bluuebunny/crossref_metadata_2025 huggingface dataset:
Capacitance bridge detector and signal lock for ion cyclotron resonance spectrometry
Authors: Marks Jeffrey , Drzaic Paul S. , Foster Robert F. , Wetzel Donna M. , Brauman John I. , Uppal Jack S. , Staley Ralph H.
Published: July 2002

The design and operational characteristics of a capacitance bridge detector and accompanying signal lock system are presented. The signal lock is especially well suited for the measurement of small changes in ion concentration during photochemical experiments, thereby alleviating problems caused by resonant frequency shifts.
Versatile power supply circuit for xenon flashlamps
Authors: Wegrzyn Jeff , Patonay Gabor , Warner Isiah , Ford Michael
Published: July 2002

A simple, versatile power supply designed to control xenon flashlamps is described. The circuit is configured to utilize an N-channel enhanced metal-oxide-semiconductor field effect transistor (MOSFET), taking the place of commonly used triggering devices such as a silicon controlled rectifier (SCR), or triac. Incorporation of the MOSFET permits flexible control of flash duty cycle and frequency by applying one signal to the transistor’s gate. The circuit’s versatility is demonstrated using an 8.3-W xenon flashlamp as an excitation source for a photodiode array based HPLC fluorescence detector. A detailed description of the power supply circuit is given, along with information on interfacing the circuit and the photodiode array.
Light scattering apparatus for angular dependent studies of anisotropic materials
Authors: Dye R. C. , Sartwell J. , Eckhardt C. J.
Published: July 2002

An improved method for light scattering from acoustic phonons in small, low-symmetry solids is described. This instrumentation greatly facilitates the determination of elastic constants in highly anisotropic materials. Elastic scattering can be greatly reduced so that weaker phonon modes can be observed. Errors associated with the determination of the polarization directions of an anisotropic material are minimized by considering crystal optics.
Development of a scanning x-ray microprobe with synchrotron radiation
Authors: Hayakawa Shinjiro , Iida Atsuo , Aoki Sadao , Gohshi Yohichi
Published: July 2002

An x-ray focusing system with two Wolter type one mirrors was developed and used in a synchrotron radiation x-ray micro analyzer (SRXMA). The SRXMA system and the characteristics of each Wolter mirror are described. The minimum beam size obtained was 1.6 μm in the sagittal plane but the beam size in the meridional plane was 34 μm because of the scattered x rays caused by the surface irregularities of the focusing mirror.
X-ray topography with highly collimated beam at photon factory
Authors: Ishikawa Tetsuya
Published: July 2002

Recent developments of a high-precision diffractometer for multiple crystal arrangement at the Photon Factory is described. New x-ray optics for topography using this diffractometer are shown, including plane-wave topography, ultraplane wave topography and equilattice-spacing mapping topography.
Description of synchrotron radiation sources in ray tracing programs
Authors: Muramatsu Yasuji , Ohishi Yasuo , Maezawa Hideki , Matsushita Tadashi
Published: July 2002

Formulations in a ray tracing program for simulating sychrotron radiation sources such as bending magnets, wigglers, and undulators are described. The characteristic spatial behavior of rays emitted from the sources is simply expressed in the ray tracing program by using the Box and Müller method. A ray tracing simulation of a multipole wiggler beamline, BL-16, at the Photon Factory is also described. The result indicated that the wiggler radiation was collimated vertically with the divergence of 4 arcsec by a collimating mirror and focused at the sample position with spot size of 1.5 mm×0.5 mm.
NTT superconducting storage ring—Super-ALIS
Authors: Hosokawa T. , Kitayama T. , Hayasaka T. , Ido S. , Uno Y. , Shibayama A. , Nakata J. , Nishimura K. , Nakajima M.
Published: July 2002

A superconducting electron storage ring fully dedicated to x-ray lithography has been developed. It has a racetrack shape, consisting of two superconducting bending magnets, other normal conducting multipole magnets, rf system, vacuum system, and beam monitoring systems. The storage ring circumference is 16.8 m. The critical wavelength (λc) is 17.3 Å. The beam size (σ) at every synchrotron radiation source point is less than 1 mm. This machine employs the energy-boost-in-the-ring scheme; electrons are injected at around 15 MeV and then accelerated to 600 MeV in the ring. The injector is a newly developed linear accelerator with an energy compression system. Higher-energy injection is also available.
Performance of a hard x-ray undulator at CHESS (invited)
Authors: Bilderback D. H. , Batterman B. W. , Bedzyk M. J. , Finkelstein K. , Henderson C. , Merlini A. , Schildkamp W. , Shen Q. , White J. , Blum E. B. , Viccaro P. J. , Mills D. M. , Kim S. , Shenoy G. K. , Robinson K. E. , James F. E. , Slater J. M.
Published: July 2002

A 3.3-cm period Nd-Fe-B hybrid undulator has been designed and successfully operated in the Cornell Electron Storage Ring (CESR). This 2-m-long, 123-pole insertion device is a prototype of one of the undulators planned for the Advanced Photon Source. In dedicated operation, the undulator produced the expected brightness at 5.437 GeV with the fundamental x-ray energy ranging from 4.3 to 7.9 keV corresponding to a change in gap from 1.5 to 2.8 cm.
Improved source of polarized electrons based on a flowing helium afterglow
Authors: Rutherford G. H. , Ratliff J. M. , Lynn J. G. , Dunning F. B. , Walters G. K.
Published: July 2002

The performance of the Rice source of spin polarized electrons, which is based on an optically pumped flowing helium afterglow, has been substantially improved. He(23S) metastable atoms contained in the afterglow are optically pumped using 1.08 μm 23S1↔23P1 radiation from an LNA laser. Spin conservation in subsequent chemi-ionization reactions with CO2 results in the production of free polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of 80%–90% are achieved. This decreases to ∼75% at 10 μA and to ∼50% near 100 μA. The polarization can be simply reversed (P→−P). The energy spread in the extracted beam is <0.4 eV, and the beam emittance is <4 mrad cm−1 at 270 eV. This source is suitable for use in a wide variety of applications, and is particularly attractive for use with the new generation of high-duty factor electron accelerators that are currently being developed.
A computer-controlled x-ray imaging scanner using a kinestatic charge detector
Authors: Wagenaar Douglas J. , DiBianca Frank A. , Tenney Charles R. , Vance Joseph E. , Reed Mark S. C. , Wilson Donald W. , Dollas Apostolos , McDaniel David L. , Granfors Paul , Petrick Scott
Published: July 2002

A prototype scanning imaging system which employs a kinestatic charge detector (KCD) and is under the control of a VAXstation II/GPX computer is described. The operating principles and advantages of the KCD method are reviewed. The detector is a 256-channel ionization drift chamber which creates a two-dimensional x-ray projection image by scanning the detector past the object of interest. The details of the drift chamber design, the signal collection electrodes (channels), and the Frisch grid geometry are given. Also described are the scanning gantry design, computer-controlled drive motor circuit, and safety features. The data acquisition system for the capture of a 1 M byte digital image is presented. This includes amplification, filtration, analog-to-digital conversion, data buffering, and transfer to the VAXstation II computer. The image processing and display techniques specific to the KCD are outlined and the first two-dimensional image taken with this system is presented.
180° low-energy impact collision ion scattering spectroscopy
Authors: Spitzl Ralf , Niehus Horst , Comsa George
Published: July 2002

A low-energy impact collision ion (neutral) scattering spectrometer [(N)ICISS] for exact 180° backscattering has been developed. The energy distribution of the backscattered particles is measured with the time-of-flight method (TOF). 180° backscattering spectra are compared with 145°/140° ones. The nearly identical trajectories for incoming and backscattered particles result in the main advantage of 180° NICISS, namely, a quasi-double focusing effect leads to extremely well behaved peaks in the measured angular patterns.
New approach to 3-D, high sensitivity, high mass resolution space plasma composition measurements
Authors: McComas David J. , Nordholt Jane E.
Published: July 2002

This paper describes a new type of 3-D space plasma composition analyzer. The design combines high sensitivity, high mass resolution measurements with somewhat lower mass resolution but even higher sensitivity measurements in a single compact and robust design. While the lower resolution plasma measurements are achieved using conventional straight-through time-of-flight mass spectrometry, the high mass resolution measurements are made by timing ions reflected in a linear electric field (LEF), where the restoring force that an ion experiences is proportional to the depth it travels into the LEF region. Consequently, the ion’s equation of motion in that dimension is that of a simple harmonic oscillator and its travel time is simply proportional to the square root of the ion’s mass/charge (m/q). While in an ideal LEF, the m/q resolution can be arbitrarily high, in a real device the resolution is limited by the field linearity which can be achieved. In this paper we describe how a nearly linear field can be produced and discuss how the design can be optimized for various different plasma regimes and spacecraft configurations.
Local crystal lattice curvature measurements for bent-crystal spectrometers
Authors: Schumacher U. , Nolte R.
Published: July 2002

The geometrical orientation and curvature radius of the lattice of cylindrically bent crystals in high-resolution x-ray spectrometers for plasma diagnostics are determined locally on the crystal surface by means of a double-crystal device in conjunction with precise transverse displacements of the x-ray beam and accurate angular recordings of the crystal. Surface areas of the crystal which have imperfect orientation and curvature quality and hence contribute to resolving power degradation are thus clearly identified.
Double-crystal x-ray spectroscopy at JET
Authors: Barnsley R. , Schumacher U. , Källne E. , Morsi H. W. , Rupprecht G.
Published: July 2002

A double-crystal monochromator has been brought into operation at JET to measure absolute wavelengths and intensities of impurity spectral lines in the soft x-ray region from about 0.1 to 2.3 nm. It is capable of operating also during the deuterium-tritium (active) phase of JET because its detector is very effectively shielded against neutrons and hard x rays. The spectrometer has been swept over a wide wavelength range, around characteristic line groups as well as monochromatic line scans.
Design of an apparatus to measure the shear response of ultrathin liquid films
Authors: Peachey James , Van Alsten John , Granick Steve
Published: July 2002

The design, calibration, and performance are described of an apparatus to study the shear response of ultrathin liquid films. The device, a modification of the surface forces apparatus, measures the resistance to shear of liquids confined between two atomically smooth solid surfaces. The surfaces are separated by distances on the order of the size of the liquid molecules (liquid film thickness <10 nm). Shear forces with periodic time dependence are applied to one surface while the second is held fixed, and any motion so induced is analyzed to determine the behavior of the liquid film. The frequency and amplitude of the shear forces applied can be varied over a wide range (0.03–60 Hz frequency and 0.1–1000 nm amplitude) to achieve different values for the magnitude of the shear rate. The dynamic response of the device is linear in the applied force at a given frequency; nonetheless, nonlinear dependence of the liquid’s shear resistance on the shear rate, net normal pressure, and film thickness can be observed with the technique. The mechanical and electrical characteristics of the device are modeled to gain insight into its behavior and facilitate analysis of the measured data. The central results of this approach are expressions for the magnitude of the shear rate and an effective friction coefficient of the liquid film in terms of easily measured electrical quantities. For convenience the friction coefficient is restated as an apparent dynamic viscosity in analogy to continuum hydrodynamics, but the validity of the approach does not depend on a particular understanding of the structure in the liquid layer. The applications and limitations of the device are discussed, as well as other potential uses to which the apparatus may be applied by rational extension to the approach presented.
Heater for high T
c oxide superconducting thin-film deposition
Authors: Oh B. , Robertazzi R. P.
Published: July 2002

A design for a heater stage capable of operating in a high oxygen partial pressure is presented. Substrates attached to the stage may be heated up to 900 °C in oxygen partial pressures from 10−3 to 760 Torr. The design of the heater allows easy replacement of all parts.
Electron polarimeter based on spin-polarized low-energy electron diffraction
Authors: Sawler J. , Venus D.
Published: July 2002

A compact electron polarimeter which operates at low scattering energies (100 eV) has been built and characterized. The polarimeter uses spin-dependent diffraction from a W(001) single crystal to measure the electron spin polarization of an incident electron beam. The design obtains reliable operation by attention to the input optics, the crystal mount, and the alignment procedure. The transport lens delivers the electron beam to the analyzer over an acceleration range of at least 2.0–0.33 while simultaneously keeping the angular convergence of the beam less than ±1.5°, and the magnification constant to within ∼30%. The crystal mount allows both orientation of the crystal normal to within 0.2° and flashes to 2500 K. Geometric instrumental asymmetries are linear in displacement (AD = 4%/mm) and angular displacement (Aθ = 3%/deg) of the sample. The alignment procedure and performance of the polarimeter are illustrated using spin-polarized low-energy electron diffraction rotation curves. Preliminary results suggest that the polarimeter may be operated for 1 h between cleaning cycles without degradation of the figure of merit.
Grazing incidence optics for soft x-ray microscopy
Authors: Voss J. , Kunz C. , Moewes A. , Storjohann I.
Published: July 2002

We have developed and brought into operation a new type of scanning soft x-ray microscope basing on a grazing incidence mirror. A ring shaped ellipsoidal mirror serves as a nonimaging but concentrating optical element to produce a microfocus. The specimen is mechanically scanned, and the image is recorded a pixel at a time. Transmission, total photoelectron yield, photoelectron spectroscopy, fluorescence, and stimulated desorption of ions and neutrals can provide information in the range of photon energies between 20 and 1300 eV. While the smallest spatially resolved structure, limited by the mirror imperfections, has a size of 0.4 μm, the minimum diameter of selected areas necessary for photoelectron microspectroscopy presently is about 4 μm.
Synchrotron radiation mirrors for high intensity beam lines
Authors: Becker K. B.
Published: July 2002

Most of the recently established synchrotron beam lines need optical components which are able to withstand high total heat loads. High beam power densities have to be tolerated without decreasing the optical quality. New mirror materials such as SiC and Si have been introduced into the optics manufacturer’s workshop, being in principle ideal for high quality optical surfaces. On the other hand, they are causing new problems resulting mainly from inherent material properties. Several possibilities of manufacturing mirrors for high intensity beam lines are discussed in this paper and related problems and possible solutions shown. Special remark is made on mirrors manufactured from a graphite core with chemical vapor deposition-SiC coating.
Performance of the Daresbury synchrotron radiation source soft x-ray double-crystal monochromator
Authors: Roper M. D. , Buksh P. A. , Kirkman I. W. , van der Laan G. , Padmore H. A. , Smith A. D.
Published: July 2002

The double-crystal monochromator on beam line 3.4 at the Daresbury synchrotron radiation source covers the energy region 0.8–4 keV, routinely using crystal pairs of beryl, quartz, InSb, Ge, and Si. The beam line has a unique system to cut off high-energy radiation. The whole beam line has been built on a swinging arm, which allows the glancing angle on a chromium coated premirror to be varied between 0.5° and 3°. This not only reduces the heat load on fragile crystals, but also reduces the higher order contributions. We have made a thorough study of the alignment problems arising in the double-crystal geometry. Crystal misalignment, Bragg angular offset, as well as heat-load effects, can cause severe beam movements. A beam-position monitor, which has recently been commissioned, is an invaluable diagnostic tool for these beam movements.
Beam line 4: A dedicated surface science facility at Daresbury Laboratory
Authors: Dhanak V. R. , Robinson A. W. , van der Laan G. , Thornton G.
Published: July 2002

We describe a beam line currently under construction at the Daresbury Laboratory which forms part of a surface science research facility for the Interdisciplinary Research Centre in Surface Science. The beam line has three branches, two of which are described here. The first branch covers the high-energy range 640 eV≤hν≤10 keV, being equipped with a double-crystal monochromator and a novel multicoated premirror system. The second branch line is optimized for the energy range 15≤hν≤250 eV, using cylindrical focusing mirrors, a spherical diffraction grating and an ellipsoidal refocusing mirror to achieve high resolution with a small spot size.
Double-crystal monochromator beam line on the Aladdin 1-GeV storage ring
Authors: Yang B. X. , Middleton F. H. , Olsson B. G. , Bancroft G. M. , Chen J. M. , Sham T. K. , Tan K. , Wallace D. J.
Published: July 2002

We report the design, construction, and performance of a soft x-ray beam line with accessible photon energy 0.8–4.0 keV at the Synchrotron Radiation Center, University of Wisconsin–Madison. The beam line features an ultrahigh-vacuum (UHV) compatible high-precision double-crystal monochromator (DCM) covering Bragg angles 12°–72°, which was designed and built at the Physical Science Laboratory (PSL), University of Wisconsin–Madison. The monochromatic x rays are focused by a bent cylindrical mirror (Ni-coated fused silica, located 7.5 m from the source) into the experimental chamber (located 5.5 m from the mirror) down to a spot less than 1 mm(h)×3 mm(v). During the initial runs, the DCM used a pair of InSb(111) crystals and covered photon energy 1.75–3.7 keV. At the silicon K edge (1840 eV), the beam line delivered about 4×1011 photons/s with stored electron beam at 100 mA at 1 Gev, among the most intense and stable sources currently available at this energy. The energy resolution is about 0.9 eV at the Si K edge.
High perfection α-57Fe2O3 crystals for nuclear Bragg scattering
Authors: Suzuki Carlos K. , Ohno Hideo , Takei Humihiko , Sakai Fumiko , Yoda Yoshitaka , Kudo Yoshihiro , Izumi Koichi , Ishikawa Tetsuya , Kikuta Seishi , Zhang Xiao W. , Matsushita Tadashi , Ando Masami
Published: July 2002

High quality single crystals or thin films containing Mössbauer isotopes are the main x-ray optical component for nuclear Bragg scattering (NBS) with synchrotron radiation. For this purpose, flux grown α-57Fe2O3 (hematite) single crystals prepared in two growth runs have been characterized by plane wave x-ray topography, which indicated the most suitable sample. Measurements of (111), (333), (555), (777), and (999) pure nuclear-reflection profiles showed a good agreement of relative reflectivity with the values calculated from theory. At the beamline NE-3, accumulation ring of TRISTAN, a Mössbauer event rate as high as 13 000 cps for (777) reflection was observed.
Radiation damage to free adenosine triphosphate and guanine molecules by monochromatic x rays
Authors: Svensson A. , Bordas J. , Hughes E. A. , Lewis R. , Mant G.
Published: July 2002

A summary description of the equipment for time-of-flight (TOF) mass spectroscopy and its uses in the x-ray region for the study of radiation damage (photofragmentation) of biologically relevant molecules is given. The technique is illustrated with some recent x-ray (∼8.1 keV) TOF results obtained from free adenosine triphosphate and guanine molecules. The well defined time structure of synchrotron radiation has been employed in order to record the molecular decomposition in real time. It has, thereby, been possible to determine which bonds are most susceptible to bond breakage following irradiation of the molecules by x rays.
Status and perspectives of high-resolution spectroscopy in the soft x-ray range (invited)
Authors: Kaindl G. , Domke M. , Laubschat C. , Weschke E. , Xue C.
Published: July 2002

The present status in high-resolution photoabsorption and photoemission spectroscopy using synchrotron radiation in the soft x-ray range (40 eV≤hν≤1000 eV) is described. With the SX700/II monochromator, operated by the Freie Universität Berlin at the Berliner Elektronenspeicherring für Synchrotronstrahlung (BESSY), a resolving power of up to ≥10 000 has been achieved. A practical feature of this monochromator is given by the fact that excellent energy resolution is achieved with a single 1221-lines/mm grating in the whole soft x-ray range considered. This opens up new opportunities in core-level photoabsorption spectroscopy of atoms, molecules, adsorbed species, and solids. A combination of the SX700/II beam line with a high-resolution electron spectrometer (ΔE≂15 meV) enables resonant photoemission studies of rare-earth materials in the 4d→4f giant-resonance region with unprecedented resolution and also at the 3d→4f absorption thresholds. This spectroscopic progress provides new insight into the correlated electronic structure of Ce systems.
(γ,eγ) spectroscopy: A new technique to determine electron momentum densities of solids (invited)
Authors: Schneider J. R. , Bell F. , Tschentscher Th. , Rollason A. J.
Published: July 2002

In the past γ-ray Compton scattering experiments proved their value for the investigation of many-body effects in the electronic structure of solids by measuring the projection of the electron momentum density onto the scattering vector, the so-called Compton profile. Due to the availability of modern synchrotron radiation facilities the momentum resolution of the technique was improved substantially and, by using circular polarized photons, ‘‘magnetic’’ Compton profiles could be determined in ferromagnetic materials. A new approach, where the Compton scattered photon is measured in coincidence with the recoiling electron, allows for a direct determination of electron momentum densities in solids. This (γ,eγ) scattering technique will reach its full potential once synchrotron radiation from undulators in electron storage rings operating at energies above 10 GeV will be available.
Characterization of 5-μm-sized icosahedral chemical vapor deposited diamond by synchrotron x-ray diffraction with Laue method
Authors: Ohsumi K. , Takase T. , Hagiya K. , Shimizugawa Y. , Miyamoto M. , Mitsuda Y. , Ohmasa M.
Published: July 2002

A system for analyzing and refining the crystal structure of a submicrometer-sized specimen has been developed at the Photon Factory, KEK, employing a Laue method with an imaging plate. The system was evaluated using two molybdenum spheres with diameters of 0.8 μm and 0.27 μm3 in volume. The result showed that the isotropic temperature factors of both spheres were successfully refined, and that one of the samples was found to be twinned. The smaller domain of the twin was determined to be 0.02 μm3 in volume, which means that the smaller domain is composed of only 109 Mo atoms. The system was applied to a 5-μm-sized icosahedral CVD diamond as a first application. Analysis of several Laue patterns revealed that the sample is composed of more than 17 domains. Among them, 16 domains are twinned with each other, and the mode of twinning is of the spinel twin type.
X-ray instrumentation for protein crystallography with SR (abstract)
Authors: Popov A. N. , Kheiker D. M. , Harutunyan E. G.
Published: July 2002

The station is intended for x-ray analysis of single crystals, primarily that of proteins with the beam of synchrotron radiation from the superconducting wiggler of a special storage ring E=2.0 GeV, I=0.3 A in the town of Zelenograd (TNK).1 The dimensions of the radiation source are 2.352 σx⋅σz=1.5×0.05 mm2, the brightness for λ=1.5 Å is 1015 photon/(s mm2 mrad.2 0.1% (Δλ/λ)). The station comprises the device forming the monochromatized primary beam (λ=0.5–2.2 Å, Δλ/λ−3∼10−4) that consists of an asymmetric focusing monochromator with triangular-shaped Si or Ge crystal curved as a round cylinder,2 a segmented mirror of total external reflection placed behind the monochromator on a rotating bench consisting of 8 flat glass 200×50×25 mm2 segments that form a surface imitating an elliptical cylinder, three pairs of horizontal and vertical slits, monitor–ionization chamber, four-circle diffractometer with scintillation counter and horizontal main axis placed on the adjustable carriage that can turn about the monochromator axis; position-sensitive proportional chamber with spherical drift space, 512×512 elements of space resolution and time resolution of 106 photons per second that can be vertically shifted and bent around the holder horizontal axis. The monochromator goniometer as well as the crystal bend and the mirror segments are driven by the multiple-turn potientiometers by the computer and CAMAC interface.

The automatic four-circle goniometer device is controlled by stepping drives, the angles being controlled by means of 16 register absolute optoelectronic detectors and the same computer. The data from the position-sensitive detector are read through the increment channel to annex memory of 256 K word (16 registered) capacity in the CAMAC block and then to the computer to be followed by visualization on the coloured display. All the station units are to be manufactured in 1991. The working out and manufacturing of the instrumentation is being fulfilled by the Institute of Crystallography of the USSR Academy of Sciences, the Department of nonfilm chambers of the High Energy Laboratory of the Joint Institute for Nuclear Research (Dubna) and the Special Design Bureau at the Institute of Crystallography.
Piezoelectric pressure transducer technique for oxidizing atmospheres
Authors: Roberts Ted A. , Burton Rodney L.
Published: July 2002

The diaphragm sensing tip of a high-speed piezoelectric pressure transducer can be destroyed when measuring transient impulse pressures in hot oxidizing atmospheres, e.g., oxygen at 3000 K and 34 atm for times of tens of milliseconds. A technique is presented to preserve the transducer under these conditions, which uses a protective layer of 0.025–0.050-mm-thick brass foil, held in place with double-sided tape. The integrity of the transducer is preserved, and the response time to a shock wave is increased from 1 to 2–6 μs using the technique.
Dry etch damage in InN, InGaN, and InAlN
Authors: Pearton S. J. , Lee J. W. , MacKenzie J. D. , Abernathy C. R. , Shul R. J.
Published: July 2002

Changes in conductivity of InN, In0.5Ga0.5N, and In0.5Al0.5N layers exposed to Ar plasmas under both electron cyclotron resonance and reactive ion etching conditions have been measured as a function of rf power, pressure, and exposure time. The combination of high microwave and high rf powers produces large increases (10–104 times) in sheet resistance of the nitrides, but conditions more typical of real etching processes (rf power <150 W) do not change the electrical properties. The nitrides are more resistant to damage introduction than other III–V semiconductors. The removal of damage-related traps occurs with an activation energy of ∼2.7 eV.
8–11-keV x-ray sources for imaging and absorption experiments
Authors: Molitoris J. D. , Morin M. M. , Phillion D. W. , Osterheld A. L. , Stewart R. E. , Rothman S. D.
Published: July 2002

We have measured the 8–11-keV emission spectra from plasmas produced by impinging 0.53-μm, 100- and 200-ps FWHM Gaussian laser pulses on targets of different materials. The experimental spectra from W and Zn are identified by comparison with local thermodynamic equilibrium plasma emission calculations.
Electron velocity distributions measured with soft x-ray PHA at RTP
Authors: da Cruz D. F. , Meijer J. H. , Donné A. J. H.
Published: July 2002

A soft x-ray pulse height analysis (PHA) system is begin used at the Rijhuizen Tokamak Project to study the electron velocity distribution. A liquid nitrogen cooled Si(Li) detector is used to view the plasma along a tangential line of sight. A gas cell in combination with Al foils is used for filtering. The data-acquisition system is set up in such a way that 16 subsequent spectra, of 1ms–1 s duration and in the energy range 4–30 keV, can be measured during a single tokamak discharge. The PHA system has been used extensively for measuring the electron temperature, the effective charge number Zeff, and the species and concentrations of high-Z impurities in the plasma. Special attention was devoted to study the effect on the electron velocity distribution of electron cyclotron resonance heating (ECRH) power (60 GHz, up to 180 kW) launched in the ordinary mode from the low-field side. During application of ECRH the temperature deduced from PHA always exceeds the value from Thomson scattering. This deviation can be explained by the presence of nonthermal components in the electron velocity distribution. Finally, the effect of boronization of the vacuum vessel on the impurity concentration was studied.
Density fluctuation measurements via beam emission spectroscopy (invited)
Authors: Durst R. D. , Fonck R. J. , Cosby G. , Evensen H. , Paul S. F.
Published: July 2002

Previous studies of plasma microturbulence have indicated that the fluctuation power scales with radial wave number, k⊥ , like k⊥−2→k⊥−3.5 for k⊥ ≥2 cm−1. This implies that low k fluctuations may dominate the spectrum. Beam emission spectroscopy (BES) has been developed to provide spatially localized measurements of density fluctuations in this low k region of the spectrum (k⊥ ≤2 cm−1). A 20-channel system has been installed on TFTR which images one of the heating neutral beams (via fiber optics) onto a set of photoconductive photodiode detectors. Fluctuations in the fluorescent Dα emission from the beam can be related to the local plasma density fluctuations via a model of the atomic excitation processes. The analysis of BES data utilizes many of the standard statistical analysis techniques such as power spectra, coherency and cross phase, and correlation analysis which are also used in the analysis of, for example, Langmuir probe data. In the case of BES however, these techniques require some special modifications to account for systematic effects such as photon statistics and fluctuations in the neutral beam density induced by the strong fluctuations near the plasma edge.
Thermal, nonthermal, and stimulated fluctuations of tokamak electron cyclotron radiation
Authors: Cima G.
Published: July 2002

Electron cyclotron radiation is the only blackbody level e.m. radiation which emerges from magnetically confined, fusion grade plasmas. Its power fluctuations and their space correlations carry information relevant to plasma transport studies. An overview is given of the properties of electron cyclotron emission fluctuations for a plasma in thermal equilibrium and when the fluctuations are enhanced by plasma turbulence or by modulated auxiliary heating.
Measurement of density and temperature fluctuations using a fast-swept Langmuir probe
Authors: Balbín R. , Hidalgo C. , Pedrosa M. A. , García-Cortés I. , Vega J.
Published: July 2002

Density and temperature fluctuations have been measured in the proximity of the velocity shear location of the TJ-I tokamak using a fast-swept Langmuir probe technique. From the current voltage characteristic we have determined the electron temperature and the density in a time scale which is small compared with the relevant times of the turbulence. Evidence of substantial temperature fluctuations has been found near the shear location.
Hard x-ray interaction with materials
Authors: Tong X. M. , Watanabe T. , Yamaoka H. , Nagasawa H.
Published: July 2002

Based on the analyses of microprocesses involved in the interaction of synchrotron radiation with materials, we have developed a simulation method to calculate heat energy distribution when the synchrotron radiation goes through insert devices (filters, mirrors, or monochromators). The absorbed x-ray energy may be taken away from materials when some scattered photon and photoelectron escape from material. We have calculated the percentage of the absorbed energy taken away by the escaped photons and photoelectrons for C, Be, and Al, these elements being very important as filter materials, and for Si which is significant as a monochromator material.
Increasing the frequency stability of single-frequency lasers
Authors: Jaffe S. M. , Rochon M. , Yen W. M.
Published: July 2002

We have developed an improved technique to increase the stability of single-frequency lasers by employing a scanning Fabry–Perot interferometer and a stabilized helium neon laser. Our instrument surpasses earlier devices in several key areas. The laser frequency can now be stabilized while scanned across its inherent single-frequency tuning range. The frequency stability is long term with an increased frequency correction rate of nearly 500 Hz. The laser frequency can be scanned repeatedly with a repetition accuracy equal to the frequency stability. Also, the electronics permit the laser frequency to be swept externally while synchronized with other instruments. Our stabilizer reduced the frequency drift of a commercial ring dye laser to ±1 MHz relative to the reference laser.
Concept of virtual instruments applied in photoacoustic measurements
Authors: Starecki Tomasz
Published: July 2002

A method is presented by which photoacoustic measurements can be done fast and with small effort. All operations are performed by an automatic measurement system based on an IBM PC personal computer. The structure and principles of the system operation are presented. The main advantages of the method described are: short time of measurement, wide chopping frequency range, high accuracy, and low error level. Owing to the computer some operations like hardware averaging, filtering, etc. can be replaced by software. This results in simplicity of the setup.
Analysis of scattering asymmetry statistics when background corrected counts are negative
Authors: Coakley Kevin J.
Published: July 2002

An asymmetry statistic of physical interest is an estimate of the ratio of the difference and the sum of the Poisson rate parameters for two scattering processes. Typically, an additive background signal contributes to measurements of each signal. Background is measured in a third experiment. Data are corrected by subtracting measured background. When the measured background is larger than one of the other measurements, background-corrected counts are negative. For this case, it would seem that no useful information can be extracted from the experiment. Here, asymmetry and an associated uncertainty interval are estimated for such cases using a bootstrap approach.
Optical pressure transducer
Authors: Lin Hank , Ho Chih-Ming
Published: July 2002

This paper presents the characteristics of an optical pressure transducer using fiber optics. The transducer consists of a cylindrical housing with a reflective mylar diaphragm attached at one end and fiber-optic bundle at the other. The fiber-optic bundle used is the bifurcated type, in which two bundles of randomly distributed fibers are joined at one end to form a Y-shaped geometry. The common end is attached to the end of the transducer housing, opposite to the diaphragm. At the branched ends, one bundle is connected to a dc light source, while the other bundle carries the light reflected from the diaphragm to a photodetector. By keeping the input light source at constant intensity, the amount of reflected light depends on the distortion of diaphragm due to pressure differential across the diaphragm surface. This pressure transducer can measure both the static pressure level and the fluctuating pressure. A simple ‘‘homemade’’ diaphragm was used in this experiment, and a sensitivity of approximately 10 mV per mm Hg was obtained over a range of 20 mm Hg. The dynamic response was linear to about 2 kHz. Both the sensitivity and the frequency response can be much increased by improving the diaphragm performance.
Simple, calibrated deposition monitor incorporated into an electron beam evaporator
Authors: Jones T. , Sawler J. , Venus D.
Published: July 2002

A simple deposition monitor has been incorporated into a thin-film evaporator. The compact evaporator uses electron bombardment of the tip of a source wire to create an atomic beam. The current of ions in that portion of the atomic beam which falls on a collimating aperture is used to monitor the film deposition. The ion current is linearly related to the atomic beam flux, therefore allowing more precise control of the deposition rate than is obtained by monitoring the heating power delivered to the source wire. Calibration of the ion monitor within limits of ±6% requires positioning of the tip of the source wire within ±0.3 mm. This is readily accomplished using a plot of the current of bombarding electrons versus wire position. For the evaporation of iron, the calibration constant of this ion monitor is (2.50±0.15)×10−4 ions/atom.
High-voltage MOSFET bipolar square-wave generator
Authors: Usher T. D. , McAuley Grant A.
Published: July 2002

The construction of a high-voltage (up to 1000 V) bipolar metal-oxide-semiconductor field-effect transistor square-wave generator is described. This generator is capable of producing both positive and negative going square waves with variable amplitude, repetition rate, and width. The circuit was designed for ferroelectrics research, however other applications are possible. The rise time of the prototype was 200 ns which was quite satisfactory for the present ferroelectric research project however the rise time can be decreased to 50 ns if necessary. The reader with a modest knowledge of electronics should be able to construct the circuit. Possible pitfalls and critical points are discussed.
Edge plasma density reconstruction for fast monoenergetic lithium beam probing
Authors: Sasaki S. , Takamura S. , Ueda M. , Iguchi H. , Fujita J. , Kadota K.
Published: July 2002

Two different electron density reconstruction methods for 8-keV neutral lithium beam probing have been developed for the Compact Helical System (CHS). Density dependences on emission and ionization processes are included by using effective rate coefficients obtained from the collisional radiative model. Since the two methods differ in the way the local beam density in the plasma is determined, the methods have different applicable electron densities. The beam attenuation is calculated by iteration from the electron density profile in method I. In method II, the beam remainder at the observation point z is determined by integrating the Li i emission intensity from z toward the position of emission tail-off. At the emission tail-off, the fast lithium beam is completely attenuated. Selecting an appropriate method enables us to obtain edge electron density profile well inside the last closed flux surface for various ranges of plasma densities (1012–5×1013 cm−3). The electron density profiles reconstructed by these two different methods are in good agreement with each other and are consistent with results from ruby laser Thomson scattering.
Effect of high x-ray fluxes on laser-plasma x-ray spectrometers
Authors: Wark J. S. , Whitlock R. R.
Published: July 2002

LiF (200) crystals were heated with the x rays produced when a 30 J, 0.35 μm laser pulse of 0.6 ns duration was incident on a gold-coated titanium target at an irradiance of 2.5×1015 W cm−2. A filter arrangement allowed half of the crystal to be heated by the broad band x radiation from the gold plasma, whilst effectively shielding the other half of the crystal. The reflectivity of both x-ray heated and unheated portions of the crystal was monitored by diffracting He-α radiation from the underlying titanium from both parts of the crystal. Significant increases in the integrated reflectivity (36%) of the heated crystal were found.
Time resolved mass flow measurements for a fast gas delivery system
Authors: Ruden E. L. , Degnan J. H. , Hussey T. W. , Scott M. C. , Graham J. D. , Coffey S. K.
Published: July 2002

A technique is demonstrated whereby the delivered mass and flow rate versus time of a short rise-time gas delivery system may be accurately determined. The gas mass M that flows past a point in a gas delivery system by an arbitrary time t=tp may be accurately measured if that point is sealed off with a fast closing valve within a time interval short compared to the mass flow time scale. If the injected mass is allowed to equilibrate in a known volume after being cut off from its source, a conventional static pressure measurement before and after injection, and application of the ideal gas law suffices. Repeating for many different values of tp, and assuming reproducibility, the injected mass time history M(t) characteristic of the system without the fast closing valve may be determined. The flow rate versus time dM(t)/dt may then be determined by numerical differentiation. Mass flow measurements are presented for a fast delivery system for which the flow of argon through a 3.2-mm-i.d., 0.76-mm-thick copper tube is isolated by imploding (θ pinching) the tube using a single turn tungsten magnetic-field coil. Optical measurements of the tube’s internal area versus time indicate that the tube is sealed in 7 μs. Results are correlated with piezoelectric probe measurements of the gas flow and 2D axisymmetric numerical simulations of the θ pinch process.
Computerization of a PARC174A polarographic analyzer
Authors: Liao Shu-Ling , Olson Carter L.
Published: July 2002

A PARC174A polarographic analyzer has been transformed into a comprehensive microcomputer controlled electroanalytical system by interfacing it with an IBM PC equipped with a Tecmar LabMaster data acquisition subsystem. Techniques implemented include square wave voltammetry, chronoamperometry, cyclic voltammetry, differential pulse, normal pulse, and sampled dc polarography, and stripping voltammetry which can be used with either linear sweep, differential pulse, or square-wave techniques. The PARC174A functions only as a potentiostat and current to voltage converter. All the potential waveforms are generated by the D/A converter of the LabMaster and the current data are sampled by the A/D converter. The software developed should be easily adaptable to most potentiostats with minor modification. Because no extra circuitry is desired to complicate the system, a small-step staircase waveform is used to approximate the linear dc ramp in cyclic voltammetry, differential pulse, and sampled dc techniques. The discrepancy in results obtained using linear dc ramp and small-step staircase waveforms was carefully examined and proven to be negligible. All the techniques implemented have been shown to give theoretically predicted results. The results are also found essentially the same as those obtained using a conventional PARC174A. This computer controlled system makes available the use of square wave voltammetry, which was otherwise not available on the original machine. Experimental data showed that 4.76×10−8 M Cd2+ could be quantitatively analyzed by square wave voltammetry when a dropping mercury electrode was used.
Bimorph stepping motor for point-contact experiments
Authors: Heil J. , De Wilde Y. , Jansen A. G. M. , Wyder P. , Grill W.
Published: July 2002

A rotating piezoelectric device, which uses the so-called slip-stick mechanism for micropositioning is presented. The device is especially designed for use in point-contact experiments at very low temperatures in high magnetic fields. Two typical applications are presented.
Decay time measurement of fluorescent fibers with photon counting
Authors: Muller A. , Gisin N. , Pellaux J.-P.
Published: July 2002

In order to characterize fluorescent light, we present a decay time measurement method based on the use of a commercial photon counting module. This module, adapted for all fiber measurements, is well adapted for the developing field of optodes for chemical and biochemical sensing. Moreover, it improves the detection sensitivity to the femtowatt and picowatt range. It is thus possible to excite the fluorescence with very low power pump pulses, down to a few nanowatts, and to measure the temporal distribution of the fluorescent signal. As sources we can use LEDs, or white lamps plus a monochromator, avoiding unwanted phenomena such as saturation, amplified spontaneous emission (ASE), and excited state absorption (ESA). We obtain a measurement accuracy of 0.1% in a couple of minutes.
Fourier transform infrared Hadamard tomography of sooting flames
Authors: Bates Stephen C. , Carangelo Robert , Knight Kim , Serio Michael
Published: July 2002

An experimental technique is described that combines tomography, Hadamard signal encodement, and a patented Fourier transform infrared (FT-IR) emission/transmission (E/T) technique to perform simultaneous spatially resolved gas species and soot measurements during combustion. Tomographic analysis of line-of-sight FT-IR data allows spatially resolved measurements to be made. Hadamard encodement of the tomographic sections increases the overall signal throughput, improving the signal to noise (S/N) ratio for each measurement. The Hadamard technique leads to a major simplification in the tomographic apparatus in that the scanning apparatus that would normally be required is eliminated, and focusing of the infrared light is much easier. An experiment demonstrating Hadamard data processing as applied to FT-IR tomography is described. Deconvolution of the encoded data is shown to be accurate and gives the predicted improvement in S/N ratio. The FT-IR Hadamard tomography is performed to measure soot in a fuel-rich diffusion flame. Spatially resolved concentration measurements agree well with previous data, and clearly show striking three-dimensional features that could not normally be measured by simple line-of-sight techniques.
Swept frequency reflectometer for correlation studies in the TJ-I tokamak
Authors: Sanchez J. , Brañas B. , de la Luna E. , Estrada T.
Published: July 2002

An improved correlation reflectometer technique has been developed and implemented on TJ-I to measure the radial correlation lengths of the density turbulence. The method uses homodyne detection and is based on the slow sweeping of one oscillator while the other remains at fixed frequency. The decay of the coherence shows maxima and minima as the distance between the two probing points increases. The maxima correspond to the relevant coherence values. The correlation length for the overall turbulence as well as the correlation length for the different frequency intervals can be directly determined in a single shot. By the operation in the Q-band (33–50 GHz) extraordinary mode, the system reaches most of the plasma radius. Correlation lengths obtained at the edge are compared with those measured at deeper positions in the plasma. The proposed method can provide the values of the differential phase delay along the sweep, avoiding the effect of lost fringes even in the presence of turbulence. This opens the possibility of obtaining the information on the density profile if several channels are used.