bluuebunny/crossref_metadata_2025 huggingface dataset:
Status of the European Synchrotron Radiation Facility insertion devices
Authors: Chavanne J. , Chinchio E. , Diot M. , Elleaume P. , Frachon D. , Marechal X. , Mariaggi C. , Revol F.
Published: July 2002

The status of development of insertion devices for the European Synchrotron Radiation Facility 6 GeV low emittance synchrotron radiation source is described. Phase I includes nine insertion devices with a magnetic field ranging from 0.4 to 1.8 T and periods from 44 to 150 mm to be commissioned in 1993. The chosen segmentation, support structure of magnetic assemblies, field measurement techniques and computational tools are described. A novel kind of helical undulator is being implemented.
Reflection absorption infrared spectroscopy at the Daresbury SRS
Authors: Slater D. A. , Hollins P. , Chesters M. A. , Pritchard J. , Martin D. H. , Surman M. , Shaw D. A. , Munro I. H.
Published: July 2002

The high brilliance of modern synchrotron radiation sources results in a significant intensity advantage over conventional sources in the far infrared region of the spectrum. For applications with inherently low étendue, such as reflection absorption infrared spectroscopy (RAIRS) of surfaces, this advantage extends into the mid-infrared (IR) region, to 1000 cm−1 or higher. The spectroscopic region between 100 and 1000 cm−1 is of particular interest in surface science since it includes the vibrational modes of the majority of direct bonds between the surface and adsorbate, but the low intensity of conventional sources renders investigations of this region difficult. In this paper, we discuss the design criteria of the new Daresbury infrared beamline.
High-speed spatial scanning pyrometer
Authors: Cezairliyan A. , Chang R. F. , Foley G. M. , Miiller A. P.
Published: July 2002

A high-speed spatial scanning pyrometer has been designed and developed to measure spectral radiance temperatures at multiple target points along the length of a rapidly heating/cooling specimen in dynamic thermophysical experiments at high temperatures (above about 1800 K). The design, which is based on a self-scanning linear silicon array containing 1024 elements, enables the pyrometer to measure spectral radiance temperatures (nominally at 650 nm) at 1024 equally spaced points along a 25-mm target length. The elements of the array are sampled consecutively every 1 μs thereby permitting one cycle of measurements to be completed in approximately 1 ms. The pyrometer output is recorded digitally with a full-scale resolution of 0.025% every 1 μs. Procedures for calibration and temperature measurement as well as the characteristics and performance of the pyrometer are described. The details of sources and estimated magnitudes of possible errors are given. An example of measurements of radiance temperatures along the length of a tungsten rod, during its cooling following rapid resistive pulse heating, is presented.
Inductive noise thermometer: Practical realization
Authors: Varpula Timo , Seppä Heikki
Published: July 2002

A new concept, called inductive noise thermometer, for measuring temperature of electrically conductive materials without any physical contact was realized in practice. In the method a low-loss coil is placed close to the electrically conductive material. The increase in the noise voltage of the coil is related to the temperature of the material. Results from laboratory experiments on steel up to temperatures of 1300 K showed an agreement with conventional thermocouple recordings within an uncertainty of 1%. The thermometer built was also tested on a continuous casting machine of a steel mill. The preliminary experimental results were encouraging although at times external rf disturbances disrupted the measurement.
A cell for the study of the electrolytic conductivity at high temperature in aqueous solutions
Authors: Bianchi H. , Corti H. R. , Fernández-Prini R.
Published: July 2002

In this paper the authors describe the construction and operation of a conductivity setup for high-temperature measurements. In the new conductivity equipment a direct current input signal and a high performance computer-controlled air oven were employed to measure the electrolyte conductance of dilute NaOH aqueous solutions up to 150 °C.
Repetitive square pulse generation by inductive pulse-forming lines with a field-effect transistor as an opening switch
Authors: Rhee M. J. , Ding B. N.
Published: July 2002

Two simple methods of repetitive square-pulse generation by inductive pulse-forming lines with a field-effect transistor as an opening switch are described. The square-pulse output voltages produced by both methods are in good agreement with those predicted for ideal circuits.
Identification of toroidal field errors in a modified betatron accelerator
Authors: Loschialpo P. , Marsh S. J. , Len L. K. , Smith T. , Kapetanakos C. A.
Published: July 2002

A newly developed probe, having a 0.05% resolution, has been used to detect errors in the toroidal magnetic field of the NRL modified betatron accelerator. Measurements indicate that the radial field components (errors) are 0.1%–1% of the applied toroidal field. Such errors, in the typically 5 kG toroidal field, can excite resonances which drive the beam to the wall. Two sources of detected field errors are discussed. The first is due to the discrete nature of the 12 single turn coils which generate the toroidal field. Both measurements and computer calculations indicate that its amplitude varies from 0% to 0.2% as a function of radius. Displacement of the outer leg of one of the toroidal field coils by a few millimeters has a significant effect on the amplitude of this field error. Because of uniform toroidal periodicity of these coils this error is a good suspect for causing the excitation of the damaging l=12 resonance seen in our experiments. The other source of field error is due to the current feed gaps in the vertical magnetic field coils. A magnetic field is induced inside the vertical field coils’ conductor in the opposite direction of the applied toroidal field. Fringe fields at the gaps lead to additional field errors which have been measured as large as 1.0%. This source of field error, which exists at five toroidal locations around the modified betatron, can excite several integer resonances, including the l=12 mode.
High-resolution Y-axis readout for delay-line microchannel anodes
Authors: Raffanti R. , Lampton M.
Published: July 2002

We have devised a method to obtain a high-resolution Y-axis event position determination from microchannel plate delay-line detectors. The method is based on the double-delay-line wedge–wedge charge partition principle of Lampton et al. [M. Lampton, O. H. W. Siegmund, and R. Raffanti, IEEE Trans. Nucl. Sci. 37, 1548 (1990)], where the X axis is read out by a pair of side-by-side delay lines and the Y-axis coordinate is determined by comparing the charges on the two parallel delay lines. However, our new method abandons the common field return path of the two delay lines, and splits them into two adjacent but independent transformer coupled timing circuits having no common ground connection except via the charge-measurement amplifiers. Thus we eliminate the large electrostatic capacitance of the delay lines from the input of the charge-measuring system. Due to the very low output return capacitance of the split delay lines, the Y-axis noise performance is improved enormously. Over its limited working field, the spatial resolution in the Y coordinate can easily equal the resolution provided in the X coordinate by the delay line. Applications to extreme and far ultraviolet photon-counting spectroscopy are envisioned.
PC-based digital apparatus with temperature compensation for measurement of thin films during deposition
Authors: Generosi R. , Barchesi C. , Luce M. , Cricenti A.
Published: July 2002

We present an apparatus for controlling the deposition of thin films. The apparatus is based on a quartz resonator whose frequency is controlled digitally by a computer. Temperature variations of the quartz during the evaporation process, attributed to the exothermic heat of condensation and radiation heating from the evaporation source, are compensated. A very stable deposition rate and a good film thickness evaluation are obtained.
A simple internally mixed photomultiplier with GHz response
Authors: Williamson C. K. , Knüttel A. , Knutson J. R.
Published: July 2002

A small head-on photomultiplier (HR2247) with ‘‘half photocathode gating’’ is being used for detection in a superheterodyne mixing scheme. The HR2247 has a spectral range of 160–650 nm, a frequency response to 1 GHz and is inexpensive. A gate mesh covers part of the photocathode surface. Internal mixing is accomplished by applying a rf signal to the gate mesh. A fiber-optic/objective assembly mounted on an X-Y stage scans the position of the incident laser beam on the mesh. In order to evaluate the suitability of the HR2247 for practical fluorescence and imaging experiments, the photocathode surface was mapped at 41, 205, 410, 615, and 820 MHz modulation frequencies for variations in phase and modulation. The mixed signal at any point on the gate mesh can be optimized by adjusting the potential at the gate mesh.
Optical instrumentation for eye length measurement using a short coherence length laser-based interferometer approach
Authors: Boyle W. J. O. , Dick G. L. , Grattan K. T. V. , Palmer A. W. , Wang D. N. , Weir K.
Published: July 2002

An optical interferometric approach is described for the measurement of axial eye length. The technique uses the short coherence length characteristics of the light source to locate, interferometrically, the position of the front surface of the eye and the retina. Results are presented from studies on an idealized model eye and the precision of the measurement is discussed. The advantages of the technique and a comparison with previously used short coherence measurements are also reviewed.
Polarization Michelson interferometer as a global polarization state generator and for measurement of the coherence and spectral properties of quasimonochromatic light
Authors: Azzam R. M. A.
Published: July 2002

For a quasimonochromatic light source with a known spectrum, the polarization Michelson interferometer (POLMINT) can be used as a global polarization state generator that produces totally or partially polarized light at its output in states of known degree of polarization that correspond to points on and within the Poincaré sphere. Conversely, the spectral and coherence properties of a quasimonochromatic source can be determined from the Stokes parameters of light at the output of the POLMINT measured by a complete polarization state detector as functions of a mirror displacement. Applications of the POLMINT as an ellipsometer are also discussed.
Reduced electron multiplier dead time in ion counting mass spectrometry
Authors: Liu Y. Alan , Fleming Ronald H.
Published: July 2002

Detector dead time in electron multiplier ion counting applications has been reduced. A first-in first-out buffer allows a traditional ion counting system to accept pulses 10 ns apart. Lower dead time (10 ns) results from elimination of electrical ringing that trails electron multiplier output pulses. The improved system has been tested on 34S/32S isotope ratio measurements.
High-pressure x-ray cell for studying the structure of fluids with the energy-dispersive technique
Authors: Gorbaty Yu. E. , Okhulkov A. V.
Published: July 2002

A cell for x-ray diffraction studies of fluids with the energy-dispersive technique at pressures of up to 9–10 kbar has been designed. The main advantages of the apparatus are a simple design, reliable sealing, absence of contribution from the container to the measured intensity of scattering, and high accuracy of intensity measurements achievable in a reasonable exposure time.
dc H−/D− sources at TRIUMF
Authors: Dutto G. , Jayamanna K. , Kuo T. , McDonald M. , Schmor P. W. , Yuan D. H.
Published: July 2002

Several H−/D− dc sources employing multicusp confinement and magnetic filtering to enhance H−/D− production have been designed, built, and tested. Source performance in terms of beam output, emittance merit as functions of arc current, confinement magnetic strength, plasma volume, beam exit diameter, and extraction lens configuration have been studied in detail. At present, up to 9 mA H− and 3 mA D− beams with a normalized emittance of 0.44 mm mrad for H− beam have been extracted. A number of sources are tailored to fit the requirements of individual projects. In this article, a general description of source structure, power and biasing algorithms, and extraction geometries of these cusp sources will be given.
Low-temperature, uniform, and high-density plasma produced by a new ultra-high-frequency discharge with a spokewise antenna
Authors: Samukawa Seiji , Nakagawa Yukito , Tsukada Tsutomu , Ueyama Hiroyuki , Shinohara Kibatsu
Published: July 2002

A low-temperature, uniform, high-density plasma is produced by an ultra-high-frequency (UHF) discharge with a new spokewise antenna. The plasma is uniform within ±5% over a diameter of 20 cm. The plasma density, 5×1010 cm−3 for low-electron temperatures of 1.5–2.0 eV, is almost proportional to the UHF power even at a low-UHF power of 100 W. No magnetic field is needed to maintain a high-density plasma. Consequently, the plasma source is fairly simple and lightweight. The plasma source should ease serious problems in etching processes that use conventional high-density plasmas.
Development of a pulsed power supply for a large-bore copper vapor laser
Authors: Seki H. , Oohashi T. , Shirakura T. , Takemori S. , Midorikawa Y. , Kameyama H. , Yamamura G. , Kotani K. , Sugawara H.
Published: July 2002

A pulsed power supply has been developed for exciting a copper vapor laser with a bore diameter of 80 mm and a discharge length of 2890 mm. The pulsed power supply has two thyratrons, an LC-inversion circuit and a two-staged magnetic pulse compression circuit. An efficiency of 82% has been obtained which is defined as the ratio of energy stored in the storage capacitor to the output energy of the magnetic pulse compression circuit, with a voltage greater than 40 kV, averaged output power of 24 kW, and voltage rise time of 70 ns. The pulsed power supply was successfully operated for more than 2000 h and an optical output power of 272 W was obtained.
Double beam bent Laue monochromator for coronary angiography
Authors: Illing G. , Heuer J. , Reime B. , Lohmann M. , Menk R. H. , Schildwächter L. , Dix W.-R. , Graeff W.
Published: July 2002

High photon fluxes are crucial in dichromatic digital subtraction angiography with line scan systems to allow for adequate image quality. To obtain images wide enough and with sufficient vertical resolution, each of the two beams used has to be at least 100 mm wide but not more than 0.5 mm high at the patient’s heart with the beam energies bracketing the iodine-K edge at 33.17 keV. A new monochromator in Laue transmission geometry has been developed, successfully tested at beamline ID11 of the European Synchrotron Radiation Facility (ESRF) and is now in use at the angiography wiggler beamline W2 at HASYLAB. The monochromator consists of two almost identical goniometer heads which are independently controlled. Within each head a bent silicon single crystal extracts a quasimonochromatic beam and focuses it vertically to the patient thus also increasing intensity compared to an unbent crystal. With a storage ring current of 50 mA the new monochromator provides 0.8×1011 photons/mm2/s in front of the patient which is an increase by a factor of 6 compared to the formerly used Bragg design with Ge crystals. Also, it is remarkably more stable against variations of the input power load.
Infrared spectroscopy of adsorbed CO2 as a probe for the surface heterogeneity of diamond C(111)-1×1:H
Authors: Chang H.-C. , Lin J.-C.
Published: July 2002

Infrared polarization spectroscopy of the stretching motion of physisorbed CO2 has been used as a probe for the heterogeneity of hydrogen-terminated diamond single crystal surfaces. At the substrate temperature of 83 K, band shape, photometry, and isotherm measurements all indicate that the CO2 molecules are first adsorbed on defect sites, followed by adsorption on terraces that yields a single sharp spectral feature at 2333 cm−1 with FWHM=6 cm−1. Nearly 20% of the surface sites on the as-polished C(111)-1×1:H surfaces are defects
Novel scheme for atomic hydrogen detection by double-resonant four-wave mixing
Authors: Czarnetzki U. , Döbele H. F.
Published: July 2002

A novel laser diagnostic scheme for the detection of atomic hydrogen in high temperature plasmas is proposed. This scheme is based on double-resonant four-wave difference frequency mixing. Two waves are resonant with the n=1→n=3 two-photon transition at 2×205 nm and a third wave is slightly detuned off the Balmer-α resonance at 656 nm. A signal wave close to Lyman-α is generated and is emitted like a laser beam within a small solid angle, comparable to that of the incoming laser beams. The signal scales with the square of the ground state density. By applying spatial and spectral filtering background radiation can be efficiently suppressed. The determining physical quantities are presented. For an atomic temperature of about 10 eV a detection limit close to N=109 cm−3 results in a spatial and temporal resolution of a few cm and about 10 ns, respectively.
Linear systems description of the CO2 laser-based tangential imaging system (abstract)a)
Authors: Lo E. , Wright J. , Nazikian R.
Published: July 2002

It is demonstrated that the phase variation produced by the projection of the density fluctuations onto a laser beam that is aligned tangent to the magnetic field lines in a toroidal plasma, is in fact a convolution of the density fluctuation profile in the tangency plane with a shift-invariant point spread function. Thus a spatial filter can be used to invert the corresponding transfer function to produce an undistorted image of the plasma density fluctuations at the tangency plane. Numerical simulations demonstrate that a spatial filter consisting of a simple and versatile step-function form of a Zernike phase mirror, will recover a reasonably accurate image of the fluctuations [Lo et al., Buld. APS 38, 2005 (1993)].
Impurity influx diagnostics on RFX
Authors: Carraro L. , Casarotto E. , Pasqualotto R. , Puiatti M. E. , Scarin P. , Valisa M.
Published: July 2002

The systems installed on the RFX reversed field pinch to study the impurity influxes are described. They comprise of telescope lenses, coupled through optical fibers and interference filters or spectrographs to photomultipliers for time-resolved analysis, and charge coupled device (CCD) cameras. The solutions adopted aim at giving an insight into the impurity production mechanisms in a situation characterized by largely asymmetric plasma–wall interactions. Main gas and various impurity influxes from the same area of the first wall are compared by means of very simple light splitters interposed between telescope lenses and narrow band filters. Four high-resolution CCD cameras also equipped with interference filters cover more than half of the first wall allowing detailed spatial studies of the impurity influx distributions.
First operation of the Alcator C-mod scanning 2D Thomson scattering diagnostic (abstract)a)
Authors: Watterson R. , Casey J. A. , Tambini F. , Rollins E. , Chin B.
Published: July 2002

The scanning Alcator C-mod 2D Thomson scattering diagnostic has been installed. This diagnostic utilizes a single Nd:YAG laser system to generate a ∼1 J pulse at a 50 pulse per second repetition rate. The nearly vertically oriented laser beam is viewed along approximately horizontal directions. Collected plasma scattered light is coupled to multiple grating spectrometers used for spectral analysis in order to derive local temperature and absolutely calibrated density information. The vertical laser beam chord may be translated by up to 2 cm during the 20 ms period between laser pulses by a counterrotating prism technique, allowing full two-dimensional profiles to be obtained over 160 ms (covering the 14 cm major radius region which is accessible) during a single tokamak discharge. Remote laser and scanner synchronization and control via a programmable logic controller and CAMAC has been installed and is fully functional. First experimental results with the initial spectrometer set will be presented.
On the possibility of determining the sawtooth location from impurity ion density profiles
Authors: Morozov D. Kh. , Rantsev-Kartinov V. A.
Published: July 2002

A new method is proposed for determination of the magnetic island location from the density profiles of multiply charged impurity ions. The method is based on (1) measuring the impurity ion’s emissivity profiles in T-10 tokamak experiments and (2) a theoretical model for the behavior of the impurities under conditions of sawtooth oscillations. The main physical basis of the method is the fact that the impurity is forced out from the sawtooth region in such a way that the profile of impurity ions appears to be a composition of two different profiles. These two profiles are determined by the Braginskii mechanism of impurity diffusion sustained in the regions r≳rs and r<(rs−Δ), whereas in the transient region (rs−Δ)≤r≤rs the impurity density has a sharp drop with decreasing minor radius. Interpretation of T-10 tokamak experimental data within the frame of a theoretical model allows one to determine the location of the surface q=1 and the width of magnetic islands. The method appears to be very sensitive to the level of large-scale MHD activity of the plasma.
Two-axis goniometer for reflectivity measurements of x-ray diffractors used in fusion research (abstract)a)
Authors: Peacock N. J. , Barnsley R. , Patel A. , O’Mullane M. , Singleton M. , Ashall J.
Published: July 2002

Quantitative measurements of the line and continua emissivities and the analyses of spectral line profiles are essential steps in the interpretation of the x-ray emission from high-temperature fusion plasmas. One method of placing the emissivities on an absolute basis is to use an absolutely calibrated spectrometer to record the data. The overall sensitivity of the spectrometer can be constructed in terms of the efficiencies of its separate components, the most intractable being Rc, the reflection integral of the diffractor. To this end, a new, compact, two-axis diffractometer, incorporating modern robotic technology, such as direct-drive servomotors with closed-loop operation from built-in arcsec optical encoders, has been constructed. Improved features of this double-axis goniometer include the use of fixed line-of-sight x-ray sources with the capability of operation in the (1,−1) parallel, nondispersive mode or the antiparallel, (1,+1), dispersive mode. The diffractometer is now being used to calibrate x-ray diffractors, filters, mirrors, and detectors associated with x-ray spectroscopy of fusion plasmas. At certain wavelengths, where line branching ratios involving visible transitions are available, the fusion plasma may itself be used as a transfer standard of x-ray luminosity, allowing an independent check on the diffractometer values of Rc. Applications to the analyses of impurity concentrations in tokamaks are described while future applications of the diffractometer to radiation damage studies of x-ray and optical components [Hill et al., Rev. Sci. Instrum. 63, 5032 (1992)] used in D-T burning plasma experiments are envisaged.
Broadband EUV survey spectrometer for short-timescale experiments (abstract)a)
Authors: Chapman B. E. , Den Hartog D. J. , Fonck R. J.
Published: July 2002

A fast and inexpensive spectrometer system has been developed to record EUV impurity spectra in the Madison Symmetric Torus (MST) Reversed-Field Pinch (RFP). To simplify the vacuum system, light is passed out of the spectrometer’s vacuum to the detector using a sodium-salicylate-coated fiber-optic coupler. This coupler is positioned such that the focal field is nearly flat over its aperture, thus minimizing defocusing at the edges of the detection plane. The system’s detector is a microchannel-plate-intensified, linear, self-scanning photodiode array. The 1024-pixel array covers a bandwidth of over 80 nm and is read out once every ms. The readout, which is four times faster than the manufacturer’s maximum rating, is fully synchronized to the experiment using a locally designed control circuit.
Measurements of molybdenum radiation in the Alcator C-Mod tokamak using a multilayer mirror soft x-ray polychromator
Authors: May M. J. , Finkenthal M. , Regan S. P. , Moos H. W. , Terry J. L. , Graf M. A. , Fournier K. , Goldstein W. L.
Published: July 2002

A photometrically calibrated polychromator utilizing layered synthetic microstructure coated flats (also known as multilayer mirrors, MLMs) as dispersive elements is operating on the Alcator C-Mod tokamak to measure the molybdenum emissions in the XUV. Molybdenum, the first wall material in C-Mod, is the dominant high Z impurity in the plasma. Three spectral regions are measured by three separate MLM-detector channels. The characteristic charge states in the region between 30–40 Å are Mo xv to Mo xx, between 65–90 Å are Mo xxiv to Mo xxvi, and between 110–130 Å are Mo xxxi and Mo xxxii. The instrument’s spectral resolution varies from 0.4 Å at λ=30 Å to 7 Å at λ=130 Å. The temporal resolution is typically 1.0 ms, but sampling rates of less than 1 ms are possible. The instrument was photometrically calibrated at The Johns Hopkins University using a Manson soft x-ray light source. Power loss estimates from Mo xxiv to Mo xxvi, Mo xxxi, and Mo xxxii have been obtained during ohmic and ICRF plasmas using the mist transport code to model the molybdenum charge state distributions in the plasma. The Mo concentrations have also been determined. Mo contributes ∼0.1 to the Zeff of 1.3 during ohmic plasmas. This contribution increases during ICRF heating to ∼0.5 of the Zeff of 2. The polychromator functions as a time-resolved soft x-ray emission power loss monitor.
Cross-correlation techniques applied to chord-integrated measurements (abstract)a)
Authors: Bravenec R. V. , Tsui H. Y. W. , Ross D. W. , Wen Y.
Published: July 2002

In an effort to determine the effects of impurities on turbulence in the edge plasma of tokamaks (electron temperature and radiative cooling rate out of phase), we would like to cross-correlate local measurements of T̃e and p̃rad. The former is provided by Langmuir probes.c) Unfortunately, only chord-integrated radiated power is available, provided by a high-resolution scannable X-UV array.d) We orient one channel of the array to intersect the flux tube sampled by the probe (taking advantage of the long parallel correlation lengths) and cross-correlate the signals in an attempt to extract the portion of the radiation signal eminating from the probe location. Preliminary results indicate a statistically significant level of correlation. A model for cross correlating a chord-integrated signal with a local signal is studied to aid the interpretation of the experimental results. If successful, this technique has important ramifications generally in that it effectively converts a chord-averaged measurement into a local one.
Charge-exchange neutral particle measurement in MeV energy range on JT-60U
Authors: Kusama Y. , Nemoto M. , Satoh M. , Tsukahara Y. , Tobita K. , Takeuchi H. , Petrov S. , Afanassiev V. , Kozlovskij S. , Kislyakov A. , Petrov M.
Published: July 2002

A charge-exchange neutral particle analyzer for the measurement of the MeV energy range ions produced by nuclear fusion or radio frequency heating has been developed and installed in JT-60U. Neutral particles entering the analyzer are ionized with a carbon foil of thickness 400 Å. The energy and mass of the stripped ions are resolved by magnetic and electrostatic fields (E∥B type). The analyzer has eight CsI(Tl) scintillator detectors. The energy range is 0.5–4 MeV for 4He0, the dynamic range is 4.08 and the energy resolution is 6%–11%. The detection efficiency for 4He0 with energy above 1 MeV is 30%–40%. A pulse height analysis (PHA) with 16 channels was adopted to distinguish particle signals from noise arising from neutrons, γ rays and optical lights emitted by JT-60U plasmas. The validity of the PHA was confirmed in a calibration experiment using a neutron source and in a high power heating experiment in JT-60U.
Direct measurement of spectral emissivity of liquid Si in the range of visible light
Authors: Takasuka Eiryo , Tokizaki Eiji , Terashima Kazutaka , Kimura Shigeyuki
Published: July 2002

Normal spectral emissivity of liquid Si was determined by direct measurement of thermal radiations from a surface of the Si melt and a blackbody cavity. The spectral emissivity has little dependence on the wavelength. The emissivity is 0.27 for the wavelength from 500 to 800 nm and is about a half of that of solid silicon at the melting point. Temperature dependence of the emissivity is very small in the temperature range from the melting point to 1550 °C. Free-electron model with a plasma frequency and relaxation time of the order of 1016 Hz gives a good agreement with the experimental result. That indicates the dominant effect of the free electrons on the optical properties of the liquid Si.
Fast pyrobolometer for magnetic heat transport measurements
Authors: Fiksel Gennady
Published: July 2002

A new version of the fast bolometer for the plasma energy transport study in plasma confinement devices is described. The bolometer represents a modification of the pyrobolometer described in Rev. Sci. Instrum. 64, 2761 (1993). The described bolometer uses crystals of LiNbO3 as the sensors. The new design incorporates a small coil for magnetic field measurement and a rigid, electrostatically shielded enclosure for the pyrocrystals, which at the same time does not affect the coil frequency bandwidth. The frequency response of the coil is measured to be in the 150-kHz range. Details of the design and calibration are presented.
Room temperature three sensor magnetic field gradiometer
Authors: Koch R. H. , Keefe G. A. , Allen G.
Published: July 2002

We have constructed a portable magnetic field gradiometer from fluxgate magnetometers using a novel common-mode rejection method. The sensor, known as a room temperature Three Sensor Gradiometer (rtTSG), is, as far as we know, the first hand-held gradiometer that can measure all components of the magnetic field gradient tensor. The rtTSG can measure these components in motion at a noise level of about 1.4×10−10 T/m√Hz at 1 Hz. Real time tracking of magnetic dipoles while the gradiometer is in motion has been demonstrated.
Multilayer anode with crossed serpentine delay lines for high spatial resolution readout of microchannel plate detectors
Authors: Friedman Peter G. , Cuza Raúl A. , Fleischman Judith R. , Martin Christopher , Schiminovich David , Doyle Dale J.
Published: July 2002

We have designed, built, and tested the first successful imaging microchannel plate (MCP) detector that uses two crossed, printed circuit, serpentine delay lines, one stacked above the other in a three-dimensional architecture. Laser ablation machining is used to cut slots that allow delay lines in two layers parallel to the MCP to sample and read out x and y image positions. Previous readouts that use delay line timing to read out both dimensions of an image employ a wire-wound anode. The goal of this readout is to provide as many picture elements (pixels) as possible in two dimensions, with high temporal resolution, high throughput, high dynamic range, and good spatial linearity. This detector achieves this goal with off-the-shelf electronics and is robust for space flight. The full width half maximum (FWHM) spatial resolution is 32 μm at the center of the detector and is typically <35 μm throughout the detector. The rms linearity is 40 μm in each readout dimension, after applying only radial corrections for fringe field effects near the perimeter, and <20 μm after applying additional simple (one-dimensional) corrections. Throughput for 10% coincidence loss is limited by the measured baseline settling time to 4×105 s−1, but the current electronics limit is 1.1×105 s−1. The walk characteristics of the detector are described. We discuss fabrication techniques, application to space-based astronomy use, and design modifications to improve performance.
Microwave-driven multipurpose ion source
Authors: Jayamanna K. , Yuan D. , Kuo T. , McDonald M. , Schmor P. W. , Dutto G.
Published: July 2002

A microwave-driven ion source being developed at TRIUMF is designed to produce stable, reliable, and gas-efficient negative and positive ion beams for cyclotrons and other accelerators. The source has been tested for H− and achieved 2.1 mA at 0.25 π mm mrad normalized emittance for 500 W of input power at a frequency of 2.45 GHz. The source was operated over one month without interruption for a H− beam stability test and demonstrated 2.5% stability over the period. For positive beam extraction H+, He+, N+, and Ar+ species have been studied. A 2 mA N+ beam was obtained at 0.3 π mm mrad normalized emittance for 1 kW of input power. A beam density as high as 7 mA/cm2 with 45% gas efficiency has been achieved for the Ar+ beam. In this paper the source parameters and characteristics are discussed.
Thermal diffusivity measurements in glass and Teflon using photopyroelectric signal spectral analysis and correlation techniques
Authors: Bonno B. , Laporte J. L. , Tascon d’Leon R.
Published: July 2002

Thermal diffusivity measurements in glass and Teflon are reported over the temperature range from 90 to 300 K. The results are obtained by multifrequency rear surface excitation combined with impulse response determination using correlation photopyroelectric techniques. A simple and versatile computer-based system performing generation of given excitation wave forms, data acquisition, and analysis is described. A one-dimensional model is proposed in order to explain the experimental results.
Thin film mechanically controllable break junctions
Authors: Keijsers R. J. P. , Shklyarevskii O. I. , Hermsen J. G. H. , van Kempen H.
Published: July 2002

An adaptation of the mechanically controllable break junction technique using thin metallic films to create point contacts and tunnel junctions is presented. The junctions that are created using this very simple method are extremely stable, and can easily be adjusted from rather large point contacts (R≊0.1 Ω) to high-resistance (1010 Ω) tunnel junctions. The electrodes can be kept very clean by breaking the sample in ultrahigh vacuum or in a very pure helium atmosphere at 1–4 K. Point-contact spectra of good quality were measured for contacts of 0.1–500 Ω. For very small contacts, the expected steplike increase of junction resistance with decreasing contact size was observed, with a jump to tunneling behavior occurring at resistances of 12–14 kΩ.
Electrodeless thin film conductance measurements using the Sommer–Tanner method
Authors: Severens R. J. , Verhoeven H. J. M. , Schaepkens M. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

A method to determine the electrical conductance of thin films such as a-Si:H that does not require contacting electrodes is presented. This method, introduced by Sommer and Tanner, is based on measuring the phase shift of a capacitive transmission line. The lower detection limit for the geometry used here is 10−11 Ω−1, which makes it suitable to determine the photoconductivity of a-Si:H thin films. The method shows reasonable agreement with classical conductance measurements using sputtered electrodes.
A new CO2 analyzer for measuring respiration rates in organic material
Authors: Balderas-López J. A. , Gutiérrez-Juárez G. , Alvarado-Gil J. J. , Frías-Hernández J. , Olalde-Portugal V. , Miranda L. C. M. , Silva M. D. , Delgadillo I. , Vargas H.
Published: July 2002

In this article, we present a new CO2 analyzer which can be used for monitoring respiration rates in organic material. To demonstrate the potentiality of the analyzer, CO2 evolution of soil samples collected from three different edaphic environments were measured. The results obtained with this compact CO2 analyzer were compared with those carried out simultaneously using the chemical method, and the correlation between them has been established.
Time-resolved pulse-counting lock-in detection of laser induced fluorescence in the presence of a strong background emission
Authors: Pelissier B. , Sadeghi N.
Published: July 2002

We describe a time-resolved pulse-counting system well adapted for the detection of continuous laser induced fluorescence (LIF) signals in repetitive phenomena, when a strong background emission is present. It consists of 256 channels coupled to a first in first out memory and interfaced to a 486 DX 33 PC, for data storage. It accepts time-averaged count rates up to 450 kcount/s. Time between channels can be set from 12.5 ns to several μs and the dead time between two consecutive cycles of the physical phenomena is less than 20 ns. In phase with a chopper, which modulates the laser beam, it adds the observed photon signal to the channel memories when the beam is on and substracts it when the beam is stopped, acting like a lock-in amplifier which detect only the modulated part of the signal. The minimum detectivity on the LIF signal is only limited by the shot noise of the plasma induced emission signal. As an application, we studied the time variation of the Ar+*(2G9/2) metastable ions, detected by LIF, in two types of plasmas. Their radiative lifetime and collisional quenching frequencies were deduced from their decay rate in the afterglow of a pulsed Helicon reactor. We also observed the evolution of their density in a 455 kHz capacitively coupled argon discharge.
Simple interferometric microscopy for in situ real-time two-dimensional observation of crystal growth
Authors: Koyama K. , Iwasaki A. , Tanimoto M. , Kudo I.
Published: July 2002

We have developed a simple interferometric microscope suitable for in situ observation of crystal growth. The device consists of a light emitting diode (LED) light source, a slightly modified microscope, and a charge coupled device (CCD) camera, all of which are inexpensive and commercially available. In addition to information on a standard 2D image from a CCD camera, this system displays interference fringes that enable one to map the temporal evolution of the distribution of thickness in real time, practically allowing 3D observation of growing crystals. LED light of a relatively low coherence can preferentially project a depth distribution of thin growing crystals as a fringe pattern, effectively suppressing parasitic interference induced by stray beams reflected off optical components. This device is as easy to use as a conventional microscope and can be routinely applied to observe a growth of zeolite crystals in a pressurized hot solution cell.
Single quantum well light emitting diodes demonstrated as excitation sources for nanosecond phase-modulation fluorescence lifetime measurements
Authors: Sipior Jeffrey , Carter Gary M. , Lakowicz Joseph R. , Rao Govind
Published: July 2002

We have characterized the output of inexpensive, commercially available single quantum well (SQW) blue and green light emitting diodes (LEDs). The SQW LEDs were amplitude modulated with the output from a frequency generator while biased through a bias tee with 5 mA of current. The blue SQW LED produced 800 μW of light centered at 466 nm, with a −3 dB bandwidth of 58 MHz. The green SQW LED produced 543 μW of light centered at 522 nm, with a −3 dB bandwidth of 26 MHz. Modulated light was available to approximately 100 MHz, allowing the measurement of ns fluorescence lifetimes. The fluorescence lifetime of a standard fluorophore (fluorescein) was measured in the frequency domain using the phase-modulation technique, and gave results similar to those obtained with a 488 nm argon ion laser modulated with a Pockels cell. To demonstrate the usefulness of the SQW LED source, we also performed measurements with the fluorescent pH indicator SNAFL-2. Again, these results compared favorably with those obtained with the laser. When compared to a laser modulated with a Pockels cell, the SQW LEDs were smaller, less expensive, required less power, generated less heat, and required less alignment. The ability to modulate the SQW LEDs at high frequencies, along with the blue or green outputs, allow their use as inexpensive light sources in fluorescence lifetime optical sensors and even fluorometers.
Application of a novel rf coil design to the magnetic resonance force microscope
Authors: Zhang Z. , Hammel P. C. , Moore G. J.
Published: July 2002

We report a rf coil design based on the Alderman–Grant coil called the modified Alderman–Grant coil (MAGC), and demonstrate its efficacy in the magnetic resonance force microscope (MRFM). The rf field of the MAGC has a magnitude comparable to that of a solenoidal coil of similar size (for the same input power) but the coil has a much smaller inductance. This is advantageous in electron spin resonance MRFM experiments which would benefit from rf frequencies in excess of 1000 MHz. The open design of the MAGC is also advantageous because it provides superior access to the sample mounted on a mechanical cantilever by the optical fiber and permanent magnet and so allows the sample to be placed at the center of the coil.
Use of tapered glass capillaries for producing microbeams
Authors: Kim Kyungha H. , Brew Dale L. , Brown Frederick C. , Stern Edward A. , Heald Steve M.
Published: July 2002

The Pacific Northwest Consortium CAT is developing tapered glass capillaries using fiber optics techniques for fabrication. Previous calculations showed that, under ideal conditions and using Undulator A as a source, glass capillaries can produce higher intensity gains than those of mirrors for an output diameter of 5 micrometer or less. Recently, we fabricated several capillaries with approximately linear tapers and tested three of them with outlet diameters of 1.3, 1.4, and 12.4 micrometers and lengths of about 35–90 cm. We obtained intensity gains over a pin hole of about 270, 240, and 30, respectively. They are about half of the calculated values expected from a perfectly linear profile. Also the angular spread of the output beam was much larger than the calculated value. We measured the profile of one capillary in detail and calculated the intensity for the capillary with the measured profile and still found significant differences. We also made calculations assuming several types of misalignment and found that they are important factors in understanding the larger angular divergence and reduced intensity. These results suggest improvements in the fabrication of the capillaries and in ways to support them during experiments.
Grid separation oscillator using resonant coaxial cavities for high power multichannel laser
Authors: Bilida W. D. , Seguin H. J. J. , Capjack C. E.
Published: July 2002

Resonant cavity techniques have been used to implement a high power source of radio frequency excitation for many parallel laser elements in a simple, compact, and low cost structure. A triode oscillator was designed capable of driving up to 48 independent and dynamic loads by utilizing the unique nature of a resonant cavity to extract multiple outputs via magnetic coupling. Over 25 kW of power has been generated at 80 MHz while driving 8 independent CO2 laser slab geometry gas discharges.
A mass resolving neutral atom imager
Authors: Scime Earl E. , Keiter Paul A.
Published: July 2002

Neutral atom imaging of space plasmas, the measurement of neutral atom flux as a function of angle and energy, can provide qualitative information about the global dynamics of a space plasma. In addition, mass and energy resolved neutral atom images can be used to remotely measure convective electric fields in planetary magnetospheres. Direct detection of neutral atoms using ultraviolet-rejecting waveguides and microchannel plate sensors has been proposed as a method of imaging low-energy neutral atoms. We discuss a new type of direct detection neutral atom imager that is capable of producing mass and energy resolved images. The imager has a large geometric factor (G≈0.2 cm2 sr eV/eV), an energy range of 1–100 keV, and single coincidence noise suppression. The estimated mass of the imager is less than 1.5 kG.
A modified feed-forward control system at the Accelerator Test Facility
Authors: Liu Y. , Cline D. , Ben-Zvi I. , Wang X. J. , Sheehan J. , Batchelor K. , Malone R. , Issapour M.
Published: July 2002

A modified feed-forward control system has been operated at the Brookhaven Accelerator Test Facility to control the phase and amplitude of two high power klystron rf systems used to power a photocathode rf gun and a traveling wave electron linac. The changes to the control algorithm include an improved handling of cross coupling between the amplitude and the phase channels, an improved calibration routine that allows for changes in the matrix elements due to the variable base-line and improved filtering. The modifications to the software include modularity, portability, and user-friendliness. Improvements to the hardware include a linearized phase and amplitude controller with dc biasing for an improved dynamic range. The feed-forward system can handle nonlinear and noninstantaneous systems. With simultaneous regulation of two channels, the phase and the amplitude fluctuations over a time span of more than 3 μS were reduced to less than ±0.2° and ±0.2%, from the initial ±2.7° and ±1.8%, respectively.
Vacuum photodiode detectors for broadband vacuum ultraviolet detection in the Saha Institute of Nuclear Physics Tokamak
Authors: Rao C. V. S. , Shankara Joisa Y. , Hansalia C. J. , Hui Amit K. , Paul Ratan , Ranjan Prabhat
Published: July 2002

We report on the application of the vacuum photodiode to detect vacuum ultraviolet (VUV) radiation emitted from the Saha Institute of Nuclear Physics (SINP) Tokamak. It is simple to fabricate and provides broadband spectral response in the VUV and ultrasoft x ray (10 eV–1 keV). In our design, a stainless steel photocathode is used, which has a response identical to tungsten in the wavelength range 100–1200 Å. Its surface is passivated, to minimize contamination and monolayer deposition, by electropolishing it. Some representative experimental results illustrating the range of applicability are presented with special emphasis on its performance in disruptive shots.
Microwave probe diagnostic for the lower hybrid multijunction antenna on TdeV
Authors: Jacquet P. , Demers Y. , Chaudron G. A. , Glaude V. , Côté A. , Dubé A. , Mireault R. , Robert A. , Vachon L.
Published: July 2002

On the TdeV tokamak a microwave probe diagnostic enables direct measurement of the electromagnetic fields in ten reduced waveguides of the lower hybrid current drive multijunction antenna. In each instrumented reduced waveguide, the local field is measured at two different locations by probes through coupling holes located in the narrow wall of the waveguides. The amplitude and phase of the signals are measured with a multichannel heterodyne circuit and are used to calculate the incident and reflected fields at the antenna mouth. The probes are under vacuum and they are bakeable up to the maximum operating temperature of the antenna (T=350 °C). They are calibrated at room temperature but the evolution of their characteristic with temperature is taken into account in the data analysis. Typical accuracies of the field measurements at the grill mouth are: ±9% for the amplitude and ±6° for the phase. The probe diagnostic has been operating reliably for the last two years and the probes do not appear to perturb the operation of the antenna nor to reduce its power handling capability. Comparisons of the probe measurements with calculations from the multijunction antenna modeling code SWAN show that the code is accurate for low rf power densities at the antenna mouth.