bluuebunny/crossref_metadata_2025 huggingface dataset:
Device for absolute calibration of x-ray imaging detectors and x-ray counters (abstract)
Authors: Kolesnikov K. A. , Lysenko A. P. , Medvedko A. S. , Panchenko V. E. , Zagorodnikov E. I.
Published: July 2002

Electronic devices intended to visualize x-ray images are intensively evolved on the basis of linear video signal shapers (LVSS): x-ray vidicons, image vidicons with x radiation-to-light conversion using luminophors and scintillators, charge-coupled devices, photodiode arrays and matrices, as well as on the basis of various electro-optical converters: electrostatically or magnetically focused and microchannel image intensifers. Their broad application to x-ray diffraction topography, structue analysis, diffractometry, tomography, and radiography has necessitated (already from 1982) the introduction of a common criterion for calibration of their sensitivity—the flux density of monoenergetic photons. In particular, when calibrating the LVSS it is necessary to find a direct, unambiguous correspondence between this criterion and the amplitude of a video signal. For this purpose, a device has been designed which is used both for absolute calibration of LVSSs and, of course, for a trivial standardization of x-ray counters with respect to their efficiency. This device is based on two commercial gas proportional counters whose position in space is aligned for a successive, one after another, ‘‘threading’’ of them to the x-ray beam monochromatized by means of the crystal-diffraction scheme (Lukirsky’s method). Both counters are identical to each other. Of course, each counter has input and output windows. The beam is shaped by diaphragms and by two slits, horizontal and vertical, with cylinders as ‘‘knives.’’ One of the slits is scanned in the diffraction plane by a stepper motor. The counters are tested for identity by selecting them depending on their counting properties and energy resolution, with the escape peaks taken into account. All these operations and the rest of the measurements are performed by electronic units in the CAMAC standard, controlled by a microcomputer. On the test monochromatized x-ray beam, the device is interchangeable with a LVSS or a counting detector being standardized. The test beam is monitored. The width of the slit being scanned is shaped up to 10 μm, thereby allowing the LVSS to be standardized for geometrical resolution.
Investigations on the consistency of optical constants in the XUV determined by different methods
Authors: Birken H.-G. , Blessing C. , Kunz C. , Wolf R.
Published: July 2002

In the photon energy range from 40 to 1000 eV, we have measured reflectances and transmittances of polyimide foils as well as reflectances and total photoelectron yields of Cu and Pt films. We compare sets of optical constants derived by the different methods applied to the same sample. The degree of agreement gives an indication of the present status of determining optical properties in the XUV. This is relevant for the planning of advanced instrumentation.
Soft x-ray transmission characteristics of an Au-coated silica hollow-core fiber (abstract)
Authors: Hidaka T. , Watanabe M. , Saito N. , Suzuki I. H.
Published: July 2002

Since the real part of the refractive index of silica glass is smaller than unity in the soft x-ray region, it has been shown1–3 that silica-glass hollow-core fibers can transmit soft x rays. However, the transmittance for the silica fibers bent over a 90° were found to be lower than 0.1%. On the other hand, the multilayer metal coating technique has been developed in fabrication of flat mirrors for soft x-ray optics. If suitable multilayers can be deposited on the inner surface of a flexible hollow glass fiber, the transmittance for soft x rays of the fiber is expected to be considerably higher than that of noncoated hollow fibers. It is important to study the transmission characteristics of the hollow-core fiber whose inner surface is coated with metal. In the present study, we report the soft x-ray transmission characteristics of a Au-coated silica hollow-core fiber. The experimental setup is similar to that previously reported.4 The inner diameter of the Au-coated silica fiber used is about 2 mm and its length is 230 mm. The Au coating on the inner surface of the fiber was achieved by chemical plating. We measured the transmittances of the Au-coated silica fiber and a noncoated silica fiber with the same size. We measured the transmittance only for the bend angles smaller than 20°, because these relatively thick silica fibers were broken at about 25°. For a large bend angle (20°), the transmittances of the Au-coated fiber were one order of magnitude lower than that of the noncoated fiber in the short wavelength region below 45 Å. In the long wavelength region (longer than 60 Å), the transmittance of the Au-coated fiber was higher than that of the noncoated fiber. At the oxygen K-shell absorption wavelength (23 Å), the strong dip in transmission was observed in the noncoated silica fiber. However, there was not seen a strong dip in the Au-coated fiber. These results, the better transmittance for the long wavelengths, and no dip at 23 Å, show that the Au coating is effective in improving the soft x-ray reflectance in the inner surface of fibers.
Data acquisition and beamline control software
Authors: Brennan S. , Cowan P. L.
Published: July 2002

A fortran program is described that runs on a 16-bit minicomputer under a single-user real-time operating system. This program combines interrupt-driven data collection, beamline positioning, and data analysis in a way that allows analysis of previously collected data while the program is collecting new data. It has been successfully used for several years on beamline X-24A at the National Synchrotron Light Source for fluorescence spectroscopy studies, surface extended x-ray absorption fine structure, and back-reflection standing-wave measurements.
Study of polarized properties of multilayer x-ray mirrors
Authors: Alexandrov Yu. M. , Fedorenko A. I. , Kondratenko V. V. , Koshevoi M. O. , Kozhevnikov I. V. , Murashova V. A. , Rupasov A. A. , Shikanov A. S. , Vinogradov A. V. , Yakimenko M. N. , Zorev N. N.
Published: July 2002

Polarized properties of interference multilayer mirrors in the soft x-ray range are studied. The possibility to achieve a radiation polarization rate of about 0.8 is shown experimentally.
Gas chromatography
Authors: Guiochon Georges , Guillemin Claude L.
Published: July 2002

Gas chromatography is a powerful separation technique for gas and vapor mixtures. Combining separation and on-line detection permits accurate quantitative analysis of complex mixtures, including traces of compounds down to parts per trillions in some particular cases. The importance of gas chromatography in quality control and process control in the chemical and drug industry, in environmental pollution investigations and in clinical analysis is critical. The principles of the technique are discussed, the main components of a gas chromatograph are described and some idea of the importance of the applications is given.
Computer-controlled compression molding system for composite processing
Authors: Farouk Alamgir , Kwon Tai Hun
Published: July 2002

A simple, inexpensive yet flexible compression molding and cure monitoring system has been developed and used in studying the processing of advanced polymer composites. Compression molding is a promising method for manufacturing thermoset polymer composites which find usage in aerospace applications. The processing history of these composites determines their final properties. To improve quality and enable mass production, the processing-property relations need to be studied in detail. Process control and process monitoring as well as provision for user intervention during processing is essential in studying such problems. The computer-controlled molding system together with the control and data acquisition software aims at demonstrating how such a system may be built from off-the-shelf components.
An electric field jump apparatus with ns time resolution for electro-optical measurements at physiological salt concentrations
Authors: Porschke Dietmar , Obst Andreas
Published: July 2002

An apparatus is described, which can be used for electro-optical measurements at high ionic strengths, including physiological salt concentrations. The electric pulse is generated by the cable discharge technique; complete matching of the load impedance is achieved by a compensation cell, which is supplied with a steady flow of electrolyte solution. At a cable length of 20 m the pulse length is limited to 200 ns; the electric field strength applied to the solution is up to 80 kV/cm. The apparatus can be used for automatic sampling with minimal exposure of the samples to irradiation and with control of temperature and absorbance of the sample. The limit time resolution is a few ns. The electric dichroism of DNA restriction fragments, for example, can be characterized at physiological salt at a high signal-to-noise ratio.
Intensity of x-ray microbeam formed by a hollow glass pipe
Authors: Furuta K. , Nakayama Y. , Shoji M. , Nakano H. , Hosokawa Y.
Published: July 2002

X-ray microbeams have been produced by utilizing hollow glass pipes. It has been observed that the intensities of ten x-ray lines (from 6.93 to 19.6 keV) transmitted through 250-mm-long hollow glass pipes of inside diameters of 27.4, 23.0, and 18.8 μm range from 1.9 to 2500 times greater than intensities reduced by inverse-square attenuation.
A stage for submicron displacements using electromagnetic coils and its application to scanning tunneling microscopy
Authors: Coratger R. , Beauvillain J. , Ajustron F. , Lacaze J. C. , Tremollieres C.
Published: July 2002

Coarse motion mechanisms have proven essential for STM investigations. The new system that we have built and that is presented here uses electromagnetic forces to clamp the feet of the ‘‘louse.’’ These forces arise from a current that flows through three electromagnetic coils. This system, fully computer automated, is found to give reliable approaches and allows lateral displacements of the sample with variable step sizes and hence, can also be used in other specific applications that require nanodisplacements.
Interface to synchronize a pulsed molecular beam source to a fast scanning Nicolet FTIR spectrometer
Authors: Christman S. B.
Published: July 2002

An interface was designed to synchronize a pulsed molecular beam source to a free-running, fast scanning, Nicolet 60SXB FTIR Spectrometer used in time-resolved studies of surfaces. Input and output lines along with their associated software drivers were developed. One of the RS-232 channels available on the Nicolet 1280 computer was used to provide digital input and digital output signals. A Convert signal was made available to allow external counting of data taking cycles. Communication was established, using another RS-232 channel, between the Nicolet 1280 computer and an AT&T 6300 computer that runs other aspects of the experiment. This interface could be applied to any time-dependent process run by any computer with a spare RS-232 channel and a TTL Convert signal indicating the start of each data taking period.
A new ultra low-field ESR spectrometer
Authors: Duret D. , Beranger M. , Moussavi M. , Turek P. , Andre J. J.
Published: July 2002

A CW electron spin resonance (ESR) spectrometer working at earth-field is described for the first time. The optimized sensitivity has allowed to reduce the size of the sample holder down to 100 mm3, a low value for such a low working frequency (1.845 MHz). At this frequency, only narrow ESR signals are significant (maximum sweep 125 μT or 100 A/m). The use of the Bloch configuration and the particular care to optimize the sensitivity lead to a design that partially compensates the lack of sensitivity due to low fields. Small material quantities are thus usable. Moreover, the spectrometer is low cost, portable, and easily reproducible with the announced performance. The main use of the spectrometer is to characterize materials for earth field magnetometry. For that purpose it has been necessary to define a figure of merit for magnetometry. Until this study, the only parameter discussed was the linewidth of the homogeneous ESR line (i.e., T2). The detailed discussion of the figure of merit, taking into account not only the material but the couple spectrometer material, considerably decreases the predominance of the linewidth and let emerge secondary factors such as packaging, susceptibility, ESR lineshape, T1 vs T2, etc. The figure of merit evaluated from the material parameters has been experimentally measured for different π radicals. Comparison with their performance in earth field magnetometry demonstrates the pertinence of the proposed figure of merit.
Measurement of electrical forces using a modified torsion balance and capacitance transducer
Authors: Kwon M. H. , Peters R. D.
Published: July 2002

The attractive force between two conducting electrodes, one charged and the other at nominally zero potential, has been measured using a modified torsion balance whose deflection is monitored by a linear rotary differential capacitance (LRDC) transducer. This device has a resolution of 10−7 rad and is simple to operate. The results for different electrode geometries as a function of separation distance and voltage on the charged conductor agree to ±20% or better with theoretical results, in most cases. In the case of aluminum electrodes, the attractive force is not stable; rather, it varies periodically as the result of an unknown discharge process.
A reliable pump-probe, broadband spectrometer for subpicosecond transient absorption
Authors: Ernsting N. P. , Kaschke M.
Published: July 2002

A pump-and-probe spectrometer is described that employs a pump pulse at 308 nm, with up to 1.4 mJ in 250 fs, and a continuum probe pulse in the spectral range 360–750 nm, of 80-fs pulse duration. The corresponding laser system is based on a colliding-pulse-mode dye laser operating at 616 nm, and a fs dye laser amplifier pumped by a XeCl* excimer laser. The amplifier has been designed specifically for pump-and-probe experiments, by multiplexing with horizontally and vertically polarized pulses for the pump and probe beam, respectively. Near-diffraction-limited output beams are achieved using a novel, capillary prismatic dye amplifier cell. The reliability of the apparatus is demonstrated by examining the photodissociation of bis-(p-aminophenyl) disulfide. The absorption band of the resulting p-aminophenyl-thiyl radicals shows a biexponential frequency shift in the course of several ps. This behavior is correlated with that of dielectric relaxation of the solvent.
Hall voltage measurements using ac lock-in detection
Authors: Tessler Leandro R. , Nissim Meir , Dai Uri , Rosenbaum Ralph L.
Published: July 2002

The measurement of the Hall constant in insulating highly resistive films is a difficult and challenging task. Owing to the small currents that may be passed through the insulating films, the Hall voltages are often very small in magnitude. A simple electronic circuit using commercial lock-in amplifiers is described which allows measuring these minute Hall voltages. Other practical measuring suggestions are also presented.
Optical diagnostics on dense Z-pinch plasmas
Authors: Riley R. A. , Lovberg R. H. , Shlachter J. S. , Scudder D. W.
Published: July 2002

A novel ‘‘point-diffraction’’ interferometer has been implemented on the Los Alamos solid fiber Z-pinch experiment. The laser beam is split into two legs after passing through the plasma. The reference leg is filtered with a pin-hole aperture and recombined with the other leg to form an interferogram. This allows compact mounting of the optics and relative ease of alignment. The Z-pinch experiment employs a pulsed-power generator that delivers up to 700 kA with a 100 ns rise time through a fiber of deuterium or deuterated polyethylene (CD2) that is 5-cm long and initially solid with radius r≊15 μm. The interferometer, using a Δt≊200 ps pulse from a Nd:YAG laser frequency doubled to λ=532 nm, measures the electron line density and, assuming azimuthal symmetry, the density as a function of radial and axial position. Calculations predict Faraday rotations of order π/2 for plasma and current densities that this experiment was designed to produce. The resulting periodic loss of fringes would provide the current density distribution.
Development of a holographic polaro-interferometer to study long-scale length plasmas
Authors: Guttmann Geoffrey D. , Gomez Camilo , Fernández Juan
Published: July 2002

Holographic polaro-interferometry represents a flexible tool for studying density and magnetic fields in an ICF plasma. The polarization and the changes in beam phase are recorded in a single hologram. Using the polarization information, the magnetic field (i.e., the Faraday rotation) of the plasma can be determined, while the density profile can be inferred from the change in beam phase. The experimental setup uses a Mach–Zender arrangement to form the hologram/interferogram. A single beam is passed through the plasma. This beam is split when entering the Mach–Zender arrangement. The reference beam is passed through a spatial filter to erase phase information generated from the passage through the plasma. This diagnostic is being developed for application to ICF plasmas. It will be tested initially on a long-scale length plasma generated by an exploding wire. An interferogram is presented.
X-ray streak camera diagnostics of picosecond laser–plasma interactions
Authors: Cobble J. A. , Fulton R. D. , Jones L. A. , Kyrala G. A. , Schappert G. T. , Taylor A. J. , Wahlin E. K.
Published: July 2002

An x-ray streak camera is used to diagnose a laser-produced Al plasma with time resolution of ∼10 ps. A streak record of filtered emission and a time-integrated transmission grating spectrum reveal that the plasma radiation is dominated by emission from He- and H-like resonance lines.
A soft x-ray multilayer mirror scanning monochromator for magnetically confined fusion plasmas
Authors: Zwicker Andrew P. , Finkenthal Michael , Huang Liang-Kang , Regan Sean P. , May Mark J. , Moos H. W. , Lippmann Stanley
Published: July 2002

A high throughput scanning soft x-ray monochromator that uses a flat multilayer mirror in a near normal incidence configuration was built and tested in the Plasma Spectroscopy laboratory at Johns Hopkins University and operated on the DIII-D tokamak. Depending upon the mirror used, the monochromator covers the range 10–170 Å, with a resolution of 0.25 to 10.8 Å. The instrument was photometrically calibrated between 10 and 45 Å. Spectra from DIII-D were obtained under a variety of discharge conditions over the entire range of the instrument. This paper describes the monochromator, the photometric calibration, and presents initial results.
Plasma temperature measurements using a time and spatially resolved x-ray camera
Authors: Benage John F. , Sherwood E. G. , Linzey S. E.
Published: July 2002

We have developed a diagnostic for measuring the blackbody temperature of a dense plasma produced in a high power capillary discharge. This diagnostic can be described as a filtered x-ray pinhole framing camera. The camera consists of a stripline microchannel plate and a filtered pinhole array. The camera is capable of producing two-dimensional images with time and spectral resolution. We utilize this camera to measure the temperature of a dense optically thick plasma. The imaging also enables us to determine temperature profiles and spatial effects which cannot be determined with other methods such as filtered x-ray diodes. We will present a complete description of the camera, our procedure for using it, and results from the experiment we carried out.
Proof-of-principle of a diagnostic for D-T fusion-product alpha particles (abstract)
Authors: Hutchinson D. P. , Richards R. K. , Bennett C. A. , Ma C. H.
Published: July 2002

Results are presented for an alpha-particle diagnostic proof-of-principle test based on CO2 laser small-angle Thomson scattering. Because the test was performed on a nonburning plasma (Advanced Toroidal Facility), which had no energetic alpha particles, scattering measurements were made on the plasma electrons. The diagnostic was configured to duplicate the requirements for an alpha-particle measurement, i.e., the measurement of a small scattered signal (≲10−9 W) in the presence of a high-power source laser (≳106 W) at small scattering angles (≲1°). The goals of this test were to eliminate stray laser light which would produce a background signal at the receiver and to maintain alignment between the pulsed laser and the receiver beams, which was set at 0.86°, while performing scattering measurements on a plasma. The proof of the diagnostic method is the measurement of the electron plasma frequency resonance feature in the scattering. Research sponsored by the Office of Fusion Energy, U.S. Department of Energy under Contract No. DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc.
Improved signal-to-noise in fluorescence scattering by means of nonlinear pumping with a frequency modulated dye laser
Authors: Forrest M. J. , Winfield R. J.
Published: July 2002

Laser-induced fluorescence (LIF) is a well established technique used to determine the neutral hydrogen density in fusion plasmas. There is a requirement to extend these measurements to the Divertor section of large plasma devices, but this is problematical due to the high levels of stray laser light and background plasma emission. Here we describe a method, based on harmonic saturated spectroscopy which depends on the nonlinear response of a saturated atomic system to discriminate against intrusive noise sources. For a pump laser modulated such that the intensity varies as I=I0 sin2 wt, the Fourier transform amplitude coefficients of the resulting fluorescence scattered signal take on finite values. Therefore selective frequency detection at, say, 4w makes possible high rejection of the dc component of plasma emission and also stray light at the modulation frequency of the laser. Excitation to the required atomic level is by a flash tube pumped frequency modulated Balmer Beta dye laser at 486 nm, with detection at the same wavelength. The optimization of the nonlinear pumping process, i.e., the degree of saturation for the most efficient production of detectable harmonics, is outlined. Also the anticipated signal-to-noise levels for the pertinent plasma conditions are given.
Self-consistent determination of low-Z
a pellet ablation and pellet penetration
Authors: Vahala Linda , Gerdin Glenn , El Cashlan A. G. , Parks Paul
Published: July 2002

The ablation dynamics of LiT pellets are solved self-consistently over a modest range of parameters using a surface dissociation model. The self-consistently determined parameters are then used to modify the standard low-Z pellet penetration codes. Since LiT pellets have certain advantages over carbon [in particular, Li conditioning of the walls and T for refueling a D–T reaction], the penetration of LiT into fusion plasmas is considered.
Crossed-sightline correlation of thermal ECE for remote measurement of absolute magnetic fields (abstract)
Authors: Thomas C. E. , Collazo I. , Hanson G. R. , Saravia E. , Woo J. T.
Published: July 2002

Many of the diagnostics that work on present magnetic fusion experiments will fail badly in the high radiation field of the burning fusion devices which are under conceptual design now. Two quantities of particular interest are the poloidal magnetic field profile versus minor radius, and radial measurements of β near the plasma center. Knowledge of the poloidal magnetic field is sufficient to infer the q profile and/or the current profile which is vital to understanding the MHD stability of the plasma and controlling the current profile. Knowledge of the ratio β of the plasma pressure to the magnetic field pressure radially resolved in the vicinity of the plasma center is also extremely useful for control and diagnosis of the plasma. A proposed new diagnostic uses crossed-sightline correlation of the thermal fluctuations in the electron cyclotron radiation emitted by the plasma to infer the local magnetic field very accurately. The field is measured at the crossing point of two sightlines into the plasma. The sightlines cross at small angles, typically 8° at the plasma center to about 18° at the plasma edge. By scanning the mirrors defining the two sightlines the absolute magnetic field across the plasma minor radius can be measured to an accuracy of better than 1 part in 103, with time resolution of the order of 10 ms per data point. This allows calculation of the q profile over most of the minor radius to an accuracy of better than 10% (given density and temperature measurements), and extremely accurate measurements of the plasma beta from r/a=0 to r/a=0.2.
Information on collective scattering spatial resolution using a two-sample-volume cross-correlation technique
Authors: Brower D. L. , Peebles W. A. , Rettig C. L. , Yu C. X.
Published: July 2002

The spatial resolution of small-angle collective scattering systems is often ambiguous due to the extended length of the scattering volume. By examining two sample volumes at the same wave vector (or scattering angle) that lie along the incident beam, and by varying the separation between these two volumes, one can examine their cross-correlation through use of simple digital signal processing techniques. As the separation between the two volumes is increased, the signals are observed to decorrelate. Application of this technique on the DIII-D and TEXT tokamaks shows that when the volumes are located at the plasma edge and core, the two signals are decorrelated indicating that fluctuations in the plasma core can be resolved.
Use of a heavy ion beam probe to measure the plasma potential on the Advanced Toroidal Facility
Authors: Aceto S. C. , Connor K. A. , Schwelberger J. G. , Zielinski J. J.
Published: July 2002

During the last operational period of ATF, a heavy ion beam probe was used to make measurements of the plasma potential, potential fluctuations, and electron density fluctuations. Due to the limited operational time and resources these measurements were made primarily on ECH plasmas, although some neutral beam heated plasma data were taken. The general results of these measurements and a discussion of the possible mechanisms which could cause uncertainties in the results will be given. The diagnostic method will be outlined with an emphasis on issues related to the operation of a beam probe in a stellarator environment.
Enhanced sensitivity detectors for potential fluctuation measurements (abstract)
Authors: Keating L. M. , Schoch P. M. , Crowley T. P. , Schatz J. G.
Published: July 2002

A method to improve the sensitivity of energy analyzers is being developed for use with heavy ion beam probes (HIBP). The method basically involves segmenting a single entrance slit into ten slits and modifying a detector. Theory and a simplified test shows that a factor of 10 improvement in sensitivity is possible. Previously, potential fluctuation measurements would have a signal to noise factor of unity when the rms fluctuation equaled 10−5×Vacc where Vacc is the accelerator voltage. The new 2-MeV HIBP on TEXT would be limited to potential fluctuations of greater than 20 Vrms when operating at full voltage. Measurements with the old system indicated that central potential fluctuations on TEXT were the order of 10 Vrms. The new detector should be able to measure down to 2 Vrms. A simplified geometry has been tested and showed a sensitivity as predicted, though a somewhat reduced range of operation. A test in an analyzer is planned. This work was supported by the U.S. Department of Energy.
Evolution of the 2-MeV electrostatic energy analyzer for TEXT-Upgrade (abstract)
Authors: McLaren P. E. , Hickok R. L. , Crowley T. P. , Lewis J. F. , Schatz J. G. , Schoch P. M. , Connor K. A. , Ouroua A.
Published: July 2002

The development of an electrostatic energy analyzer to be used with the 2-MeV heavy ion beam probe on the TEXT-Upgrade tokamak has presented several very interesting voltage breakdown phenomena. In order to maintain a 400-kV potential on large surface area plates (46.2 cm×152 cm) various configurations of support dielectrics, voltage feedthrough, plate materials, and plate geometry have been evaluated. Experimental evaluation of several designs and the resulting modifications leading to a working analyzer will be presented. This work was supported by the U.S. Department of Energy.
Rutherford scattering at TEXTOR
Authors: Tammen H. F. , van Blokland A. A. E. , Oyevaar T. , Schüller F. C. , Donné A. J. H.
Published: July 2002

The Rutherford scattering diagnostic at TEXTOR is used to perform temporal and spatial resolved measurements of the ion temperature. Function parametrization techniques are used for fast analysis of the complex spectra, which also contain information about the presence of impurities in the scattering volume. The (perpendicular) central ion temperature has been determined for a series of discharges, where neutral beam coinjection (hydrogen) was applied to plasmas of different densities. A temperature of 2.8 keV was found for a line-averaged electron density of 1.5×1019 m−3, decreasing monotonically for higher densities to 0.8 keV at 6.0×1019 m−3. When deuterium was used as heating beam species, scattering on a high-Z impurity, probably tungsten from the filaments of the NBI sources, gave a dominant contribution to the spectra.
On a nonintrusive spectroscopic method to determine fluctuating electric fields in hot plasmas (abstract)
Authors: Zurro B. , Burgos C. , Castejón F.
Published: July 2002

A nonintrusive method to measure low level stochastic electric fields in hot plasmas is being investigated in the TJ-I tokamak (R=30 cm, a=10 cm, Ip<60 kA, BT<1.5 T). It is based on the measurement of ion temperature of particles with different masses, i.e., protons and impurities, by the Doppler line width of their emission lines. It is hypothesized that its difference is due to gross mass motion produced by Ẽ×B. As a guide for data interpretation, we compare our results with typical values of fluctuating electric fields obtained by Langmuir probes at the plasma periphery. The ion temperatures of representative impurities like C V and O V, have been measured by the Doppler line width of near UV lines 2271 and 2781 Å, respectively. The proton temperature has been measured analyzing the Hβ and Hα line wings whose emission is due to highly energetic neutrals. Results of fluctuating electric fields obtained by this method as a function of radius and plasma density will be presented. The deduced fluctuating electric fields are higher at the plasma periphery than at the plasma center and in the latter much higher at low than at high densities. An approach to distinguish between radial and poloidal electric field fluctuations is being addressed by modeling experimental results with a simulation code.
Forward scattered light measurements for the calibration of a differential absorption LIDAR system in the laboratory
Authors: Kitriotis D.
Published: July 2002

It is shown that forward scattered light measurements done in the laboratory space can be used for monitoring the performance of a differential absorption LIDAR system during its initial developing stages, as an accurate and convenient alternative to remote measurements. On the contrary, backscattered light measurements in the laboratory do not allow for such task. The differential absorption coefficient of NO2 in the atmosphere is measured in the wavelength region 446.4–450.4 nm as a demonstration.
A nuclear quadrupole resonance spectrometer with automatic gain control and sideband suppression
Authors: Rukmani K. , Ramakrishna J.
Published: July 2002

A cw nuclear quadrupole resonance spectrometer centered on the superregenerative oscillator and working in the range 20–40 MHz is described. Both automatic gain control and sideband suppression have been incorporated by using external quench waveforms of variable mark-to-space ratio. Extensive use of ICs in these circuits leads to ease of construction as well as increased reliability. The S/N obtained remains unaffected by the automatic gain control while the sideband suppression does give rise to a small degradation. The spectrum of NaClO3 has been recorded.
Determination of the critical current density in HTSC thin-film multilayers
Authors: Behner H. , Rauch W. , Gornik E.
Published: July 2002

In this paper the limitations and perspectives of a simple remanent field technique for the determination of the critical current density (jc) in high-temperature superconductor (HTSC) thin films and in HTSC thin-film multilayers at 77 K were examined. As the comparison with resistive jc measurements on microbridges shows, jc values down to 104 A/cm2 can easily be measured with high accuracy. The method is nondestructive, fast, and inexpensive. It is especially suitable for jc measurements of double-sided coated substrates, where the determination of the individual jc values of both thin-film layers is possible.
Charged fusion product diagnostics in Alcator C-Mod
Authors: Boivin R. L. , Kurz C. , Lo D. H. , Fiore C. L. , Granetz R. , Petrasso R. D.
Published: July 2002

With a plasma current of up to 3 MA, toroidal field of up to 9 T, the confinement of the charged fusion products (CFPs) in Alcator C-Mod is expected to be excellent. For example, at maximum current and field, classical losses of the 0.8 MeV 3He, 1 MeV triton, 3 MeV proton, 3.5 and 3.7 MeV alphas are expected to be less than 5%. For the study of the global confinement of CFPs, we plan to measure the burnup of the 1 MeV triton (from the D–D reaction) using a proton recoil detector (NE-213) for the detection of the 14 MeV neutron resulting from the secondary fusion reaction (D–T). On the other hand, loss measurements of CFPs will be made inside the first wall with two detectors (one at the bottom, one at the midplane) using silicon based detectors. The midplane detector will be used to diagnose D–3He plasmas by looking at the unconfined 14.7 MeV proton. In addition to the derivation of fusion yield, energy distribution of the escaping protons will provide information about the ion velocity distribution of the reactants. The bottom detector is time, pitch angle and energy resolved, and thus will be used to study loss mechanisms such as first orbit, toroidal field ripple and magnetohydrodynamics-induced diffusion.
A method of evaluation of gas gain in proportional counters
Authors: Akande Wole
Published: July 2002

A method of evaluation of gas amplification in proportional counters, independently of gas gain measurements, is presented. The approach, particularly useful for high regions of the reduced electric field, (S=E/P), involves the fit of an analytic expression to all the S regions of the Townsend first ionization coefficient, (α/P), experimental data. This approach is also useful for the estimation of gas gain for established gas mixtures but of nonstandard proportions such as Ar/Xe/CO2. The constants obtained in the process were used to evaluate the fundamental gas gain equation. An appropriate formula was then found to fit the resulting data. A component of the method is the generation of (α/P) data for gas mixtures. Comparison of this work with various gas amplification models in the literature was effected. Physical phenomena which may be responsible for differences between calculated and experimental gas gain are discussed.
A spectrometer for the measurement of reflectance-difference spectra
Authors: Lastras-Martínez L. F. , Lastras-Martínez A. , Balderas-Navarro R. E.
Published: July 2002

We describe a spectrometer (visible-ultraviolet photon energy range) for the measurement of reflectance-difference spectra of cubic semiconductors. The spectrometer employs a photoelastic modulator to modulate the polarization of the light incident on the sample and allows for a simple procedure to correct the measured spectra for parasitic components associated with such modulation. The instrument reported has a higher throughput than more conventional setups. To illustrate the spectrometer performance we report on reflectance-difference spectra of (001) oriented GaAs single crystals doped with silicon donors at a level of 1018/cm3.
Variable attenuator for high-power lasers
Authors: Hanton Scott D.
Published: July 2002

A novel variable attenuator is described for use with pulsed, high-power ultraviolet lasers. The attenuator is comprised of a number of fine metal meshes. The attenuation is accurately and easily changed by varying the number of meshes in the laser beam path.
Devices for maintaining optical access in high-temperature coal combustion environments. II. Sonic and supersonic flow regions
Authors: Cook Robert L. , Lineberry John T.
Published: July 2002

Application of optical diagnostic techniques and instruments in the high-temperature coal combustion environments of large-scale facilities requires a clear optical path into and out of the particle-laden gas stream for long periods of time. In this paper, we describe devices for making long-term optical measurements in the sonic and supersonic regions of a coal combustion flow where, in general, the gas stream is a high-speed flow at high temperature and pressure. The design and operation of the devices are discussed and schematics are presented. Successful operation of the devices for over 900 h demonstrates their long-term reliability.
Amplitude stabilization of a multiwavelength laser beam by an acousto-optic tunable filter
Authors: Tran Chieu D. , Furlan Ricardo J.
Published: July 2002

A novel method has been developed to stabilize the amplitude of a multiwavelength laser beam. The method is based on the use of an acousto-optic tunable filter to diffracted light which has more than one wavelength. The number of the wavelengths in the diffracted light is controlled by the number of the rf signals which are applied into the filter. Because the intensity of each wavelength in the diffracted beam is dependent on the power of the corresponding applied rf signal, the total amplitude of the multiwavelength diffracted beam can be stabilized, i.e., adjusted at a constant amplitude and maintained at that level, by individually controlling the intensity of each corresponding wavelength by use of an rf driver with a feedback loop for each wavelength. In addition, the method also provides a unique means to amplitude-modulate one (or more) wavelength(s) of a multiwavelength beam at a specific frequency while keeping the other wavelengths at a constant amplitude level.
Summary of the satellite workshop on synchrotron computed microtomography
Authors: Spanne P. , Jones K. W.
Published: July 2002

Synchrotron computed microtomography is a field that has developed rapidly over the last ten years. The next few years should bring about further rapid advances because of the introduction of third-generation synchrotron x-ray sources, rapid improvements in the computer hardware and software used for the reconstructions and display of the data, and improvements in x-ray detector technology. The purpose of the workshop was to look at the status of current technology and applications and to present some ideas about future improvements in the technology. Brief summaries of the presentations are given in the following sections.
A technique for mapping three-dimensional number densities of species in laser produced plumes
Authors: Al-Wazzan R. A. , Lewis C. L. S. , Morrow T.
Published: July 2002

The potential of a diagnostic technique to provide quantitative three-dimensional (3D) density distributions of species in a low temperature laser-produced plume is shown. An expanded, short pulse, tunable dye laser is used to probe the plume at a set time during the expansion. Simultaneous recording of two-dimensional in-line absorbance maps and orthogonal recording of laser induced fluorescence permits the 3D density mapping by scanning the dye laser frequency. Preliminary data, supported by a simple model, is presented for the case of Ba II ions in a YBCO plume heated by a KrF laser.
A sample holder design and calibration technique for the quantum design magnetic properties measurement system superconducting quantum interference device magnetometer
Authors: Lewis L. H. , Bussmann Konrad M.
Published: July 2002

Magnetic measurements performed on low-susceptibility materials often generate concern for the contribution of the sample holder’s moment to the resultant measurement value. In this article, we present a unique design of a sample holder and accompanying calibration technique used to obtain accurate magnetic-moment values from compact, low-susceptibility samples measured with the quantum design magnetic properties measurement system superconducting quantum interference device (SQUID) magnetometer. The sample holder design is simple, highly symmetric, easily fabricated, useful over the full temperature range of the magnetometer and is amenable to a correction algorithm that allows the experimentalist to determine accurately the contribution of the sample holder to the measured value. The sample holder is modeled as a semi-infinite linear density of dipoles, and the response of the internal SQUID coil sections to these dipoles is summed to represent the system response to the sample holder. When the correction algorithm was applied to a measurement of NIST SRM 763 aluminum mounted in the sample holder, the error in the magnetic susceptibility decreases substantially from 41.9% down to 1.1%.
Digitally controlled interferometer prototype for gravitational wave detection
Authors: Barone Fabrizio , Calloni Enrico , Di Fiore Luciano , Grado Aniello , Milano Leopoldo , Russo Guido
Published: July 2002

In this article, we describe the architecture of the 3 m suspended Michelson interferometer prototype for gravitational wave detection which is operational in Napoli. The characteristic which makes this interferometer different from the existing ones is the digital implementation of the control system, the monitoring system, the data acquisition system, and the archiving system. This architecture makes this interferometer a good test bench for the study, the development, and the test of general techniques for the automatic control of interferometers for gravitational wave detection. In particular, it is now being used for the development and the test of some subsystems of the very long baseline interferometric VIRGO antenna for gravitational wave detection. [The Virgo Project, Final Design of the Italian–French large base interferometric antenna Virgo for gravitational wave detection of which the authors are proponents and in whose construction the Authors are collaborating (INFN, Italy, and CNRS, France, 1989, 1992, 1995).]
A detailed examination of stimulated pump-probe measurements of vibrational population relaxation
Authors: Blanchard G. J.
Published: July 2002

We have developed and demonstrated a pump-probe laser spectroscopic scheme to measure ground state vibrational population relaxation. There are two significant advantages to this technique over alternative measurement methods. The first is that the detection sensitivity of the pump-probe method is limited by the shot noise present on the probe laser and the second is that, because of the manner in which the ground state vibration(s) are populated, it is possible to interrogate T1 processes for degenerate donor–acceptor conditions. We detail in this article the form of the experimental stimulated signal, the effect of the detection scheme used, and the consequences of spontaneous (Boltzmann) population of ground state vibrations. A central conclusion of this work is that, even for small signal limit pump-probe experiments, absorption, stimulated emission, and spontaneous emission all play important roles in collectively determining the form of the experimental signal.
An inline optical electron polarimeter
Authors: Trantham K. W. , Gay T. J. , Vandiver R. J.
Published: July 2002

The design and operation of a simple inline optical electron polarimeter is presented. It is based on exchange excitation of ground state neon atoms. The electron polarization is determined from the degree of circular polarization of the subsequent 2p53p 3D3→2p53s 3P2 (6402 Å) fluorescence. This device can characterize both longitudinally and transversely polarized electron beams in a nondestructive fashion, and is inexpensive and easily constructed.
Fast pyroelectric detector for broadband radiated power measurements
Authors: Côté C. , DeSilva A. W.
Published: July 2002

Basic design requirements are presented for pyroelectric detectors to be used effectively when the radiation source emits part or all of its power in the vacuum ultraviolet range, as is the case for a typical plasma in magnetic confinement fusion research. The difficulty associated with the VUV wavelength range lies in the high photoelectric yield of the associated energetic photons. A relatively inexpensive, commercially available detector was modified to eliminate the spurious currents resulting from photoelectrons. The modifications have little effect on the basic characteristics of the commercial detector (time response, sensitivity, etc).
Inexpensive circuit for the measurement of capture cross section of deep level defects in semiconductors
Authors: Reddy C. V. , Fung S. , Beling C. D.
Published: July 2002

A simple and inexpensive circuit to facilitate the direct measurement of capture cross section, when synchronized with a deep level transient spectroscopy system, is described. It avoids the most commonly encountered problem of loading and distortion of the bias (trap filling) pulses of nanosecond duration in the capture cross-section measurement. The capacitance meter, whose internal circuitry is responsible for the distortion, is connected and disconnected from the rest of the apparatus with the help of simple and low-cost reed relay switches featuring high operating speed and low contact resistance. Sharp bias pulses as small as 30 ns can successfully be applied to the sample with no observable distortion. Finally, a representative measurement is shown to demonstrate the simplicity and high performance of the circuit.
A miniature magnetometer based on the superconducting quantum interference device with direct readout electronics
Authors: Polushkin V. , Wallis M. , Glowacka D. , Matthews A. , Lumley John M.
Published: July 2002

A novel miniature superconducting quantum interference device magnetometer with direct readout electronics has been developed. A high flux-to-voltage transfer factor of up to 2500  μV/Φ0 is achieved without additional positive feedback (Φ0 is the flux quantum). A flux resolution of 8×10−7 Φ0/Hz1/2, corresponding to a magnetic moment sensitivity of approximately 2×10−20 A m2/Hz1/2, has been measured. This magnetometer can be used to study the dynamic magnetization properties (including nuclear magnetic resonance and magnetic resonance imaging) of micron and submicron size particles and for high-resolution surface magnetometry.
Laser deposition of diamondlike carbon films at high intensities
Authors: Qian F. , Singh R. K. , Dutta S. K. , Pronko P. P.
Published: July 2002

Unhydrogenated diamondlike carbon (DLC) thin films have been deposited by laser ablation of graphite, using a high power Ti: sapphire solid state laser system. DLC films were deposited onto silicon substrates at room temperature with subpicosecond laser pulses, at peak intensities in the 4×1014–5×1015 W/cm2 range. A variety of techniques, including scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, spectroscopic ellipsometry (SE), and electron energy loss spectroscopy (EELS) have been used to analyze the film quality. Smooth, partially transparent films were produced, distinct from the graphite target. Sp3 volume fractions were found to be in the 50%–60% range, with Tauc band gaps ranging from 0.6 to 1.2 eV, depending on laser intensity. Kinetic energies carried by the carbon ions in the laser induced plasma were measured through time-of-flight (TOF) spectroscopy. Their most probable kinetic energies were found to be in the 700–1000 eV range, increasing with laser intensity.