFP indicate that the toroidal flow velocity drops and ion temperature increase during sawtooth events in MST.
Photoluminescence decay dynamics in an InGaN/AlGaN/GaN double-heterostructure blue-light-emitting diode
Authors: Mohs Georg , Fluegel Brian , Giessen Harald , Tajalli Habib , Peyghambarian Nasser , Chiu Pei-Chih , Phillips B. Scott , Osiński Marek
Published: July 2002

The impurity-related and band-to-band photoluminescence of a commercially available III–N blue-light-emitting diode is time-resolved using femtosecond excitation and streak-camera detection. Photoluminescence decay times are reported and stimulated band-to-band emission is observed. The data are compared to a simple recombination model capable of explaining the measured behavior of the photoluminescence.
LIF probing with high spatial resolution in the process zone of a photolysis laser
Authors: Strube W. , Rossberg M. , Wollbrandt J. , Linke E.
Published: July 2002

A laser-induced fluorescence (LIF) method for spatially resolved fragment detection and characterization in the radiation field of a photolysis laser is described. Measurements of the radiation field of a focused beam showed up highly inhomogeneous irradiation conditions, resulting in a strong local dependence of the laser-induced processes. The spatial resolution of the method is based on stepping-motor-controlled motion of the focusing lens of the photolysis laser versus the probe laser focused to a diameter (1/e2) of 58 μm. This diameter corresponds to the spatial inhomogeneities of the quantities studied in this article. However, the monitored volume (5.3×10−6 cm3) also represents a compromise between acceptable S/N ratio and spectral resolution. The advantages and limits of this spatially resolved fluorescence (SRF) technique are discussed. Owing to its simplicity it can be readily implemented in existing laser photolysis equipment with conventional LIF detection. This method is currently being applied to the study of IR laser chemical reactions. A few examples illustrate the range of applicability of the method by providing information on the fluence dependence of product formation, on mass transport kinetics of molecular species in the context of heterogeneous laser processing, and on the internal energy distribution of the dissociation products. They show the much higher information content of SRF measurements as compared with conventional LIF measurements.
Modular digital box-car for applications in pulsed laser spectroscopy
Authors: Dygdal/a R. , Fuso F. , Arimondo E. , Zielínski M.
Published: July 2002

A digital box-car, designed to work with sources producing signals composed of single pulses or series of pulses, is described. Thanks to its modular design, the system can be employed as a single-photon counting or as a coincidence unit in many experimental situations. The box-car is based on a digitally controlled delay line, producing a delay in the interval 17 ns–327.692 μs by 5 ns steps, a fast gate with an opening time adjustable in the range 10 ns–20.0 μs, and an 8-bit binary counter operating at a maximum frequency of 250 MHz. It also employs two pulse amplifiers, accepting negative pulses with a duration larger than 2 ns and an amplitude in the range 30–500 mV, and a fan-out unit. Applications to fluorescence and ion detection in experiments involving pulsed laser sources are briefly discussed.
Properties of YBa2Cu3O7−δ thick films on flexible buffered metallic substrates
Authors: Wu X. D. , Foltyn S. R. , Arendt P. N. , Blumenthal W. R. , Campbell I. H. , Cotton J. D. , Coulter J. Y. , Hults W. L. , Maley M. P. , Safar H. F. , Smith J. L.
Published: July 2002

We report superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) thick films on Ni-based alloys with a textured yttria-stabilized zirconia (YSZ) buffer layer. The YBCO and YSZ layers were deposited by pulsed laser deposition and ion beam assisted deposition, respectively. It was found that the transport critical current density (Jc) correlates very well with the YBCO mosaic spread. Jc over 1×10 6 A/cm2 at 75 K and ∼1×107 A/cm2 at 4 K were obtained in the 1-μm thick YBCO films. Zero field critical current of 120 amps at 75 K was obtained in a 2-μm-thick and 1-cm-wide YBCO film. Angular dependence measurement revealed Jc peaks for both H∥c and H∥a-b. The peak for H∥c implies additional pinning due to defects such as small angle grain boundaries or twin boundaries. Bending tests at 75 K showed that the YBCO thick films on the metallic substrates could sustain a strain of 0.4% and over 1% for tension and compression, respectively.
Scanning tunneling microscope with a rotary piezoelectric stepping motor
Authors: Yakimov V. N.
Published: July 2002

A compact scanning tunneling microscope (STM) with a novel rotary piezoelectric stepping motor for coarse positioning has been developed. An inertial method for rotating of the rotor by the pair of piezoplates has been used in the piezomotor. Minimal angular step size was about several arcsec with the spindle working torque up to 1 N×cm. Design of the STM was noticeably simplified by utilization of the piezomotor with such small step size. A shaft eccentrically attached to the piezomotor spindle made it possible to push and pull back the cylindrical bush with the tubular piezoscanner. A linear step of coarse positioning was about 50 nm. STM resolution in vertical direction was better than 0.1 nm without an external vibration isolation.
Removal of phototubes from Pb–glass detectors. III
Authors: Alburger D. E.
Published: July 2002

A technique is described for removing a 13-cm-diam phototube from the 7.5×15 cm end of a Pb–glass detector. Glass blocks and rubber gaskets ‘‘square-off’’ the detector, thereby allowing the use of a previously developed method for tube removal by means of heated chloroform.
Multiple hollow-cathode vacuum-ultraviolet plasma source excited by pulsed glow discharge
Authors: Suzuki Setsuo , Noda Etsuo
Published: July 2002

A multiple hollow-cathode vacuum-ultraviolet source excited by a pulsed glow discharge in a mixture of Xe and He has been developed. A MgF2 window with a diameter of 55 mm was used, and the repetition frequency was varied between 3 and 9 kHz. Stable output was maintained for about 3 h. Measurements of 147 nm radiant illumination were made at various distances from the window at various repetition frequencies. The peak radiant illumination decreased while the average radiant illumination increased with increasing repetition frequency. The output power density near the center of the window could be estimated from the relationship between measured radiant illumination and distance from the window. The peak and average output power densities at 6 kHz were 30 and 1.5 W/m2, respectively.
Volume source of hydrogen negative ions based on reflexive discharge: Theory and experimenta)
Authors: Goretsky V. P. , Ryabtsev A. V. , Soloshenko I. A. , Tarasenko A. F. , Schedrin A. I.
Published: July 2002

The results of theoretical and experimental studies of the stationary volume source of hydrogen negative ions based on reflexive discharge are presented. Measurements of plasma parameters and emission characteristics are accomplished, and the optimization of ion source geometry is provided. The best parameters of the ion beam extracted from the source across the magnetic field are as follows: current 40 mA, current density—80 mA/cm2, emittance along the magnetic field—3×10−5 cm rad, emittance across a magnetic field—1×10−5 cm rad. The calculation of basic beam properties is performed by numerical solution of the Boltzmann equation for electrons, balance equations for more than 300 elementary processes in gas discharge plasma, and equations of ion and electron motion. The calculated dependencies of hydrogen negative ions’ current density in the plane of emission slit on the gas pressure and the discharge current are found to be in a good agreement with the experimental data.
A simple electron cyclotron resonance ion sourcea)
Authors: Welton R. F. , Moran T. F. , Feeney R. K. , Thomas E. W.
Published: July 2002

A simple, all permanent magnet, 2.45 GHz electron cyclotron resonance ion source has been developed for the production of stable beams of low charge state ions from gaseous feed materials. The source can produce ∼1 mA of low energy (3 kV) singly charged ion current in the 10−4 Torr pressure range. The source can also be operated in a more efficient low-pressure mode at an order of magnitude lower pressure. In this latter range, for example, the ionization efficiency of Ar is estimated to be 1% with charge states up to Ar8+ present. Operation in the low-pressure mode requires low power input (∼20 W). These features make the source especially suited for use with small accelerator systems for a number of applications including ion implantation, mass spectrometry, and atomic collision experiments where multiply charged ions are desirable. Design details and performance characteristics of the source are presented.
Cooling solutions for high heat load optics (abstract)
Authors: Morris D. , Harding G. H. , Cox M. P. , Lunt D.
Published: July 2002

Heat loads on optical components at third-generation synchrotron sources, such as the APS, present beamline designers with difficult and complex engineering problems. A number of solutions have been proposed, such as pin-post water cooling, cryogenic cooling, and liquid gallium cooling. This paper describes both a cryogenic cooling system and a liquid gallium pumping system that have been developed specifically for the APS high heat load beamlines. Also presented is a potential solution for the first mirrors on high heat load beamlines, based on liquid gallium internal cooling of a silicon carbide mirror.
Improved monochromator design for high heat load beamlines at CHESS (abstract)
Authors: Smolenski K.W. , Pahl R. , Doing P. , Conolly C. , Clark B. , Ehen J. , Shen Q.
Published: July 2002

The use of water-cooling channels in silicon x-ray monochromators for the Cornell High Energy Synchrotron Source (CHESS) high power wiggler beamlines has been studied by finite element analysis. The efficiency from channels of different dimensions, ranging from 25 mm to 2 mm width and 5 mm depth, has been calculated. The new crystals are designed to replace the indirect cooled monochromators currently used at CHESS wiggler stations. At typical operation parameters of 150 mA electron current at 5.3 GeV and a gap of 40 mm, the 24-pole wiggler at CHESS provides an x-ray beam with a total power of 2.7 kW at the monochromator. Procedures have been developed for fabrication of internally cooled crystals using a silver-glass dye attach paste. Tests of a new crystal with a conventional x-ray source revealed very small amounts of residual strain. Experiments with synchrotron radiation are scheduled in the near future.
Further tests on liquid-nitrogen-cooled, thin silicon-crystal monochromators using a focused wiggler synchrotron beam
Authors: Rogers C. S. , Mills D. M. , Fernandez P. B. , Knapp G. S. , Wulff M. , Hanfland M. , Rossat M. , Freund A. , Marot G. , Holmberg J. , Yamaoka H.
Published: July 2002

A newly designed, cryogenically cooled, thin Si crystal monochromator was tested at the European Synchrotron Radiation Facility (ESRF) beamline BL3. It exhibited less than 1 arcsec of thermal strain up to a maximum incident power of 186 W and average power density of 521 W/mm2. Data were collected for the thin (0.7 mm) portion of the crystal and for the thick (≳25 mm) part. Rocking curves were measured as a function of incident power. With a low power beam, the Si(333) rocking curve at 30 keV for the thin and thick sections was <1 arcsec FWHM at room temperature. The rocking curve of the thin section increased to 2.0 arcsec when cooled to 78 K, while the thick part was unaffected by the reduction in temperature. The rocking curve of the thin section broadened to 2.5 arcsec FWHM and that of the thick section broadened to 1.7 arcsec at the highest incident power. The proven range of performance for this monochromator has been extended to the power density, but not the absorbed power, expected for the Advanced Photon Source (APS) undulator A in closed-gap operation (first harmonic at 3.27 keV) at a storage-ring current of 300 mA.
High precision, high-heat-load mirror for the APS diagnostics beamline (abstract)
Authors: Rotela E. , Yang B. , Sheng I. C. , Sharma S. , Lumpkin A.
Published: July 2002

A high precision mirror for measuring the storage ring beam size is under fabrication for the APS diagnostics beamline. The mirror, which will be located at 12.9 meters from the bending magnet source, is required to maintain less than 1.6 microradian slope error. The mirror design consists of a slot in the center in order to reduce incident power from the 300-mA, 7-GeV beam during normal operation. Water channels with fins are machined in the GlidCop mirror body to protect it against extremely high heat loads under accidental beam deviations. The mechanical design of the mirror, and results from a thermal analysis are presented in this paper.
Preparation of microfocusing optics using synchrotron radiation sources (invited, abstract)
Authors: Cerrina Franco
Published: July 2002

X-rays are used for microfabrication of high-aspect-ratio structures because of their high penetrating power for microfabrication of integrated circuits because of their very high spatial resolution. An uncommon application is the development of phase-shifting optics for hard x-rays, where both requirements (high aspect ratio and high resolution) must be met at the same time. In the hard x-ray region (8 keV and up), conventional absorbing binary diffractive optics are very inefficient because of the low contrast of most elements. It is instead possible to achieve very high efficiency using phase-shifting optics. To achieve a phase shift of Pi, several microns of material are needed. At the same time, the spatial resolution is determined by the finest line in the pattern, of the order of 0.2–0.1 μm. This yields aspect ratios of 10-50, posing great challenges to microfabrication because the submicron dimensions require a much more delicate process than that found, for instance, in LIGA. We have overcome these hurdles, and succeeded in manufacturing Fresnel phase plates with 0.1 μm smallest features for operation at 8 keV. We use a combination of x-ray and electron-beam lithography to process the masks. In particular, the use of an x-ray aligner, capable of multiple exposures, has allowed us to fabricate multilevel FPPs, with ‘‘blazed’’ zone profile of efficiency approaching 80% in the first order focus. We will review the techniques that are at the basis of our fabrication process, describe our approach, and present some of the most recent results.
X-ray fluorescence analysis with high energy resolution
Authors: Caliebe Wolfgang A. , Bajt Sas̆a , Kao Chi-Chang
Published: July 2002

The analysis of x-ray fluorescence lines with total energy resolution of 1 eV or better can provide detailed information on the electronic structure of the sample in addition to quantitative elemental analysis of the sample. A perfect crystal spectrometer was developed for this purpose. Preliminary results from a series of chromium oxides will be presented.
Trace element analysis using the fluorescence microprobe at the Advanced Light Source (abstract)
Authors: Thompson Al , Chapman K. C.
Published: July 2002

The fluorescence microprobe beamline at the Advanced Light Source (ALS) is a unique instrument for analysis of trace elements. The beamline is on a bending magnet port of the synchrotron and uses a pair of multilayer-coated mirrors to focus the x-ray source to a spot size of 1–5 μm2. Since the multilayer mirrors limit the energy bandpass of the system to 5–10%, the trace element sensitivity is significantly improved compared to the use of grazing incidence mirrors. Different pairs of mirrors have been used to operate at 8.5, 10, and 12.5 keV. The detection limits for elements from Si to As will be presented for operation at both 1.5 GeV and 1.9 GeV. Results that illustrate the features of the instrument will be presented from the many samples that have been studies.
A high-precision self-adapted optical structure
Authors: Wang Zhibi , Yun Wenbing , Kuzay Tuncer
Published: July 2002

Third-generation synchrotron x-ray facilities, such as the Advanced Photon Source, generate a very high heat flux in a very small area. When an optical component is subjected to a heat load, there will be thermal deformation caused by a temperature increase. 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 functionality in the optical component. In order to preserve photons, optical components have to be designed to have very small thermal deformation or small change of slope in the surface. Typically the change of slope is limited to a few microradians. The structure proposed here offers advantages in terms of cost, complexity, and operations.
Liquid-metal-cooled curved-crystal monochromator for Advanced Photon Source bending-magnet beamline 1-BM
Authors: Brauer S. , Rodricks B. , Assoufid L. , Beno M.A. , Knapp G.S.
Published: July 2002

We describe a horizontally focusing curved-crystal monochromator that invokes a 4-point bending scheme and a liquid-metal cooling bath. The device has been designed for dispersive diffraction and spectroscopy in the 5–20 keV range, with a predicted focal spot size of ≤100 μm. To minimize thermal distortions and thermal equilibration time, the 355×32×0.8 mm crystal will be nearly half submerged in a bath of Ga-In-Sn-Zn alloy. The liquid metal thermally couples the crystal to the water-cooled Cu frame, while permitting the required crystal bending. Calculated thermal profiles and anticipated focusing properties are discussed.
Monochromatic beam mammography studies using synchrotron radiation (abstract)
Authors: Gmür Nicholas F. , Thomlinson W. , Johnson R. E. , Washburn D. , Pisano E. , Arfelli F. , Chapman L. D. , Menk R. , Zhong Z. , Sayers D.
Published: July 2002

Preliminary experiments have been carried out on the X27C R&D beamline at the National Synchrotron Light Source (NSLS) to explore the potential improvement in contrast in breast imaging using monochromatic synchrotron x-rays [R. E. Johnson et al., SPIE (1995) (to be published)]. In our present study, images have been obtained of ACR, contrast detail and anthropomorphic phantoms at 16 to 24 keV. Phantom thickness varied from 42 to 80 mm. Synchrotron images using a Fuji image plate detector and standard mammographic film have been compared to each other and with conventionally produced images. The preliminary results show an improved contrast over the conventional images with lower absorbed dose in the phantoms. The image plate detector was used for our fist experiments because it was readily available and produces digital data. Experiments using an additional analyzer crystal as a scatter rejection element are also underway at the NSLS [D. Chapman, SRI ‘95 (these proceedings)]. We plan to evaluate a variety of detectors and monochromatic beam geometries in order to develop a system that optimizes mammography image contrast and spatial resolution.
A pressure- and temperature-controlled sample cell for the structural investigation of lyotropic liquid crystals using a small-angle x-ray diffraction line source
Authors: Duesing P. M. , Templer R. H. , Seddon J. M.
Published: July 2002

We present the design and performance of a temperature- and pressure-controlled sample cell for the small-angle x-ray diffraction analysis of lyotropic liquid crystalline materials. The particular requirements for such a system of high resolution, high intensity, and control on sample homogeneity can be particularly well fulfilled using line-source diffraction. We thus designed a sample cell that will allow the use of a line source. Sample volume is kept small (20 μl) to keep the contained energy low. The hydrostatic system, based on beryllium x-ray windows, Bridgman type seals with lead O rings and a stainless-steel body is rated to achieve pressure control within ±3 bar between 0 and 3000 bar at ramping rates of 30–100 bar/s. Temperature control is achieved within ±0.03 K between room temperature and 180 °C. Maximum heating rates correspond to 0.8 K/s. Control algorithms are implemented on a Microrobotics K4 controller, using a modest amount of computing power.
Improved detection method for evanescent wave interferometric chemical sensing
Authors: Lenferink A. T. M. , Schipper E. F. , Kooyman R. P. H.
Published: July 2002

A phase modulation system for a waveguide Mach–Zehnder interferometer sensor system has been developed which is capable of direct detection of optical phase changes smaller than 2.2π milliradians. When implemented in a chemical sensor interferometer system this corresponds to a sensitivity for refractive index changes of the analyte of better than 10−6, provided temperature variations are kept below 0.1 °C during the measuring period. The sensitivity of the instrument is demonstrated by a stepwise addition of low concentrations of glucose in water. The possibility to reset the instrument by a whole number of fringes makes it feasible to combine the high sensitivity with a virtually unlimited range. The accuracy of the detection system is independent of interferometer visibility changes during the measurement. This makes it possible to perform accurate measurements in solutions with varying degrees of opaqueness, such as milk, blood, or wastewater. These features are demonstrated with adsorption experiments of proteins to the underlying waveguide substrate. Also, the possibility to have the visibility as an extra parameter during the measurements can be of importance for further investigation of protein adsorption processes.
A technique for efficiently generating bimetallic clusters
Authors: Wagner R. L. , Vann W. D. , Castleman A. W.
Published: July 2002

Reactivities of bimetallic clusters can be controlled by varying their composition, making them potentially valuable as catalysts and for use in elucidating the reactivities of such subnanoscale surfaces. A dual rod laser vaporization source coupled to a fast flow reactor is developed for the study of bimetallic clusters and their reactions. In order to establish the versatility of the technique, the results of studies are presented in which Nb/Al clusters are formed in two plasmas induced by the second harmonic (532 nm photons) of a single Nd:YAG laser and then detected by a quadrupole mass spectrometer. The beam from the laser is split and then focused onto each rod, allowing the mixing ratio within the cluster to vary by altering the laser fluence on each rod. With a low fluence on the Nb rod and a high fluence on the Al rod, an Al rich cluster distribution is formed, NbAlm− (m=2–20), and Alm− (m=5–31). By increasing the fluence on the Nb rod and decreasing the fluence on the Al rod, a Nb rich cluster distribution is formed, NbnAlm− (n=3–8 and m=1–3), NbnOAlm − (n=3–8 and m=1–5), and NbnO− (n=3–8). Additional characterization is also performed on V/Al clusters.
Fluorescent imaging system for global measurement of liquid film thickness and dynamic contact angle in free surface flows
Authors: Johnson M. F. G. , Schluter R. A. , Bankoff S. G.
Published: July 2002

Fluorescent dye dissolved in a liquid flow was used to outline liquid-gas free boundaries and, with digital imaging, to observe quantitatively surface wave propagation and pattern formation, as well as contact-line velocity and contact angle in thin film flows on horizontal and inclined substrates. Using the relatively inexpensive system described here, a fluid depth measurement with a precision of ±0.02 mm is obtained routinely in flows of several millimeters depth over an area of approximately one square meter, and essentially unlimited continuous time spans. Dynamic contact angles are measured, for the first time, on liquid fronts with significant three-dimensional curvature such as rivulets draining down an inclined plate at any speed or global location. Procedures to normalize results quantitatively for any nonuniformities of the incident illumination are given. Estimates of the contribution to the experimental error by other effects, such as variations in dye concentration and temperature, and image digital register capacity, are also discussed. Illustrative results for two fluids and several dyes are given. Refinements to decrease the local error further to ±0.005 mm or less are described.
Novel gas-doping technique for local spectroscopic measurements in pulsed-power systems
Authors: Arad R. , Ding L. , Maron Y.
Published: July 2002

A novel method for doping plasmas in pulsed-power experiments with gaseous elements has been developed. A fast gas valve, a nozzle, and a skimmer are used to generate an ultrasonic gas beam that is injected into a planar-geometry microsecond plasma-opening switch (POS). An array of ionization probes with relatively high spatial and temporal resolutions was developed for diagnosing the absolute injected-gas density and its spatial profile. The properties of the gas column were also studied using spectroscopy of line emission that results from the interaction of the doped gas with the POS prefilled plasma. The doped column is found to have a width of ≈1 cm and a density of (0.8–1.7)×1014 cm−3. Observations of characteristic emission lines from the doped atoms and their ions allow for various spectroscopic measurements, such as the magnetic field from Zeeman splitting and the ion velocity distributions from Doppler shifts, that are local in three dimensions. It is shown that this gas doping technique can also be used to study proton-dominated plasmas that cannot be studied with simple emission spectroscopy due to the lack of light emitting ions. The variety of gases used with this method, together with the small valve dimensions and its fast opening, make it potentially useful for broad diagnostics of various short-duration plasma experiments.
Measurement system for optical Kerr effect induced by continuous wave laser
Authors: Oki Yutaka , Sakamoto Naoto , Sakai Keiji , Takagi Kenshiro
Published: July 2002

An experimental technique was developed for studying the optical Kerr effect induced by a cw Ar+ laser with 500 mW output. A Pockels cell was used for modulating the pump laser so that the polarization changed periodically between the vertical and horizontal plane. The dielectric anisotropy thus induced in a sample liquid was probed in the ellipsometry with a He–Ne laser. The system was applied to nitrobenzene and p-n-hexyl p′-cyanobiphenyl (6CB), a nematogen in the isotropic phase. The observed birefringence showed a linear dependence on the pump laser intensity and the gradient yielded the Kerr constant: B=5.75×10−14 V−2 m at 30 °C in nitrobenzene and B=6.72×10−12(T−T*)−1 V−2 m in 6CB, T* being the virtual transition temperature to the nematic phase. This technique can be used for investigating the relaxation of molecular orientation in frequency domain.
Gas-coupled laser acoustic detection at ultrasonic and audio frequencies
Authors: Caron James N. , Yang Yuqiao , Mehl James B. , Steiner Karl V.
Published: July 2002

Airborne acoustic waves have been detected by a laser-beam deflection technique in both the ultrasonic and audio frequency ranges. For ultrasonic applications, a probe beam is directed parallel to the surface of a sample. Ultrasonic waves in the solid are detected when an acoustic wave is radiated from the surface into the ambient air, where the density variations cause a beam deflection. Gas-coupled laser acoustic detection (GCLAD) has been used to record well-resolved through-transmission and surface-acoustic wave forms in various materials. GCLAD has also been incorporated into a C-scanning system where it has been used to image subsurface flaws in graphite/polymer composite panels. Because the laser beam is not reflected from the sample surface, the technique is not dependent upon the surface optical properties of the material under investigation. It is particularly useful for testing graphite/polymer composites and other materials with rough surfaces. The beam-deflection technique has been tested quantitatively in the kHz frequency range by passing a probe beam through a cylindrical resonator. The acoustic spectrum of the resonator was measured from 4 to 13.5 kHz by scanning the frequency of a source and recording the acoustic field with both a microphone and the beam-deflection system. The acoustic fields of the lower-frequency modes are well known and enable both qualitative and quantitative tests of the beam-deflection technique. Measurements on the lowest-frequency plane-wave mode were used for absolute calibration of the microphone. The noise level of the beam-deflection measurements at 4.3 kHz was found to be 0.05 nrad (rms), corresponding to an acoustic pressure of 0.005 Pa (rms).
Determination of local high temperature excursion in an intrinsic doped fiber fluorescence-based sensor
Authors: Sun T. , Zhang Z. Y. , Grattan K. T. V. , Palmer A. W.
Published: July 2002

A fluorescence-based intrinsic doped fiber temperature sensing system for determining local extremes of high temperatures has been demonstrated in this work. Data on this temperature rise are analyzed using a mathematical relationship, based on a correlation coefficient ratio scheme, to relate to the reduced fluorescence decay time information thus associated with the hot part of the fiber. In schemes incorporating this mathematical analysis, two separate sensor configurations have been demonstrated, one of which is to use short, single lengths of fiber spliced into a network and the other a long single length of doped fiber, using both Nd and Er doped fiber materials. The results show that the correlation coefficient ratio, R, will deviate from and be smaller than unity with the increase of the temperature of the localized region where the heat is applied, providing the mechanism for a simple high temperature excursion detection system.
Design of solid/liquid–liquid/solid trilayer systems for the measurement of diffusion coefficients in liquid metals
Authors: Zhao J. H. , Liu R. P. , Zhang M. , Zhou Z. H. , Zhang X. Y. , Cao L. M. , Dai D. Y. , Xu Y. F. , Wang W. K.
Published: July 2002

A new method for investigation of diffusion processes in liquid metals with solid/liquid–liquid/solid trilayer systems is described. The design of this kind of trilayers enables diffusion processes with no effects from gravity-induced convection and Maragoni-convection conditions. The Ta/Zn–Sn/Si trilayers were prepared and the interdiffusion of liquid zinc and tin at 500 °C was investigated. The interdiffusion coefficients range from 1.0×10−4 to 2.8×10−4 mm2/s, which are less than previous values measured by capillary reservoir technique under 1 g environment where various kinds of convection exist. It is the removing of disturbances of these kinds of convection that brings about the precise interdiffusion coefficients in liquid metals.
Partial pressure measurements with an active spectrometer
Authors: Brooks N. H. , Jensen T. H. , Colchin R. J. , Maingi R. , Wade M. R. , Finkenthal D. F. , Naumenko N. , Tugarinov S.
Published: July 2002

Partial pressure neutral gas measurements have been made using a commercial Penning gauge in conjunction with an “active spectrometer.” In prior work utilizing band pass filters and conventional spectrometers, trace concentrations of the hydrogen isotopes H, D, T and of the noble gases He, Ne, and Ar were determined from characteristic spectral lines in the light emitted by the neutral species of these elements. For all the elements mentioned, the sensitivity was limited by spectral contamination from a pervasive background of molecular hydrogen radiation. The active spectrometer overcomes this limitation by means of a digital lock-in method and correlation with reference spectra. Preliminary measurements of an admixture containing a trace amount of neon in deuterium show better than a factor of 20 improvement in sensitivity over conventional techniques. This can be further improved by correlating the relative intensities of multiple lines to sets of reference spectra.
Modeling a one-dimensional bremsstrahlung and neutron imaging array for use on Sandia’s Z machine
Authors: Rochau G. A. , Derzon M. S. , Fehl D. , Rochau G. E. , Lazier S. , Droemer D.
Published: July 2002

Inertial confinement fusion is being studied on the Z facility at Sandia National Laboratories. Z is a large z-pinch machine which can provide 20 MA of current to z-pinch loads producing ∼1.8 MJ of soft x rays in less than 10 ns. Within the pinch region, decelerated electrons produce a strong source of bremsstrahlung radiation which varies from shot to shot. Additionally, a variety of inertial confinement fusion targets may produce fusion neutrons, the intensity and distribution of which depend on the temperature and density of the pinch. In this article, we describe the computer modeling behind the shielding design of a simple time-resolved, one-dimensional imaging array. This diagnostic will provide a time history for both the bremsstrahlung and neutron production as a function of height in the target. Calculations show that by building an array of scintillator fibers separated by long, thin tungsten collimator plates, a sampling rate of 0.254 mm at the target can be achieved. The corresponding channel-to-channel discrimination for such a design is shown to be better than 1000∷1 for <4 MeV photons and 100∷1 for 2.45 MeV neutrons. By coupling scintillator fibers to a fiber-optic streak camera system, the system time response is expected to be dominated by the scintillator response (∼1.2 ns).
Ion temperature and plasma rotation velocity measurements using visible spectroscopy on TdeV
Authors: Condrea I. , Haddad E. , Gregory B. C. , Lafrance D. , Lachambre J. L. , Pacher G. , Meo F. , Mai H. H.
Published: July 2002

A visible spectroscopic imaging system has been developed on Tokamak de Varennes (TdeV) that provides profile measurements of the ion temperature and plasma rotation velocity. Multiple poloidal and tangential chords were coupled to the entrance slit of a spectrometer equipped with a back-illuminated charge coupled device camera at its exit slit. The camera records spatially and spectrally resolved emission profiles with real time digitization and up to 70 ms/frame as temporal resolution. Line-integrated radiation from different ionization stages in the visible range (B V, C III, He II, and N IV) were chosen as representative of the plasma in their regions of maximum emission. Three types of plasma discharges are compared: ohmic and electron cyclotron resonance heated L and H modes. Preliminary results show that with an L–H transition, there is a 20%–30% increase of the ion temperature at midradius, without a pedestal and an increase of the toroidal velocity shear at r/a∼0.8.
Implementation of a normal incidence spectrometer on an electron beam ion trap
Authors: Utter S. B. , Beiersdorfer P. , López-Urrutia J. R. Crespo , Träbert E.
Published: July 2002

Spectroscopic instrumentation is one of the keys to the exploration of high-temperature plasmas. The electron beam ion trap (EBIT) can serve as a tool for precise studies of highly charged ions in the laboratory and can help in setting spectroscopic standards for plasma studies. Recent efforts have focused on investigating the EUV, vacuum ultraviolet (VUV), and UV regimes. We present here the implementation of a 1 m normal incidence spectrometer for use on the Lawrence Livermore National Laboratory high-energy EBIT (Super-EBIT) for spectral analysis of line emission of highly charged ions. Using two different gratings, our study encompasses a wide range of wavelengths spanning the VUV through the visible. Examples of measurements of optical spectra from krypton and argon are given.
Effects of neutrons on semiconductor x-ray detectors including n-type Joint European Torus and p-type GAMMA 10 tomography detectors
Authors: Cho T. , Kohagura J. , Hirata M. , Sakamoto Y. , Numakura T. , Minami R. , Sasuga T. , Nishizawa Y. , Okamura T. , Tamano T. , Yatsu K. , Miyoshi S. , Hirano K. , Maezawa H.
Published: July 2002

Characterization experiments have been carried out so as to investigate the effects of fusion-produced neutrons on the x-ray-energy responses of semiconductor detectors for x-ray tomography in the Joint European Torus (JET) tokamak (n-type silicon) and the GAMMA 10 tandem mirror (p-type silicon). Neutron effects on the x-ray-energy responses of these detectors are studied using synchrotron radiation from a 2.5 GeV positron storage ring at the Photon Factory. Changes in the material properties of the detectors have been investigated using an impedance analyzer to estimate neutron effects on x-ray-sensitive depletion thicknesses. A cyclotron accelerator is employed for well-calibrated neutron irradiation onto these plasma x-ray detectors; a fluence of 2–5×1013 neutrons/cm2 is utilized for simulating the effects of fusion-produced neutrons in JET. Modifications of the x-ray responses after neutron exposure due to fusion plasma shots in JET as well as cyclotron-produced neutron irradiations are found to have a functional dependence on x-ray energy. Also, recovery of the detector energy response is found when detector bias is applied. Our theory consistently interprets such properties in terms of the neutron effects on the diffusion length and the resistivity of detectors.
X-ray diagnostic systems for the TJ–II flexible heliac
Authors: Medina F. , Rodrı́guez-Rodrigo L. , Encabo-Fernández J. , López-Sánchez A. , Rodrı́guez P. , Rueda C.
Published: July 2002

The set of diagnostics that are being installed in TJ–II are meant to cover the full photon energy range expected in TJ–II during the electron cyclotron resonance heating phase. The obtained information will be used to evaluate the energy contained in the superthermal electron populations and its possible relevance in the global power balance as well as for standard electron temperature estimations. Two NaI(Tl) detectors located at the equatorial plane of the machine will be used to analyze the highest energy photons (over 50 keV). One Si(Li) and a planar Ge detector will be used to obtain the emission spectra between 1 and 100 keV. Tomographic reconstruction of plasma emissivity (up to 10 keV) will be carried out using four p-n silicon photodiodes arrays of 16 detectors, located at the same poloidal section. An additional camera will be used to detect toroidal asymmetries.