bluuebunny/crossref_metadata_2025 huggingface dataset:
A micro-Raman cell for studying aqueous solutions at high temperatures and pressures
Authors: Palmer Donald A. , Begun G. M. , Ward F. H.
Published: July 2002

The wetted surfaces of the high-temperature, high-pressure Raman cell (400 °C and 1 kbar) were constructed of inert materials (i.e., sapphire or quartz and platinum with gold seals) and designed to allow spectroscopic measurements to be made with small volumes (<0.5 cm3 at temperature) of corrosive solutions. This design permits solution to be forced slowly through the cell at experimental temperatures and pressures for cases where the solute may be unstable thermally over prolonged periods of time. The entire pressure-generating equipment, temperature controller and readout, solution separation vessels, and cell can be mounted on a cart for convenient transport to various laboratories. Raman spectra of bichromate/dichromate solutions were obtained from ambient conditions to 300 °C and 1 kbar in order to test the capabilities of this apparatus and to allow comment on the controversy surrounding the existence of HCrO−4 raised by recent Raman studies of the aqueous chromate system at ambient conditions.
Pulsed laser photoionization technique for recording atomic flux variations during deposition
Authors: Bhatia M. S. , Dasannacharya B. A. , Sharma G. L.
Published: July 2002

Depositions at rates higher than 1 nm/s show differences in properties when one deposits with a vapor stream that is modulated against those that are deposited with a steady vapor stream. For carrying out investigations along these lines, it was necessary to develop a real-time, noninvasive, and sensitive technique for determining the nature and extent of flux variations in atomic streams close to the deposition plate. A pulsed laser based resonant photoionization technique is proposed for meeting these requirements. The paper describes the method and its application to a case where modulation is caused by residual ripple in high voltage accelerating supply used in the electron gun of the evaporator. The proposed technique overcomes the limitation on sensitivity due to background pressure experienced in the nonresonant approach. Other attractive features are the use of much lower laser intensities for a given sensitivity and the employment of a simpler ion detection system.
Megahertz far-infrared frequency shifting via multiple diffraction by a rotating grating
Authors: Allmendinger A. , Platz R. , Dodel G.
Published: July 2002

Frequency shifts in the megahertz region, as required under certain conditions in far-infrared diagnostics of magnetically confined fusion plasmas, can be achieved via multiple diffraction by a cylindrical diffraction grating rotating at moderate speed. We present a compact modular concept to correct the beam distortion at the grating. The concept is based on two elliptical mirrors and a sequence of (n−1) identical concave mirrors for n diffractions. Design parameters are derived for λ=119 μm (H2O laser), λ=195 μm (DCN laser), and λ=337 μm (HCN laser). The concept was successfully realized for λ=119 μm using four diffractions. A frequency shift of 3 MHz was achieved with a grating driven by an electric micromotor. The quality of the beam exiting from the grating was excellent. The total efficiency after four diffractions was measured as 64%, corresponding to an overall efficiency (i.e., mirror and other losses included) of 0.641/4=89% per diffraction.
An intense, high-repetition nanosecond light source using a commercially available Xe-arc lamp
Authors: Araki Tsutomu , Yamada Akihisa , Uchida Teruo
Published: July 2002

We describe the construction and emission characteristics of a Xe light source that produces broadband emission spectrum (250–650 nm) and high-repetition pulsed light of nanosecond duration. The standard dc-operated Xe-arc lamp, which is commercially available, is employed as the primary light source, with modified circuitry to realize pulsed operation. A dc voltage higher than 5 kV is applied to the electrode gap through a high-value resistor in order to generate a periodical discharge of current between the electrode gap. In order to further increase the intensity of the light pulses, the electrical polarity of the electrode must be in inverse connection relative to the normal connection under the dc operation. Intense light pulses as large as 20 W (peak value) of 3 ns width were generated repetitively from the Xe lamp. Fluorescence lifetimes of a quinine-sulfate solution and a fluorescent cell nucleus were measured to demonstrate the usefulness of the light source.
Supersonic CO laser with rf excitation
Authors: von Bülow H. , Zeyfang E.
Published: July 2002

A supersonic CO laser with a maximum output power of 990 W has been developed. The gas is excited in a dielectrically stabilized radio-frequency discharge before it is cooled to a temperature of 90 K by the adiabatic expansion in a supersonic nozzle. After extraction of laser power the gas is recompressed by a supersonic diffuser and a Roots-pump system. No liquid nitrogen is needed for the operation of the laser. At a pressure of 500 mbar the rf discharge could be operated homogeneously with a specific input power of 180 W/cm3. It could be shown that the length of the discharge region and the distance between the discharge and the supersonic nozzle should be rather short. By this the vibrational relaxation of the carbon monoxide is reduced and more laser power can be obtained. The laser power can be increased by using a folded resonator system. If the laser is operated at a low Fresnel number by inserting an aperture inside the cavity, a nearly diffraction limited beam quality can be obtained. Using a supersonic nozzle with a low Mach number enables the operation of the diffuser with a high pressure recovery. Thereby the overall system efficiency is increased.
Solid-state bandpass detector for inverse photoemission spectroscopy
Authors: Sheils W. , Leckey R. C. G. , Riley J. D.
Published: July 2002

This paper presents the details of a new arrangement for the bandpass detection of radiation in the vacuum ultraviolet region. The detector is based on two wide bandpass filters that share the diminishing quantum efficiency of a microchannel plate as their common low-energy cutoff, but have high-energy cutoffs determined by the transmittance limits of different crystal windows. The detector has been used to perform an inverse photoemission experiment on a sample of polycrystalline gold. From the results of this experiment the detector is estimated to have a bandpass centered at 11.4 eV and a resolution of 0.57 eV. (FWHM).
A new ion cyclotron resonance cell for simultaneous trapping of positive and negative ions
Authors: Wang Y. , Wanczek K. P.
Published: July 2002

In Fourier transform ion cyclotron resonance (ICR) spectrometry until now either positive or negative ions (including electrons) could be trapped, due to the trapping potential applied. In the present article, the theory of simultaneous trapping of positive and negative ions, and the experimental realization are presented. Trajectory calculations for the ions trapped with both charge polarities are described. The new ICR cell employs a new kind of trapping electrodes, constructed with layers of grids. The simultaneous storage is illustrated by experimentals with sulfur hexafluoride.
Path integral effects in heavy ion beam probe density measurements: A comparison of simulation results and experimental data
Authors: Heard J. W. , Crowley T. P. , Ross D. W. , Schoch P. M. , Hickok R. L. , Zhang B. Z.
Published: July 2002

The heavy ion beam probe (HIBP) signal used to measure local density fluctuations in a plasma is also sensitive to modulation due to density fluctuations along the entire beam trajectory. A modulation model of the HIBP experiment on the Texas experimental tokamak (TEXT) is presented. The model includes profile information for equilibrium and fluctuating parameters, allows for differences in the radial and poloidal characteristics of the fluctuations, and uses realistic beam trajectories. It is shown that profile effects are important in understanding HIBP modulation and that modulation does not simply increase with line average density in TEXT. In addition, calculations of the modulation effects show that only the terms which correspond to in-phase signals at the two sample volumes are significant. Therefore, the modulation effects can be approximated with a real parameter. Under these assumptions, it is shown that only long correlation length, low wave number modes will contribute significantly to the corruption of the measured signal. The calculation of the modulation effects are consistent with the experiment. It is illustrated herein how the measured data can be used to set limits on the modulation signal without doing extensive model calculations. These limits show that there must be long wavelength fluctuations in the plasma.
A miniaturized scanning tunneling microscope with large operation range
Authors: Kleindiek S. , Herrmann K. H.
Published: July 2002

A small sized (<1 cm3) and low mass (2.5 g) scanning tunneling microscope (STM) with automatized large range tip approach is introduced. By concentric arrangement of two piezotubes a temperature drift compensation is realized. Using a simple likewise concentric glass tube inside the inner piezotube as a frictional wire holder, an unlimited longitudinal adjustment range by stepwise inertial translation could be obtained. High mechanical resonance frequencies due to the low mass as well as the mechanical independency of the environment by purely electronic control reduce remarkably the effort for mechanical damping and make the system fast and particularly suited for special applications such as low temperature STM. Sample change and restoration of the tip position require only a few seconds.
Space- and time-resolved measurements of CF and CF2 radicals in high density CF4 plasmas by laser-induced fluorescence
Authors: Suzuki Chihiro , Kadota Kiyoshi
Published: July 2002

Ground-state CF and CF2 radicals in CF4 helicon plasmas of high density were detected by laser-induced fluorescence (LIF). The LIF was used to measure the spatial and temporal variations of CFx concentrations. The CF2 concentration increases near 5–10 ms after the extinction of rf power, and the degree of this increase depends upon the discharge condition; plasma duration, plasma density, and CF4 pressure. The result indicates that this behavior in the afterglow is closely related to the interactions of the rf-on phase between radicals and a quartz surface with deposited fluorocarbon polymers.
High-quality GaN epitaxial layer grown by metalorganic vapor phase epitaxy on (111) MgAl2O4 substrate
Authors: Kuramata Akito , Horino Kazuhiko , Domen Kay , Shinohara Kouji , Tanahashi Toshiyuki
Published: July 2002

We grew GaN crystals by metalorganic vapor phase epitaxy on (111) and (100) MgAl2O4 substrates. We obtained a single-crystal GaN layer with a specular surface on the (111) substrate. The full width of half-maximum of the x-ray rocking curve for a 3.6 μm thick GaN layer was 310 s, comparable to the reported values for GaN on Al2O3 substrates. In the room-temperature photoluminescence, a band-edge emission at around 360 nm was dominant. A smooth cleaved (11̄00) facet of the GaN epitaxial layer was obtained, assisted by the inclined (100) cleavage of the (111) MgAl2O4 substrate. We intend this cleaved facet, which is normal to the surface, to be used as a cavity mirror in a laser diode.
Time-resolved x-ray absorption spectroscopy on microsecond timescales: Implications for the examination of structural motions
Authors: Chance Mark R. , Wirt Michael D. , Scheuring Eva M. , Miller Lisa M. , Xie Aihua , Sidelinger Dean E.
Published: July 2002

We demonstrate a system for collecting high quality x-ray absorption spectroscopy data on microsecond and longer timescales. The method uses a fast-multiscaling board to partition output pulses from a germanium energy resolving detector into a microsecond timebase. Full spectra accumulation and kinetic spectrophotometry are demonstrated for 1–4 mM biological samples. The use of an energy resolving detector promises that the dynamic behavior of a wide range of chemical elements (in conjunction with photochemical, rapid mixing, and temperature jump perturbations) can be observed with this method. We have successfully tested the system by examining the structural evolution of the iron atom of a myoglobin-carbon monoxide complex subsequent to photolysis at low temperature.
A low-temperature total electron yield detector for x-ray absorption fine structure spectra
Authors: Kemner K. M. , Kropf J. , Bunker B. A.
Published: July 2002

A design of a total electron yield detector to collect x-ray absorption fine structure spectra between 80 K and room temperature is described. In addition, a three-stage goniometer setup has been incorporated into the detector to facilitate manipulation of the sample. The results of simple linearity checks to investigate the detector’s electrical performance are presented. Finally, the detector’s thermal stability is discussed.
New technique to enable measurement of the x-ray absorption spectra of single crystals
Authors: Pant J. , Hayes T. M.
Published: July 2002

X-ray absorption spectroscopy measurements of single-crystal samples have not been possible due to the appearance of diffraction features in the spectra. To deal with this problem a unique magnetically driven sample oscillator has been designed and built. Its effectiveness in enabling x-ray absorption spectroscopy studies of single crystals is demonstrated. Furthermore, it is compatible with a cryogenic environment in size, mass, and principle of operation.
Tomography on tokamak fusion test reactor
Authors: Nagayama Y.
Published: July 2002

Reconstruction techniques have been developed to obtain 2D images of plasmas from the electron cyclotron emission (ECE) and soft x-ray emission signals by taking advantage of the large toroidal rotation rate on the tokamak fusion test reactor (TFTR). From the numerical examination using the sawtooth crash model, we found that the rotational tomography is effective if the crash time is longer than the two rotation periods.
Multichannel submillimeter interferometer/polarimeter for TdeV
Authors: Lachambre J.-L. , Gagné M.
Published: July 2002

An interferometer/polarimeter has been developed and tested for operation on the TdeV tokamak. The system operates at 393.6 μm on 7 channels equally spaced over the plasma diameter. The interferometer has operated routinely for six years and is used for density feedback control on TdeV, with very little supervision and maintenance. A sensitivity of 2.5×10−16 m−2 and a response time of 5 μs enables small density perturbations (Δn≥0.005n̄e) and fast transients to be resolved. With the appropriate choice of assumptions and boundary conditions, the system can supply credible electron density profiles together with their temporal evolution, using as isocontours the flux surfaces obtained from equilibrium calculations. When operated as a polarimeter, the system now routinely provides current-density profile measurements as well. Optical cross-talk between channels, identified as the main obstacle to the extension of the interferometer to polarimetry, was mastered using optical isolation techniques. The system can now resolve, on each chord, a Faraday rotation of 1.5 mrad, limited by vibration, cross-talk and deflection. Using a parametric approach, poloidal field and current-density profiles, as well as the axial safety factor and internal inductance of the discharge, are made available after each shot. The apparatus will be used for current-transport, MHD-equilibrium and current-drive studies on TdeV.
Experimental investigation and analysis of the operation characteristics of a planar Cs–Ba tacitron
Authors: Wernsman Bernard , El-Genk Mohamed S. , Kaibyshev Vladimir Z.
Published: July 2002

The experimentally measured modulation characteristics of a planar Cs–Ba plasma switch (tacitron) are presented and discussed. Tests are performed that focus on characterizing the operation capabilities of a planar Cs–Ba tacitron. Results show that the operation characteristics of the device are independent of geometry (cylindrical or planar). The forward voltage drop decreases as either the grid-collector (GC) gap size and/or the Cs pressure increases. Also, stable current modulation is easier to sustain when the grid is placed closer to the collector, at the expense of increasing the forward voltage drop across the device.
Fabrication of high voltage square pulse generators for electro-optic Kerr relaxation studies
Authors: Usha R. , PrasadaRao T. A.
Published: July 2002

High voltage square pulse generators, with fall times of 1 μs and 45 ns have been fabricated for the measurement of electro-optic Kerr relaxation studies in macromolecules. These have been fabricated with a pulse forming network in the Blumlein line configuration with discrete components. The switching is brought about by high voltage spark gaps, instead of the thyratrons and silicon controlled rectifiers (SCRs), which have voltage limitations. The performance of these pulse generators are found to be consistent and stable, without any change in the pulse shape even at very high voltages and repetition rates. The Kerr constants and relaxation times measured with these pulse generators for the liquid crystal p-(methoxybenzelidene)-p-butylaniline (MBBA) at its nematic to isotropic phase transition temperature (43.5 °C) are found to be in very good agreement with the reported values obtained from the optical Kerr effect investigations using high power Q-switched solid state lasers.
A new continuum-source atomic absorption spectrometer
Authors: Williams David T. , Green Alex E. S.
Published: July 2002

Metallic toxics such as mercury, lead, cadmium, manganese, and other species are now of particular importance in relationship to coal-based utilities, waste-to-energy plants, medical waste incinerators, and other industrial sources of atmospheric emissions or residues deposited in landfills. These metals are strong emitters or absorbers of middle ultraviolet light in the same general spectral region where important molecular pollutants are active. The furnace system of a commercial atomic absorption spectrometer, a continuum ultraviolet light source (a deuterium arc), and an oscillating entrance slit (adapted from second derivative spectroscopy) are applied to the measurement of toxic metals. The second-harmonic ripple in the output of the photomultiplier tube is amplified by use of a tuned amplifier. A large signal-to-noise improvement is achieved when this system is calibrated and optimized with the metallic species of interest. This approximately compensates for the selectivity loss in using a continuum source in place of special lamps. Employment of this system is described in detail for the detection of mercury and the results are given for eight metals (Hg, Cd, Mn, Zn, Pb, Ni, Cu, and Cr). Data scatter when using this second-harmonic spectrometer system is roughly 1/10 that of standard procedures.
Effects of sheath potential of source plasma on characteristics of low energy beam extraction
Authors: Ueda Yoshio , Sakashita Yoshiaki , Yoshikawa Takafumi , Isobe Michiro , Nishikawa Masahiro , Goto Seiichi
Published: July 2002

In order to obtain a high brightness ion beam from a plasma ion source in the low energy region (150 eV), the effects of sheath potential on the ion beam characteristics such as beam divergence and brightness have been studied experimentally. A bucket-type ion source (magnetic multicusp ion source) with an accel–decel triode extraction system is used for the experiment. Bias voltage between a discharge chamber and a positive (plasma) electrode is applied for sheath potential control. Two types of electrode systems have been examined, such as straight hole aperture (S type) and recessed hole aperture (R type), and have found that the effects of the bias voltage on the beam characteristics depend on the type of aperture and the deceleration voltage. For an S-type system, the application of bias voltage improves the beam performance in a low deceleration voltage (−600 V), but not in a high deceleration voltage (−1600 V). For an R-type system, almost no improvement is observed in all deceleration voltages. Although the highest brightness is obtained in a deceleration voltage of −1600 V without the application of bias voltage in the S-type system, the significant fraction of the intersecting beam to the electrodes is present in this case.
Computer controlled probe diagnostic system and applications in a magnetized laboratory plasma
Authors: Hansen K. , Klinger T. , Piel A.
Published: July 2002

A computer controlled acquisition and evaluation system for electrostatic probes is presented. Fully automatic evaluation of the probe characteristics yields electron temperature, plasma potential, and density during the recording. Two-dimensional probe positioning is accomplished with stepping motors. The system is characterized by 12-bit probe current resolution and extremely wide probe voltage range (±130 V). It is tested in a collisionless argon magnetoplasma and compared to standard wave diagnostic techniques for magnetized plasmas, i.e., the resonance cone technique. The influence of the probe radius on the electron current in a magnetized plasma is studied experimentally. The two techniques yield identical density and temperature values within 20% accuracy and therefore show the reliable applicability of the automatic evaluation system.
A wavemeter for measuring changes in wavelength of pulsed dye lasers
Authors: Thattey S. S. , Dongare A. S. , Dasgupta K. , More S. R. , Nair L. G.
Published: July 2002

The performance of a simple wavemeter for measuring changes in wavelength of a pulsed dye laser is described. Details of optics and electronic circuitary used, along with the algorithm for wavelength measurement, are given. Using this instrument wavelength changes of a dye laser could be measured, as well as introduced through a user interface, with an accuracy of 1 ppm.
A compact neutron counter telescope with thick radiator (COTETRA) for fusion experiments
Authors: Osakabe M. , Itoh S. , Gotoh Y. , Sasao M. , Fujita J.
Published: July 2002

A new type of neutron spectrometer, which is called COTETRA (counter telescope with thick radiator), has been developed for diagnosing DT fusion plasma. It is based on the recoil proton measurement and has such advantages as: (1) direct measurement of the neutron energy without the unfolding procedure, (2) sufficiently fine energy resolution and high detection efficiency for 14 MeV neutrons, (3) wide dynamic range of counting rate, and (4) good n–γ discrimination. A prototype of COTETRA was constructed and tested using a DT neutron accelerator. The energy resolution of 5.3%±0.9% was obtained for 14 MeV neutron with the detection efficiency of 1.3×10−4 [counts/(n/cm2)]. A Monte Carlo simulation code was developed and the performances of COTETRA were examined. The calculation agrees with the results of the experiment within its margin of error and suggests that energy resolution up to 3% with a detection efficiency of 10−5 [counts/(n/cm2)] could be achieved if the condition of the radiator could be successfully adjusted.
First use of the UV Super-ACO free-electron laser: Fluorescence decays and rotational dynamics of the NADH coenzyme
Authors: Couprie M. E. , Mérola F. , Tauc P. , Garzella D. , Delboulbé A. , Hara T. , Billardon M.
Published: July 2002

Significant improvements in the performances of the Super-ACO storage ring free-electron laser (FEL) at 800 MeV have been obtained recently: enhancement of the output power in the ultraviolet, laser duration of 10 h for the same injection of positrons, long-term stability with a micropulse of 60 ps FWHM. A first series of experiments using this FEL has then been successfully performed. Taking advantage of the time structure, the polarization and the high power of the source at 350 nm, the polarized fluorescence decays of the reduced nicotinamide adenine dinucleotide coenzyme (NADH) were studied in aqueous solution, using the single-photon counting (SPC) technique. The experimental setup is described, including the Super-ACO FEL characteristics and diagnostics. The FEL working point has been first optimized by monitoring the SPC apparatus function. A complete fluorescence experiment required about 30 min of data acquisition, during which the best integrated instrumental response had a FWHM of 110 ps. Measurements performed in such a way lead to the unambiguous separation of two close lifetime components of 0.28 and 0.62 ns in the fluorescence decays of NADH at 20 °C, in good agreement with previous works. The thermodynamic parameters obtained from temperature studies show that the NADH fluorescence heterogeneity is consistent with the ground-state folding equilibrium of the coenzyme, as characterized by many other spectroscopic techniques. From the fluorescence anisotropy decays, an apparent hydrodynamic radius of about 6 Å is determined, while on the other hand, a large initial depolarization of the fluorescence indicates a fast independent motion of the nicotinamide ring. The quality of the collected data fully meets the requirements for the study of more complex systems such as fluorescent compounds bound to proteins or membranes. Thus, the feasibility of use of a storage ring UV FEL for this type of time-resolved experiments on the subnanosecond time scale has been demonstrated.
Broadband Pockels cell and driver for a Mark III-type free electron laser
Authors: Becker Klaus , Johnson J. Bruce , Edwards Glenn
Published: July 2002

A Pockels cell with an operating range of 2 to 10 μm has been designed, constructed, and tested for use with the Vanderbilt free electron laser. The Pockels cell can be continuously adjusted to switch out from 80 ns to the full 6 μs duration of the FEL macropulse. The extinction ratio is better than 180:1 and the optical pulse is square with rise and fall times under 10 ns. The high voltage drivers are based on semiconductor switches that are compact and mounted directly to the Pockels cell; this design avoids problems associated with fast, high voltage pulses traveling in cables. In addition, designs for two alternative drivers to generate optical pulses with durations ranging from a few nanoseconds down to the subnanosecond regime are presented here. Prototypes using single high voltage transitions have been constructed and tested electrically.
Construction of a time-frequency two-dimensional multiplex coherent anti-Stokes Raman scattering spectrometer having 15 ps time resolution
Authors: Tahara Tahei , Hamaguchi Hiro-o
Published: July 2002

A picosecond time-resolved multiplex coherent anti-Stokes Raman scattering (CARS) spectrometer based on a new principle has been constructed using a femtosecond laser, nanosecond lasers, and a streak camera. The second harmonic of the output from the femtosecond Ti:sapphire oscillator/regenerative-amplifier system is used for the photoexcitation. The second harmonic of a nanosecond Nd:YLF laser is used as CARS probing ω1 radiation, and the output of a nanosecond broadband dye laser is used as ω2 radiation. CARS signals, which are generated from the sample during the nanosecond probing pulses, are analyzed in the frequency domain by a spectrograph and are resolved in the time domain by a streak camera. This enables us multiplex CARS measurements not only in the frequency domain but also in the time domain (termed two-dimensional multiplex CARS). Consequently, CARS spectra at various delay times are obtainable with a single measurement. Owing to the short duration and high stability of the femtosecond pumping pulses, time resolution as high as 15 ps has been achieved. Picosecond time-resolved CARS spectra of all-trans retinal and β-carotene are presented to demonstrate the high capability of the constructed system. The factors which determine the time resolution of this CARS spectrometer are discussed.
Twin-horseshoe resonator—An investigation
Authors: Gonord Patrick , Kan Siew
Published: July 2002

Two parallel-plate copper rings with diagonally opposite gaps separated by a dielectric medium form a resonator the natural resonant frequency which is a function of the transmission line propagation constant, its characteristic impedance, as well as the series inductance of the two loops. By means of an extra capacitor connected to each gap, one can easily vary the frequency of the resonator. The derived expressions, valid also for coaxial line devices, relating resonant frequency to other circuit constants, can serve as a tool for those who intend to use this kind of resonator to design NMR surface coil antennas. Experimental results are in good agreement with theory provided the circuit constants are accurately known.
Experimental verification of the three-dimensional diffusion effect of x-ray-produced charges in semiconductor x-ray detectors on the quantum-efficiency enhancement
Authors: Cho T. , Kohagura J. , Hirata M. , Sakamoto Y. , Yatsu K. , Tamano T. , Miyoshi S. , Hirano K. , Sekitani T. , Yagishita A. , Maezawa H. , Saitoh Y. , Sato K. , Miyahara S. , Kondoh T. , Tanaka S. , Snider R. T.
Published: July 2002

One of the characteristic physical principles of our recently proposed theory on the x-ray-energy response of a semiconductor x-ray detector is the effect of the three-dimensional diffusion of x-ray-produced charges in a semiconductor field-free substrate region. It is found and reported that the quantum efficiency of a semiconductor x-ray detector is enhanced when this phenomenon is taken into account, and the data on the x-ray-energy response of the semiconductor detector using monochromatized synchrotron radiation at the Photon Factory are actually well fitted by the theory. In addition, we measure the diffusion length L of the detector using a precisely collimated x-ray narrow beam and a multichannel detector array setting on a μm-order position-controllable stage. The verification of the consistency between this observed value of L and the predicted value of L from our theory on the quantum efficiency, has been achieved.
Efficiency and stray light measurements and calculations of diffraction gratings for the Advanced Light Source
Authors: McKinney Wayne R. , Mossessian Dmitri , Gullikson Eric , Heimann Philip
Published: July 2002

Water-cooled gratings manufactured for spherical grating monochromators of the Advanced Light Source beamlines 7.0, 8.0, and 9.0 were measured with the laser plasma source and reflectometer in the Center for X-ray Optics at Lawrence Berkeley Laboratory. The square-wave gratings are ion milled into the polished electroless nickel surface after patterning by holographic photolithography. Absolute efficiency data are compared with exact electromagnetic theory calculation. Interorder stray light and groove depths can be estimated from the measurements.
Improvement of beam divergence in pseudoparaboloidal bending of an x-ray mirror
Authors: Mori Takeharu , Sasaki Satoshi
Published: July 2002

The surface of a flat-plate quartz mirror has been investigated by bending it into a pseudoparaboloid with the mirror bender in BL-3A. The evaluation of the beam collimation and actual mirror curvature have been made by x-ray diffraction using the (+,−,−) arrangement of Si(111) crystals. The FWHM in (+,−,−) rocking curves of a whole beam was reduced from 42.7 to 14.1 arcsec with the collimating mirror. The distances deviating from the ideal paraboloid were found to be very small, i.e., less than 0.6 and 3.5 μm in ±200 and ±400 mm in the mirror length, respectively. The efficiency of the mirror was also estimated from the CeO2 diffraction patterns which were slightly but significantly improved in FWHM and peak intensity with the collimation.
Comments on the use of asymmetric monochromators for x-ray diffraction on a synchrotron source
Authors: Nave Colin , Gonzalez Ana , Clark Graham , McSweeney Sean , Cummings Stewart , Hart Michael
Published: July 2002

Crystals of germanium or silicon provide monochromatic radiation on synchrotron radiation beamlines. By using asymmetrically cut crystals, it is possible to alter the properties of the beam in position, angle, wavelength space. The results obtained from using two types of asymmetrically cut monochromators are compared with theory. For single crystal focusing monochromators, the asymmetry results in a dispersion term and a resultant broadening of the focal spot. The expression for the broadening given here differs from that given previously for these type of monochromators and has implications for the design of beamlines where the x-ray source has a small size. Asymmetric channel cut monochromators are not commonly used for x-ray diffraction on a synchrotron. However, we show here that, compared with a symmetric monochromator, intensity gains of three or more can be obtained with a simple compact design.
Anticlastic curvature measurements on unribbed crystal optics for synchrotron radiation
Authors: Quintana J. P. , Dolin Yu. , Georgopoulos P. , Kushnir V. I.
Published: July 2002

Various methods have been proposed for measuring the distortion in perfect crystals using double-crystal methods. The majority of these methods rely on making comparisons between double-crystal rocking curve measurements under the spatial extent of an extended x-ray beam. Unless the beam is large and parallel (such as at a synchrotron bending magnet), these methods are not easily scalable to large crystals (e.g., crystal focusing elements for synchrotron beamlines) due to the mechanical inaccuracies inherent in moving the various optical components. We present a method based on a scanning source which simplifies the problems in scaling double-crystal methods to large optics. In addition, results using this method are presented on a ribless sagittal focusing Si(111) crystal demonstrating that the anticlastic deviation can be made to be less than ±1 s of arc over a 1-cm-long section parallel to the sagittal axis.
Design and thermal stress analysis of high-power x-ray monochromators cooled with liquid nitrogen
Authors: Rogers C. S. , Assoufid L.
Published: July 2002

Cryogenically cooled, single-crystal silicon, x-ray monochromators offer much better thermal performance than room-temperature silicon monochromators. The improved performance can be quantified by a figure-of-merit equal to the ratio of the thermal conductivity to the coefficient of thermal expansion. This ratio increases by about a factor of 50 as the temperature is decreased from 300 to 100 K. An extensive thermal and structural finite element analysis is presented for an inclined, liquid-nitrogen-cooled, Si monochromator crystal diffracting 4.2 keV photons from the [111] planes using undulator A at the Advanced Photon Source. The angular size of the beam accepted on the crystal was chosen to be 50 μrad vertically and 120 μrad horizontally. The deflection parameter, K, was 2.17 for all cases. The peak power density at normal incidence to the beam was calculated to be 139 W/mm2, and the total power was 750 W at a distance of 30 m from the source for a positron current of 100 mA. The crystal was oriented in the inclined geometry with an inclination angle of 85° for all cases. The performance of the crystal was investigated for beam currents of 100, 200, and 300 mA. The calculated peak slopes of the diffraction plane over the extent of the beam footprint were −1.17, −2.35, and 0.33 μrad, and the peak temperatures were 88.2, 102.6, and 121.4 K, respectively. The variation in the Bragg angle due to change in d spacing across the beam footprint was less than 1 μrad for all cases. These results indicate that a properly designed, cryogenically cooled, inclined silicon monochromator can deliver the full brilliance of undulator A at even the highest machine currents.
p
e
p
o: A program for the calculation of the reflectivity of cylindrically bent Laue crystal monochromators
Authors: Schulze C. , Chapman D.
Published: July 2002

p e p o is a program for the calculation of the reflection profiles of cylindrically bent Laue crystal monochromators based on the Penning and Polder theory of x-ray diffraction in slightly strained crystals. The creation of new wave fields as well as an anisotropic model for the crystal deformation has been added to the original theory. The program runs under the computing environment IDL and is widget based. The calculation of perfect flat crystal reflectivity curves in Bragg and Laue geometry using the formulas presented by Zachariasen is included. The agreement with experimental results is excellent, allowing the derivation of focal properties from the calculated reflectivity curves.
Heat load problem of an entrance slit on an undulator beamline
Authors: Senf F. , Menthel U. , Peatman W. B.
Published: July 2002

The heat load on the entrance slit of a spherical grating monochromator on a high-flux undulator beamline at BESSY has been studied. The effect of the concentrated power profile was analyzed for two different slit geometries by using a finite element method. In the worst case of a mis-steered beam a slit blade would have to withstand 50 W and a maximum power density of 780 W/mm2. The temperature in the focal spot rises by about 90 and 110 K above the water temperature in the cooling at the back side. As a result of this, the slit blade itself expands depending on the slit model, by 15.3–16.5 μm. Even though most of the expansion could be compensated for, a bump remains in the center of the slit blade.
Backscattering analyzer geometry as a straightforward and precise method for monochromator characterization at third-generation synchrotron-radiation sources (abstract)
Authors: Snigirev A. A. , Lequien S. , Suvorov A. Yu.
Published: July 2002

With the assessment of the third generation of synchrotron-radiation sources, insertion devices (ID) are going to become extensively used. The choice of the ID field configuration allows the optimization of the photon flux at the desired energy. This attractive situation results in a much higher flux on optical elements, mainly on monochromators for which new cooling schemes have to be developed. These latter must be characterized under operating conditions and generally, the figure of merit for monochromators is the rocking curve (RC) measurement. By varying the ID field, the monochromator may be fully characterized with regard to the heat load. To achieve this aim, we have proposed and tested a double-crystal setup where a Si analyzer crystal installed in backscattering geometry (BSG) is coupled with a silicon p-i-n photodiode as the detection system (Fig. 1). The analyzer was a standard Si wafer (111) orientation, from which we used the following Bragg reflections: 333, 444, 555, 777, 888, 999, ... to measure the RCs of monochromators keeping the analyzer fixed. We were then able to probe the formers at the respective energies 5.9, 7.9, 9.9, 13.8, 15.8, 17.8 keV, etc. Setting the analyzer crystal in BSG, we get several-fold benefits from the method: (1) A very good angular resolution (∼10−6 rad) when one combines the BSG analyzer with narrow slits (∼100 μm). (2) A high-energy resolution yielding to a calibration of the monochromator with an accuracy better than 1 eV.

(3) The analyzer crystal attenuates the reflected intensity which avoids the use of any scatterer foil to count the number of photons. We directly used photodiodes which are well known to respond linearly to radiation intensities and to have a high dynamic range (more than 6 decades). (4) No fine mechanics is needed for the analyzer, just a simple manual turntable can be used to set the analyzer in BSG through the utilization of a laser beam. Results on different tests for operating liquid–N2-cooled channel-cut monochromators at microfocus and high brilliance beamlines will be presented and discussed. We gratefully acknowledge the support of the ESRF EDS group, especially C. Riekel, P. Engström, I. Snigireva, M. Kocsis, P. Bösecke, and O. Diat.
Compact monochromator for the multipurpose X3 synchrotron beamline at NSLS
Authors: Darovsky A. , Meshkovsky I. , Coppens P.
Published: July 2002

A newly designed monochromator assembly for the State University of New York (SUNY) X3 beamline at the National Synchrotron Light Source (NSLS) consists of two monochromators enclosed in a single vessel, positioned at 7813 mm from the bending magnet source. It allows delivery of monochromatic radiation into two independent end stations. The first unit contains two crystals reflecting in the vertical plane, and operating in a ‘‘channel-cut’’ mode. The second of the crystals can be bent for sagittal focusing of the beam. The second monochromator unit reflects 2 mrad of the radiation fan between the A2 and B branches of the beamline at a fixed angle of 2Θ=12°, and serves the sideways experimental station A1. Four interchangeable triangular crystals, mounted on a rotary holder, provide x rays of four different energies.
Performance check of β-alumina as a soft x-ray monochromator crystal
Authors: Hiraya Atsunari , Matsuda Kazunori , Hai Yang , Watanabe Makoto
Published: July 2002

In order to extend the available photon energy range of the double-crystal monochromator (DXM) to lower energy than that obtainable with beryl crystal, β-alumina crystals (Na2O [Al2O3]11, 2d=22.53 Å) were tested as the monochromator crystal. The intensity and resolution of the monochromatized x ray from the DXM with the β-alumina crystals were compared to those with beryl crystals. The β-alumina crystals cover the energy region from 580 to 1740 eV (Bragg angle 71.5°–18.5°) with an intensity more than ten times higher than that obtained with the beryl crystals. The resolution of a pair of the β-alumina crystals used is estimated to be about 1 eV at 931 eV, which is almost two times wider than that of beryl crystals (0.46 eV).
Multilayer coated laminar gratings in the soft x-ray region
Authors: Ishiguro Eiji , Kawashima Tsutomu , Yamashita Koujun , Kunieda Hideyo , Yamazaki Takashi , Sato Kuninori , Koeda Masaru , Nagano Tetsuya , Sano Kazuo
Published: July 2002

Multilayer diffraction gratings have been fabricated by depositing platinum-carbon on a laminar grating with an electron beam evaporation method. Their reflectivities and diffraction efficiencies were measured by using monochromatized synchrotron radiation in the 1.2–2.8 keV region and the characteristic x-rays of Cu Kα (8.05 keV) and evaluated in comparison with calculated values based on a dynamical theory.
Precision demanded of a Rowland circle monochromator: Its realization
Authors: Senf F. , Lammert H. , Flechsig U. , Zeschke T. , Peatman W. B.
Published: July 2002

A new monochromator design for high-energy resolution requires precise angle positioning of the grating during simultaneous linear motion of the grating vessel. The results obtained show that the required precision in the tilt angle of 0.05 arcsec can be met by the prototype of this monochromator. This is mainly achieved by a compensation of unavoidable systematic—time dependent and time independent—deviations from the ideal shape of the granite block on which an air bearing system moves. The compensation can be performed using the angle positioning system of the grating. The positioning accuracy here is better than 0.1 arcsec and shows a reproducibility of about 0.01 arcsec rms. The accuracy is provided by an angle encoder directly connected to the axis of rotation to be measured. A closed loop connection of the positioning and measuring system then allows a control on the grating angle within ± 0.03 arcsec. Thus, the mechanical precision made necessary by the use of the nearly perfect geometric surfaces of present day plane and spherical mirrors and gratings has been experimentally shown to be achievable.
Powder diffraction using imaging plates at the Australian National Beamline Facility at the Photon Factory
Authors: Garrett R. F. , Cookson D. J. , Foran G. J. , Sabine T. M. , Kennedy B. J. , Wilkins S. W.
Published: July 2002

A novel x-ray diffractometer was installed at the Australian National Beamline Facility at the Photon Factory, Japan, in October 1993. One of the major capabilities of the instrument is high speed high resolution powder diffraction using imaging plate detectors. The diffractometer combines a two circle goniometer and a large cassette in which imaging plates can be loaded covering 320° of 2θ. The diffractometer is enclosed in a large vacuum chamber and can be operated in air, vacuum, or helium. Recently, powder data has been obtained from rutile (TiO2) and NBS Si 640b at wavelengths from 0.62 to 1.9 Å using imaging plates, and has been used to characterize the performance of the instrument. The data has been refined using the Rietveld method and R values of under 2% obtained. The resolution of the system varies from a minimum of about 0.04° to around 0.25° at 2θ angles around 160°, which is the equal of most synchrotron based powder diffractometers, and only slightly worse than that obtained using an analyzer crystal and scintillation detector. Using the imaging plates, 160° of data is simultaneously acquired in an exposure of about 10 min, compared to conventional counter diffractometer scans which routinely exceed 10 hours.
A two-color spatial-scanning pyrometer for the determination of temperature profiles in combustion synthesis reactions
Authors: Anselmi-Tamburini U. , Campari G. , Spinolo G. , Lupotto P.
Published: July 2002

This article describes a new two-color pyrometer able to obtain multiple temperature reading using charge couple device type sensors. The device was tailored to fit the characteristics of self-propagating high-temperature synthesis processes in order to be able to detect temperature profiles and propagation rates of the combustion front. The light intensities at the two working wavelengths and the relative temperature profile are detected in 512 or 1024 points on the sample surface. The time between the acquisition of two profiles can be varied between 100 ms and 10 s. The pyrometer is interfaced with the BUS of a PC and is fully software programmable. The constructive details, procedure for sensors alignment, and temperature calibration are described. Few examples of applications are discussed.
Development of lithium beam emission spectroscopy as an edge fluctuation diagnostic for DIII-D (invited)
Authors: Thomas D. M.
Published: July 2002

As part of the DIII-D diagnostic complement designed to address L–H transition physics issues, we have developed and commissioned a diagnostic neutral lithium beam and multichannel fluorescence detection system to investigate the edge plasma density and its associated fluctuations. The use of lithium offers several advantages for tokamak edge beam emission spectroscopy studies, including large excitation cross sections which are relatively insensitive to temperature variation, the availability of the 670.8 nm resonance line well separated from most plasma line emission, and the suitability of modest beam energies and currents to probe even dense H-mode plasmas. These features permit measurements of collisionally induced fluctuations to be obtained with good spatial (<1 cm) and temporal (<10 μs) resolution. The improvements over previous lithium beam diagnostics which were required to successfully make these measurements in a large, remotely controlled machine environment will be discussed, along with the present state of the diagnostic system and our plans for future improvements of this technique.