bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of dynamic/advancing/receding contact angle by video-enhanced sessile drop tensiometry
Authors: Lin Shi-Yow , Chang Hong-Chi , Lin Lung-Wei , Huang Pao-Yao
Published: July 2002

A sessile drop tensiometer enhanced by video-image digitization is designed for the experimental measurement of dynamic/advancing/receding contact angle. A collimated light beam passes through the sessile drop of liquid and a silhouette of the drop is created. The equipment video images the silhouette, digitizes the image, and locates the edge coordinates of the drop. A new technique, replacing the classical selected plane method, is developed to obtain the values of capillary constant and the radius of curvature at apex from the edge coordinates of digitized drop profile. Four parameters (location of apex, radius of curvature at apex, and the capillary constant) are calculated from the best fit between the edge coordinates and the theoretical curve obtained from the Laplace equation. The contact angle is then obtained from the location of the air/solid interface and the best-fitted sessile drop profile. By controlling the humidity of air phase surrounding the drop, this technique can measure the advancing and receding contact angles and monitor the rate of advancing and receding of the three-phase line simultaneously. This technique works well on contact angle measurement for sessile drops with or without an equator. Preliminary studies on the dynamic contact angle have been made for water drops on paraffin, polymethylmethecrylate, and glass. The technique is capable of giving contact angle of 0.2° precision.
Flux, irradiance, and transmission calculations for the ALS wiggler beamline 5.0
Authors: Marks S. , Cork C.
Published: July 2002

A protein crystallography facility is being constructed for the Advanced Light Source (ALS) wiggler beamline 5.0. The radiation source is a 38 pole, 2.0 T wiggler. Calculations have been performed to determine the source phase space characteristics and the power loading on and transmission of various beamline elements. A set of computer codes have been developed for this purpose. The wiggler horizontal and vertical phase space flux density is calculated by phasex and phasey, respectively. WrFlux calculates the spectral flux density along the principal ray of the optical system. WrPwr calculates the power impinging on a target. If a filter function is specified, the transmitted, or reflected, power is calculated. The theory and operation of the codes will be presented as well as several results of calculations.
Beam stabilization at SPEAR (invited)
Authors: Corbett J.
Published: July 2002

The SPEAR storage ring began routine synchrotron radiation operation with a dedicated injector in 1990. Since then, a program to improve beam stability has steadily progressed. This paper, based on a seminar given at a workshop on storage ring optimization (1995 SRI conference) reviews the beam stability program for SPEAR.
Ray tracing: Experience at SRC (invited)
Authors: Severson Mary
Published: July 2002

SHADOW [B. Lai and F. Cerrina, Nucl. Instrum. Methods A 246, 337 (1986)] is the primary ray-tracing program used at SRC. Ray tracing provides a tremendous amount of information regarding beamline layout, mirror sizes, resolution, alignment tolerances, and beam size at various locations. It also provides a way to check the beamline design for errors. Two recent designs have been ray traced extensively: an undulator-based, 4-meter, normal-incidence monochromator (NIM) [R. Reininger, M.C. Severson, R.W.C. Hansen, W.R. Winter, M.A. Green, and W.S. Trzeciak, Rev. Sci. Instrum. 66, 2194 (1995)] and an undulator-based, plane-grating monochromator (PGM) [R. Reininger, S.L. Crossley, M.A. Lagergren, M.C. Severson, and R.W.C. Hansen, Nucl. Instrum. Methods A 347, 304 (1994)].
The APS optics topography station
Authors: Krasnicki Szczesny (Felix)
Published: July 2002

An in-house station for topographic testing of x-ray optical elements for the Advanced Photon Source experimental beamlines was set up by the Experimental Facilities Division of Argonne National Laboratory. A new double-crystal x-ray diffractometer was designed and built keeping in mind the need for testing large crystals possibly attached to cooling manifolds and lines. A short description of the new facility is given. The instrument performance fully satisfies imposed requirements, and the machine was successfully used for testing several silicon and diamond crystals.
Beamline control and data acquisition software (invited)
Authors: Mooney T.M. , Cha B.K. , Goetze K.A. , Reid D.R. , Winans J.R.
Published: July 2002

An international collaboration of software developers has been working for several years to advance the state of the art of control systems and has produced software and development methods that are directly applicable to synchrotron radiation (SR) instrumentation. The software is collectively entitled EPICS and is essentially an extensible tool kit for implementing distributed control systems. The EPICS collaboration now includes developers representing many of the Advanced Photon Source (APS) beamlines, as well as developers from the Stanford Synchrotron Radiation Laboratory, the Advanced Light Source, and the Gemini and Keck telescopes. As part of this collaboration, we have developed software tools for controlling and acquiring data from SR beamlines and combined them with tools developed by others to support laboratories and experiments at the APS and other SR facilities. Applications of EPICS-based software in SR instrumentation will be described, some consequences of collaborative development will be discussed, and the intended impact of this software on the science conducted at SR facilities will be discussed.
Digital closed orbit feedback system for the Advanced Photon Source storage ring
Authors: Chung Y. , Barr D. , Decker G. , Galayda J. , Lenkszus F. , Lumpkin A. , Votaw A. J.
Published: July 2002

Closed orbit feedback for the Advanced Photon Source (APS) storage ring employs unified global and local feedback systems for stabilization of particle and photon beams based on digital signal processing. Hardware and software aspects of the system will be described. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral, and derivative) control algorithm, application of digital signal processing to compensate for vacuum chamber eddy current effects, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through the APS control system, and system performance in the frequency and time domains. The system hardware, including the digital signal processor (DSPs), is distributed in 20 VME crates around the ring, and the entire feedback system runs synchronously at 4-kHz sampling frequency in order to achieve a correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically networked reflective memories.
Digital x-ray processing electronics for fluorescence EXAFS and spectroscopy
Authors: Hubbard B. , Warburton W.K. , Zhou C.Z.
Published: July 2002

We have developed a digital x-ray processor (DXP) for x-ray fluorescence spectroscopy, implemented in a 4-channel CAMAC module, which accepts inputs of either polarity from reset or tail preamplifiers, and outputs one spectrum per channel. Digital trapezoidal shaping and efficient pileup rejection are implemented in dedicated logic, with programmable peaking times from 0.5 to 20 msec. The energy resolution is comparable to good analog units at equivalent peaking times. A maximum input count rate (ICR) of 500,000 cps per channel can be accomodated at a peaking time of 0.5 msec. A digital signal processor on each channel is used to collect the data, apply corrections, and update the spectrum. The capabilities of the DXP prototype at high rates was tested at SSRL. Using an Ortec single-element germanium detector, the resolution was seen to degrade somewhat with increasing ICR above 150,000 cps, due to effects that we are still investigating. Collaborating with Hewlett-Packard and SSRL, the DXP was also used with a Kevex Si(Li) detector for trace element detection on silicon wafers in comparison with Kevex readout electronics. At 4 msec peaking time, DXP’s resolution was slightly worse (10–15 eV) due to some excess noise pickup, though the background levels in the spectra were essentially identical in the two systems and the DXP’s maximum count rate was several times higher.
Alignment and commissioning of the APS beamline front ends
Authors: Shu D. , Barraza J. , Ramanathan M. , Chang J. , Kuzay T.M.
Published: July 2002

Fifteen out of forty initial beamline front ends have been installed in the storage-ring tunnel at the 7-GeV Advanced Photon Source (APS). For the front-end installation, a four-step alignment process was designed and consists of (1) prealigning the front-end components with support tables in the preassembly area, (2) installing the components with tables in the storage-ring tunnel and aligning relative to the APS global telescope survey network, (3) confirming the alignment using a tooling laser alignment system, and (4) performing adjustments with the synchrotron-radiation beam during commissioning. The laser alignment system and the prealignment database have been of great importance for the expedient maintenance of front-end components. These tools are very important to a large synchrotron radiation facility, such as the APS, since they make a quick alignment setup possible and minimize alignment time inside the tunnel. This paper will present the four-step alignment process, the laser alignment system, and discuss the alignment confirmation results.
Precise lattice location of trace elements within minerals and at their surfaces with x-ray standing waves (abstract)
Authors: Qian Y.
Published: July 2002

Using x-ray standing waves (XSW) generated by dynamical Bragg diffraction, we have precisely measured lattice locations of trace elements within and at the surface of mineral single crystals. Natural calcite samples were cleaved along the (1014) plane to obtain pristine surfaces. After cleavage, some samples were reacted with a dilute aqueous Pb solution to obtain Pb-sorbed surfaces. XSW measurements were then performed on both unreacted and reacted samples using the calcite (1014) Bragg reflection. Results of these XSW measurements show that the naturally occurring trace element M substitutes for C. On the Pb-reacted calcite sample, Pb was located on the calcite (1014) lattice plane where C atoms also reside. Our measurements clearly demonstrate a new and powerful application of synchrotron radiation in earth and environmental sciences to provide element-specific atomic-scale structural information within and at the surface of minerals. The XSW measurements were made at the NSLS X15A and X25 beamlines.
Surface-micromachined free-space micro-optical systems containing three-dimensional microgratings
Authors: Lee S. S. , Lin L. Y. , Wu M. C.
Published: July 2002

Free-space micro-optical systems on a chip containing three-dimensional microgratings have been demonstrated using surface-micromachining technique. The micrograting is integrated with a rotary stage, a collimating micro-Fresnel lens, and an edge-emitting laser held by three-dimensional alignment structures on a single Si substrate. Diffraction patterns for various grating rotation angles are observed. Another optical interconnect module consisting of three cascaded microgratings is also demonstrated. The micrograting is a basic building block for many micro-optical systems and is very attractive for applications in microspectrometers, free-space optical interconnect, optoelectronic packaging, and wavelength-division multiplexed integrated micro-optical systems.
Characterization of x-ray spatial coherence and its propagation
Authors: Lin B. , Schlossman M. L. , Meron M. , Williams S. M. , Viccaro P. J.
Published: July 2002

X-ray beams of varying degrees of partial spatial coherence have been prepared and characterized, and the diffraction of these beams from patterned surfaces measured. The experiments were carried out at a bending magnet source at the NSLS (X-19C). The resulting diffraction patterns for a pair of slits and an optical grating are analyzed in terms of an x-ray mutual coherence function used to describe the propagation of the coherent wave front in the visible light regime. The diffraction and speckle pattern from the surface are the result of the mutual coherence function convoluted with the interference function of the grating. Forming diffraction patterns, or x-ray speckles, with partially coherent x-rays relaxes the requirement for the interference, thereby increasing the ‘‘effective’’ coherent flux. This detailed knowledge of the propagation of the x-ray spatial coherence aids in defining the physical characteristics of beamline optical elements that must preserve the coherent x-ray wave front.
Polarization measurement and vertical aperture optimization for obtaining circularly polarized bend-magnet radiation
Authors: Kortright J.B. , Rice M. , Hussain Z. , Padmore H.A. , Adamson A. , Huff W.R.A. , Young A.T. , Moler E.J. , Kellar S.A. , Ynzunza R.X. , Palomares F.J. , Daimon H. , Tober E.D. , Fadley C.S.
Published: July 2002

Using multilayer linear polarizers, we have characterized the polarization state of radiation from bend-magnet beamline 9.3.2 at the Advanced Light Source as a function of vertical opening angle at photon energies of 367 and 722 eV. Both a fine slit and a coarse semi-aperture were stepped across the beam to accept different portions of the vertical radiation fan. Polarimetry yields the degree of linear polarization directly and the degree of circular polarization indirectly assuming an immeasurably small amount of unpolarized radiation based on the close agreement of the theoretical and experimental results for linear polarization. The results are in good agreement with theoretical calculations, with departures from theory resulting from uncertainty in the effective aperture of the measured beam. The narrow 0.037-mrad aperture on the orbit plane transmits a beam whose degree of linear polarization exceeds 0.99 at these energies. The wide semi-aperture blocking the beam from above and below transmits a beam with a maximum figure of merit, given by the square root of flux times the degree of circular polarization, when the aperture edge is on the orbit plane thus blocking only half of the total available flux.
BESSY Bragg-Fresnel multilayer beam monitors
Authors: Holldack K. , Erko A. , Peatman W.B.
Published: July 2002

X-ray optical systems based on Bragg-Fresnel multilayer components imaging an electron beam in a storage ring with μm resolution are presented. Design concepts are compared to alternative methods, and the aberrations and limits of Bragg-Fresnel multilayer optics are discussed. Experimental results of imaging the BESSY I source with sub-10-μm resolution are presented, and the development of a compact Bragg-Fresnel multilayer telescope as a BESSY II standard beam monitor is described.
Monte Carlo simulations of the vacuum performance of differential pumps at the Advanced Photon Source
Authors: Liu C. , Shu D. , Kuzay T. M. , Kersevan R.
Published: July 2002

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.
Fiber scintillator/streak camera detector for burn history measurement in inertial confinement fusion experiment
Authors: Miyanaga N. , Ohba N. , Fujimoto K.
Published: July 2002

To measure the burn history in an inertial confinement fusion experiment, we have developed a new neutron detector based on plastic scintillation fibers. Twenty-five fiber scintillators were arranged in a geometry compensation configuration by which the time-of-flight difference of the neutrons is compensated by the transit time difference of light passing through the fibers. Each fiber scintillator is spliced individually to an ultraviolet optical fiber that is coupled to a streak camera. We have demonstrated a significant improvement of sensitivity compared with the usual bulk scintillator coupled to a bundle of the same ultraviolet fibers.
Streaked laser shadowgraphy of tungsten wire array implosions on the Saturn generator
Authors: Deeney C. , McGurn J. , Noack D. , Porter J. L. , Spielman R. B. , Seamen J. F. , Jobe D. O. , Vargas M. F. , Gilliland T. , Douglas M. R. , Matzen M. K.
Published: July 2002

A combination of a 400 ns, 300 mJ, 640 nm dye laser, and an optical streak camera have been used to demonstrate that time-resolved shadowgrams can be made of the implosion phase of tungsten wire arrays. Initial experiments have shown that mirror lifetime and spatial resolution are issues for this diagnostic technique. Nonetheless, these experiments have provided new information on wire array dynamics; specifically, they show that even with a 0.46 mm wire spacing, the high density regions formed by the wires, are separate until 30 ns into the main drive current. Peak currents of 6.6 MA were obtained 40 ns after the start of the current, while peak radiated powers of 85 TW were measured at 50 ns.
New high luminosity “double toroidal” electron spectrometer
Authors: Miron C. , Simon M. , Leclercq N. , Morin P.
Published: July 2002

In this article we describe the design and the operation of an original, high transmission, electrostatic “double toroidal” electron energy analyzer. The double toroidal analyzer allows the high resolution and high luminosity simultaneous measurement of the kinetic energy, and angular distribution of electrons, using a two-dimensional position sensitive detector. The exact shape of the electrodes is deduced from both analytical and numerical electron trajectory calculations. The electron detector is based on a charge analysis and optimized to attain a 100 kHz counting rate. The actual performances of the analyzer are illustrated with spectra obtained after resonant Auger decay of N2O excited around the nitrogen K shell (hν=401 eV), and of Kr after 3d5/2→5p excitation at hν=91.2 eV. A “étendue” of 15% of the pass energy, as well as a resolving power (Ep/δE) of 100were measured.
Scanning tunneling microscope with continuous flow cryostat sample cooling
Authors: Behler Stefan , Rose Mark K. , Dunphy James C. , Ogletree D. Frank , Salmeron Miquel , Chapelier Claude
Published: July 2002

We have constructed an ultrahigh vacuum scanning tunneling microscope (STM) for operation in the temperature range 20–300 K. The design consists of a vibration isolated sample holder mounted on a continuous flow cryostat. By rotation and linear motion of the cryostat, the sample can be positioned in front of various surface preparation and analysis instruments contained in a single vacuum chamber. A lightweight beetle-type STM head is lowered from the top onto the sample by a linear manipulator. To minimize helium convection in the cryostat, the entire vacuum system, including a liquid helium storage Dewar, can be tilted by a few degrees perpendicular to the cryostat axis, which improves the operation. The performance of the instrument is demonstrated by atomically resolved images of the Pd(111) surface and adsorbed CO molecules.
Laser ion source for heavy ion synchrotrons (invited)
Authors: Sharkov B. Yu. , Kondrashev S. , Roudskoy I. , Savin S. , Shumshurov A. , Haseroth H. , Kugler H. , Langbein K. , Lisi N. , Magnusson H. , Scrivens R. , Schnuringer J. C. , Tambini J. , Homenko S. , Makarov K. , Roerich V. , Stepanov A. , Satov Yu.
Published: July 2002

A status overview of the development of laser ion sources suited to heavy ion synchrotrons is presented. The results of experimental and theoretical studies, recently obtained at a number of laboratories, for laser-produced highly charged heavy ions are summarized for plasmas heated by long wavelength lasers. Design of a powerful repetition rate CO2 laser, target interaction chamber, and extraction system suited for reliable long term operation mode with real accelerators is discussed. Requirements for the final performance of the laser ion sources for ion beam injectors at the ITEP-Moscow and CERN accelerator facilities are given.
Optical transduction chain for gravitational wave bar detectors
Authors: Conti L. , Cerdonio M. , Taffarello L. , Zendri J. P. , Ortolan A. , Rizzo C. , Ruoso G. , Prodi G. A. , Vitale S. , Cantatore G. , Zavattini E.
Published: July 2002

A new signal extraction chain for gravitational wave bar detectors is proposed. Signal transduction is made by means of a Fabry–Perot cavity. Using a reference cavity for frequency comparison a sensitivity of hmin=3×10−20 with a bandwidth of about 50 Hz is estimated for an ultracryogenic bar detector. The first prototype implementation as well as room-temperature measurements on it are reported.
A novel low profile atomic force microscope compatible with optical microscopes
Authors: Nakano Katsushi
Published: July 2002

A novel low profile atomic force microscope (AFM) compatible with conventional optical microscopes has been developed. This AFM can be fitted with two types of scanners for varying applications. For small area scanning, three stacked lead zirconite titanate (PZT) actuators are employed: a short-stacked PZT which moves the AFM cantilever vertically and two long-stacked PZTs which move the cantilever horizontally. For wide area scanning, flexures are used to enlarge the scan area horizontally. To measure cantilever deflection by the optical level method, mirrors are attached to the actuators enabling the laser beam to track the cantilever's movement. Each scanner has a total height of 13 mm, and can comfortably fit between a sample and a 50× objective lens in an upright optical microscope, or fit between a sample and a condenser lens in an inverted optical microscope. The range of the small area scanner is 16×16×4 μm while that of the wide area scanner is 100×100×4 μm. This low profile AFM achieved a noise performance of 0.6 Å rms. According to experimental results and finite element method simulations, the performances of the low profile scanners were comparable with that of conventional tube scanners.
Bragg–Fresnel optics for hard x-ray microscopy: Development of fabrication process and x-ray characterization at the Advanced Photon Source
Authors: Li Youli , Wong Gerard C. L. , Safinya Cyrus R. , Caine Ernie , Hu Evelyn L. , Haeffner Dean , Fernandez Patricia , Yun Wenbing
Published: July 2002

Results are presented on development of processes for fabricating linear and circular Bragg–Fresnel lenses (BFLs) on Si and III–V compound material substrates, and on x-ray characterization of linear BFLs at the Advanced Photon Source (APS). Processes were developed for fabricating long (zone length >5 mm) linear BFLs on Si with enhanced capability for focusing high-energy x rays. By stitching together 20 sequentially exposed 400-μm-long linear BFLs, we were able to fabricate 8-mm-long linear BFLs with 0.5-μm finest zone width. BFLs were also fabricated on III–V compound semiconductor substrates GaAs and InP, with improved process control due to the substantially reduced zone thickness required (∼50% less than Si). Reduction of the zone aspect ratio (thickness/width) lessens the demand on the process technology, and may lead to higher lens resolution and pattern transfer accuracy. A process was explored to fabricate BFLs on a GaAs/AlGaAs heterostructure incorporating a built-in “etch stop” layer to ensure uniform zone thickness. Experimental characterization of the focusing properties of a field-stitched 8-mm-long linear BFL on Si (zone aperture=150 μm) was conducted at APS undulator beamline 1-ID-C using 10-keV x rays. Based on measured focal plane intensity distribution, the focus was estimated to be 1.2 μm, comparable to the geometrically demagnified source size of ∼1 μm. Lens efficiency was estimated to be ∼30%. Work is underway to incorporate the BFL-microprobe in x-ray microdiffraction and fluorescence microscopy experiments to study spatially confined complex materials.
A white-light Michelson interferometer in the visible and near infrared regions
Authors: Fuji Takao , Arakawa Mariko , Hattori Toshiaki , Nakatsuka Hiroki
Published: July 2002

A white-light Michelson interferometer in the visible and near infrared regions is described which can obtain the cross-correlation interferogram between the incident light and the transmitted light through samples or optical components. By comparing the autocorrelation interferogram of the incident white light with the cross-correlation interferogram between the incident light and the transmitted light, we can obtain linear response functions of samples or optical components with femtosecond time resolution. Fourier analysis of the interferograms gives also the complex optical constants of the samples without relying on the Kramers–Kronig relation.
Saturation of multiplication mechanism in silicon avalanche photodiodes used for single electron detection
Authors: Osakabe Nobuyuki , Endo Junji , Tonomura Akira , Urakami Tsuneyuki , Ohsuka Shinji , Tsuchiya Hiroshi , Tsuchiya Yutaka , Kodama Tetsuji
Published: July 2002

We have examined the multiplication factor of silicon avalanche photodiodes designed for fast timing detection of monoenergetic electrons. The multiplication mechanism was found to be saturated. The highly concentrated space charge generated by a primary electron causes the saturation. This was confirmed by a Monte Carlo simulation of electron trajectories in silicon and an experiment exploiting a subpicosecond laser pulse with a variable illuminating spot size to simulate an electron bombardment.
A “shunt” Fabry–Perot resonator for high-frequency electron spin resonance utilizing a variable coupling scheme
Authors: Barnes Jeff P. , Freed Jack H.
Published: July 2002

We report on the performance of a Fabry–Perot resonator for far-infrared electron spin resonance (FIR-ESR) at 250 GHz designed to accommodate a thin, disk-shaped sample that must rest with its flat surface perpendicular to the incident FIR beam. This geometry minimizes dielectric losses, making it possible to obtain FIR-ESR spectra of aqueous or lossy samples with a macroscopic ordering, at canonical values of the director tilt of 0° and 90°. The resonator also utilizes an adjustable interferometer to achieve variable coupling in the FIR regime.
An in-situ hot stage for temperature-dependent tapping-mode™ atomic force microscopy
Authors: Prilliman S. G. , Kavanagh A. M. , Scher E. C. , Robertson S. T. , Hwang K. S. , Colvin V. L.
Published: July 2002

Tapping-mode atomic force microscopy (TM-AFM) is a widely used method for the study of the nanometer scale morphology of soft materials such as biological samples and polymers. Many of these materials have structures and properties which are a sensitive function of temperature even below 100 °C making the control of temperature in such an instrument quite valuable. This paper describes the construction of a heater for a commercial TM-AFM which can reach surface temperatures as high as 100 °C. Temperature variations affect many experimental parameters in an atomic force microscope, and to compare images collected at different temperatures it is critical to evaluate these instrumental effects. In particular, the cantilever resonance frequency decreases as samples become hot; this effect is easily corrected by frequently resetting the drive frequency at high temperatures. As an example of the utility of this technique images of the nanoscale changes that occur prior to the bulk melting of paraffin crystals are presented.
Tritium concentration measurements in the Joint European Torus divertor by optical spectroscopy of a Penning discharge
Authors: Hillis D. L. , Morgan P. D. , Ehrenberg J. K. , Groth M. , Stamp M. F. , von Hellermann M. , Kumar V.
Published: July 2002

Obtaining precision measurements of the relative concentrations of hydrogen, deuterium, tritium, and helium in the divertor of a tokamak is an important task for nuclear fusion research. Control of the deuterium–tritium isotopic ratio while limiting the helium ash content in a fusion plasma are key factors for optimizing the fuel burn in a fusion reactor, like the International Tokamak Experimental Reactor. A diagnostic technique has been developed to measure the deuterium–tritium isotopic ratio in the divertor of the Joint European Torus with a species-selective Penning vacuum gauge. The Penning discharge provides a source of electrons to excite the neutral hydrogen isotopes in the pumping duct. Subsequently, the visible light from the hydrogen isotopes is collected in an optical fiber bundle, transferred away from the tokamak into a low radiation background area, and analyzed in a high resolution Czerny–Turner spectrometer, which is equipped with a fast charge coupled device camera for optical detection. The intensity of the observed line emission (Dα−6561.03 Å and Tα−6560.44 Å) is directly proportional to the partial pressure of each gas found in the divertor. The line intensity of each isotope is calibrated as a function of pressure. The ratio of the line intensities thus provides a direct measurement of the deuterium–tritium isotopic ratio. The lower limit for the determination of the deuterium–tritium isotopic ratio is about 0.5%. The applicable pressure range for this system is from 10−5 to a few times 10−3 mbar.
Vacuum ultraviolet, extreme ultraviolet, and x-ray line intensity normalization technique applied to tokamak plasmas
Authors: Peacock N. J. , Lawson K. D. , Barnsley R. , Chen H.
Published: July 2002

An empirical procedure, “LINT,” for relating emission line intensities of intrinsic impurity ions to their elemental contributions to the total, bolometric, radiation loss and the volume-averaged effective ion charge, Zeff, has been developed and applied to limiter plasmas in the JET tokamak. In this article we discuss extensions to the data base to include x-ray lines and continua intensities, applicable to a wider range of tokamak plasma configurations such as X-point plasmas and quasi-steady-state, edge-cooled ELMy H modes. Examples are shown of the technique applied to reference discharges during which the plasma configuration is changed continuously. The total data set, comprising line and continua irradiances, tomographic bolometry, and x-ray emission and Zeff imposes constraints on the diffusion parameters used in models of impurity ion transport.
On the transparency of foam in low-density foam Z-pinch experiments
Authors: MacFarlane J. J. , Derzon M. S. , Nash T. J. , Chandler G. A. , Peterson D. L.
Published: July 2002

Z-pinch experiments have been performed on the SATURN and Z machines at Sandia National Laboratories to study physics issues related to x-ray radiation generation and inertial confinement fusion. Some of these experiments utilize a CH foam located on-axis to convert energy to radiation and act as a radiative transfer volume. A significant issue for foam Z-pinch experiments is the transparency of the heated foam as a function of time and wavelength. Foam transparency will be important in future foam Z-pinch experiments both because it influences the time-dependent radiation field seen by an inertial confinement fusion capsule embedded in the foam, and because it is an important factor in making high-resolution spectral measurements of a capsule or tracers embedded in the foam. In this article, we describe results from simulations and experiments which address the issue of foam transparency. We discuss imaging data from one Z experiment in which x-ray emission from a half-Au/half-CH disk located at the bottom of a 1-cm-tall, 14 mg/cc TPX foam is observed. Simulation results predicting CH foam optical depths as a function of plasma conditions are presented. In addition, we present results from spectral calculations which utilize 2D magnetohydrodynamic (MHD) simulation predictions for the time-dependent foam conditions. Our results indicate that the observed x-ray framing camera images are consistent with early-time (several ns prior to stagnation) foam electron temperatures of ≳30 eV, which is somewhat hotter than the foam electron temperatures predicted from the 2D MHD simulations at early times.
In situ x-ray diffraction study of the role of annealing ambient in epitaxial CoSi2 growth from Co/Ti bilayers on Si(001)
Authors: Selinder T. I. , Miller D. J. , Gray K. E.
Published: July 2002

The reactions during annealing of a Co/Ti bilayer structure on Si(001) were studied in situ to reveal the roles of the Ti interlayer and the annealing ambient on the formation of epitaxial CoSi2. We shown that an oxygen contaminant in the nitrogen annealing gas is needed to form a stable, Co–Ti–O (spinel) membrane at the metal/Si interface that limits diffusion and is crucial for the perfection of epitaxial CoSi2. Annealing in vacuum or otherwise inert environments led to polycrystalline CoSi2 films and no spinel phase.
Grazing-incidence measurements of L-shell line emission from highly charged Fe in the soft x-ray region
Authors: Utter S. B. , Brown G. V. , Beiersdorfer P. , Clothiaux E. J. , Podder N. K.
Published: July 2002

Line emission from highly charged ions in the soft x-ray region represents an important diagnostic for high-temperature plasmas. The wavelength region of 10–30 Å is occupied by lines from the K-shell transitions in N through Ne and L-shell transitions in Ti through Ni. Crystal spectrometers have previously been used to investigate Fe line radiation under well controlled conditions using the LLNL electron beam ion trap facility in this wavelength region. To complement this work we have instituted a grazing-incidence spectrometer with a variable line-spaced, concave grating and a flat field of focus which is suited for a multichannel detector. Simultaneous observations of the Ne-like Fe16+ n=3→2 transitions were made with this instrument and a flat-crystal spectrometer in order to establish the linear polarization of the Fe XVII lines. We present a description of the grating spectrometer and discuss its performance in comparison with Rowland circle based grazing incidence instruments.
Time-autocorrelated two-photon counting technique for time-resolved fluorescence measurements
Authors: Borst Walter L. , Liu Lin-I
Published: July 2002

We describe a new instrumental technique for the excitation, acquisition, and analysis of fluorescence decays from a variety of substances, in the present case plastic scintillators. The fluorescence is excited by β particles from a radioactive source (100 μCi Sr-90). A random photon from the resulting fluorescence decay provides a trigger pulse to start a time-to-amplitude converter (TAC), while another random photon from the same β-excitation event provides the stop pulse. The optical components and geometry for detecting these two photons, i.e., the two photomultipliers (PMT), the filters, and the pulse counting system, are identical. As a consequence, the measured fluorescence signal is the autocorrelation function of the fluorescence decay from the sample. A delay line of 50 ns is inserted between the “stop” signal PMT and the TAC so that those “stop” pulses which arrive before “start pulses” also are recorded. Thus the acquired fluorescence signal versus time is symmetric about the delay time and contains twice as many counts as without delay. We call the new technique the “time-autocorrelated two-photon counting technique” (TATPC) in distinction to the conventional “time-correlated single-photon counting technique” (TCSPC). We compared both techniques with the same equipment and scintillators, where in the TCSPC case, a β particle is used for the start of the TAC instead of a random photon in the TATPC technique. We find that under similar experimental circumstances, the signal count rate with TATPC is about 50 times larger than with TCSPC. The new method is well suited for obtaining fluorescence decay times from plastic scintillators, which we use in this article to exemplify the technique. More generally, β-particle excitation in combination with TATPC should prove useful for materials with high energy levels or band gaps, which cannot be excited with pulsed lasers in the visible region. The length of our excitation pulse is less than 20 ps and is negligible compared to the temporal response of about 1 ns of the rest of the apparatus. By employing mathematical deconvolution, we are able to measure fluorescence decays from the subnanosecond range and to longer times.
Acceleration of large size deuterium pellets to high speeds using a small two-stage pneumatic gun
Authors: Frattolillo A. , Migliori S. , Angelone G. , Capobianchi M. , Dommo C. , Ronci G. , Griffin D. K.
Published: July 2002

The technology of two-stage pneumatic pellet injectors represents by far the most reliable way to perform deep plasma fueling, with pipe gun devices capable of routinely launching small or medium size (up to 4 mm) D2 pellets at speeds in excess of 3 km/s, using rather small two-stage guns. It is still an open question, however, if scaling of the pellet size to the International Thermonuclear Experimental Reactor relevant values (6–8 mm) will or will not require a somewhat proportional increase in the physical size of the two-stage gun. In order to investigate this question, an extensive study was carried out at ENEA Frascati, using numerical simulation codes. It clearly indicated that a “compact” two-stage gun may have the potential to accelerate large size pellets at speeds up to 5 km/s. A low cost experiment was also scheduled. A spare pipe-gun cryostat of the single-shot two-stage pneumatic injector, previously used for high-speed pellet fueling of the Frascati tokamak upgrade, was modified in order to accommodate larger bore (up to 6 mm) launching barrels. In this article, we will mainly discuss the results of numerical simulations. A very early experimental campaign, carried out in 1996, will also be briefly reported, during which intact 6 mm D2 pellets were launched at speeds up to 2.5 km/s.
A solution flow system for hydrothermal–electrochemical growth of multilayered thin films
Authors: Suchanek Wojciech L. , Watanabe Tomoaki , Sakurai Bungo , Kumagai Naoki , Yoshimura Masahiro
Published: July 2002

A solution flow system equipment for hydrothermal–electrochemical synthesis of advanced thin films has been designed, constructed, and successfully tested. The synthesis using recyclable (aqueous) solutions as precursors can be carried out up to temperature of 200 °C and pressure of 50 kg cm−2 utilizing electrochemical activation of the nucleation and growth processes. Any clear solution can be used as a precursor; there are almost no limitations of the substrates used. The equipment is easy to use, versatile, and inexpensive. Applicability of the solution flow system for synthesis of advanced materials has been demonstrated using single-layer and multilayer BaTiO3–SrTiO3 thin films. Our equipment allows control of the microstructure of the films in a nanometric scale by changing the preparation conditions, for example the growth rate can be increased by increasing the flow rate. In addition, the multilayered films can be prepared in only one experiment just by changing the kind of flowing solution. The technique using the solution flow under the hydrothermal–electrochemical conditions is an important step in integration of the solution processing with the advanced device technology.
A 200 GHz near field measurement system
Authors: Yang S. C. , Chin C. C. , Hu Robert , Shen S. S.
Published: July 2002

We have designed a near field measurement system operating at 200 GHz which has a dynamic range of 60 dB. The system has a short term and long term phase variation less than 0.5° and 2°, respectively. On averaging 128 times at each measurement point by using the averaging function of the network anaylzer, the short term phase variation decreases to less than 0.2°. The phase variation mentioned above is observed with the testing probe pointing to the center of the antenna under test. The contours of the near field obtained shows that the field is highly circular as expected from the theoretical predication. We have shown that the system can distinguish the quality of the corrugated feed horn by near field measurement.
Performance of new infrared beamline U12IR at the National Synchrotron Light Source
Authors: Lobo R. P. S. M. , LaVeigne J. D. , Reitze D. H. , Tanner D. B. , Carr G. L.
Published: July 2002

The instrumentation and performance of the new infrared beamline U12IR at the National Synchrotron Light Source of Brookhaven National Laboratory is described. This beamline utilizes infrared synchrotron radiation from a bending magnet. A combination of beamline design features and spectroscopic instrumentation allows the facility to reach the extremely low frequency limit of ∼2 cm−1 (i.e., 60 GHz or a photon energy of 250 μeV). The infrared light from the synchrotron emission at U12IR is compared to standard thermal sources and reveals substantial benefits for the study of small samples. In particular, the intensity of the synchrotron radiation in the far infrared can be as much as 200 times greater than that from a blackbody when millimeter-sized samples are measured. The effects of diffraction and noise on beamline performance are also discussed.
New apparatus with double supersonic molecular beams for epitaxial growth and surface reaction studies
Authors: Ohashi M. , Ozeki M. , Cui J.
Published: July 2002

To understand surface reaction dynamics in III–V compound semiconductor growth, we have developed an apparatus to study both surface chemical reactions and epitaxial growth. This apparatus has double supersonic III and V compound molecular beam cells and an analytical chamber with a rotatable differentially pumped liquid-nitrogen-cooled quadrupole mass spectrometer to measure angular and time-of-flight distribution of reflected beams. It also has reflection high-energy electron diffraction to analyze surface structures. Tertiarybutylarsine beam energies of 1.6 eV were obtained for He, 0.22 eV for Ar, and 0.06 eV for Xe seeding. An organometallic molecular beam of translational energy is varied over a wide range, enabling source molecules to be brought to a well-defined epitaxial surface in well-characterized ways. High-purity GaAs layers were grown by alternatively supplying triethylgallium and tertiarybutylarsine molecules to the analytical chamber. Our apparatus bridges the gap of studies between epitaxial growth and surface chemical reactions. Dynamic measurement on the growth surface revealed a number of interesting reactions not ordinarily observed on well-defined surfaces.
Electrostatic force-feedback force sensor incorporated in an ultrahigh vacuum force microscope
Authors: Yakimov V. , Erlandsson R.
Published: July 2002

A force sensor based on a fiber-optic interferometric displacement transducer incorporated in an ultrahigh vacuum atomic force microscope is described. The operation of the sensor is based on balancing the tip-sample interfacial force using an electrostatic actuator. The electrodes of the actuator are formed by the grounded W cantilever and the metallized end facet of the optical fiber used by the interferometer. Chemical reduction of Ag by a wet chemical method is used for metal coating of the fiber end. A special masking procedure is used to obtain a window hole in the metal coating at the position of the fiber core to allow for optical beam output. Using a window instead of a semitransparent metal film allows us to save the low-finesse characteristics of the interferometer which facilitates the calibration of cantilever displacement. The performance of the sensor is discussed and exemplified by experimental results from force-separation measurements on the W–Au system in ultrahigh vacuum.
Feasibility tests of transmission x-ray photoelectron emission microscopy of wet samples
Authors: De Stasio Gelsomina , Gilbert B. , Nelson T. , Hansen R. , Wallace J. , Mercanti D. , Capozi M. , Baudat P. A. , Perfetti P. , Margaritondo G. , Tonner B. P.
Published: July 2002

We performed feasibility tests of photoelectron emission spectromicroscopy of wet samples in the water window (285–532 eV) soft x-ray spectral region. Water was successfully confined in an ultrahigh vacuum compatible compartment with x-ray transparent sides. This water cell was placed in the MEPHISTO spectromicroscope in a transmission geometry, and complete x-ray absorption spectra of the water window region were acquired. We also show micrographs of test samples, mounted outside of the compartment, and imaged through the water. This technique can be used to study liquid chemistry and, at least to the micron level, the microstructure of wet samples. Possibilities include cells in water or buffer, proteins in solution, oils of tribological interest, liquid crystals, and other samples not presently accessible to the powerful x-ray photoelectron emission spectromicroscopy technique.
Study of a fast ablative capillary discharge dedicated to soft x-ray production
Authors: Hong D. , Dussart R. , Cachoncinlle C. , Rosenfeld W. , Götze S. , Pons J. , Viladrosa R. , Fleurier C. , Pouvesle J.-M.
Published: July 2002

A capillary discharge has been developed to produce pulses of intense soft x-ray radiation of tens of nanoseconds duration. The soft x-ray photons were emitted in a plasma column resulting from polyethylene in capillary wall ablation. The spectrum was dominated by the C IV, C V, and C VI emission lines in the soft x-ray spectral range. The experimental value of the electrical circuit inductance has been measured and compared to the calculated one. The electron temperature was estimated to be higher than 50 eV from the plasma resistivity measurement. The time dependence of the electron density outside the capillary channel has been determined using spectroscopic measurement in the visible range. The time dependence of the electron temperature has been determined from the intensity ratio of C V and C VI emission lines, using a collisional radiative equilibrium code.
Visible light scattering to measure small scale turbulence
Authors: Antar G.
Published: July 2002

A laser scattering optical bench using ionized argon laser was set up to study the small scales of turbulence. Scales between 200 and 10 μm are resolved. The signal being proportional to the Fourier transform of the density fluctuations, heterodyne detection is used to recover its real and imaginary parts. The optical and electronic facilities are described in detail. The minimum density fluctuations for a signal-to-noise ratio greater than 1 is assessed. Using an acoustic wave, the spatial bandpass filter of the Fourier transform is demonstrated. A sample of recorded signals on a turbulent air jet is shown and the dependence of their intensity on the analyzing wave vector is discussed. The frequency spectra are shown to reflect the temperature and the pressure fluctuations. One can thus measure the flow and sound speed.