bluuebunny/crossref_metadata_2025 huggingface dataset:
Array of neutral particle analyzers at DIII-D
Authors: Carolipio E. M. , Heidbrink W. W.
Published: July 2002

Local measurements of the fast-ion distribution in auxiliary-heated plasmas are key to understanding the behavior of energetic particles under a variety of conditions, such as beam–ion transport during Alfvén instabilities and the acceleration of beam ions by fast waves. For the first time at DIII-D, line-averaged and local measurements of the energetic-particle density (for E=5–75 keV) are possible using an array of four compact charge–exchange analyzers [P. Beiersdorfer et al., Rev. Sci. Instrum. 58, 2092 (1987)]. The installation consists of three vertically viewing analyzers with fixed sightlines, measuring particles with χ=90° (where χ is the angle between the particle’s velocity and the toroidal direction), and one horizontally viewing analyzer with a variable sightline, measuring particles with 2°≲χ≲60°. All the analyzers can make passive measurements while three detectors, with sightlines that intersect deuterium heating beams, can make active charge–exchange measurements.
Diagnostic strategy of the W7-X stellarator (abstract)
Authors: Hartfuss H. J. , Brakel R. , Endler M. , Geist T. , Grigull P. , Hofmann J. V. , Junker J. , Kick M. , Kühner G. , Niedermeyer H. , Ringler H. , Teubel A. , Wagner F. , Weller A.
Published: July 2002

The Wendelstein 7-X experiment is a concept test for properties of reactor relevant plasmas in advanced stellarators. Prominent features include a modular superconducting coil assembly, a five-fold toroidal symmetry, and a helical magnetic axis. Due to the optimization process, W7-X is characterized by a vacuum magnetic field configuration with smooth magnetic surfaces, improved magnetic field configuration with smooth magnetic surfaces, improved equilibrium properties with a weak dependence of rotational transform and shear on the plasma pressure β, good magneto-hydrodynamic stability properties due to magnetic well stabilization, reduced neoclassical transport losses and negligible bootstrap current in the long mean-free-path regime, good collisionless α-particle confinement in an equivalent reactor, and, as a technical aspect, good feasibility of the superconducting modular coils. W7-X will be heated by continuous electron cyclotron resonance heating and pulsed neutral beam injection and ion cyclotron resonance heating. The envisaged parameters are Te⩽10 keV, Ti⩽6 keV central densities ⩽3×1020 m−3 with an averaged 〈β〉⩽5%. Despite the complicated geometrical structure, all basic diagnostics are compatible with W7-X. Generally, diagnostic methods and applications in a stellarator are not different from those in tokamaks. However, special efforts are being made to equip the experiment with those diagnostics necessary to measure the quantities directly related with the optimization of the machine: the verification of the predicted magnetic topology and characterization of the configuration throughout the entire parameter range, the identification of equilibrium and stability, and the determination of the confinement properties. The article describes the strategy developed which assures that the detailed measurement needs of the W7-X experimental program can be met.
Development and characterization of semiconductor ion detectors for plasma diagnostics in the range over 0.3 keV
Authors: Cho T. , Sakamoto Y. , Hirata M. , Kohagura J. , Makino K. , Kanke S. , Takahashi K. , Okamura T. , Nakashima Y. , Yatsu K. , Tamano T. , Miyoshi S.
Published: July 2002

For the purpose of plasma-ion-energy analyses in a wide-energy range from a few hundred eV to hundreds of keV, upgraded semiconductor detectors are newly fabricated and characterized using a test-ion-beam line from 0.3 to 12 keV. In particular, the detectable lowest-ion energy is drastically improved at least down to 0.3 keV; this energy is one to two orders-of-magnitude better than those for commercially available Si-surface-barrier diodes employed for previous plasma-ion diagnostics. A signal-to-noise ratio of two to three orders-of-magnitude better than that for usual metal-collector detectors is demonstrated for the compact-sized semiconductor along with the availability of the use under conditions of a good vacuum and a strong-magnetic field. Such characteristics are achieved due to the improving methods of the optimization of the thicknesses of a Si dead layer and a SiO2 layer, as well as the nitrogen-doping technique near the depletion layer along with minimizing impurity concentrations in Si. Such an upgraded capability of an extremely low-energy-ion detection with the low-noise characteristics enlarges research regimes of plasma-ion behavior using semiconductor detectors not only in the divertor regions of tokamaks but in wider spectra of open-field plasma devices including tandem mirrors. An application of the semiconductor ion detector for plasma-ion diagnostics is demonstrated in a specially designed ion-spectrometer structure.
Fast charged-coupled device spectrometry using zoom-wavelength optics
Authors: Carolan P. G. , Conway N. J. , Bunting C. A. , Leahy P. , O’Connell R. , Huxford R. , Negus C. R. , Wilcock P. D.
Published: July 2002

Fast charge-coupled device (CCD) detector arrays placed at the output of visible spectrometers are used for multichord Doppler shift analyses on the COMPASS-D and START tokamaks. Unequal magnification in the horizontal and vertical axes allows for optimal matching of throughput and spectral resolution at the CCD detector. This involves cylindrical lenses in an anamorphic mounting. Optical acuity is preserved over a very wide range of wavelengths (220 nm→700 nm) by separate repositioning of all the optical elements which is accomplished by the use of zoom mechanisms. This facilitates rapid changes of wavelength allowing edge and core observations depending on the location of the emitting impurity ions. Changes to the ion temperature and velocity are recorded using 20 chords simultaneously with typical accuracies of Δvi<1 km s−1 and ΔTi/Ti<10% with a time resolution of <1 ms.
All-high-T
c superconductor rapid-single-flux-quantum circuit operating at ∼30 K
Authors: Shokhor S. , Nadgorny B. , Gurvitch M. , Semenov V. , Polyakov Yu. , Likharev K. , Hou S. Y. , Phillips Julia M.
Published: July 2002

We have implemented a simple circuit of the rapid single-flux-quantum (RSFQ) logic family using a single-layer YBa2Cu3O7−x thin-film structure with 14 in-plane Josephson junctions formed by direct electron beam writing. The circuit includes two dc/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip-flop, and an SFQ/dc converter (readout SQUID). Low-frequency testing has shown that the dc-current-biased circuit operates correctly and reliably at T∼30 K, a few degrees below the effective critical temperature of the junctions. Prospects for a further increase of the operation temperature and implementation of more complex RSFQ circuits are discussed in brief.
Measurement of storage-ring lattice functions: Application to the Pohang Light Source
Authors: Yoon Moohyun , Lee Taeyeon
Published: July 2002

Measurement of the lattice functions was carried out in the storage ring for the light source. The measurement includes β, dispersion functions, phase advances, tunes, momentum compaction, chromaticities, and linear coupling. Two methods were used for the β measurement; a quadrupole-tweaking method and a method using a sensitivity matrix. Using the sensitivity-matrix method gives additional information on the phase between monitors and correctors, as well as the fractional part of the tunes. The linear-coupling constant was obtained by driving the tunes across the coupling resonance and measuring the minimum tune separation. It is also shown that by using four skew-quadrupole circuits, the coupling constant can be varied arbitrarily. In this article, a detailed method for the lattice-function measurement is presented, and the result applied to the storage ring of the Pohang Light Source is given. The measured results are compared with the design values and shown to be in good agreement.
New gas feeding system at the JYFL electron cyclotron resonance ion source
Authors: Koivisto H. , Hendolin M. , Ärje J.
Published: July 2002

A new gas feeding system for an electron cyclotron resonance ion source was developed at the University of Jyväskylä. With the aid of the system, pressures of a few hundred millibars in gas lines remain constant within less than 1 mbar. Due to a very stable gas flow in the buffer and ion gas lines, the source can now deliver practically constant current beams of highly charged ions for long period runs.
The resonant behavior of segmented piezoceramic tubes
Authors: Tapson J. , Greene J. R.
Published: July 2002

Segmented piezoceramic tubes are widely used as the scanning actuators in scanning probe microscopes. A good understanding of the tube behavior is necessary in order to implement the electronic feedback control that is required for image scanning. Previous studies of the tubes have given contradictory results for the phase change between the driving signal and mechanical displacement at the lowest resonance frequency. In addition, the commonplace method of measurement of resonance frequency by piezoelectric self-excitation occasionally gives anomalous results. In this paper, new measurements are described, which explain some of these anomalies. The measurements of off-axis resonant response are reported. The resonant behavior is shown to depend on the mounting of the tube base, as well as the tube itself. A potential pitfall in the common method of resonance measurement by self-excitation is shown to exist.
Enhancement technique in the measurement of alternating current susceptibility
Authors: Mukherjee S. , Chakravarti A. , Ranganathan R.
Published: July 2002

The enhancement technique is basically the measurement of the ac susceptibility in the presence of a second biasing field (pulsed dc or ac). This useful technique will be adopted for modification of the ac susceptometer. A proportional integral derivative controller, commonly used in temperature controllers, and a voltage to current converter with variable gain and sign, play special roles in this measurement technique. A second sinusoidal ac field (in addition to the measuring field) is used as the biasing field. The technique is a very useful one to obtain quantitative information about domain wall pinning, domain contribution to magnetization, etc. in the magnetic systems.
Monitoring of nitrogen gas purity by the hot filament method
Authors: Buhlmann H. J. , Ilegems M.
Published: July 2002

A hot filament can be used as a simple, reliable, and inexpensive sensor to measure quantitatively ppm-level concentrations of oxidizing species present in high-purity nitrogen. A coiled tungsten filament of a 1 W signal lamp acts as a sensing element, which, by high-temperature reaction with O2 and H2O, forms volatile oxides. The resulting decrease in filament diameter and rise in filament resistance is monitored by measuring the current at constant voltage. The sensor’s response is linear with the O2 concentration over an extended range of “burn-down” and is relatively insensitive to the gas velocity. The reaction appears to be rate limited by the diffusion of oxygen along its concentration gradient toward the filament. The sensor’s sensitivity, operated in nitrogen at Ufil=6.3 V, is determined to S=21 ppm O2/(mA/min).
An automatic radon sensor for borehole measurements
Authors: Lenzen M. , Neugebauer H. J.
Published: July 2002

The understanding of radon migration in the earth’s crust is important in many applications, such as radiation protection in residential buildings, uranium ore prospecting, or earthquake prediction. Recent studies also show correlations of radon exhalation with short-periodic rock stresses induced by tidal forces. The borehole radon sensor presented can be used to investigate subsurface radon migration in situ. It is capable of measuring the concentration of both radon and thoron in air with a time resolution of less than an hour and a detection limit of approximately 1 Bq m−3, even in volumes as small as 100 ml. The sensor is fully automated and can be calibrated in situ.
Guidance characteristics of some displacement devices used in a high-precision He–Ne laser displacement measurement system
Authors: Brand U. , Miyashita K. , Hannemann J.
Published: July 2002

The guidance characteristics of three different translation stages for application as the driver in a high precision displacement transducer calibration instrument (measuring laser) were assessed. A high voltage PZT tube, a low voltage three-segment PZT, and a corrugated diaphragm displacement device with a magnetic coil drive were investigated. The maximum yaw and pitch angles of the PZT tube were 8 and 5′′, respectively, for a translation of 3 μm. The maximum guiding deviation of the three-segment PZT for a displacement of 13 μm was 38′′ (yaw) and 17′′ (pitch) when applying the same voltage to all segments. The maximum guiding deviation, however, was able to be reduced to ±0.4′′ by applying different voltages to individual PZT segments. The guiding deviation of a corrugated diaphragm with a magnetic coil drive was ±0.6′′ (yaw) and ±0.4′′ (pitch) for a displacement of ±100 μm. The corrected three-segment PZT as well as the corrugated diaphragm device are suited for application with the measuring laser of this article.
Studies of the localization paradox of fluctuation reflectometry via multidimensional SOFTSTEP simulations (abstract)
Authors: Afeyan Bedros B. , Chou Albert E. , Luhmann Neville C.
Published: July 2002

The initial value problem of the scalar wave equation modeling the propagation and scattering of O modes in a fluctuating plasma is solved numerically. Using split operator and FFT techniques, SOFTSTEP codes solve the slow temporal envelope equations that describe fluctuation reflectometry in the presence of space and time varying density profiles. Previous studies have revealed an inexplicable sensitivity of the scattered phase signal to input microwave frequency. This might suggest that the fluctuations that give rise to the scattered signals are highly localized in space, much more so than one might expect on physical grounds. Our simulations attempt to resolve this paradox by demonstrating the existence of additional interference between various signals that contribute to the same measured phase. As the launching and detecting antennas are a few wavelengths wide, the measured phase is an average over their surface areas. This results in added sensitivity and wavelength selectivity which might be overcome if more than one detector is used to simultaneously measure the scattered signal at various angles.
Application of a Fourier transform based filtering technique to improve signal-to-noise ratio in modulation spectroscopy experiments
Authors: Ghosh Sandip , Arora B. M.
Published: July 2002

It is shown that a simple rectangular filter is a good approximation to Wein’s optimal filter for improving the signal-to-noise ratio in a typical modulated reflectance spectroscopy experiment. This enables one to obtain identical information from data recorded with much smaller time constants for data averaging and therefore faster scan speeds. The limitations of this method are also discussed.
Stand-alone microprocessor controlled fast sweep Langmuir probe driver
Authors: Cheetham A. D. , Davidson L. , Jakobsen J. , Lund T. , Rayner J. P.
Published: July 2002

This article describes a power supply and data logger for a Langmuir probe interfaced to a personal computer. The system provides a voltage sweep range from −125 to +100 V in 100 steps in a time ∼0.15 s. Restricted sweep ranges and single point operation are also possible. Probe current measurements are in the range from −1.0 to +100 mA with a precision of 5 μA on the most sensitive range, while the voltage may be set with a precision of 56 mV. Novel features of the system include: the use of integrate-and-dump techniques to implement the process of analog-to-digital conversion and to provide effective noise suppression; a solution to the problem of floating the power supply on top of the potential developed across the grounded current sensing resistor based on the power supply rejection ratio characteristics of a high voltage operational amplifier; and the development of an interface and control board employing the GPIB protocol to communicate with a host computer. Successful operation of the system has been demonstrated in the electrically noisy environment of a helicon plasma source.
A continuous-purge pulsed valve suitable for high-temperature applications
Authors: Senkan Selim M. , Deskin Scott C.
Published: July 2002

A continuous-purge pulsed valve has been designed to introduce supersonic jet samples into a vacuum chamber. The new valve design separates the heated sampling and transfer lines from the solenoid coils with a long metal valve stem, which is kept cool with annular cooling fins. The valve is heated using electrical heating elements wrapped around the valve stem. A precision-machined stainless steel plunger maintains a metal-to-metal seal at the valve orifice, which is broken when the induced magnetic field from the solenoid pulls the plunger upward. Stable gas pulse widths were obtained down to 200 μs, which compares favorably with the 165 μs value for the commercial unit which uses a small Teflon poppet instead of the metal plunger.
Design of a short-pulse, far-infrared free electron laser with a highly overmoded waveguide
Authors: Lin Li Yi , van der Meer A. F. G.
Published: July 2002

We report the design of a long wavelength extension to the free electron laser for infrared experiments. A parallel plate is inserted in the resonator to reduce diffraction losses. It will be shown that with a 10 mm gap waveguide, single transverse mode operation can be expected over a wavelength range from 300 down to 40 μm, allowing pulses as short as a few optical cycles to be produced.
Gas-discharge neutralizer for ion-beam system
Authors: Bizyukov A. A. , Kashaba A. Y. , Sereda K. N.
Published: July 2002

The design and operation of a gas-discharge neutralizer of positive ion beams is presented. It is based on the discharge with crossed electric and magnetic fields initiated by the ion beam, which travels through the device, without an additional energy source. Depending on the pressure, there are two types of the discharge inside the neutralizer: high-voltage (at a low pressure p<3×10−4 Torr) and magnetron (at a high pressure p>3×10−4 Torr). In the high-voltage regime, the ion beam is partially neutralized. Full ion beam compensation is achieved in the magnetron regime.
A complex probe for measurements of turbulence in the edge of magnetically confined plasmas
Authors: Castro R. M. , Heller M. V. A. P. , da Silva R. P. , Caldas I. L. , Degasperi F. T. , Nascimento I. C.
Published: July 2002

To improve the turbulence characterization and the estimation of the transport processes at the plasma edge, we designed and installed, in the Brazilian tokamak (TBR), a complex probe that consisted of five single Langmuir probes, a four-channel triple probe, and magnetic probes. In this work, we describe in detail this diagnostic system and present experimental examples of simultaneously measured plasma parameters and electrostatic and magnetic turbulent fluctuations in the TBR tokamak. This procedure permits to investigate any coupling between these two kinds of oscillations. Furthermore, our results confirmed that corrections due to electron temperature fluctuations are relevant for turbulence characterization.
Liquid-to-gas differential pressure transmitter with small hydrostatic error
Authors: McWhirter J. D. , Crawford M. E. , Klein D. E.
Published: July 2002

A design is described for a device which transmits steady-state differential pressure from a liquid process to a gas differential pressure signal. By appropriate design, the hydrostatic error inherent in liquid-to-gas pressure transmission can be made negligibly small in relation to the accuracy of the differential pressure transducer. The instrument is a design modification of the “gas trap” method of pressure measurement for liquid-metal systems. The design described results in a simple, inexpensive, and easy to implement technique for liquid-metal differential pressure measurement, and, by appropriate design, with a negligible hydrostatic error. The design and implementation of such a system was undertaken with highly satisfactory results. Operational aspects of such a system are described. The design is applicable to a system where highly accurate steady-state differential pressure measurements are needed, while avoiding introduction of the process directly within the differential pressure transducer.
The optimum dynamic parameters of digital rate meter algorithms
Authors: Arandjelović V. Dj. , Koturović A. M.
Published: July 2002

The definition of the “Quality,” Q, of a count-rate meter algorithm is introduced as the reciprocal of the algorithm’s (τ×ε) product, where τ is the response time of the algorithm to a sudden change in the average count rate and where ε is the fractional standard deviation of the steady-state measurement of a constant average count-rate pulse stream. Analytical expressions for τ and ε of digital rate meter algorithms are used to calculate maximum values of Q for both linear and exponential algorithms. The values of the basic algorithm parameters necessary to achieve these minimum (τ×ε) products are derived for both algorithms. The use of these values results in algorithms that have relatively short response times and, simultaneously, relatively small steady-state errors.
Ion sources for fission fragment accelerators
Authors: Köster U. , Kester O. , Habs D.
Published: July 2002

At the Grenoble and Munich high-flux reactors fission fragment accelerators are under design which will deliver beams of very neutron-rich fission products with a final energy between 3 and 6 MeV/u. In order to obtain an efficient acceleration in a compact accelerator, charge conversion of the 1+ ion beams from the in-pile ion source to a q/A⩾0.16 has to take place. In the chain from production to acceleration, ion sources are the key elements to reach high beam intensities of over 1010 s−1. For the in-pile part the target-ion source assembly has not only to be very efficient, but should also be highly selective for the desired elements (which go from nickel to europium) on one hand and robust against the hostile environment (high neutron and gamma flux) on the other hand. Foreseen types are a surface ionization source, which could also be run as laser ion source for resonant photo ionization, and, for rare gases, a plasma ion source coupled via a transfer line to the target. For the charge state breeding several different schemes are considered: the combination of a Penning trap for bunching, cooling, and mass separation and an electron beam ion source (EBIS) as charge breeder, similar to REX-ISOLDE, an EBIS with direct injection of a dc beam of 1+ ions (“accu-EBIS”) or an electron cyclotron resonance ion source (ECRIS) with either continuous or bunched extraction. The EBIS may provide higher charge states, whereas the ECRIS is able to work with much higher beam intensities and allows cw-operation. The advantage of each scheme is explained and some design requirements of the different sources are presented.
Thermal parameters of dental materials determined by photoacoustic phase lag measurements
Authors: Pelá C. A. , Rocha S. , de Paula E. , Baffa O.
Published: July 2002

A method of measuring the phase lag of the photoacoustic signal obtained by rear surface excitation is employed for the determination of the thermal properties of insulating dental materials such as calcium hydroxide cement, a cavitary varnish and photopolymerized restoration resins. Disk shaped dental materials were glued to the front surface of the thin metal foil window of the photoacoustic cell and illuminated by pulsed light. A three layer model was developed to fit the measurements of the phase angle as a function of the frequency of excitation. The thermal diffusivity and conductivity of the dental material were determined to good precision. The instrumentation employed in the present work is simple and easily obtainable by any laboratory.
The design and sensitivity of microwave frequency optical heterodyne receivers
Authors: Bingham S. J. , Börger B. , Suter D. , Thomson A. J.
Published: July 2002

Recent advances in high speed photodetector and microwave receiver technology make microwave frequency optical heterodyning an attractive approach for the detection of a number of coherent Raman and Brillouin scattering experiments. We have therefore analyzed the sensitivity of microwave frequency optical heterodyne receivers. Experimental tests on a visible wavelength receiver operating at 13.5 GHz confirm the expectation of shot noise limited sensitivity. The relative merits of microwave frequency optical heterodyne detection and the alternative Fabry–Pérot interferometry approach are discussed.
Measurement of quantum efficiency of a charge coupled device
Authors: Hashimotodani K. , Toneri T. , Kitamoto S. , Tsunemi H. , Hayashida K. , Miyata E. , Ohtani M. , Asakura R. , Katayama K. , Kohmura T. , Hiraga J. , Katayama H. , Shoho M. , Kinugasa K. , Imayoshi T. , Sumi Y. , Ohono Y.
Published: July 2002

We report a measurement of the quantum efficiency of a charge coupled device (CCD) with a simple method and report a resultant quantum efficiency in the energy range from 0.47 to 9 keV. The CCD is a front side illuminated device and is fabricated by Hamamatsu Photonics K.K. The quantum efficiency for 4.5 keV x rays is 11% for the single pixel events, 33% for the spectroscopic events, and 60% for flux mode operation. We present the quantum efficiency as a function of the energy.
Utilization of coherent transition radiation from a linear accelerator as a source of millimeter-wave spectroscopy
Authors: Takahashi Toshiharu , Matsuyama Tomochika , Kobayashi Katsuhei , Fujita Yoshiaki , Shibata Yukio , Ishi Kimihiro , Ikezawa Mikihiko
Published: July 2002

A spectroscopic system for the millimeter-wave region has been constructed on the coherent radiation beamline at the KURRI-LINAC of the research reactor institute, Kyoto University. Coherent transition radiation has been used as the light source. The observed spectrum of radiation was distributed throughout the entire millimeter-wave region and the intensity was four orders of magnitude larger than that of the conventional light source which has the continuous spectrum, i.e., a mercury-arc lamp. The interference between wave packets emitted from successive bunches was observed. It showed that the spectrum of coherent transition radiation was constituted of the higher harmonics of the L-band radio frequency (1.3 GHz) and that the high resolution spectrum was not a continuous spectrum. The diameter of the light beam at the position of a sample was about 9 mm (full width half maximum) and it increased as the wavelength became long because of the diffraction effect for the finite sizes of the optical components. Using the spectroscopic system, the pure rotational spectrum of N2O gas was observed in the millimeter-wave region.
Dynamic surface force measurement. I. van der Waals collisions
Authors: Attard Phil , Schulz Jamie C. , Rutland Mark W.
Published: July 2002

Theoretical calculations and experimental measurements are used to show that hitherto neglected inertial effects can be significant in computer-controlled surface force measurement devices such as the atomic force microscope. The problem is analyzed in detail for the case of the van der Waals attraction in air. It is demonstrated that equating the cantilever deflection to the surface force systematically underestimates the magnitude of the surface force, increasingly so as the speed of approach is increased. It is also shown that the surface separation becomes lost at high accelerations due to a dynamic uncoupling of the cantilever deflection and angle. The effects of elastic deformation of the bodies are taken into account, including the collision-induced elastic vibrations in the solids. Experimental data are obtained for the van der Waals attraction and collision of glass surfaces in air using the measurement and analysis of surface forces device. All of the effects found in the theoretical calculations are identified in the experimental data.
Measurements of mass ablation rate of laser-irradiated target by the face-on x-ray backlighting technique
Authors: Shigemori K. , Azechi H. , Nakai M. , Mima K.
Published: July 2002

We report a novel method to measure the value of mass ablation rate per unit surface (ṁ) in laser-irradiated targets. The face-on x-ray backlighting technique was utilized for the measurement. Flat polystyrene foils were irradiated by the partially coherent light at the intensity of 0.7 or 1.4×1014 W/cm2. We observed the residual areal mass of the planar targets to deduce temporally resolved mass ablation rate. Observed mass ablation rates are well reproduced both by the steady-state ablation model and by one-dimensional simulation.
A pulsed photoacoustic instrument for the detection of crude oil concentrations in produced water
Authors: Freeborn S. S. , Hannigan J. , Greig F. , Suttie R. A. , MacKenzie H. A.
Published: July 2002

The development of a pulsed photoacoustic instrument for the detection of crude oil concentrations in produced water is reported. The instrument utilizes fiber-optic delivery of pulsed diode laser sources to an in-line sensor head, incorporating a gradient-index lens for optical delivery into the flow line and a piezoelectric transducer for acoustic detection. A crude oil concentration detection range of 5–8000 parts per million in water is demonstrated. The sensitivity of response was confirmed during preliminary field testing and is independent of various interfering analytes, flow rate, and droplet size.
Flashlamp instruments for measuring the Midcourse Space Experiment satellite contamination environment
Authors: Galica G. E. , Green B. D. , Atkinson J. J. , Aurilio G. , Shepherd O. , Lesho J. C. , Uy O. M.
Published: July 2002

The xenon flashlamp (XF) and krypton lamp and radiometer (KLR) are two of a suite of instruments that monitor the particulate and gaseous contamination environments of the Midcourse Space Experiment spacecraft. The near-field particulate measurement comprises the high-intensity XF that illuminates a volume of space in the field of view of a wide field-of-view visible imager. Radiation scattered by illuminated contaminant particles is imaged. The intensity of the radiation is related to a particle’s size and composition. The particle’s track yields information about its velocity and trajectory. From ground calibration data we estimate a sensitivity to detect particles smaller than 1 μm and to determine cross-field velocities from 1 mm s−1 to 50 m s−1. We present early mission particulate data from known particle-generating events and from comparatively quiescent times. These results are consistent with previous measurements. The KLR measures the local H2O density in a volume of space approximately 0.5 m from one corner of the spacecraft. The instrument comprises an array of krypton vacuum ultraviolet line source lamps that dissociate H2O and a near-UV radiometer that detects the chemiluminescence from the OH dissociation products. Ground calibrations indicate that the instrument has sufficient sensitivity to detect H2O densities as low as 1.5×107 molecules cm−3. H2O is the primary outgassed species during the early part of a spaceflight, and is a particular concern to cryogenic sensors, such as the Spatial Infrared Imaging Telescope III (SPIRIT III) on this spacecraft. Early mission results are in overall agreement with prelaunch predictions.
A calorimeter to detect freezing in supercooled water droplets
Authors: Harrison R. G. , Lodge B. N.
Published: July 2002

This apparatus suspends a 1 μl water droplet on an ultraminiature thermistor and uses a Peltier cooling device to supercool the droplet. Electrical connections to the thermistor allow the temperature of the droplet to be constantly monitored, and they also permit direct electrical heating of the droplet after freezing has occurred. Deionized water droplets can be readily supercooled to temperatures of −20 °C before freezing, and repeated determinations of the freezing temperature for the same droplet are straightforward. The temperature characteristics of the phase change are very well defined, and the apparatus therefore permits many other investigations on the provocation of freezing in a supercooled droplet.
Characterization of a sub-micron liquid spray for laser-plasma x-ray generation
Authors: Mountford L. C. , Smith R. A. , Hutchinson M. H. R.
Published: July 2002

A high-density source of liquid droplets has been developed and characterized for use in laser interaction studies. Mie scattering and attenuation measurements show that droplets with a radius of (0.5±0.1) μm and atomic densities of 1019 atoms/cm3 can be produced. These densities are comparable to those of cluster media used in laser interaction experiments. The droplet spray therefore provides a way to produce particles sized between clusters and macroscopic solids. Lower density (1016 atoms/cm3) sprays can also be produced and these can be electrostatically split to provide smaller droplets with a radius of (0.3±0.1) μm. Varying the aperture diameter, through which the spray is formed, controls the spray density and droplet size. Preliminary laser-plasma interaction studies with the spray show that the laser attenuation is highly nonlinear with pulse intensity. We have observed over 90% attenuation for a 2 ps pulse at high intensity, ∼1017 W/cm2, compared to 32% at low intensity, ∼109 W/cm2. X-ray emission in the (0.1–8) keV range correlates with this nonlinear attenuation and is comparable to solid targets of similar atomic number.
Apparatus for dynamical thermal measurements of low-thermal diffusivity particulate materials at subambient temperatures
Authors: Murashov Vladimir V. , White Mary Anne
Published: July 2002

Apparatus for measurement of thermal diffusivity of particulate matter in the temperature range of 10–300 K is described. The basis of the measurement is modulated radial heat flow into a cylindrical sample, with a relatively small temperature gradient. Data is analyzed by Fourier transformation, and thermal diffusivity is determined from both the phase lag and amplitude ratio of the temperature at various locations along the cross section of the cylinder. This apparatus was tested with solid benzene, and found to give measurements within ±30%, in accord with the error analysis. It is especially useful for the determination of low thermal diffusivity materials, in the range of 1×10−8 to 5×10−6 m2 s−1.
Impedance independent optical carrier lifetime measurements in semiconductor lasers
Authors: Pikal J. M. , Menoni C. S. , Temkin H. , Thiagarajan P. , Robinson G. Y.
Published: July 2002

We present a novel, simple, and accurate approach to determining the differential carrier lifetime in semiconductor lasers. This technique has lower crosstalk, fewer fitting parameters, and allows the lifetime to be extracted from data collected at lower frequencies than previous methods. These characteristics make our method very useful, particularly in quantum well lasers where additional high frequency poles/zeros due to capture, escape, and transport may affect the extraction of the carrier lifetime.
Optical pumping magnetic resonance in Cs atoms for use in precise low-field magnetometry
Authors: Kim Cheol Gi , Lee Ho Seong
Published: July 2002

Magnetic resonance experiments were conducted on optically pumped Cs to investigate the use of atomic magnetic resonance in Cs atoms for precision magnetometry. The resonance frequencies agreed within 4 ppm with the theoretically calculated ones. The different amplitudes of the separate signals were ascribed to differences in the population densities in the sublevels. The noise level for low-field measurements was 10 pT/Hz.
High frequency ultrasonic transducers with near optimal efficiency
Authors: Lippert M. , Bruneel C. , Bruneel F.
Published: July 2002

We present a technique for indium bonding lithium niobate single crystal (LiNbO3) on a substrate using a vacuum evaporation. This bonding is realized at room temperature and under atmospheric pressure. We also present a technique of characterization based on the measurement of the electric impedance of these transducers and we show that with this bonding we obtain good piezoelectric transducers, with an electromechanical coupling coefficient of about 98% of theoretical value.
Temperature fluctuations and their correlation with density fluctuations in W7-AS
Authors: Häse M. , Hirsch M. , Hartfuss H. J.
Published: July 2002

Correlations between electron density and temperature fluctuations have been measured in the core plasma of W7-AS. The simultaneous use of transmitting and receiving antennas of a heterodyne reflectometer by a crossed sightline ECE correlation radiometer enables the cross-correlation analysis of the reflectometer phase signal and ECE radiation temperature signals in overlapping plasma volumes. Correlations have been found in the spectral range 25–100 kHz, indicating an in-phase correlation between electron density and temperature fluctuations.
Design and performance of a dual polarizing detector system for broadband astronomical spectroscopy at submillimeter wavelengths
Authors: Naylor D. A. , Gom B. G. , Ade P. A. R. , Davis J. E.
Published: July 2002

The design and performance of a dual polarizing bolometer detector system for use with a polarizing Fourier transform spectrometer to conduct broadband astronomical spectroscopy at submillimeter wavelengths is presented. The system features a fully differential electronics design which virtually eliminates common mode noise. The optical design efficiently rejects unwanted radiation, both spectrally and spatially, while minimizing the effects of resonant optical cavities. The system is cooled by an efficient, closed cycle He4–3He refrigerator which is cycled under computer control. The noise performance of the system is determined from analysis of electrical, optical, and spectral measurements, and the results are compared with a theoretical bolometer model.
Design of the Joint European Torus motional stark effect diagnostic
Authors: Hawkes N. C. , Blackler K. , Viaccoz B. , Wilson C. H. , Migozzi J. B. , Stratton B. C.
Published: July 2002

This article describes the overall design of the Joint European Torus (JET) motional Stark effect (MSE) diagnostic. The principle of this diagnostic has been proven on other tokamaks (TFTR and DIII-D) but its implementation on JET involves specific difficulties associated with optical access and neutral beam geometry. The solutions adopted for the access problem include the use of a novel “Air Amici” prism for beam deviation and low Verdet coefficient glass for the relay optics. MSE signals from the different beam sources are distinguished by their Doppler shift; the diagnostic uses the π+ components of the Stark spectrum to avoid contamination with signals from different beam sources. The optimum viewing location for good space resolution across the plasma profile is also one that allows good accuracy in the reconstruction of the q profile from the measurements. An assessment of the optical throughput predicts a measurement accuracy of the polarization angle of better than 0.15° with 1–10 ms time resolution.
Z
eff
spatial profiles from Bremsstrahlung emission in the near infrared spectral region
Authors: Orsitto F. , Belforte M. R. , Brusadin A. , Giovannozzi E. , Pacella D. , May M. J.
Published: July 2002

Measurements of plasma radiation in the infrared (IR) BREM_IR range (λ=978 nm, Δλ=38 nm), at 16 horizontal lines of sight intersecting the central vertical chord of the [Frascati Tokamak Upgrade (FTU) R=0.935 m, a=0.3 m, B=4–8 T], from z=−0.22 m below, to z=0.08 m above the equatorial plane, are performed using the detection system of the Thomson scattering apparatus [F. Orsitto et al., Appl. Opt. 34, 2712 (1995)] (TS). The measured BREM_IR intensity is equal I(z)=〈ZeffGne2/Te1/2〉 where 〈〉 means line average. For determining the Zeff, the Gaunt factor (G) is needed, and the Born–Elwert formula is used. The Zeff spatial profiles are determined using the plasma temperature (Te) and density (ne) measured by the TS, DCN interferometer, and Abel inverted intensity profiles. Zeff(r) versus time behavior in FTU discharges is presented for krypton injection experiments aimed to investigate the particle confinement behavior during strong injection of impurities.
Low-temperature homoepitaxial growth of Si by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Rogers J. L. , Andry P. S. , Varhue W. J. , McGaughnea P. , Adams E. , Kontra R.
Published: July 2002

Epitaxial Si films have been deposited at low substrate temperatures of 400 and 500 °C, by plasma enhanced chemical vapor deposition using an electron cyclotron resonance source. Samples were analyzed using Rutherford backscatter spectrometry, cross-sectional transmission electron microscopy, and x-ray diffraction. The ion-to-adatom arrival ratio was found to be an important parameter in determining epitaxial film quality. This ratio was controlled by the SiH4 feed rate, microwave power level, and shape of the magnetic field in the substrate region. Incident ion energy and ion flux were monitored with a gridded energy analyzer located at the substrate location.
Simple low-drift heating stage for scanning probe microscopes
Authors: Oulevey F. , Gremaud G. , Kulik A. J. , Guisolan B.
Published: July 2002

A simple low-cost heating stage for scanning probe microscopes has been developed. The goal of this design is to minimize the drift due to thermal expansion of the sample and of the heater itself both in the vertical and the in-plane directions. It is composed of materials with different thermal expansion coefficients. The key point is to adjust the relative length of the different elements in such a way that the sample surface’s position is fixed when temperature changes. It has been proven to drift laterally less than 60 nm per degree and vertically less than 42 nm per degree. It allows one to access temperatures up to 150 °C. This stage can be adapted to most commercial microscopes and does not require modifications of the microscope itself. The design of the heating stage is presented with calibration results providing the good thermal stability of the design.
Tracking and stepping control of the tip position of a scanning tunneling microscope by referring to atomic points and arrays on a regular crystalline surface
Authors: Aketagawa Masato , Takada Koji , Minao Yoshihisa , Oka Yuki , Lee Jong-Doo
Published: July 2002

In this article tracking and stepping control of the tip position of a scanning tunneling microscope (STM) by referring to atomic points and arrays on a regular crystalline surface which is used as a two-dimensional reference scale is described. Highly oriented pyrolytic graphite (HOPG) crystal, whose lattice spacing is approximately 0.25 nm, was used as the reference. To utilize the topographic features on the crystalline surface as a reference, a method for determining two-dimensional lateral gradient signals, i.e., the X, and Y axes gradient signals, of the crystalline surface was applied to the control. A rigid STM consisting of a tip scanner and a sample XY stage, and control instruments were developed. The X and Y axes gradient signals were obtained simultaneously using two-phase lock-in modulations of a tunneling current modulated with circular dither motion applied to the tip XY scanner. Modulation frequency and amplitude of the tip were 1 kHz and less than 0.04 nm, respectively. The sample XY stage was controlled for tip positioning by feedback of the X and Y axis gradient signals. First, the tracking control of the STM tip onto an atomic point of the HOPG surface for a maximum duration of about 10 min was performed. Second, tracking and motion control of the STM tip along a crystalline axis of the HOPG surface was demonstrated. The STM tip continued “back and forth” motion along the crystalline axis of the HOPG surface for a maximum duration of 200 s with a maximum tip speed of 6 nm/s. The maximum displacement deviation from the crystalline axis was less than 1/3 lattice spacing (∼0.08 nm). Third, the quantized stepping of the STM tip with lattice spacing stepping with a repetitive rate of 0.5 Hz along the crystalline axis was examined. The maximum displacement deviation from the crystalline axis was less than 1/2 lattice spacing (∼0.12 nm). The feasibility of tracking and stepping control of the STM tip position by referring to atomic points and arrays was confirmed, and the proposed method can be applied to real-time length measurement with subnanometer resolution using a regular crystalline lattice.
Coupling of gas chromatography and molecular beam/mass spectrometry analytical techniques: Application to flame structure study
Authors: Turbiez A. , Devynck P. , Desgroux P. , Pauwels J. F.
Published: July 2002

A new experimental technique coupling both molecular beam and mass spectrometry (MBMS) and gas chromatography (GC) is developed to improve the analysis of low pressure reactive systems using a probe sampling procedure. The sensitivity of gas chromatography is greatly enhanced by using a compression procedure for the samples before injection into the chromatograph, and its selectivity allows one to separate isomers and to study very complex mixtures. By contrast MBMS is well suited to atoms and radical species detection. Moreover, the temperature dependence of the fragmentation pattern of heavy hydrocarbons during MBMS ionization is pointed out and it can be resolved alternatively by GC calibration. The complementarity of these two analytical techniques is demonstrated in the case of low pressure natural gas flames study.
New method of designing pole profile in combined function magnets of high field quality
Authors: Sarma P. R. , Pattanayak S. K. , Bhandari R. K.
Published: July 2002

Combined function magnets are often used in synchrotrons and beam lines. The field quality of such magnets depends mainly on the pole profile. A new method is described for determining the finite pole shapes of such magnets for obtaining field qualities of 1×10−4 or better. Profiles of the typical quadrupole-sextupole and dipole-quadrupole magnets are presented.
Spatially resolved spectra of resonantly pumped laser produced plasmas of lithium
Authors: McCormack Tom , O’Sullivan Gerry
Published: July 2002

Spatially resolved visible spectra emitted from a plasma formed by focusing the output of a flashlamp pumped dye laser onto solid targets of lithium have been recorded. The effects of laser wavelength on plasma formation have been analyzed by tuning the laser to the first resonance transition in lithium at 6708 Å and comparing the results with those obtained at an off resonance wavelength of 6728 Å. Laser energies varied from 430 to 645 mJ and were focused to a spot diameter of 300 μm with a pulse length of 850 ns. Light from the plasma was focused onto the slit of a Hilger spectrograph, which incorporated a Pellin–Broca prism whose output was focused onto a charge-coupled device camera. Electron densities of 1016–1018 cm−3 were deduced from Stark width and shift measurements of the Li II 2s–2p line at 5485 Å and from the Li I 2p–4d line at 4603 Å. In this way the electron density could be mapped as a function of distance from the target. By observing emission at 5485 Å the electron density was observed to increase when the laser was tuned on resonance compared to off. This was not the case when the neutral Li I 2p–4d line was used as a diagnostic. The anomaly is accounted for by referring to both the ionization rates involved and the temporal profile of the emission.