bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron diffraction investigation of pulsed supersonic jets
Authors: Bartell Lawrence S. , French Richard J.
Published: July 2002

A pulsed nozzle source has been developed for electron diffraction studies of molecular clusters. Disturbances of the electron beam by the field actuating the pulser have been reduced to a negligible magnitude by introducing magnetic shielding and by carefully timing the electron shutter. Advantages of pulsed operation in diffraction experiments with a Laval nozzle source are considerable. In the Michigan unit stagnation pressures can be increased by an order of magnitude, and pumping requirements are greatly reduced. Moreover, cleaner diffraction patterns can be obtained because exposures can be adjusted to probe a freshly developed jet before gas scattered from the walls can reach the region of sampling. Timing works so effectively that good diffraction patterns can be recorded even when the skimmer isolating the diffraction chamber from the nozzle chamber is removed. Indeed, patterns from unskimmed jets can be particularly informative when cluster beams are composed of mixed structural forms. An unorthodox ‘‘vee’’ skimmer has proven to be useful for examining narrow regions in a jet. Moreover, the vee skimmer makes it possible to measure the diffraction geometry much more precisely than has been the case with conventional skimming configurations. Pulsed operation also facilitates an accurate characterization of the density and velocity distributions in the supersonic jet. The principal design features of a pulsed apparatus are presented together with characteristic results.
Versatile apparatus for electron impact ionization experiments at high energies (500 keV)
Authors: Ruoff H. , Schüle E. , Bonfert J. , Graf H. , Nakel W.
Published: July 2002

A new high-energy (500 keV) electron–electron coincidence apparatus is described making possible for the first time triply differential cross-section measurements of inner-shell ionization of atoms of a high atomic number. Moreover, the apparatus has also been designed to deliver doubly differential ionization cross sections of the individual shells by using electron–x-ray coincidences as well as noncoincident low background spectra of inelastically scattered electrons. A special feature of the apparatus is the use of electron spectrum analyzers consisting of a nondispersive magnet and a surface barrier detector. Magnetic electron spectrum analyzers consisting of a sector field magnet and a scintillation detector have been built up. Selected measurements on tantalum (Z=73), silver (Z=47), and aluminum (Z=13) target foils are presented.
Synchrotron radiation apparatus for supersonic jet experiments
Authors: Kimura Katsumi , Achiba Yohji , Shiromaru Haruo
Published: July 2002

In this article, we report the layout of our VUV beamline including a VUV monochromator and a molecular-beam photoionization apparatus. This experimental system has recently been completed at a UVSOR Facility of this Institute for studying van der Waals complexes produced by supersonic expansion. Several experimental results are also presented to show the characteristics of the apparatus.
Characterization of sliced multilayer zone plates for hard x rays (invited)
Authors: Saitoh Kazuya , Inagawa Konosuke , Kohra Kazutake , Hayashi Chikara , Iida Atsuo , Kato Norio
Published: July 2002

Circular zone plates for hard x rays, fabricated by dc planar magnetron sputtering, have been characterized using monochromatized synchroton x rays. The zone plates consisted of either 5 or 20 pairs of altenating WSi2 and C layers. The minimum focal spot size attained was less than 3 μm× 10 μm in the vertical and horizontal directions, respectively. The efficiency of the zone plate with 20 layer pairs was determined to be about 4.5%. An x-ray transmission image of a No. 2000 mesh Cu grid and an x-ray fluorescence image of a patterned Co thin film were measured, and it was demonstrated that a high-resolution image could be obtained with the present zone plate. The possibility of implementing the phase zone plate in hard x-ray range is considered.
Parametric-mode-excitation/dipole-mode-detection Fourier-transform–ion-cyclotron-resonance spectrometry
Authors: Schweikhard L. , Lindinger M. , Kluge H.-J.
Published: July 2002

A new excitation/detection scheme for Fourier-transform–ion-cyclotron-resonance (FT-ICR) studies is described. The ions are created in the center of a hyperbolic Penning trap and excited to a large magnetron radius. Parametric-mode excitation is used to drive the cyclotron motion. The ions are detected in the conventional dipole-mode detection scheme by use of a segmented ring electrode. Since the resonance frequencies of excitation (ν+−ν−) and detection (ν+, the reduced cyclotron frequency) differ by the magnetron frequency (ν−), this method allows the simultaneous excitation and detection of the ion motion.
Line broadening of Ne-like xenon as a diagnostic for high-density implosion experiments
Authors: Keane C. J. , Lee R. W. , Hammel B. A. , Osterheld A. L. , Suter L. J. , Calisti A. , Khelfaoui F. , Stamm R. , Talin B.
Published: July 2002

The broadening of x-ray spectral lines has become an established diagnostic of Ne in high-density plasmas, particularly those of interest in inertial confinement fusion (ICF). Work to date has concentrated mostly on the broadening of K-shell lines in moderate Z (Z∼10–20) ions in plasmas with electron densities up to 1024 cm−3. In this paper we report on calculations of line broadening for Ne-like Xe (Xe44+) appropriate for diagnosis of higher density plasmas with Ne∼1025 cm−3. These calculations have been performed with a recently developed state of the art computer code which treats the ion and electron broadening in the quasi-static and impact approximations, respectively. In this paper, we summarize recent work examining the behavior of the width of the Ne-like Xe 3–2 and 4–2 transitions with electron density. The broadening of the 1s–3p line in H-like Ar and the 1s2–1s3p transition in He-like Ar is also studied in order to benchmark the code used in the calculations.
An electron diffraction apparatus for studies on small particles in a molecular beam
Authors: Hall B. D. , Flüeli M. , Reinhard D. , Borel J.-P. , Monot R.
Published: July 2002

An electron diffraction apparatus is described that has been designed specifically for use with molecular beams containing small particles in the nanometer size range. A novel electron detection system has been developed, using linear charge coupled device imagers, which allows rapid parallel measurement of the diffraction signal in a direct electron counting mode. The apparatus also features a 100 kV electron gun and electron optics derived from a Philips EM 300 electron microscope. Details of the apparatus are presented and measurement results on small silver particles in a beam of helium carrier gas are also given; these are interpreted using an icosahedral structure for the small particles.
An ultrasmall angle scattering instrument for the DORIS-III bypass
Authors: Gehrke R.
Published: July 2002

The layout of the optics for a new small angle x-ray scattering instrument at the DORIS-III wiggler beamline BW4 was investigated by means of ray tracing and finite element calculations. The absolute intensity distributions at different locations of the beamline, especially in the focal plane, have been computed. The first crystal of a double crystal monochromator is the optical element that is most strongly influenced by thermal load. Thus, the distortion of this crystal surface due to thermal load was taken into account as well as the intended cooling system. The results show that the photon flux density at the focus is decreased by a factor of 0.2 due to this distortion.
Size dependence of band gaps in silicon nanostructures
Authors: Delley B. , Steigmeier E. F.
Published: July 2002

The size dependence of the energy band gap for hydrogen saturated silicon clusters, wires and slabs are calculated using all electron density functional theory. The hydrogen saturation is considered as a model for a wider band gap insulator enclosing the silicon structures. With this perspective in mind, an effective mass model with finite barriers for both valence and conduction band is found to semiquantatively account for the numerical findings.
The superconducting electron cyclotron resonance 6.4 GHz high-B mode and frequency scaling in electron cyclotron resonance ion sourcesa)
Authors: Antaya T. A. , Gammino S.
Published: July 2002

We would like to present the initial results and description of the superconducting electron cyclotron resonance ion source (SCECR) operating in the high-B mode—a new high magnetic field, low-frequency mode of operation. First, we describe the operating characteristics of this mode, which include very high mirror confinement in all directions, yet having a minimum field low enough for electron cyclotron resonance heating of 6.4 GHz. The source performance for oxygen, neon, argon, krypton, and xenon is presented and comparisons are made with several existing high-performance ECR sources. In this high-B mode the SCECR matches or exceeds the performance of all existing ECR sources. These results perhaps invalidate the classical frequency squared source performance scaling law, and suggest the new possibility of high-performance, low-frequency (and hence low cost) sources as will be discussed.
Fiber optic microbend sensor for detection of dynamic fluid pressure at gear interfaces
Authors: McCollum Tom , Spector Garry B.
Published: July 2002

An intensity-based microbend fiber optic pressure sensor has been developed and tested that is capable of detecting the dynamic fluid pressure between spinning gears. The microbend response of various fibers was measured in order to select the best fiber for the application and to determine the optimum deformer periodicity. The sensing fiber was embedded into the root of a modified gear, using a deformer method based on the compression of silicone rubber under pressure. Embedded gear sensors were calibrated under static pressure to 100 psi, yielding consistent results with different sensors. Gearbox tests demonstrated successful detection of dynamic fluid pressures at gear interfaces, and the ability to perform in a highly rugged environment.
Deuterium pellet injector for speeds up to 3400 m/s
Authors: Perin J. P. , Claudet G. , Disdier F.
Published: July 2002

The injection of pellets of frozen deuterium into magnetically confined, hot plasmas is one of the most attractive methods for refueling fusion power reactors. High injection speeds for solid deuterium pellets are necessary for improving the experimental analysis of pellet ablation in a hot plasma and the effects of the pellet on the plasma properties, in particular the confinement parameters. The optimization of a two-stage light gas gun is being pursued; the search for the cryogenic conditions of freezing deuterium with good mechanical properties is carried out. In particular, the impurities concentration in deuterium during the condensation process has been studied. These developments have allowed one to reach velocities up to 3400 m/s for integer bare deuterium pellets (3 or 4 mm in diameter, 1–3×1021 particles) with a reliability of 80%.
Ripple due to asymmetry in symmetrical Cockcroft–Walton cascade rectifier circuit
Authors: Zhang Haibo , Takaoka Akio
Published: July 2002

We experimentally examine the ripple and its spectra in the dc output of a symmetrical Cockcroft–Walton (CW) cascade rectifier circuit. Results show that the ripple due to the load consists of even harmonics and the ripple due to the circuit asymmetry consists of odd harmonics. In the latter, the ripple caused by the asymmetry of circuit elements cannot be compensated for completely through the asymmetry of the input voltage because of nonlinearity of a CW circuit. Approximately, the residual ripple is inversely proportional to the load resistance.
Electron field emission from diamond and other carbon materials after H2, O2, and Cs treatment
Authors: Geis M. W. , Twichell J. C. , Macaulay J. , Okano K.
Published: July 2002

This letter reports, diamond field emitters, Cs treated, air stable, that emit electrons at the lowest reported field, <0.2 V μm−1. Field emission from B-, Li-, P-, and N-doped diamonds and carbonized polymer was characterized as a function of surface treatment. A treated with an O2 plasma, coated with Cs, heated, and exposed to O2 exhibited increased emission for all samples except for B-doped diamond. The best emission was obtained from N-doped diamond samples, followed by carbonized polymer, the Li-doped, and polycrystalline P-doped diamond. Li- and N-doped samples treated with Cs were stable in laboratory air for several days. This stability of the surface-activated diamond is believed to be due to the formation of a diamond–O–Cs salt. If the sample is treated with a H2 plasma instead of an O2 plasma, the Cs-enhanced emission degrades with heat and exposure to O2. Subbands formed by Li and N impurities are believed to be responsible for this enhanced emission. The surface treatment on N-doped diamond results in emission at fields as low as 0.2 V μm−1.
High temperature metal atom beam sources
Authors: Ross K. J. , Sonntag B.
Published: July 2002

This paper presents a survey of the factors governing the performance and operation of high temperature subsupersonic metal atom beam sources. After an initial statement of the requirements placed on such sources a section is presented which considers the factors determining atomic beam intensities and profiles. The section which considers the materials used in source construction discusses the choice of crucible material, and in so doing presents a table of the most suitable materials, hazard assessments, and other information for all those elements which can be vaporized. Two further parts of this section are devoted to resistive heater materials and ceramics. The review of the sources is divided between resistively heated sources, sources heated by electron bombardment, and inductively heated sources. Finally there is a section which briefly discusses the monitoring of source performance.
β-NMR on single-crystal surfaces: Method
Authors: Widdra W. , Detje M. , Ebinger H.-D. , Jänsch H. J. , Preyss W. , Reich H. , Veith R. , Fick D. , Röckelein M. , Völk H.-G.
Published: July 2002

A new and highly sensitive β-NMR method to study adsorbates on single-crystal surfaces is presented. Contrary to conventional NMR, this method combines (via optical pumping) a high, nonthermal polarization of the adsorbed species with a particle counting method. Here, the β-active isotope 8Li is produced in the nuclear reaction D(7Li, 8Li)H using a high-pressure deuterium gas target. The fast 8Li ions are subsequently implanted into a hot graphite block where they thermally diffuse to the surface and desorb. The desorbing thermal velocity 8Li atoms are shaped into an atomic beam. Using a frequency modulated laser beam the atoms are transferred into a single hyperfine state by optical pumping. The so-achieved nuclear polarization of the atoms (before impinging on the single-crystal surface) is approximately 0.8 and can be switched in sign by an adiabatic high-frequency transition. The atoms adsorb on the single-crystal surface and their polarization—either freely decaying on the surface or driven by an external radio-frequency field—is observed via the decay asymmetry of the nuclear β-decay of the 8Li nuclei. This method realizes an effective sensitivity to the active NMR isotope of 5×103 atoms/cm2, which corresponds to a stationary coverage of 10−11 of a monolayer. The typical electron count rate is 400 Hz during β-NMR experiments.
Progresses of synchrotron radiation applications at the NSRL
Authors: Zhang Yunwu , Shi Chaoshu , Xu Pengshou , Xie Xingshu , Hu Yiguan , Zhang Xinyi
Published: July 2002

The Hefei light source has been open to users all over the country since April 1 of last year. Five beamlines and corresponding experimental stations are under operation at present. Synchrotron radiation research includes photoelectron spectroscopy, optical spectroscopy, photochemistry, soft x-ray microscopy, and x-ray lithography. One hundred and twenty proposals have been approved and about 40 of them carried out. We report some results in this paper.
Motional Stark effect upgrades on DIII-D
Authors: Rice B. W. , Nilson D. G. , Wróblewski D.
Published: July 2002

The measurement and control of the plasma current density profile (or q profile) is critical to the advanced tokamak program on DIII-D. A complete understanding of the stability and transport properties of advanced operating regimes requires detail poloidal field measurements over the entire plasma radius from the core to the edge. In support of this effort, we have recently completed an upgrade of the existing motional Stark effect (MSE) diagnostic, increasing the number of channels from 8 to 16. A new viewing geometry has been added to the outer edge of the plasma which improves the radial resolution in this region from 13 to ∼2 cm. This view requires the use of a reflector that has been designed to minimize polarization effects. Vacuum-compatible polarizers have also been added to the instrument for in situ calibration. Future use of the MSE diagnostic for feedback control of the q profile will also be discussed.
Contribution of neutral production to ion flux from a vacuum arc source
Authors: Humphries Stanley , Lockner Thomas R.
Published: July 2002

This article describes studies of the effect of electrode spacing on the performance of vacuum arc plasma sources for ion accelerators and other applications. We measured the time-resolved emission of neutrals from a compact arc source with a titanium cathode and 100 A drive current and found that the source emitted roughly 100 atoms for each extracted ion. The inferred neutral pressure in the arc gap was about 500 mTorr. The result suggested the possibility of achieving significant ionization in the plasma expansion region by increasing the anode–cathode gap length, thereby forcing the drive current to flow through the gas column. With a new two-stage trigger, we were able to ignite arcs with gaps as long as 20 cm. Extended gaps doubled the ion flux, gave better output directionality, and helped to stabilize the location of emission spots on the cathode. These improvements, coupled with direct observations of discharge luminosity, support the hypothesis of ionization of the expanding vapor.
Performance of Advanced Photon Source insertion devices at high photon energies (50–300 keV)
Authors: Shastri S. D. , Dejus R. J. , Haeffner D. R. , Lang J. C.
Published: July 2002

Since high-energy photons (≳50 keV) are well suited for certain types of x-ray scattering experiments, we present calculated results for the Advanced Photon Source (APS) Undulator A and APS Wiggler A at high energies. The undulator calculations include the effect of magnetic field errors, which is to smear the high-order spectral harmonics. At their anticipated initial minimum gap settings, Undulator A should perform better than Wiggler A from the point of view of most high energy experiments up to at least ∼280 keV. A comparison of APS insertion devices to high energy insertion devices in other synchrotron radiation laboratories is also provided.
Extended x-ray-absorption fine structure studies of levitated undercooled metallic melts
Authors: Jacobs G. , Egry I. , Maier K. , Platzek D. , Reske J. , Frahm R.
Published: July 2002

We report the first attempt to combine electromagnetic levitation with extended x-ray-absorption fine structure (EXAFS) spectroscopy for the determination of nearest-neighbor distances in the metastable state of an undercooled metallic melt. The experiments have shown that it is possible to measure EXAFS spectra for a freely suspended liquid droplet up to temperatures of 1390 °C. In particular, spectra at an undercooling of 325 °C were recorded. The spectra show certain differences between the overheated and the deeply undercooled regime. Modeling of the pair distribution function is required for correct interpretation, because asymmetric effects due to the large disorder in the hot liquid have to be considered.
Multipole and phase tuning methods for insertion devices
Authors: Gottschalk S.C. , Robinson K.E. , Quimby D.C. , Kangas K.W. , Vasserman I. , Dejus R. , Moog E.
Published: July 2002

Multipole and phase tuning of insertion devices is important for maintaining beam dynamics and reaching the high brightness goals of the Advanced Photon Source. Several general approaches are described: mechanical adjustments, end-pole shaping, and magnetic shimming. Off-axis Hall probe measurements after assembly guide magnet exchanges and local mechanical adjustments. A recent development has been the use of potential theory applied to end-pole shaping. The wide gap tuning range of the APS devices requires careful matching of device errors and correct gap dependencies in the gap/period range of 0.18 to 0.6. Shims are especially sensitive at small gaps. We describe signatures, gap dependencies, algorithms, modeling, and experimental results for these techniques.
New diamond-anvil cell design for far infrared magnetospectroscopy featuring in situ cryogenic pressure tuning
Authors: Chen R. J. , Weinstein B. A.
Published: July 2002

A novel diamond-anvil cell (DAC) adaptation for far infrared (FIR) cryogenic magnetospectroscopy in a small-bore magnet is reported. A design featuring a multibellows ram is employed to generate amplified force for in situ pressure tuning of the DAC at cryogenic temperatures without increasing the overall diameter of the apparatus. A constructed version, using a 26-mm-diam double-bellows ram, is capable of producing 5 kN force (scalable to 10 kN with four bellows) when driven by 4He at 4.2 K. Signals are enhanced using paraboloidal cones to focus the FIR radiation on the sample and collect the transmitted signal. It is feasible to record transmission spectra to energies as low as 80 cm−1 with this apparatus using appropriate gasket-hole sizes and detectors. The pressure, magnetic field, and temperature can be tuned independently in the ranges 0–20 GPa (in steps as small as 0.05 GPa), 0–15 T, and 2–300 K. We present high pressure (4.2 K) Fourier-transform FIR spectra at fixed magnetic fields, and laser (118.8 μm) magnetospectroscopy data on the 1s–2p+ transition of Si donors in GaAs measured with this apparatus.
Performance analysis of a novel monochromator design for the APS SRI-CAT beamline 2-ID-E
Authors: Wang Zhibi , Yun Wenbing , Kuzay Tuncer
Published: July 2002

Third-generation synchrotron x-ray facilities, such as the Advanced Photon Source, produce x-ray beams that generate a very high heat flux in a very small area. In order to preserve the brilliance of the source, optical components have to be designed to undergo very small thermal deformation (or a change of slope of a flat surface). When an optical component is subjected to a heat load, there will be thermal deformation caused by a temperature increase from the initial state. For a plate-like structure, the temperature difference over the thickness causes bending, and the average temperature increment causes axial deformation. For an optical element, the slope change due to bending is the main reason for the degradation of the performance of the optical component. The change of slope should be limited to a few microradians. There are many ways to control the thermal deformation, such as cryogenic cooling, inclined geometry, liquid-metal cooling, pin-posts or microchannels, using a high-heat-conductivity material, such as diamond, etc. In an accompanying conference paper, an adaptive design technique has been proposed to make use of a novel self-adapted smart structure. Its performance is essentially independent of the heat-load intensity. When such a device is exposed to a heat load, the flat surface remains flat in the area of interest. Therefore this technique can potentially be used to achieve a high precision optical component. Application of the proposed design technique to the monochromator for the SRI-CAT Sector 2 insertion device beamline (Sector 2-ID-E) is explained, and initial analytical results are presented on its performance.
TaSi2-Si composites as wide-bandpass optical elements for synchrotron radiation (abstract)
Authors: Stock Stuart R. , Neumann Hans-Bernd , Suessenback Joerg , Schneider Jochen R. , Rek Zofia U.
Published: July 2002

The wide matrix rocking curves of the in situ eutectic composite TaSi2-Si make it attractive as a wide-bandpass monochromator for synchrotron radiation. Wafers with Si[111], Si[110], or Si[100] orientation were studied to determine the origin of the wide rocking curves. The high degree of preferred orientation of the TaSi2 rods relative to the Si matrix was examined using synchrotron Laue patterns and the TaSi2 [100], TaSi2 [003], and TaSi2 [102] reflections. Double and triple axis diffractometry were used to show that the large widths were due to strain and mosaic and not long-range bending; copper radiation (for some double axis results) and 120 and 160 keV synchrotron radiation were used. At 8 keV, rocking curve widths were about twenty times broader than those from perfect Si, and peak reflectivities approached 20%. Rocking curves from Si[333] and Si[444] (120 and 160 keV, respectively) had identical profiles and reflectivities of about 25%. The triple axis results show compressive strains in the Si matrix along Si[111] (i.e., parallel to the rods) and dilational strains orthogonal to the rods. These results confirm the promise of TaSi2-Si as a wide-bandpass optical element for synchrotron radiation.
Progress in multielement silicon detectors for synchrotron XRF applications (abstract)
Authors: Rossington Carolyn S. , Ludewigt Bernhard , Kipnis Issy , Ivy Sharonda , Krieger Bradley
Published: July 2002

Multielement silicon strip detectors, in conjunction with integrated circuit pulse-processing electronics, offer an attractive alternative to conventional lithium-drifted silicon and high purity germanium detectors for high count rate, low noise synchrotron x-ray fluorescence applications. We have been developing these types of detectors specifically for low noise synchrotron applications, such as extended x-ray absorption fine structure spectroscopy, microprobe x-ray fluorescence and total reflection x-ray fluorescence. The current version of the 192-element detector and integrated circuit preamplifier, cooled to −25 °C with a single-stage thermoelectric cooler, achieves an energy resolution of <200 eV FWHM (at 5.9 keV, 2 microseconds peaking time), and each detector element is designed to handle a ∼20 kHz count rate. The detector system will soon be completed to 64 channels using new IC amplifier chips, CAMAC ADCs, CAMAC histogramming modules, and Macintosh-based data acquisition software. We will report on the characteristics of this detector system, the characteristics of the next generation system (192 channels with IC ADCs), and the use of these detector systems in synchrotron XRF applications.
Contact heat conductance at a diamond-OFHC copper interface with GaIn eutectic as a heat transfer medium
Authors: Assoufid L. , Khounsary A.M.
Published: July 2002

The results of an experimental study of the contact heat conductance across a single diamond crystal interface with OFHC copper (Cu) are reported. Gallium-indium (GaIn) eutectic was used as an interstitial material. Contact conductance data are important in the design and the prediction of the performance of x-ray optics under high-heat-load conditions. Two sets of experiments were carried out. In one, the copper surface in contact with diamond was polished and then electroless plated with 1 μm of nickel, while in the other, the copper contact surface was left as machined. The measured average interface heat conductances are 44.7±8 W/cm2-K for nonplated copper and 23.0±8 W/cm2-K for nickel-plated copper. For reference, the thermal contact conductances at a copper-copper interface (without diamond) were also measured, and the results are reported. A typical diamond monochromator, 0.2 mm thick, will absorb about 44 W under a standard undulator beam at the Advanced Photon Source. The measured conductance for nickel-plated copper suggests that the temperature drop across the interface of diamond and nickel-plated copper, with a 20 mm 2 contact area, will be about 10°C. Therefore temperature rises are rather modest, and the accuracy of the measured contact conductances presented here are sufficient for design purposes.
Fundamental harmonic of ripples in symmetrical Cockcroft–Walton cascade rectifying circuit
Authors: Zhang Haibo , Takaoka Akio
Published: July 2002

On the basis of a conventional Cockcroft–Walton (C–W) cascade rectifying circuit, an expression is derived for the fundamental harmonic of ripples due to asymmetry of driving voltage in a symmetrical C–W circuit. The expression is validated from good agreement with experimental results of both a low-voltage model circuit and a high-voltage circuit used in an ultrahigh-voltage electron microscope.
The applications of a short-wavelength FEL (invited, abstract)
Authors: Arthur John
Published: July 2002

The third-generation synchrotron light sources today offer exciting new scientific capabilities due to the high brightness of their hard x-ray beams. Yet further dramatic increases in source brightness are becoming technically feasible, with the advent of free-electron lasers (FELs) operating in the hard x-ray region. The peak brightness of machines under consideration exceeds that of today’s third-generation sources by more than ten orders of magnitude. In addition, an FEL would produce an x-ray beam with very high transverse coherence and subpicosecond pulse length. These characteristics should open up completely new areas of x-ray science, such as nonlinear x-ray optics and femtosecond time-domain spectroscopy. Some areas of current research, such as imaging and interferometry, could be extended to much shorter wavelengths and faster measurements. The intense beam could also be used to modify materials on a nanometer scale. Formidable technical problems in the areas of optics, sample preparation, and data collection will need to be solved before an FEL beam could be effectively utilized. Research in these areas is now beginning to be pursued in the U.S., Germany, and Japan.
Elliptical multipole wiggler for the production of variably polarized radiation (invited, abstract)
Authors: Gluskin E.
Published: July 2002

A new insertion device has been designed, manufactured, and tested as a result of a collaboration between the Advanced Photon Source, the Budker Institute of Nuclear Physics, and the National Synchrotron Light Source. The device—an elliptical multipole wiggler (EMW)—is a source of variably polarized x-rays. It has a period of 16 cm and consists of two magnetic structures. The hybrid magnet structure produces a vertical wiggler field with a peak value of 8 kG. The horizontal wiggler field (1 kG) is generated by electric coils capable of operating with a switching frequency up to 100 Hz. After fabrication, the EMW was measured and magnetically tuned. When installed on the NSLS X-ray Ring, the EMW produces variably polarized radiation in the 1–10 keV energy range.
Orbit compensation for the time varying elliptically polarized wiggler (invited)
Authors: Singh O. , Krinsky S. , Ivanov P.M. , Medvedko E.A.
Published: July 2002

In December 1994, an elliptically polarized wiggler was installed in the X13 straight section of the NSLS X-ray Ring. This device generates circularly polarized photons in the energy range of 0.1–10 keV with AC modulation of polarization helicity. The vertical magnetic field is produced by a hybrid permanent magnet structure, and the horizontal magnetic field is generated by an electromagnet capable of operating with a switching frequency of up to 100 Hz. The elliptically polarized wiggler was commissioned during spring 1995 at an operating frequency of 2 Hz. Here, we discuss the compensation of the residual-orbit motion-utilizing trim coils at the wiggler ends and the high precision orbit measurement system of the X-Ray ring.
Design and performance of a compact, versatile crystal bender for sagittal focusing of x-ray beams (abstract)
Authors: Adler David
Published: July 2002

A focusing element that can be added to new and existing x-ray monochromators is described. The bender is used to focus 4 mrad of light into a 300 micron spot (4:1 demagnification). The focus is dynamically adjusted over the energy range 2.1 to 25 keV. This device is a working part of beamline X16C at the NSLS and is routinely used to collect surface diffraction, DAFS, and EXAFS data. Suggestions for its use in other beamlines, including insertion device lines at the APS, will be discussed.
Multilayer optics for harmonic control of angiography beamline sources
Authors: Tatchyn R. , Cremer T. , Boyers D. , Li Q. , Piestrup M.
Published: July 2002

In recent work, multilayers with band-tailored optics for dual energy digital subtraction angiography (DDSA) applications have been designed and tested at SSRL. Control of various multilayer parameters, including period grading, ratio of high-to-low Z material thickness, number of layers, etc., was used to produce reflectors with bandwidths ranging from 0.6%–10% and efficiencies in the 30%–95% range. In this paper, we consider the control of multilayer bandshapes and the implementation of double-reflection multilayer configurations to further control the first harmonic (33 keV) bandwidth and to suppress or eliminate the 66 keV and 99 keV harmonics present on angiography beamlines driven by wiggler or micropole undulator sources.
Optics for high energy x-ray scattering applications (invited)
Authors: Tschentscher Thomas
Published: July 2002

High energy photons in the range from 80 to 500 keV are a relatively new tool, which is provided with sufficient fluxes only by the latest generation of synchrotron sources. Due to the high energies and, respectively, very short wavelengths, new arrangements for monochromators or mirrors have to be investigated in addition to standard monochromator concepts. An overview of possible monochromator setups is given and the need for experiments to be performed at these energies is evaluated. Low absorption enables the use of rather thick absorbers in order to reduce the heat load problem, which is due to the high power synchrotron beam. Even monochromator crystals become semitransparent, thus giving the possibility of operating more than one experimental station using the same synchrotron beam. Focusing techniques may be applied, and monochromators with an increased bandwidth are of interest for providing sufficient monochromatic flux. The optical concept of the High Energy beamline ID15 at the ESRF is presented, where two different insertion devices can be used alternatingly. Monochromatic beam in the range from 30 to 80 keV is provided by the use of bent cooled Si monochromators and the results of the performance tests are shown.
A cryogenic monochromator for third-generation synchrotrons (abstract)
Authors: Morris D. , Harding G.
Published: July 2002

A double-crystal monochromator has been developed based upon the cooling of a pair of silicon (111) crystals using liquid nitrogen. This monochromator features Bragg angle accuracy and a resolution of 0.36 arc seconds and is also compatible with sagittal focusing of the second crystal. The design of this monochromator is described, and performance data are presented.
Fabrication of mm-wave undulator cavities using deep x-ray lithography
Authors: Song J.J. , Feinerman A.D. , Kang Y.W. , Kustom R.L. , Lai B. , Nassiri A. , White V. , Well G. M.
Published: July 2002

The possibility of fabricating mm-wave radio frequency cavities (100–300 GHz) using deep x-ray lithography (DXRL) is being investigated. The fabrication process includes manufacture of precision x-ray masks, exposure of positive resist by x-ray through the mask, resist development, and electroforming of the final microstructure. Highly precise, two-dimensional features can be machined onto wafers using DXRL. Major challenges are: fabrication of the wafers into three-dimensional rf structures; alignment and overlay accuracy of structures; adhesion of the PMMA on the copper substrate; and selection of a developer to obtain high resolution. Rectangular cavity geometry is best suited to this fabrication technique. A 30- or 84-cell 108-GHz mm-wave structure can serve as an electromagnetic undulator. A mm-wave undulator, which will be discussed later, may have special features compared to the conventional undulator. First harmonic undulator radiation at 5.2 keV would be possible using the Advanced Photon Source (APS) linac system, which provides a low-emittance electron beam by using an rf thermionic gun with an energy as high as 750 MeV. More detailed rf simulation, heat extraction analysis, beam dynamics using a mm-wave structure, and measurements on 10x larger scale models can be found in these proceedings [Y.W. Kang et al., ‘‘Design and Construction of Planar mm-wave Accelerating Cavity Structures’’]
Siemens SMART CCD detector applied to protein crystallography with synchrotron and rotating anode x-ray sources
Authors: Phillips J. , Chambers J. , Fait J. , Schuster M. , Sparks R.
Published: July 2002

The performance of the Siemens CCD detectors with 1K and 2K chips is evaluated using radiation from bending magnet beamlines at SSRL and NSLS and from a rotating anode source with three types of optics. Structure solution quality data are obtainable in short times for macromolecular (up to 300 Å cell) and small molecule crystallography. General experiments, such as time-resolved powder diffraction and overlayer diffraction are also possible.
Replica grating radiation damage in a normal incidence monochromator
Authors: Hansen Roger W. C.
Published: July 2002

Experience with the Synchrotron Radiation Center 4 meter normal incidence monochromator has revealed short operational life for the high energy gratings. Within periods as short as 6 months, the resolution of the gratings degraded sufficiently to limit the resolution to values expected with 80 micron slits. This decrease in resolution occurs without any noticeable changes in the efficiency or throughput of the grating. The resolution degradation has been shown to have been caused by light between 100 and 200 eV, which was transmitted through the gold layer of the replica grating and caused shrinkage of the epoxy. This resulted in distortion of the surface. The problem was solved by ordering a special replica grating with a double layer of gold. Calculations indicate that a thicker gold layer should decrease the flux penetrating the epoxy layer by a factor of ten slowing down the deterioration of the grating figure. A grating with a double thickness gold layer has been operating in the monochromator for more than one year with no noticeable decrease in the resolution.
Nitrogen laser system for diagnosing z-pinch and x-pinch plasmas
Authors: Kalantar Daniel H. , Hammer David A. , De Silva Alan W.
Published: July 2002

A nitrogen laser system built to probe dense z-pinch and x-pinch plasmas is described. This low-cost system consists of an atmospheric pressure oscillator and a low pressure amplifier. It generates a 1-cm-diam 3371 Å laser beam with approximately 0.33 mJ in a ≲1 ns pulse, and with a coherence length of at least 5 cm. This laser has been used in several modes of operation, such as for simultaneous schlieren and interferometry imaging of dense z-pinch and x-pinch plasmas. Example results are presented.
Experimental setup for Fourier transform infrared spectroscopy studies in condensed matter at high pressure and low temperatures
Authors: Bini R. , Ballerini R. , Pratesi G. , Jodl H. J.
Published: July 2002

An experimental setup for Fourier transform infrared (FTIR) studies in condensed matter at high pressure and low temperatures is described. We have adapted a close-cycle cryostat (T=20–300 K) to the sample compartment, which is used as a cryo chamber, of a FTIR spectrometer (frequency range 10–15 000 cm−1). A Cassegrain-type beam condenser is assembled to measure infrared absorptions of samples contained in a membrane diamond anvil cell (P up to 100 GPa). The tuning of the pressure and the cell alignment is performed from outside the evacuated instrument. An additional light path allows visual observation and in situ pressure calibration. The advantages of this system, demonstrated by its application to CH4 and Ar–(H2)2 crystals, are high radiation throughput, long time stability, visual observation of the sample, remote measurement and variation of the local pressure, and remote alignment of the cell with the IR beam.
An optical probe for local measurements of fast plasma ion dynamics
Authors: Fiksel G. , Den Hartog D. J. , Fontana P. W.
Published: July 2002

A novel insertable probe for local measurements of equilibrium and fluctuating plasma ion flow velocity and temperature via Doppler spectroscopy is described. Optical radiation is collected by two fused silica fiber optic bundles with perpendicular viewlines. Spatial resolution of about 5 cm is achieved by terminating each view with an optical dump. The collected light is transported by the fiber bundles to a high-resolution spectrometer. Two components of the velocity are measured simultaneously—the radial along the insertion of the probe and a perpendicular component (which can be varied by simply rotating the probe by 90°). The accuracy of the velocity measurements is better than 1 km/s. The probe is armored by a boron nitride enclosure and is inserted into a high temperature plasma to obtain radial profiles of the equilibrium and fluctuating plasma velocity. Initial measurements have been done in Madison Symmetric Torus reversed field pinch.
Magnetic measurements on the TCV Tokamak
Authors: Moret J.-M. , Buhlmann F. , Fasel D. , Hofmann F. , Tonetti G.
Published: July 2002

The TCV Tokamak was designed to create a large variety of plasma shapes. Such a large flexibility requires high precision magnetic measurements with a good spatial coverage. This article gives a detailed description of the magnetic sensor geometry, fabrication, calibration, the associated electronics, and the diagnostic operation and monitoring. A substantial effort has been made to quantify the precision in the measurements and a novel method has been developed to derive corrections in the sensor position and calibration which optimise the consistency of the entire measurement set. Accuracy of 0.5 mWb in the poloidal flux and 1 mT in the magnetic field with a position error of a few mm have been achieved.
Proposal for a new electron temperature diagnostic for fusion reactors
Authors: Orsitto F. , Tartoni N.
Published: July 2002

The possibility of determining the plasma electron temperature by measuring the depolarization of the radiation scattered by the high temperature fusion reactor plasma is explored in this article. A numerical calculation based on the theory of the article [Sov. J. Plasma Phys. 7, 669 (1981)] in the case of 90° scattering, with the incident radiation linearly polarized and the polarization plane at 45° with respect to the scattering plane, is carried out. The result is that there is a one to one relationship between plasma electron temperature and depolarization, being independent from the detection wavelength. As an example electron density and temperature of 1020 m−3 and 20 keV, respectively, are taken, a wavelength and energy of the incident radiation pulse of 1064 nm and 8 J, respectively, and for a wavelength detection range of 1050–660 nm, a depolarization value of 0.19 and an estimated error on it of 1.7% are found, if the scattering volume is 2 cm long and the collection solid angle is 7.85×10−3 sr. A prototype of the diagnostic apparatus based on beamsplitting Thompson prism is proposed.
More vertical etch profile using a Faraday cage in plasma etching
Authors: Cho Byeong-Ok , Hwang Sung-Wook , Ryu Jung-Hyun , Moon Sang Heup
Published: July 2002

Scanning electron microscope images of sidewalls obtained by plasma etching of an SiO2 film with and without a Faraday cage have been compared. When the substrate film is etched in the Faraday cage, faceting is effectively suppressed and the etch profile becomes more vertical regardless of the process conditions. This is because the electric potential in the cage is nearly uniform and therefore distortion of the electric field at the convex corner of a microfeature is prevented. The most vertical etch profile is obtained when the cage is used in fluorocarbon plasmas, where faceting is further suppressed due to the decrease in the chemical sputtering yield and the increase in the radical/ion flux on the substrate.
Active low frequency vertical vibration isolation
Authors: Hensley Joel M. , Peters Achim , Chu Steven
Published: July 2002

We have constructed a system that isolates a key element of our experimental setup from vertical motions of the ground and the surrounding apparatus. This system combines the passive isolation of mechanical springs and an optical table floating on compressed air with an active system that measures the acceleration of the mass to be isolated and feeds back to a solenoid actuator to cancel this motion. Passive isolation alone reduces the acceleration error signal by a factor of 30–1000 from 10 to 100 Hz and by as much as a factor of 1000 above 100 Hz. With the feedback path closed, the system acts like a spring-mass system with a natural resonance frequency of 0.033 Hz. The acceleration error signal is reduced by an additional factor of up to 300 from 0.1 to 20 Hz. This system has enabled us to make precision atom interferometric measurements that would have been impossible without vibration isolation.
Nondispersive infrared monitoring of NO emissions in exhaust gases of vehicles
Authors: de Castro A. J. , Meneses J. , Briz S. , López F.
Published: July 2002

Road traffic is one of the most important contributors to air pollution, being that a small fraction of the running vehicles is responsible for more than a half of the emissions. Roadside emission monitoring of individual cars appears to be an efficient way to identify these gross polluters. In this sense, nondispersive infrared (NDIR) systems have been developed to monitor the gas emissions of individual vehicles. However, these systems do not include NOx detection because of the strong interference of NO and NO2 absorption bands with the water band. This work is focused on the roadside monitoring of NO emissions by NDIR techniques. A theoretical study of the interference between NO and H2O absorption bands in the 1800–1950 cm−1 spectral region has been performed. Two absorption lines, centered at 1876 and 1900 cm−1 have been selected due to the very low water interference. The development of a new application based on the buildup of a high order interference filter, the solid state Fabry–Pérot filter, is presented. Design of the filter system has been done, optimizing the transmittance at these two absorption lines. Finally, the ability of such a filter to discriminate NO absorption has been tested by using experimental absorption spectra measured by a commercial Fourier transform infrared spectroradiometer working in the active mode. The buildup of such a filter would permit us to increase the capabilities of on road exhaust monitoring systems using the NDIR technique, extending the range of analyzed gases to the nitrogen oxides.
Strain compensation in Si1−xGex by heavy boron doping
Authors: Tillack B. , Zaumseil P. , Morgenstern G. , Krüger D. , Ritter G.
Published: July 2002

Strain compensation in SiGe by heavy boron doping was demonstrated. For this purpose, SiGe layers containing up to several percent of boron were deposited using rapid thermal chemical vapor deposition. The strain compensation effect was evaluated by double crystal x-ray diffraction measuring the difference between the diffraction peak distances of the boron doped samples and a reference sample without boron which can be directly related to the decrease of the lattice constant in Si1−x−yGexBy due to the incorporation of boron. The films were characterized by cross-sectional transmission electron microscopy (XTEM), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS).