bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-calibration of semiconductor photodiodes in the soft x-ray region
Authors: Krumrey M. , Tegeler E.
Published: July 2002

A self-calibration procedure is presented for semiconductor photodiodes to be used as detectors in the soft x-ray region. In this procedure the spectral responsivity is calculated according to a model from experimentally accessible parameters of the detector. The thicknesses of the dead layer and the space charge region as well as the diffusion length have been determined in monochromatic radiation by investigating the angular dependence of the photocurrent. The mean energy for electron-hole pair creation has been determined in calculable undispersed synchrotron radiation of the primary standard source BESSY. The obtained uncertainties of the spectral responsivity in the photon energy region between 150 and 2500 eV are ≤4.2% for newly developed Si n on p diodes and ≤6% for GaAsP/Au diodes. The calibrated photodiodes were used to determine the quantum efficiency of photoemissive gold diodes which is up to four orders of magnitude lower than that of semiconductor photodiodes.
Measurement of radii of curvature of slightly bent crystals using a one-dimensional detector
Authors: Gao Dachao , Wilkins Stephen W. , Stevenson Andrew W. , Pogany Andrew P.
Published: July 2002

A new x-ray diffraction method is described for measuring radii of curvature of crystals using a one-dimensional solid-state detector together with an extremely parallel incident x-ray beam. The present method is based on the measurement of the slope of loci of rocking curve maximum in a contour map of x-ray rocking curves versus position on the sample. The detection limit for the radius of curvature is estimated to be a few thousand meters using this method. The local variation of the curvature over a sample is easily revealed and precisely determined from the contour map of x-ray rocking curves. Several examples of curvature determination by the present method are presented and compared with the results of the commonly used double-crystal diffractometer method.
Triple-pendulum vibration isolation system for a laser interferometer
Authors: Tsubono Kimio , Araya Akito , Kawabe Keita , Moriwaki Shigenori , Mio Norikatsu
Published: July 2002

We have developed a triple-pendulum vibration isolation system for suspended mirrors used in a laser interferometer for gravitational wave detection. Owing to the passive damping method using high-performance permanent magnets, the system has a very simple, compact structure. We measured the isolation ratio for vibration below 40 Hz and confirmed that the observed and calculated values are in good agreement. The stability of the system has been demonstrated by operating a Michelson laser interferometer incorporated with a mirror mounted on the vibration isolation system.
Low-energy-electron-diffraction system using a high-performance electron gun and position-sensitive detectors
Authors: Men F.-K. , Clothier B. L. , Erskine J. L.
Published: July 2002

A new low-energy-electron-diffraction (LEED) instrument is described that combines resistive-anode-based position-sensitive detectors with a high-resolution electron gun capable of producing a beam having high spatial coherence (large instrument transfer width). The system produces digitized images of LEED patterns as well as high-resolution spot profiles of individual beams using incident currents in the picoampere range, thus vastly reducing or eliminating electron beam damage to sensitive surfaces. The display resolution of both spot profile and full display images is 1024×1024 channels, and the dynamic range is 16 bits (≊104) per channel. The resistive anode pulse processing electronics limits maximum data acquisition rates to 1×106 s−1. Specially developed software permits manipulation and numerical processing of the digitized two-dimensional images at full resolution to produce spot contour maps, spot line profiles along arbitrary directions, Fourier transforms of spot profiles, integrated spot intensities, and intensity vs voltage curves with suitably subtracted background.
Sintered diamond anvil high-pressure cell for electrical resistance measurements at low temperatures up to 50 GPa
Authors: Akahama Y. , Kobayashi M. , Kawamura H. , Endo S.
Published: July 2002

This study reports the construction and working of a sintered diamond anvil high-pressure cell for performing electrical resistance measurements using a four-probe method at cryogenic temperatures. The apparatus has been designed to minimize the pressure shift during the cooling cycle from room temperature to 1.2 K. Pressure is calibrated using the pressure dependence of the superconducting transition temperature (Tc) of Bi to 50 GPa. The usefulness of the apparatus is demonstrated by electrical resistance and Tc measurements on Se and Zr up to 60 GPa.
Response of X-UV photodiodes to 1.5–17.5 keV x rays and MeV alpha particles
Authors: Wenzel Kevin W. , Li Chi-Kang , Petrasso Richard D. , Lo Daniel H. , Bautz Marshall W. , Ricker George R. , Hsieh Ed
Published: July 2002

The absolute x-ray response of three X-UV photodiodes was measured over an energy range of 1.5–17.5 keV so that they could be used to calibrate x-ray imaging systems for the ASCA satellite mission. An intense electron-beam x-ray generator was used to test both the dc and ac x-ray response at 1.5, 4.5, 8.0, and 17.5 keV, and an 55Fe source was used to examine one of the photodiodes at 5.9 keV. The x-ray response was determined by comparing the X-UV diode signal to that of a previously calibrated silicon surface barrier diode (SBD). The X-UV detector response was similar to the SBD response at low energies (1.5 and 4.5 keV). At 8 keV, the X-UV detectors exhibited about 70% of the SBD response, and at 17.5 keV, about 50%. This result is surprising, because the X-UV diodes actually have a greater silicon thickness than the SBD. In contrast to our findings for SBDs in the past, this implies that not the entire physical volume of these detectors comprises the active volume. The X-UV detector x-ray response was also examined as a function of the applied bias voltage. No significant bias voltage dependence of the x-ray signal was found, which indicates that the depletion layer thickness does not determine the active volume either. However, the detector noise was found to decrease substantially as the applied bias was raised from zero to a few volts. Response of these detectors, operated in pulse mode, to 226Ra α particles indicated large charge carrier recombination in the bulk silicon. This feature renders these detectors unsuitable for most charged-particle spectroscopy applications.
Improved Foucault imaging of magnetic domains with a modified 400 kV transmission electron microscope
Authors: Doole R. C. , Petford-Long A. K. , Jakubovics J. P.
Published: July 2002

Modifications have been made to a 400 kV side-entry transmission electron microscope fitted with a low-field objective pole piece, in order to position apertures close to the back focal plane of the objective lens, as there is no direct access to the required position in the column. The modifications have facilitated developments in the imaging of magnetic domain structure in magnetic materials using the Foucault technique, for which the correct positioning of the objective aperture is crucial. All usual transmission electron microscopy facilities are retained, allowing a full range of specimen holders and imaging modes to be used along with TV recording and electron energy loss spectroscopy. Some initial results are presented from Fe/Cr and Co/Pt multilayer films, for which the Lorentz deflection angle is very small, and for which the Fresnel imaging mode is of limited use as the grain structure contrast masks the magnetic contrast. Initial results are also presented from NdFeB permanent magnet material for which the use of a high electron accelerating voltage is necessary.
A high-resolution thrust stand for ground tests of low-thrust space propulsion devices
Authors: Sasoh Akihiro , Arakawa Yoshihiro
Published: July 2002

A new type of thrust stand for accurately measuring a low-level (10 mN to 1 N) thrust produced by a space propulsion device in its ground tests has been developed. Vacuum bellows are utilized both as a feedthrough tool from electrical power, propellant, and coolant supplies to a thruster installed in a vacuum chamber, and as an elastic support. In order to improve thrust resolution, friction force on radial bearings at a fulcrum is minimized by eliminating bearing radial forces. 0.5 mN thrust resolution was experimentally obtained. Utilizing thrust stand vibration characteristics measured in advance, a computer-processed, quick thrust reading system has been established.
Time modulation of an x-ray beam by surface acoustic waves
Authors: Roshchupkin D. V. , Brunel M.
Published: July 2002

X-ray time modulation was investigated in the total external reflection conditions in the process of x-ray diffraction on the surface of the YX cut of a LiNbO3 crystal modulated by the rectangular pulses of the surface acoustic waves. It is shown that the period and the width of the x-ray pulses are determined by the period and the width of the rectangular surface acoustic waves pulses. Through the use of surface acoustic waves pulses it is possible to form the x-ray pulses with special forms of x-ray beam control, for investigation of time modulated process in microelectronic materials, and also for x-ray/acoustic microscopy, which can be based on thermal or thermoelastically generated acoustic waves by x-ray pulses at the depth of x-ray penetration in investigating materials. These experiments have been made at CNRS (Grenoble, France) using a rotating copper anode.
Distortion-free, calibrated LiNbO3 piezoscanner for probe microscopes with atomic resolution
Authors: Heider U. , Weis O.
Published: July 2002

We developed a piezoelectric scanner for probe microscopes that uses only single-domain LiNbO3 crystals as a piezoelectric transducer material in order to avoid nonlinearity, hysteresis, and creep that is always present in piezoelectric ceramics. A raster area of about 50×50 nm2 is within reach of a scanner that uses three double-plate translators and a scanning voltage of 300 V peak to peak. The performance of monocrystal scanners for investigations in the range of atomic resolution is demonstrated by imaging the well-known surface of highly oriented pyrolytic graphite.
Photopyroelectric detection of hydrogen/oxygen mixtures
Authors: Christofides C. , Mandelis A. , Rawski J. , Rehm S.
Published: July 2002

It has been found that the photopyroelectric (PPE) sensor made of thin-film polyvinylidene fluoride, sputter coated with palladium, can detect trace hydrogen gas in the presence of pure oxygen without significant drift and stabilization problems. Presently, hydrogen concentration as low as 0.1% in flowing 99.9% oxygen has been detected under standard temperature and pressure conditions. The detector has been used without a reference sensor (single mode) which simplifies the sensor system compared to previous work, at the expense of sensitivity limits. This paper describes the detection of hydrogen gas in hydrogen/oxygen mixtures, and deals with some instrumental aspects of the PPE sensor device such as background noise and signal drift. Some techniques for stabilization are also discussed.
Emissive probe as a reference electrode in probe measurements
Authors: Kimura T. , Ohe K.
Published: July 2002

An emissive probe is used as a reference electrode in probe measurements. Some conditions for its use are discussed in a typical plasma. Application of the method to a He positive column results in good agreement of probe current–voltage characteristics with those conventionally detected with respect to the discharge electrode.
Analog ramp generator for a fast scanning tunneling microscope
Authors: Curtis Robert , Krueger Michael , Ganz Eric
Published: July 2002

We present an analog ramp generator for use in fast scanning tunneling or scanning probe microscopes. The analog design achieves low noise with a relatively simple circuit layout. The circuit requires minimal computer overhead because the X and Y ramps are generated using just two clocks and one digital control line. The resulting X and Y ramps are automatically set equal in magnitude, yielding images which remain square despite changes in scan size, number of lines per image, and tip velocity. We have used the circuit at X ramp frequencies above 10 kHz.
In-laboratory stopped-flow extended x-ray absorption fine structure apparatus in the dispersive mode for determination of the structure of short-lived intermediates
Authors: Inada Yasuhiro , Funahashi Shigenobu , Ohtaki Hitoshi
Published: July 2002

We have constructed an in-laboratory stopped-flow extended x-ray absorption fine structure (EXAFS) apparatus by combining laboratory EXAFS equipment in the dispersive mode and a stopped-flow unit with two 150-μm-thick boron nitride windows. The rotating anode x-ray generator with a Mo target was used as an x-ray source. The self-scanning photodiode array was adopted as a position sensitive-linear x-ray detector. In order to obtain a suitable x-ray flux intensity, the accumulation of weak intensities during a short gate time was carried out by repeating the measurements. We have confirmed the performance of our apparatus by repeatedly measuring a number of static EXAFS spectra of 0.20 mol dm−3 aqueous solution of copper(II) sulfate. By use of our newly developed apparatus, we have succeeded in the direct determination of the structure of the reaction intermediate, the heterodinuclear copper(II)/mercury(II) complex, formed in the copper(II) ion incorporation into the homodinuclear mercury(II) complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine.
Two-dimensional electron gas in GaN–AlGaN heterostructures deposited using trimethylamine-alane as the aluminum source in low pressure metalorganic chemical vapor deposition
Authors: Asif Khan M. , Chen Q. , Sun C. J. , Shur M. , Gelmont B.
Published: July 2002

In this letter, we report the fabrication of high quality GaN–Al0.1Ga0.9N heterostructures using trimethylamine-alane as the aluminum source. The two-dimensional electron gas (2DEG) with mobility values as high as 5000 cm2/V s at 150 K is demonstrated. We also present the results of our calculations of the 2DEG mobility at the GaN–Al0.1Ga0.9N heterointerface. Our calculations show that the mobility enhancement in the 2DEG is related to a much larger volume carrier concentration (compared to bulk GaN) and, therefore, to a larger Fermi energy and to a more effective screening of impurity and piezoelectric scattering.
Obliquely backscattered Thomson scattering system on the compact helical system
Authors: Narihara K. , Minami T. , Yamada I. , Yamauchi K.
Published: July 2002

A Thomson scattering system with an obliquely backscattered configuration with a novel, high throughput collection system was developed and tested on a plasma confinement device, the compact helical system. It can yield the full profiles of electron temperature and density along a major radius with the spatial resolution ranging from 1.5 to 4 cm at a repetition rate of up to 250 Hz.
Advances in the measurement of density and thermal expansion of undercooled liquid metals
Authors: Racz L. M. , Egry I.
Published: July 2002

The determination of thermophysical properties of liquid metals in the undercooled state must, in the current state of the art, be accomplished by a contactless method. Presented here is an improvement of the existing image acquisition and processing techniques that are used in determining the density of undercooled metallic melts. The contactless method used is electromagnetic levitation. The levitation apparatus, method of image acquisition, digital image processing, and calculation methods are described, followed by an analysis of the errors implicit in the technique.
Development of a hard x-ray imaging microscope
Authors: Lai B. , Yun W. , Xiao Y. , Yang L. , Legnini D. , Cai Z. , Krasnoperova A. , Cerrina F. , DiFabrizio E. , Grella L. , Gentili M.
Published: July 2002

A hard x-ray imaging microscope based on a phase zone plate has been developed and tested. The zone plate, with a 5 cm focal length and a 0.2 μm smallest linewidth, was used to image 8 keV x rays from the samples. The imaging microscope can be used to obtain nearly diffraction-limited resolution over the entire imaging field, and its resolution is almost independent of source size and source motions. We have tested such an imaging microscope, and a resolution of about 0.4 μm was obtained. The images were obtained with an exposure time of less than 1 min, for a magnification factor of 30 in the x rays. The x rays were then converted into visible light, and another 7 times magnification were obtained by using a lens system coupled to a charge coupled device camera. The results from the imaging microscope, and possible applications, will be discussed.
A low pressure parallel plate proportional counter optimized for detection of nitrogen fluorescence
Authors: Crowder T. , Ade H.
Published: July 2002

Detection of nitrogen fluorescence at 400 eV has been inefficient with proportional counters using polymer windows due to the low transmission of photons at this energy by carbon based compounds. Typically, two polypropylene films in a differentially pumped arrangement are used. We have chosen a single 230 nm silicon nitride (Si3N4) film as a window for a parallel plate avalanche counter. The Si3N4 window provides efficient N fluorescence detection while effectively filtering lower energy fluorescence. It can withstand atmospheric pressure and has extremely low gas leakage. It is therefore possible to operate the detector within a wide pressure range, even in an ultrahigh vacuum (UHV) environment. The detector has been constructed and its energy resolution is currently being tested. Results to date as well as future goals and applications will be discussed.
X-ray signal processing electronics for solid state detectors
Authors: Farrow R. , Derbyshire G. E. , Dobson B. R. , Dent A. J. , Bogg D. , Headspith J. , Lawton R. , Martini M. , Trammell R. , Buxton K.
Published: July 2002

With recent improvements in synchrotron sources and x-ray optics great pressures have been placed on detector systems to produce higher count rates and better resolutions. Present high performance 13 element germanium detector systems can give reasonable count rates with good resolution (∼104–105 kHz per channel and ∼250 eV FWHM at Fe55 with 0.5 μs shaping time). However, these systems are restricted by limitations in both the detector and in the analog pulse processing after the detector. With respect to the detector, increasing the number of channels without degrading the energy resolution is a great challenge due to increased crosstalk and capacitance. The analog pulse processing electronics are significantly limited by the dead time introduced by the shaping amplifier. This dead time causes pulse pileup at higher rates which leads to nonlinearity and poor resolution. This paper describes the XSPRESS system which has been developed at Daresbury Laboratory for the new Wiggler II beamline 16. This system overcomes previous limits in both signal processing and detector fabrication to give great improvements in system performance. The signal processing electronics departs from standard analog processing techniques and employs sophisticated adaptive digital signal processing hardware to reduce the dead time associated with each event to a minimum. This VME based technology allows us to vastly increase the count rate for each channel yet still retain the ability to gain very good resolution. The detector has been developed through a collaborative agreement with EG&G ORTEC and packs an unprecedented 30 germanium crystals into an extremely small area while still retaining the energy resolution of smaller arrays. This system has increased the throughput rate by an order of magnitude per channel and when all channels are implemented, an increase of at least two orders of magnitude for the whole array should be seen. Data have been taken using this system on the SRS at Daresbury Laboratory and these results will be given along with a detailed explanation of the operation of this system.
Control at 11.4 nm of an XUV Schwarzschild objective
Authors: Mercier R. , Polack F. , Fournet P. , Tissot G. , Marioge J. P.
Published: July 2002

The progress in the quality of XUV and soft x-ray optics requires adapted methods of control. Knife-edge methods have numerous interesting aspects, yielding the information that is usually sought in optical systems. Preliminary results are given, obtained with a simple XUV photodiode as detector.
The penta-prism LTP: A long-trace-profiler with stationary optical head and moving penta prism (abstract)a)
Authors: Qian Shinan , Jark Werner , Takacs Peter Z.
Published: July 2002

Metrology requirements for optical components for third generation synchrotron sources are taxing the state-of-the-art in manufacturing technology. We have investigated a number of effect sources in a commercial figure measurement instrument, the Long Trace Profiler II (LTP II), and have demonstrated that, with some simple modifications, we can significantly reduce the effect of error sources and improve the accuracy and reliability of the measurement. By keeping the optical head stationary and moving a penta prism along the translation stage, the stability of the optical system is greatly improved, and the remaining error signals can be corrected by a simple reference beam subtraction. We illustrate the performance of the modified system by investigating the distortion produced by gravity on a typical synchrotron mirror and demonstrate the repeatability of the instrument despite relaxed tolerances on the translation stage.
Photon channeling in the vacuum-ultraviolet wavelength range
Authors: Rowe J. E. , Malic R. A. , Chaban E. E. , Chichester R. J. , Chiang C.-M. , Royer W. A. , Smith N. V.
Published: July 2002

Experimental measurements in the laboratory have shown a new type of focusing of far ultraviolet light, λ<1000 Å, using tapered capillary tubes similar to those first developed for the near-field scanning optical microscope which we call photon channeling. Silica tubes with taper half angles of ∼0.5°–6° have been tested. An array of capillaries mounted on a rotatable drum placed in front of a collimated photon source obtained from a rare-gas discharge lamp were used. By rotation of the drum, successive capillaries can be brought into alignment, and the photoemission detected by a channeltron-grid detector. The straight capillary intensity shows no significant light guide effect; it simply decreases as the area of the capillary. However, the tapered capillaries show an enhanced transmission (or photon channeling effect). In quantitative agreement with simple numerical estimates, it is found that the transmission enhancement factor varies from ∼10 to 500 times the collimated transmission of a pinhole aperture of the same dimensions with an approximately linear dependence of channeling factor on inverse of the half angle. Useful intensity suitable for photoelectron energy analysis with capillary openings of ∼0.8 μ has been demonstrated.
Thermal analyses of premirrors for a SPring-8 undulator beamline
Authors: Uruga Tomoya , Ohtomo Kiyotaka , Yamaoka Hitoshi
Published: July 2002

Large heat power will be loaded on a premirror in a SPring-8 undulator beamline. It has to be handled without reducing the optical performance of the premirror using as simple devices as possible. Thermal analyses using the finite element method for directly and indirectly water-cooled mirrors were performed for a high-power undulator beam assumed with a total power of up to 660 W and a peak power density of 1.1 W/mm2. The peak temperature rise calculated at the mirror surface is lower than 25 K. The performance of a four point load bending system was simulated to compensate the thermal slope error on the mirror surface in the meridional direction while also taking into account the effects of gravity sag. It is found that the correction of the mirror surface shape can be theoretically expected to produce a cylindrically bent figure in the area of incidence of the first harmonic radiation with a residual slope error less than 0.5 μrad.
Beamline optimization and phase space transformation (abstract)a)
Authors: Bahrdt J. , Flechsig U. , Senf F.
Published: July 2002

The transformation of ray coordinates through a complete beamline is described via a single matrix. This transformation matrix can be used either for conventional ray tracing or for phase space transformation. The matrix elements represent the optical aberrations of the complete system. An optimization program is described that minimizes a weighted sum of the matrix elements.
Fixed-exit double-crystal monochromator for the diffraction beamline at ELETTRA: A new concept for crystal movements
Authors: Bernstorff S. , Busetto E. , Savoia A. , Colapietro M.
Published: July 2002

A fixed-exit double-crystal x-ray monochromator has been constructed for use at the macromolecular crystallography beamline at the Sincrotrone Trieste. For its design a new concept has been developed, which is based on a single rotational stage to control the ϑ or Bragg angle for both the first and second crystal. The stage rotation axis lies in the center of the surface of the first crystal, thus the incoming photon beam remains centered on it over the whole tuning range, which opens the possibility to, e.g., optimize the crystal cooling system. The fixed-exit aspect of the monochromator is achieved by translating the second crystal on one slide only forming an angle α with the surface of this crystal. In this way the translation distance can be kept small thus minimizing detuning effects of the monochromator due to not-perfect slides. The cost is, that during energy scans the beam footprint will wander somewhat on the second crystal surface. It is demonstrated that, by choosing a suitable angle α, both the translation distance T and the length of the second crystal can be reasonably minimized. In fact, e.g., a monochromator having a vertical beam offset of 17 mm and an angular tuning range 5°–30°, T can be kept as small as 25 mm by not even doubling the length of the second crystal with respect to the first one.
A cryogenically cooled, sagittal focusing scanning monochromator for ESRF
Authors: Comin Fabio
Published: July 2002

A double crystal monochromator for fast scans over large energy ranges has been designed, constructed, and tested at ESRF. The instrument is based on a drive unit operated in air that rotates a large wheel sitting in UHV and supporting the two crystal assemblies. The link between the drive and the wheel is realized by a differentially pumped feedthrough. In order to withstand the full power of typical ESRF undulators without noticeable deformation, the first crystal is cooled by liquid nitrogen via pipes located in the hollow core of the differentially pumped feedthrough. The second crystal mount is based on an elastically deformable structure driven by piezoelectric and pneumatic actuators for precise angular adjustments. In its basic version the relative distance between the first and second crystal is kept constant (channel cut type of design), but a nearly fixed beam at the focal plane can be obtained, as the Bragg angle is changed, by the partial compensation of two different effects: the vertical displacement of the exit beam typical of channel cut designs and its divergence with respect to the incoming one due to the difference in lattice spacing between the first cooled crystal and the second one at room temperature. Horizontal focusing of the beam is achieved by sagittal bending of the second crystal. The major drawbacks of crystal focusing, the necessity of changing the radius of curvature while scanning, and the losses in throughput due to the anticlastic deformation experienced at high energy are circumvented by an appropriate choice of the crystal geometry and orientation.
Performance of a bender for a water cooled monochromator crystal at a high power wiggler beamline of the ESRF
Authors: Yamaoka Hitoshi , Freund Andreas K. , Ohtomo Kiyotaka , Krumrey Michael
Published: July 2002

A bender has been developed for a directly water cooled monochromator crystal. The performance was tested at the materials science wiggler beamline (BL2) of the European Synchrotron Radiation Facility. The x rays were reflected by a 0.6 mm thick silicon wafer bonded to a 40 mm thick silicon substrate with grooved cooling channels at the surface. These channels are 0.5 mm wide and 2 mm deep with 1 mm fins in between. The input power on the monochromator crystal was measured using a calorimeter. At an input power of 1440 W the rocking curve width of the Si (111) reflection at 13 keV could be decreased by using the bender mechanism from 17 to 9.5 arcsec. The remaining broadening compared to the low power rocking curve was about 1.5 arcsec and was due to residual bonding or bending strain. Result of finite elements analysis is also shown.
High-resolution grazing incidence plane grating monochromator for undulator radiation
Authors: Koike Masato , Namioka Takeshi
Published: July 2002

A grazing incidence monochromator consisting of a spherical mirror, a varied spacing plane grating, movable plane mirror, and a fixed exit slit has been designed by means of a hybrid design method which takes advantage of both the ray-tracing and analytic methods. In the design, higher-order suppression and on-blaze feature were also taken into consideration. A spectral resolving power of ∼30 000–70 000 is expected for the monochromator over a wavelength range of 0.5–10 nm when used on an undulator beamline at the Advanced Light Source.
X-ray optics—Science—Trend and trial towards a fourth-generation light source started from the PF 2.5 GeV Ring and through the TRISTAN 6.5 GeV accumulation ring and the 10 GeV main ring (invited)
Authors: Ando Masami , Zhang Xiaowei , Namikawa Kazumichi , Kikuta Seishi
Published: July 2002

A few kinds of x-ray optics together with x-ray sciences developed at the Photon Factory ring and the Tristan accumulation ring are described. As an extension a description is also given about a feasibility study under preparation for using the 5 nm rad synchrotron radiation from a 120 pole undulator at the Tristan main ring. This activity, if achieved, will function as a bridge between a third- and a fourth-generation light source because a few of these experiments in planning are considerably related to the coherent nature of fourth-generation light in the x-ray domain, so that a perspective view on that will be available.
Measurements of x-ray spectral flux of high brightness undulators by gas scattering
Authors: Ilinski P. , Yun W. , Lai B. , Gluskin E. , Cai Z.
Published: July 2002

Absolute radiation flux and polarization measurements of the Advanced Photon Source (APS) undulators may have to be made under high thermal loading conditions. A method that may circumvent the high-heat-load problem was tested during a recent APS/CHESS undulator run. The technique makes use of a Si(Li) energy-dispersive detector to measure 5–35 keV x rays scattered from a well-defined He gas volume at controlled pressure.
25 ps neutron detector for measuring ICF-target burn history
Authors: Lerche R. A. , Phillion D. W. , Tietbohl G. L.
Published: July 2002

We have developed a fast, sensitive neutron detector for recording the fusion reaction-rate history of inertial-confinement fusion (ICF) experiments. The detector is based on the fast rise time of a commercial plastic scintillator (BC-422) and has a response <25 ps FWHM. A thin piece of scintillator material acts as a neutron-to-light converter. A zoom lens images scintillator light to a high-speed (15 ps) optical streak camera for recording. A retractable nose cone positions the scintillator between 1 and 50 cm from a target. A simultaneously recorded optical fiducial pulse allows the streak camera time base to be calibrated relative to the incident laser power. Burn histories have been measured for deuterium-tritium filled targets with yields ranging between 108 and 2×1013 neutrons.
Witness foam-ball diagnostic for Nova hohlraum time-dependent drive asymmetry
Authors: Amendt Peter , Glendinning S. G. , Hammel B. A. , Hay R. G. , Suter L. J.
Published: July 2002

Backlighting of low-density SiO2 aerogel balls (0.3 g/cc) in Nova hohlraums enables direct imaging of the indirectly driven ablative shock trajectory versus time. An immediate application of the technique is a new method for measuring drive temperature and asymmetry in Nova hohlraums. Measured drive asymmetries are exaggerated due to an increased shock speed in low-density foam balls. From the backlighter-imaged distortion of the radially converging shock, a potentially useful time-dependent flux asymmetry diagnostic is obtained. Results from a 3:1 peak-to-foot contrast ratio pulse shape (ps22) are analyzed and shown to agree with modeling. The current goal of the witness-ball effort on Nova is to identify the transition in flux on capsule from waist high (sausaging) to pole high (pancaking), thereby validating the technique as a promising symmetry diagnostic for the proposed National Ignition Facility.
Multichord calibrated bolometer array for the RFX experiment
Authors: Murari A. , Mast K. F. , D’Ambra L. , Lang P. T. , Marrelli L. , Martin P. , Romagnolo A.
Published: July 2002

A new multichord bolometer array has been installed for the first time in the RFX experiment, a large machine designed to study plasma confinement at high current in the reversed field pinch configuration. The main purpose of the diagnostic is to provide emissivity spatial profiles with good time resolution for the measurement of the total radiated power. The detectors used are miniaturized metal foil bolometers which are mounted in a water cooled pinhole camera covered by a graphite shield. The bolometers can be absolutely calibrated in situ according to a technique originally developed for the Asdex tokamak. In order to prove the electrical calibration technique a blackened bolometer was optically irradiated with a monochromatic light over a wide spectral range with wave numbers from 2.7 up to 47 000 cm−1. In the visible and UV spectral range an absorptivity of 80% was measured while in the IR and far-infrared regions only 7% of the incoming light was absorbed by the bolometer foil. In the mm wavelength range less than 1% of the radiation was absorbed.
Miniature, vacuum compatible 1024×1024 charge-coupled device camera for x-ray, ultraviolet, or optical imaging
Authors: Conder Alan D. , Dunn James , Young Bruce K. F.
Published: July 2002

We have developed a very compact (60×60×75 mm3), vacuum compatible, large format (25×25 mm2, 1024×1024 pixels) charge-coupled device (CCD) camera for digital imaging of visible and ultraviolet radiation, soft to penetrating x rays (≤20 keV), and charged particles. This camera provides a suitable replacement for film with a linear response, dynamic range, and intrinsic signal-to-noise response superior than current x-ray film, and provides real-time access to the data. The spatial resolution of the camera (<25 μm) is similar to typical digitization slit or step sizes used in processing film data. This new large format CCD camera has immediate applications as the recording device for streak cameras or gated microchannel plate diagnostics, or when used directly as the detector for x-ray, x-ray ultraviolet, or optical signals. This is especially important in studying high-energy plasmas produced in pulse-power, inertial confinement fusion, and high powered laser-plasma experiments, as well as other medical and industrial applications.
Structural determination of hydrogen site occupation in proton-exchanged LiNbO3 by nuclear magnetic resonance
Authors: Engelsberg M. , de Souza R. E. , Pacobahyba L. H. , do Nascimento G. C.
Published: July 2002

1H nuclear magnetic resonance measurements in proton-exchanged LiNbO3 were employed to determine structural positions of sites believed to be responsible for the desirable optical properties of this material. Contributions from other proton sites were first subtracted from the line shape which was subsequently analyzed by Van Vleck’s second moment method using a spin-echo technique to separate like-spin from unlike-spin contributions. Among various models examined, only one in which protons are located on oxygen planes nearest to normal lithium sites, midway between two oxygen anions in an oxygen triangle, was found to be consistent with the data.
Ultrashort-pulse reflectometry (invited)
Authors: Domier C. W. , Luhmann N. C. , Chou A. E. , Zhang W-M. , Romanowsky A. J.
Published: July 2002

Time-of-flight radar diagnostics are envisaged as having great potential for determining electron density profiles in next generation tokamaks such as TPX and ITER. Ultrashort-pulse radar reflectometry is a promising new time-of-flight diagnostic capable of making instantaneous density profile determination utilizing a single source and a single set of measurements. A proof-of-principle eight channel system has been constructed for use on the CCT tokamak at UCLA, and has undergone extensive testing in the laboratory.
Edge fluctuation measurements by phase contrast imaging on DIII-D
Authors: Coda S. , Porkolab M.
Published: July 2002

A novel CO2 laser phase contrast imaging diagnostic has been developed for the DIII-D tokamak, where it is being employed to investigate density fluctuations at the outer edge of the plasma. This system generates 16-point, 1D images of a 7.6-cm-wide region in the radial direction, and is characterized by long-wavelength (7.6 cm) and high-frequency (100 MHz) capability, as well as excellent sensitivity (ñ≳109 cm−3). The effects of vertical line integration have been studied in detail, both analytically and numerically with actual flux surface geometries generated by the EFITD magnetic equilibrium code. It is shown that in the present configuration the measurement is mostly sensitive to radial wave vectors. Experimental results on fluctuation suppression at the L- to H-mode transition and on the L-mode wave number spectrum are discussed briefly. Finally, future plans for extending the measurement to the core of the plasma and for investigating externally launched fast waves are presented.
Diamond crystal monochromator in a SPring-8 undulator beamline
Authors: Yamaoka Hitoshi , Ohtomo Kiyotaka , Ishikawa Tetsuya
Published: July 2002

Analytical results of SPring-8 undulator beam heat load on a diamond crystal monochromator are described. Pure heat power of a diamond crystal after a graphite filter, Be window, and slit system is calculated by using OEHL (Optical Element Heat Load Analysis) program as a function of crystal thickness. Thermal distortion of an indirectly edge-cooled crystal is less than about 1 arcsec with a slit system for the total power of the order of 50 W and the power density of the order of 10 W/mm2. The relation between the crystal thickness and temperature rise by purely absorbed x rays shows that thicker crystal gives lower temperature rise for the edge-cooled crystal. Result of three dimensional finite element analysis (ANSYS) is also presented.
Noise reduction in atomic force microscopy: Resonance contact mode
Authors: O’Connor S. D. , Gamble R. C. , Eby R. K. , Baldeschwieler J. D.
Published: July 2002

Noise reduction has been accomplished in atomic force microscopy by applying a high frequency, low amplitude vibration to the cantilever while it is in contact with a surface. The applied excitation (≳200 kHz; ∼1 nm) is acoustically coupled to the tip and dampens the resonance Q factors of the system. The applied frequency is well above the bandwidth of the acquisition system (50 kHz). We call this mode ‘‘resonance contact’’ mode. The nonlinear behavior of the tip–sample interaction allows the high frequency excitation to effectively broaden the frequency response of the system resonances.
A new simple emissive probe
Authors: Siebenförcher A. , Schrittwieser R.
Published: July 2002

We present a novel and very simple method to construct miniature emissive probes. This new technology guarantees a reliable electrical contact between the emissive wire and the copper leads during the lifetime of such a probe and can also be applied to other types of probes. Moreover, the probe can be made especially small so as to minimize the perturbance of the plasma.
Signal processing, data acquisition, and initial commissioning results of the APS storage ring vertical beam missteering wire monitor
Authors: Wang X. , Decker G. , Lumpkin A. , Lenkszus F. , Shu D. , Chang J. , Chung Y.
Published: July 2002

Two wire monitors have been developed and installed in the Advanced Photon Source (APS) storage ring insertion device (ID) front ends to directly detect synchrotron radiation exiting the storage ring vacuum chamber that is missteered by ±5 mm. Each wire monitor employs four in-vacuum tungsten wires positioned above and below the normal x-ray orbit. The temperature change of the wire under x-ray irradiation causes a resistance change that is detected by a local high-sensitivity low-noise signal processing electronics unit with four independent channels. The four outputs of the local unit are linked to a central VME wire resistance measurement and interlock module via 4–20 mA current loops. The central VME module can accept inputs from up to eight wire monitors and has a heartbeat that feeds a MPS summation module. In this paper, an overview of the wire monitor signal processing and data acquisition system design is presented together with recent commissioning results.
On filter design and critical thickness of synchrotron x-ray filters
Authors: Wang Zhibi , Kuzay Tuncer M.
Published: July 2002

A ‘‘critical thickness’’ for a synchrotron radiation x-ray filter exists. Because x-ray absorption in media is an exponential function of depth and because radiation and conduction both play a role in the cooling of the filter assembly, the heat transfer mechanism changes from radiation dominant to conduction dominant as the thickness increases. For a thin filter, radiative heat transfer is the main mechanism. The maximum temperature in the filter increases as the thickness increases due to the fact that the total heat load increases while the total area for radiative heat transfer remains the same. For a thick filter, conductive heat transfer is the main cooling mechanism. When the filter thickness increases, the heat absorption per unit thickness decreases and so does the maximum temperature. At a certain thickness, the temperature in the filter is the maximum. This is the critical thickness. For third-generation synchrotron radiation facilities, the maximum temperature and thermal stresses in a filter are the main factors considered in a filter assembly design. It is very important to avoid designing a filter inside the critical thickness range.
Thickness and effective electron mass measurements for thin silicon dioxide films using tunneling current oscillations
Authors: Zafar S. , Conrad K. A. , Liu Q. , Irene E. A. , Hames G. , Kuehn R. , Wortman J. J.
Published: July 2002

A novel method is presented for measuring the thicknesses of thin (<60 Å) silicon dioxide (SiO2) films using the oscillations in the Fowler-Nordheim tunneling currents. An important feature of the proposed method is that the accuracy of this method increases with decreasing oxide thickness and thicknesses changes of ∼1 Å can be detected. The oscillations are also used for measuring the average effective electron mass in the conduction band of SiO2.
Shear light scattering photometer with optical microscope for the study of polymer blends
Authors: Kim Sanghoon , Yu Jae-Woong , Han Charles C.
Published: July 2002

A shear light scattering photometer with an optical microscope was constructed for the study of polymer blends in a simple shear field. This instrument utilizes a cone and plate or parallel plate geometry for the generation of shear field. The shear rates are controlled by a microstepping motor. The controllable range of shear rate is between 0.002 and 1000 s−1. The bottom plate of the shear cell has a special design to accommodate the microscope objective and a thin disk-type heater for temperature control. The accessible q range is from 0.7 to 4.6 μm−1 with a 632.8 nm He–Ne laser or from 0.9 to 6.0 μm−1 with a 488 nm Ar ion laser. The temperature can be controlled from ambient temperature to 250 °C with ±0.1 °C accuracy. A phase contrast microscope and a fluorescence microscope are built into this photometer for the in situ morphological study of materials of interest. The optics for light scattering and microscopy can be switched back and forth by a simple translational movement of a rail-mounted optical platform, without any realignment, for comparison of data from reciprocal space with that from real space. A bulk polystyrene/polybutadiene blend and a polystyrene/polybutadiene/dioctylphthalate blend were used to demonstrate the performance and versatility of this instrument.
Flux and resolution requirements for studies of electronic excitations in solids (invited)
Authors: Isaacs E.D. , Platzman P.M.
Published: July 2002

Advances in synchrotron sources promise to open a new frontier in the use of inelastic x-ray scattering to probe electronic excitations on the eV and sub-eV energy scales. In this paper we present the flux and resolution requirements for inelastic scattering in condensed matter systems. A review of several recent results will be given along with several proposed experiments.
Cryogenic high resolution x-ray detectors—status, theoretical limits, and suitability for synchrotron radiation inelastic scattering experiments (invited)
Authors: Stahle Caroline K.
Published: July 2002

There are several kinds of low temperature solid-state x-ray detectors presently under development, motivated primarily by the need for high resolution, efficient spectrometers for x-ray astronomy. These include calorimeters, nonequilibrium phonon sensors, and charge collection devices using superconducting tunnel junctions. Energy resolution at 6 keV of order 1 eV has been predicted for all of these devices, though the best measured to date, 7 eV FWHM, has been obtained with calorimeters with semiconductor thermistors. This paper will address the difference between prediction and performance for the different classes of devices. The theoretical limits will be discussed in light of the need in inelastic scattering experiments for using x rays with energy greater than 20 keV. The potential for sub-eV resolution will also be addressed.
Mechanical design of a missteered beam safety monitor at the Advanced Photon Source
Authors: Chang J. , Shu D. , Decker G. , Nian T. , Kuzay T.M. , Lumpkin A. , Wang X.
Published: July 2002

A missteered beam safety monitor (MBSM) has been designed to protect the accelerator ring of the Advanced Photon Source against incursions of the missteered synchrotron radiation. When the orbit of the particle beam in the accelerator shifts out of its safety limits, the photon beam from the bending magnet will pass through the square apertures on the cooled mask of the MBSM and will heat up a very thin tungsten wire (0.025 mm in diameter) behind the mask. Acting as a resistance thermometer, the electrical resistance of the tungsten wire increases proportionally with temperature rise. As soon as the electrical resistance of the tungsten wire reaches a preset point, a signal is triggered immediately to dump the particle beam in the accelerator. The tungsten wire is inclined to the photon beam at 4.5 degrees in the vertical direction to prevent it from being overheated by the high power photon beam. Detailed mechanical design and thermal analysis are presented.