bluuebunny/crossref_metadata_2025 huggingface dataset:
Subsonic multiple-jet aerodynamic window
Authors: Masuda W. , Maeda Y. , Shirafuji Y.
Published: July 2002

An experimental apparatus, which simulates a subsonic multiple-jet aerodynamic window, is fabricated and aerodynamic characteristics of the single-curved jet and the multiple-curved jets are studied. A nondimensional quantity ξ is introduced in order to represent the magnitude of the power consumption. Then, the effect of the window configuration on ξ is evaluated experimentally. Within the range of the present experiments, it is shown that the power consumption of the multiple-jet aerodynamic window can be made less than that of the single-jet scheme, if at least three stages of jets are utilized. It is also shown that the design of the window configuration is important to reduce the power consumption and to obtain the stable operation of multiple-curved jets.
Measurement and calculation of the efficiency of fission detectors designed to monitor the time dependence of the neutron production of JET
Authors: Swinhoe M. T. , Jarvis O. N.
Published: July 2002

Three pairs of fission counters (each pair one 235U and one 238U) are used at the Joint European Torus to determine the time dependence of the neutron production. In order to determine the absolute value of the neutron flux at the detector location it is necessary to know the neutron detection efficiency of the counter assemblies. This was measured using monoenergetic neutrons (at 2.5 and 14 MeV) and Cf and Am/Be sources. The fraction of fissions detected was determined by extrapolation of the pulse-height spectrum to zero pulse height. The calculation of efficiency was made with the Monte-Carlo neutron transport code MORSE. It was found that the detailed structure of the counter significantly affected the calculated efficiency and that the thermal cross-section values of the DLC37F nuclear data library had to be replaced with room-temperature values. The mean difference between calculation and experiment is (5.5±6.3)%.
Approaches to ultrafast neutron detectors
Authors: Wang C. L. , Kalibjian R. , Singh M. S. , Wiedwald J. D. , Campbell D. E. , Campbell E. M. , Cable M. D. , Graves W. R. , Lane S. M. , Lerche R. A. , Price R. H. , Stearns D. G. , Mourou G. A. , Prussin S. G.
Published: July 2002

We discuss two approaches to obtain neutron detectors of very high temporal resolution. In the first approach, a uranium-coated cathode is used in a streak tube configuration. Secondary electrons accompanying the fission fragments from a neutron-uranium reaction are accelerated, focused through a pinhole, and streaked. Calculations show that 20-ps time resolution can be obtained. In the second approach, a uranium-coated cathode is integrated into a transmission line. State-of-the-art technology indicates that a time resolution of 20 ps can be obtained by gating the cathode with a fast electric pulse.
14-MeV neutron pulse source
Authors: Garconnet J. P. , de Mascureau J. , Boutry B. , Pauwels J. C. , Bernardet H.
Published: July 2002

In order to study the neutron measurement techniques set up in laser interaction experiments with D–T filled targets, we have designed and operated a 14-MeV neutron short pulse source. The device is a sealed neutron gas tube with a hot cathode supplied by an adjustable high-voltage pulse generator. Its principle consists in discharging a coaxial cable, held at the generator voltage, into the high-impedance neutron head. We then obtain a neutron pulse train with each pulse duration determined by the length of the cable. This source generates a total routine yield of 107 neutrons. A small sized head will be inserted into interaction chambers.
Electron temperature measurements with heavy ion beam probes
Authors: Schoch P. M. , Goyer J. R. , Solensten L. , Michael J. D. , Saravia E. , Connor K. A. , Jennings W. C. , Hickok R. L. , Bieniosek F. M. , Bresnock F. J.
Published: July 2002

The total abundance of secondary ion current detected from a heavy ion beam probe (proportional to nσeff ) is a function of the electron temperature through the collision cross section. n and Te can be separated by probing the same volume with two different ion species or monitoring two different charge states produced from the same ion. Measurements at Rensselaer (RENTOR) have demonstrated the technique by using a single detector system to look at Cs++ and Cs+++ on successive plasma shots. Data from EBT-S has shown a sensitivity to electron energies up to 1 MeV, but accurate determination of bulk temperatures is limited to a few hundred volts. Two new analyzers have been installed on RENTOR to demonstrate the capability of providing Te profiles during a single shot. Calibration of these measurements requires a detailed accounting of all input beam ions, reaction products, and sample volumes.
High-performance double-focusing mass spectrometer
Authors: Nier A. O. , Schlutter D. J.
Published: July 2002

A small size double-focusing mass spectrometer employing the Mattauch–Herzog geometry is described. Although developed primarily for helium isotope analyses, the design is such that it can be modified for a wide range of problems. The maximum radius of curvature of ions in the magnetic analyzer is 9.53 cm. With reasonably wide slits 3He can be separated from the HD+H3 combination usually present as an impurity while making analyses of helium in a static mode. At xenon the overlap at adjacent mass numbers is less than 1/10 000. In static operation the sensitivity approaches that of some of the large high sensitivity instruments employing special ion sources. The response is linear over a large pressure range. Since a conventional electron bombardment ion source is employed, ionizing electron energies may be varied, eliminating doubly charged ions such as 40Ar2+ which may interfere with 20Ne analyses. Because of the compact and rugged construction as well as low power consumption, the design lends itself to portable use in field operations.
Simple and compact neutral metal vapor laser assembly operating in a low-temperature region
Authors: Saito Hiroshi , Taniguchi Hiroshi , Nozawa Hajime , Owashi Ken-ichi
Published: July 2002

A compact and inexpensive technique is reported for a discharge-excited pulsed metal vapor laser (MVL) at a low operating temperature utilizing an air-blown-type spark-gap switch. A laser is excited in an aperiodic pulse train by successive pulsed discharges of a storage capacitor through a spark-gap switch. A variety of neutral metal vapor laser (MVL) using metal compound as a lasant is briefly reported with the compact device.
Computer-compatible, self-contained, precision ac resistance bridge suitable for thermometry
Authors: Corson M. R.
Published: July 2002

A precision, self-contained, four-terminal ac resistance bridge with phase-sensitive detection is described. The variable element in the bridge is a digital-to-analog converter, so that the setting of the bridge can be computer controlled. If computer control is not required, the bridge can be set using thumbwheel switches. The accuracy of the bridge is ±(0.03% of reading +0.01% of full scale). The dissipation in the unknown resistor is less than 1 μW for a full-scale range of 99.99 Ω, and less than 1 nW for a full-scale range of 99.99 kΩ. The low-power dissipation, ac excitation, and four-terminal configuration make the bridge especially suitable for resistance thermometry.
Strip heater for ohmic contacts to semiconductors
Authors: Wehmann H.-H. , Aytac S. , Schlachetzki A.
Published: July 2002

A fast sheet-molybdenum strip heater for alloying of ohmic contacts to semiconductor devices is described. Its temperature/time program is microprocessor controlled, so that heating and cooling rates of 3700 and 2800 °C/min, respectively, can be achieved reproducibly.
Interactive water monitoring system accessible by cordless telephone
Authors: Volpicelli Richard , Andeweg Pierre , Hagar William G.
Published: July 2002

A battery-operated, microcomputer-controlled monitoring device linked with a cordless telephone has been developed for remote measurements. This environmental sensor is self-contained and collects and processes data according to the information sent to its on-board computer system. An RCA model 1805 microprocessor forms the basic controller with a program encoded in memory for data acquisition and analysis. Signals from analog sensing devices used to monitor the environment are converted into digital signals and stored in random access memory of the microcomputer. This remote sensing system is linked to the laboratory by means of a cordless telephone whose base unit is connected to regular telephone lines. This offshore sensing system is simply accessed by a phone call originating from a computer terminal in the laboratory. Data acquisition is initiated upon request: Information continues to be processed and stored until the computer is reprogrammed by another phone call request. Information obtained may be recalled by a phone call after the desired environmental measurements are finished or while they are in progress. Data sampling parameters may be reset at any time, including in the middle of a measurement cycle. The range of the system is limited only by existing telephone grid systems and by the transmission characteristics of the cordless phone used as a communications link. This use of a cordless telephone, coupled with the on-board computer system, may be applied to other field studies requiring data transfer between an on-site analytical system and the laboratory.
Rotating mirror device for nonresonant laser Raman difference spectroscopy
Authors: Martin J. C.
Published: July 2002

A novel sample switching device for laser Raman difference spectroscopy (LRDS) has been designed for use with nonresonant samples. The device utilizes a single motor driven rotating mirror, fabricated by diamond turning techniques, which switches both exciting and scattered light 60 times per second. Electronic timing signals are obtained to gate photon counting pulses into separate scalers. The use of fixed capillary sample cells allows for the first time in LRDS the examination of fibers, single crystals, and liquid samples of 10-μl volume and improved access to samples for thermostating, etc. Alignment of the optics is described. Proper operation of the system is illustrated by examination of pyridine and pyridine-d5. Comparing spectra of the neat liquids and a mixture of them gives examples of a frequency shift of <1 cm−1, a width change, and other bands with no changes. Advantages, limitations, and future extensions of the instrument are described.
Simple and novel method to detect the gel structure by light scattering
Authors: Kobayasi Syoyu
Published: July 2002

A simple method is proposed to detect a gel structure using a light-scattering technique. A sample in a cylindrical cell was rotated in a typical dynamic light-scattering setup. The measurements were made on a solution of gelatin in which polystyrene latex spheres were added as the light-scattering probes. When the solution became a gel state, the light intensity observed at a fixed scattering angle showed a large fluctuation during rotation of the sample. The amplitude of the fluctuation was found to be a good measure of the gel structure.
Versatile spectrophotometer for photosynthesis (light-induced changes in absorbance and fluorescence yield, circular and linear dichroism) and other biophysical measurements
Authors: Ke Bacon , Breeze Robert H. , Dolan Edward , Vore Duane
Published: July 2002

The construction of a versatile, single-beam spectrophotometer expanded from a previously reported circular dichrometer utilizing an elasto-optic modulator (EOM) for producing circular polarization, is described. The new spectrophotometer is capable of measuring circular dichroism as well as linear dichroism and light-induced changes in absorbance and fluorescence yield, the latter being two of the most commonly measured properties in photosynthesis research. The use of an EOM, along with a phase-sensitive detector, affords high sensitivity and at the same time, in conjuction with a mechanical phosphoroscopic device, a high degree of immunity from artifacts in studies employing actinic light. A description is given of the generation and use of timing signals essential for control and signal processing. Its performance is illustrated by examples drawn from light-induced absorbance and fluorescence-yield changes associated with photosynthetic electron transport and changes in redox state of electron carriers. This photometer, with very little modification, may also be used to perform a host of other types of measurements.
Uniaxial stress device for use with a SQUID magnetometer
Authors: Osterman D. P. , Williamson S. J.
Published: July 2002

A device for applying compressive uniaxial stress has been developed to fit within the pickup coils of a SQUID magnetometer. Forces of up to 300 N may be applied from liquid-helium temperature up to room temperature. Strain gauges provide a voltage output proportional to stress that is linear and reproducible to within 3% of full scale. Combined with a SQUID moment sensitivity of 1.2×10−8 G cm3, detailed studies of the stress dependence of the magnetization are possible. Stress-induced shifts in magnetic, superconducting, and other types of transition temperatures can also be observed easily.
Apparatus for multipoint Thomson scattering measurements in the ETA-BETA II reversed field pinch experiment
Authors: Bassan M. , Buffa A. , Giudicotti L.
Published: July 2002

A multipoint Thomson scattering apparatus under development for the measurement of spatial Te and ne profiles in the ETA-BETA II reverse field pinch experiment is described. The apparatus is based upon the two-channel analysis method already adopted in the TFR tokamak. The 90° scattered light is collected simultaneously from seven spatial positions along a plasma diameter by means of high-efficiency, quartz, fiber-optic light guides. The detection system consists of a set of high aperture (f/2.4), plane grating, Littrow spectrometers developed to match the high throughput of the collection optics. These instruments employ photomultipliers with a GaAs photocathode (quantum efficiency ≂20%, λ=700 nm) and have a stray light rejection ratio of 3×10−4. Laboratory tests and preliminary measurements in ETA-BETA II have shown good sensitivity and a S/N ratio sufficient to diagnose plasmas with ne≥1013 cm−3.
Position-sensitive detector performance and relevance to time-resolved electron energy loss spectroscopy
Authors: Richter Lee J. , Ho W.
Published: July 2002

The use of position-sensitive detectors (PSDs) has become common in many spectroscopies. The increased signal provided by the parallel detection of many spectral elements affords increases in sensitivity and/or time resolution. Recently, the use of a PSD to increase the temporal resolution of an electron energy loss (EEL) spectrometer has been demonstrated in our laboratory. This article summarizes the present development of EEL spectrometers and then presents a detailed review of four classes of PSDs in the context of their potential application to EEL spectroscopy (EELS). The four classes considered are (a) discrete channel detectors, (b) coincidence array detectors, (c) charge division detectors, and (d) optical detectors imaging phosphor screens. All four designs, as typically implemented, utilize microchannel plates (MCPs) as spatially imaging electron multipliers. The performance of MCPs is reviewed and the constraints that MCP behavior at the high count rates achievable in EELS places on acceptable PSD performance are outlined. The inability of present MCPs to maintain saturation gain at count rates above 1 MHz mm−2 implies that the PSD must tolerate significant gain reduction in the electron multiplier. The possibility of eliminating the MCP and using an electron-bombarded silicon gain mechanism is proposed. Such a device could, in principle, support count rates in excess of 100 MHz/channel, providing an order of magnitude increase in performance over the best existing detectors.
Performance of piezoresistive carbon sensors in contact with porous materials
Authors: Gourdin William H. , Weinland Stuart L.
Published: July 2002

Piezoresistive carbon sensors were used to determine the stress-time history in unsintered powders during shock-wave compaction in a gas gun. Powders of both spherical and irregular shape were examined, including steel, aluminum–silicon alloy, copper, tungsten, and aluminum nitride. A calibration relationship was established between direct sensor response and stress levels determined by impedance matching; it corrects apparent systematic errors in the manufacturer’s calibration for stresses in excess of about 2.0 GPa.
Magnetic-field measurement based on Zeeman effect in lines excited by charge exchange recombination
Authors: Wróblewski D. , Moos H. W.
Published: July 2002

It is suggested that the poloidal magnetic field in a tokamak may be deduced from the analysis of circular polarization of light impurity ion lines excited by charge-exchange recombination. Visible or near-ultraviolet transitions in hydrogenlike oxygen and carbon are considered. Estimations of the linewidths and the magnitude of the Zeeman effect show that, with appropriate polarization analyzer and the experiment geometry, the poloidal component of the magnetic field can, in principle, be measured. Uncertainties of the model used to calculate the polarized line profiles do not affect the interpretation of the measurement in a fundamental way and may be accounted for experimentally by calibrating the polarization effect against the components of the toroidal field. In principle, the analysis of only one transition may provide information about the whole poloidal field profile.
Viscometer timer using low-cost electronic stopwatch
Authors: Gardner R. J. , Senanayake P. C.
Published: July 2002

Light pipes and optical level detectors are used to automatically start and stop a low-cost electronic stopwatch which measures the efflux time of a liquid in a glass capillary viscometer. Operator reaction time is eliminated and viscosities of clear, translucent, or opaque liquids can be measured to ±0.03%. The construction and circuitry are described and sample results for water and butanol are presented.
Low-temperature, high-pressure optical system with a compact diamond-anvil cell and a closed-cycle refrigerator
Authors: Tanino Hiroshi
Published: July 2002

An optical system for low-temperature high-pressure measurements of polarized absorption, reflectance, and luminescence with a compact diamond-anvil high-pressure cell, a closed-cycle helium refrigerator, and toroidal mirrors to focus on the sample is described. It enables us to get a temperature–pressure diagram of optical spectra easily and rapidly in the region between 200 nm and 14 μm at 15–300 K at pressures up to about 100 kbar with in situ monitoring of pressure by the ruby fluorescence method.
Gyro-electron ghost images due to microchannel-plate operation in transverse magnetic fields
Authors: Roquemore A. L. , Medley S. S.
Published: July 2002

A multianode microchannel-plate (MCP) detector was operated in a transverse magnetic field. When a collimated ion beam of ∼4 mm diameter impinged on one area of the plate, ghost images were observed elsewhere on the plate at anodes up to several centimeters from the beam spot. This effect is due to secondary electrons which are emitted from the interstitial surfaces around the MCP pores and returned to the surface of the plate under the influence of E×B fields, where E is the electric field perpendicular to the plate due to the MCP bias potential and B is the externally applied transverse magnetic field. A regenerative process is observed in which the secondary electrons traverse the surface of the plate in the E×B direction by successive gyro-orbit steps. A method for suppressing the ghost images is discussed.
Experiment demonstration of a 100-ps microchannel plate framing camera
Authors: Young B. K. F. , Stewart R. E. , Woodworth J. G. , Bailey J.
Published: July 2002

We report on the construction and testing of a 100-ps framing camera based on a gated microchannel plate. The gating is obtained by applying a fast voltage pulse directly across the microchannel plate detector. An infinite ground-plane microstrip transmission-line configuration is used. We have measured the transit time for electrons through the microchannel plate to be 150±35 ps and the rise and fall times of the detector to be less than 100 ps. The time resolution computed using the experimentally measured edge response times is less than 100 ps.
Plasma and operational conditions in a high species filter bucket source
Authors: Pincosy P. A. , Ehlers K. W. , Lietzke A. F.
Published: July 2002

Experimental details of operation and plasma flow are presented for bucket ion sources having magnetic flux that bridges the source between the regions of electron injection and ion extraction. The basic goal is to increase the atomic fraction of hydrogen and deuterium by 15% and yet retain an ion-flux-density uniformity over the extraction region to within ±7%. A rod structure containing permanent magnets produces a known bridging flux filter across a well-defined region. This provides an experimental apparatus useful for the study of the effect of magnetic flux on the source plasma flow. The parameters of filter position, filter strength, filter orientation, arc power, and gas pressure are related to species fractions, profile uniformity, and electrical efficiency. The option of having the bridging flux without a rod structure is presented, and experimental results of sources thought to contain this field configuration are discussed.
Design and operation of a 30-kV accelerator for negative ion beams
Authors: Holmes A. J. T. , Nightingale M. P. S.
Published: July 2002

A 30-kV triode accelerator has been constructed to test the design and operating characteristics of accelerators for negative hydrogen ion beams. Incorporating both a quadrupole electron trap and an octupole electron suppressor, the accelerator has been used to extract, accelerate, and focus H− ion beams of up to current densities of 20 mA cm−2. The results suggest that this accelerator design is capable of focusing across a wide range of ion current densities (0–20 mA cm−2) and acceleration voltages (15–30 kV) using the variation of a single-gap potential to achieve the required focusing. Applying a bias voltage of up to 2 V between the beam forming electrode and the anode of the source suppresses electrons and has allowed accelerator power efficiencies of over 73% to be obtained for all ion current densities up to 20 mA cm−2 so far extracted. Initial evidence that the extracted and accelerated negative ion beam may be undergoing self-focusing is discussed.
Efficient 4He cryostats for storage Dewars
Authors: Swartz E. T.
Published: July 2002

We have designed 4He cryostats which can be inserted into storage Dewars. These cryostats have the advantages of extremely low (and recoverable) helium consumption, fast cool-down and warm-up times, excellent temperature range and stability, and they supply a low electrical noise and low vibration environment for electrical and thermal measurements. Design and construction details of one such cryostat are presented. We further present specific heat data on crystalline boron to demonstrate the performance of one of these cryostats in a particularly sensitive experiment.
2-GHz frequency-domain fluorometer
Authors: Lakowicz Joseph R. , Laczko Gabor , Gryczynski Ignacy
Published: July 2002

We developed a frequency-domain fluorometer which operates from 4 to 2000 MHz. The modulated excitation is provided by the harmonic content of a laser pulse train (3.76 MHz, 5 ps) from a synchronously pumped and cavity dumped dye laser. The phase angle and modulation of the emission are measured with a microchannel-plate photomultiplier (PMT). Cross-correlation detection is performed outside the PMT. The high-frequency signals for cross correlation were obtained by multiplication of the output from a 500-MHz frequency synthesizer. The performance was verified in several ways, including measurement of known time delays and examination of standard fluorophores. The detector displayed no detectable color effect, with the 300–600-nm difference being less than 5 ps. The precision of the measurements is adequate to detect differences of 20 ps for decay times of 500 ps. A correlation time of 53 ps was found for indole in water at 20 °C. The shortest correlation time we measured was 15 ps for indole in methanol/water (75/25) at 40 °C. Also, the 2-GHz data reveal the time-dependent ((t)1/2) terms found in the presence of collisional quenching. The degree of random error is about 0.3° of phase and 0.005 in modulation throughout the frequency range.
Polarization spectrophotometer for measurements of both polarized emission and excitation spectra
Authors: Shimizu Okiyasu , Watanabe Jun
Published: July 2002

The construction of a polarization spectrophotometer coupled with a microcomputer is described. The new spectrophotometer enables the continuous recording of a polarized emission spectrum of luminescent molecules as well as a polarized excitation spectrum. The instrument’s optics were designed to separately detect each polarized component of the emission utilizing an optical fiber bundle composed of two blanches. The use of the optical bundle, along with phase-sensitive detectors, permits precise polarization measurements at low signal-to-noise ratios and, at the same time, affords a high degree of immunity from artifacts arising from the measurement of the polarized spectrum of emission. Data acquisition and various manipulations, such as instrument response and polarization calculations, were performed by a Fujitsu Micro 8 microcomputer equipped with an 8-bit analog-to-digital converter. Several examples of the instrument’s performance are provided including a polarized phosphorescence emission spectrum of 0.05 mM indole in ethylene glycol–water (v/v=1) at 77 K.
Automation of liquid 4He transfer
Authors: Fukushima Akio , Okuda Yuichi
Published: July 2002

The easy-made automation of the liquid 4He transfer is reported. This automation needs little modification of the present system. We only added the liquid 4He levelmeter and two electromagnetic valves to the conventional liquid 4He transfer equipment. The automation saves much time in charging liquid 4He. The performance is satisfactory.
Automatic laser beam alignment for a Thomson scattering system
Authors: Bassan M. , Flora F. , Giudicotti L.
Published: July 2002

A system for the automatic alignment of a pulsed ruby laser beam is under development for the Thomson scattering diagnostics of RFX, a large reversed-field pinch machine now under construction. In this experiment the laser will be 11 m from the machine and the beam alignment at the 750×4-mm scattering volume will be actively maintained to within 0.5 mm. The beam direction in space is measured in two reference planes fixed to the collection optics frame by means of two 80-mm2 fast quadrant photodiodes. A double-channel preamplifier is used for each quadrant in order to measure both the 30-ns FWHM ruby pulse and a low-power cw He–Ne beam propagating through the same optical path. Every time the main laser is fired, the relative direction of the two beams is determined so that the position of the He–Ne beam can be used for feedback control of the steering optics between plasma shots.
Measuring sound velocities along release adiabats with Manganin stress gauges
Authors: Rosenberg Z. , Brar N. S.
Published: July 2002

We propose a new technique to measure the state of shock-loaded specimens along their release adiabats. The technique is based on symmetric impacts of equal thickness flyer and target disks. A Manganin stress gauge is embedded at the back of the target and backed by a thick Plexiglas disk. The stresses at the specimen–Plexiglas interface are relieved in a stepwise manner which is typical for this type of experiment. From the time duration between consecutive release waves one can determine the sound speed in the released specimen. Drastic changes in sound speed, as in melting, can be detected by these time durations adding more information on the state of the specimen as it unloads from very high shock stresses.
Comment on ‘‘Design considerations for the construction of a reflecting symmetric multipass cell for use in laser molecular-beam experiments’’ [Rev. Sci. Instrum. 5
8, 2238 (1987)]
Authors: Zipin Richard B.
Published: July 2002

This subject has been treated in a paper published previously.
Reply to ‘‘Comment on ‘Design considerations for the construction of a reflecting symmetric multipass cell for use in laser molecular-beam experiments’’’ [Rev. Sci. Instrum. 5
9, 1004 (1988)]
Authors: Lethbridge P. G. , Stace A. J.
Published: July 2002

There is some overlap between our analysis and work previously published by Zipin, but the former is more applicable to the specific problem addressed.
Compact high flow dye cell for laser-pumped dye lasers
Authors: Stankov K. A.
Published: July 2002

The rotor of a split-pole asynchronous motor is used to circulate a dye solution in a cylindrical dye cell. A compact high flow dye cell which is suitable for high repetition rate (>100 Hz ) pumping has been thus developed.
Refracting instrument for ultraviolet inverse photoemission spectroscopy
Authors: Royer W. A. , Smith N. V.
Published: July 2002

An instrument is described for k-resolved ultraviolet inverse photoemission spectroscopy using a LiF lens monochromator and a rotatable high-perveance electron gun. The energy resolution from all sources at ℏω=11 eV is 0.6 eV (FWHM). The angular spread of the incident electrons is calibrated using the properties of a well-known and well-characterized surface state on Cu(111), and is found to be 7°(FWHM).
Bridged loop–gap resonator: A resonant structure for pulsed ESR transparent to high-frequency radiation
Authors: Pfenninger Susanne , Forrer J. , Schweiger A. , Weiland Th.
Published: July 2002

A new and inexpensive X-band resonator structure for pulsed electron-spin resonance and electron-nuclear-double-resonance applications is introduced. The resonator consists of a bridged loop structure and is distinguished by a good reproducibility and reliability. It has a high filling factor and an adjustable Q value and is transparent to radio frequency fields with an upper limit >100 MHz. The inner diameter of 5 mm allows convenient sample access of standard 4-mm quartz tubes in the temperature range between 4 and 300 K. Numerical computations of the resonant frequencies, the Q values, and the three-dimensional distributions of the electromagnetic fields are presented. They are based on a discretization method for the solution of Maxwell’s equations and include all dielectric elements of the resonator structure. The field homogeneity in the sample area and the influence of the dimensions and the thickness of the metallic layers on field intensity, quality factor, and resonant frequency are determined experimentally. The performance of the resonator is demonstrated by a novel field-swept echo-induced electron-spin-resonance experiment with jumping magnetic field vectors.
Magnetic probes for small-signal detection in a large background field
Authors: Chen Xing
Published: July 2002

High-precision Hall probes and B-dot probes are described. These probes are designed to measure magnetic field changes of a few gauss on a time scale of 2–3 s in a 5-kG background field. A digital, drift-free sample-and-hold circuit is used with the Hall probe to subtract the vacuum field.
Pneumatic stressing mechanism for magnetomechanical studies
Authors: Schönbächler M. , Atherton D. L.
Published: July 2002

A low-pressure pneumatically controlled stressing mechanism for investigating the effects of uniaxial stress on the magnetostrictive and magnetomechanical behavior of 2% Mn pipeline steel is described. The apparatus uses microcomputer control and data logging. It has been developed to allow convenient stress cycling so that reversible and irreversible changes can be separated. Irreversible stress-induced changes in magnetization are toward the anhysteretic, in accordance with Jiles–Atherton theory. Reversible magnetomechanical effects may be correlated with reversible magnetostrictive effects.
Impedance probe to measure local void fraction profiles
Authors: Teyssedou A. , Tapucu A. , Lortie M.
Published: July 2002

A conductivity-type local void measurement system has been developed. The effects of the sensor tip geometry, the unbalance of the front-end bridge, the comparator threshold level, and the mass fluxes on the response of the instrument have been studied. The system has been calibrated under air–water two-phase flow conditions using the quick-closing-valve technique. Comparison of the void profiles obtained with the conductivity probe with those obtained using an optical probe confirms the applicability of this system for two-phase (air–water) flows.
Interferometric measurement of refractive indices
Authors: Betzler K. , Gröne A. , Schmidt N. , Voigt P.
Published: July 2002

A simple method for the measurement of the refractive indices of parallel plate samples is described that uses the shift of the interference pattern when rotating the sample in one arm of a Mach–Zehnder interferometer. The theoretical fringe pattern shift is calculated and the accuracy of the method is derived. A typical accuracy of about 10−4 can be achieved at low refractive indices. The method is especially useful when—because of other reasons—the samples are provided as plates or when prisms are difficult to fabricate.
Small pump for liquid nitrogen
Authors: Ebisu Takeo , Watanabe Tadashi
Published: July 2002

We present a small pump which is particularly useful when the conventional transfer method for pressurizing liquid nitrogen is unavailable. Its transfer rate ranges from 0.2 to 0.8 l/min depending on the speed of reciprocating motion of a piston driven by an electric motor.
High power picosecond laser system at 248 nm
Authors: Tighe W. , Nam C. H. , Robinson J. , Suckewer S.
Published: July 2002

We describe a powerful picosecond KrF* laser system consisting of a synchronously pumped dye oscillator, a three-stage dye amplifier, frequency conversion to 248 nm, and amplification through a series of excimer modules. Characteristics are given at each stage of the system. With the first stage of the system complete, a focused intensity of ∼1016 W/cm2 is obtained. Initial visible spectra obtained by interaction with various targets are presented.
Simple torque magnetometer for anisotropy measurements in magnetic thin-film media
Authors: Agarwala A. K.
Published: July 2002

A simple and novel torque magnetometer for the magnetic anisotropy measurements of magnetic thin-film samples is described. A Brookfield LVTD viscometer, normally used in the viscosity measurements of liquids and fluids, is utilized as a torque measuring device. A HP series 310 computer along with the HP 7090 measurement plotting system interfaced to the torque magnetometer perform data acquisition, any calculations required for data correction, and plotting of the torque curves.
Description and testing of three moisture sensors for measuring surface wetness on carbonate building stones
Authors: See Randolph B. , Reddy Michael M. , Martin Richard G.
Published: July 2002

Three moisture sensors were tested as a means for determining the surface wetness on carbonate building stones exposed to conditions that produce deposition of moisture. A relative-humidity probe, a gypsum-coated circuit grid, and a limestone-block resistor were tested as sensors for determining surface wetness. Sensors were tested under laboratory conditions of constant relative humidity and temperature and also under on-site conditions of variable relative humidity and temperature for eight weeks at Newcomb, NY. Laboratory tests indicated that relative humidity alone did not cause sensors to become saturated with water. However, the rates of drying indicated by the sensors after an initial saturation were inversely related to the relative humidity. On-site testing of the relative-humidity probe and the gypsum-coated ciruit grid indicated that they respond to a diurnal wetting and drying cycle; the limestone-block resistor responded only to rainfall.
Automatic capillary viscometer for fluids with variable opacity
Authors: Habib S. , Gruner K.
Published: July 2002

We have designed a simple, low cost automatic optoelectronic meniscus sensor for a capillary tube viscometer with a timing resolution of 0.01 s. The sensor is specifically designed for use with critical composition binary liquids, which undergo a change in fluid opacity as a function of temperature. The sensor works over the temperature range −65°–150 °C.
Variable-temperature accessory for Q-band ESR measurements down to 4.2 K
Authors: Desfonds G. , Rius G.
Published: July 2002

Variable-temperature measurements can be performed at Q band (35 GHz) with a modified standard X-band gas flow system. The modification is simple and not very expensive. The temperature is stabilized within ±0.2 K in the range 4.2–100 K.
Helical magnetic configuration formed by using shaped ferromagnetic material
Authors: Nishimura K. , Komori A. , Koide Y. , Sato N.
Published: July 2002

Formation of a straight helical magnetic field is attempted by using ferromagnetic material. A shaped ferromagnetic cylinder, which modifies an external uniform magnetic field, is demonstrated to realize an l=3 helical magnetic field that is suitable for plasma experiments. The measured values for the angle of rotational transform and shear length agree with the predictions within a factor of 2, which is calculated without taking account of the self-demagnetization. This indicates that a rough configuration of magnetic field can be obtained even if the self-demagnetization is not known accurately. It is also suggested that this method is widely applicable to the formation of other complicated configurations of magnetic field.
Charged-particle imaging video monitor system
Authors: Iida Takao
Published: July 2002

A charged-particle imaging video monitor system was constructed for video imaging of the distributions of alpha-emitting and low-energy beta-emitting nuclides. The imaging video monitor system consists of a detector head, a silicon intensifier target (SIT) camera, a video frame memory, and a personal computer. The system can display not only the scintillation image due to radiation on the video monitor, but also the integrated video image becoming gradually clearer on another video monitor. The integrated image is transferred to a personal computer for image processing. The distortion of the image is about 5%, and the spatial resolution is about 2 line pairs (lp) mm−1.
Constant-resolution tunneling spectroscopy
Authors: Hipps K. W. , Mazur Ursula
Published: July 2002

An inelastic electron tunneling spectrometer is described which is capable of providing constant-resolution spectra over the 0 to greater than 16 000-cm−1 range. Constant-resolution data acquisition is especially beneficial in the case of electronic transitions studied by tunneling spectroscopy. Data acquired as d2V/dI2, (d2V/dI2)/(dV/dI)2, and in constant-resolution mode are compared. At intermediate and at high bias, either of the two latter data-acquisition methods is superior to the first. At high bias voltage, constant-resolution spectra are superior.
Neutron yield measurements with current-mode neutron time-of-flight detectors (abstract)
Authors: Cable M. D. , Nelson M. B.
Published: July 2002

Current-mode neutron time-of-flight detectors (e.g., a scintillator and photomultiplier tube) are frequently used as sensitive detectors for laser fusion neutron yield measurements. For very low yields, as in the measurement of secondary (dt) neutrons from deuterium targets, some subtle effects involving limited statistical samples and the broad ‘‘pulse-height distribution’’ of a neutron sensitive scintillator arise. These effects are discussed and error treatments are presented. A technique using a pulsed neutron generator is shown to provide, experimentally, all the information required for characterization of a detector. Comparisons to yield measurements made at Nova will be presented. This work was performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
Gyrotron collective Thomson scattering from plasma fluctuations in a Tara axicell
Authors: Machuzak J. S. , Woskov P. P. , Myer R. C. , Mulligan W. J. , Cohn D. R. , Gerver M. , Golovato S. N. , Horne S. , Kubota S. , Post R. S. , Rhee D. , Sullivan J. , Temkin R. J.
Published: July 2002

Collective Thomson scattering in the Tara Tandem Mirror axicell at MIT was accomplished with a 137-GHz, ∼0.4-kW, 75-ms pulsed gyrotron. Ion cyclotron waves, ion Bernstein wave harmonics, and other plasma fluctuations possibly due to microinstabilities and magnetohydrodynamic (MHD) activity have been observed during ion cyclotron resonance frequency (ICRF) heating. The observation of ion Bernstein waves may be due to an enhanced ion thermal fluctuation spectrum in an ICRF heated plasma.
Frequency-modulation spectrometer for Mössbauer studies
Authors: Reittinger P. W. , Sinor T. W. , Wagal S. S. , Collins C. B.
Published: July 2002

A nuclear frequency-modulation spectrometer (NFMS) for high-resolution gamma-ray spectroscopy is described in this article. As the name implies, this device operates by modulating the cross section for gamma-ray absorption. The automation of this spectrometer required the development of an interface to an Apple computer which provides a real-time data display. This interface also enables the Apple computer to control up to two Mössbauer spectrometers at once, with a real-time data display for each. A nuclear frequency-modulation spectrometer makes it possible to observe directly the phenomenon known as ‘‘rf sidebands’’ in Mössbauer spectroscopy, without interference from the ‘‘parent transitions.’’ The high resolution of NFMS makes it possible to examine the ‘‘rf sidebands’’ for any fine structure.
Soft x-ray imaging using Polaroid Land films
Authors: Wong C. S. , Choi P. , Deeney C.
Published: July 2002

It is demonstrated in this note that optical Polaroid Land films can be used as a convenient detector in the soft x-ray region. The performance of Polaroid 667 film has been found to be comparable to that of the Kodak direct exposure film (DEF) for soft x-ray pinhole imaging. By a suitable choice of multiple filters, qualitative information about a dense plasma has been obtained.
Emissive probe current bias method of measuring dc vacuum potential
Authors: Diebold D. , Hershkowitz N. , Bailey A. D. , Cho M. H. , Intrator T.
Published: July 2002

It is experimentally demonstrated that, with proper current bias, emissive probes can accurately measure dc electric potential in a vacuum. A comparison is made of the accuracy and time response of this ‘‘vacuum current bias’’ method with two other emissive probe techniques, the inflection point in the limit of zero emission, and the floating potential of a strongly heated probe.
A transit-time flow meter for measuring milliliter per minute liquid flow
Authors: Yang Canqian , Kümmel M. , So/eberg H.
Published: July 2002

A transit-time flow meter, using periodic temperature fluctuations as tracers, has been developed for measuring liquid flow as small as 0.1 ml/min in microchannels. By injecting square waves of heat into the liquid flow upstream with a tiny resistance wire heater, periodic temperature fluctuations are generated downstream. The fundamental frequency phase shift of the temperature signal with respect to the square wave is found to be a linear function of the reciprocal mean velocity of the fluid. The transit-time principle enables the flow meter to have high accuracy, better than 0.2%, and good linearity. This flow meter will be used to measure and control the small liquid flow in microchannels in flow injection analysis.
Computer-assisted video microscopy for the investigation of monolayers on liquid and solid substrates
Authors: Meller Paul
Published: July 2002

Fluorescence microscopy is a sensitive and nondestructive optical method to directly study the properties of monolayers at the gas/water interface and to control their transfer on solid substrates. The method requires only small amounts (≤1 mol %) of fluorescent probe molecules for optical detection. In this article, an integrated system for optical investigations on mono- and multilayer structures is described. The experimental equipment consists of a monolayer trough, a deposition unit to built-up ordered layers and a fluorescence microscopic attachment. The modular construction allows the use of any desired trough design for the monolayer investigations. The system comprises video-assisted microscopy to observe and analyze dynamic nucleation processes taking place during phase transitions on liquid and solid substrates. Using the spatial two-dimensional digital image signal, kinetic studies can be performed.
Sampling procedure for measuring Hall coefficients using the van der Pauw method
Authors: Ndlela Zolili , Bates Clayton W.
Published: July 2002

It is shown that care must be exercised in using digital equipment when making Hall measurements in a van der Pauw setup employing the ASTM standard method. This arises because of quantization error when working near the sensitivity limit of the equipment. For materials with small Hall mobilities (<100 cm2/V s) this can lead to an incorrect specification of the carrier type and inconsistent mobility behavior. A simple averaging and sampling procedure is suggested to suppress this type of behavior and is found to be sufficient to obtain reliable and repeatable Hall voltages and coefficients.
TFTR neutral beam injected power measurement
Authors: Kamperschroer J. H. , Grisham L. R. , Dudek L. E. , Gammel G. M. , Johnson G. A. , Kugel H. W. , Lagin L. , O’Connor T. E. , Shah P. A. , Sichta P. , Stevenson T. N. , Halle A. von , Williams M. D. , Bastasz R.
Published: July 2002

Energy flow within TFTR neutral beamlines is measured with a waterflow calorimetry system capable of simultaneously measuring the energy deposited within four heating beamlines (three ion sources each), or of measuring the energy deposited in a separate neutral beam test stand. Of the energy extracted from the ion source on the well-instrumented test stand, 99.5±3.5% can be accounted for. When the ion deflection magnet is energized, however, 6.5% of the extracted energy is lost. This loss is attributed to a spray of devious particles onto unmonitored surfaces. A 30% discrepancy is also observed between energy measurements on the internal beamline calorimeter and energy measurements on a calorimeter located in the test stand target chamber. Particle reflection from the flat plate calorimeter in the target chamber, which the incident beam strikes at a near-grazing angle of 12°, is the primary loss of this energy. A slight improvement in energy accountability is observed as the beam pulse length is increased. This improvement is attributed to systematic error in the sensitivity of the energy measurement to small fluctuations in the supply water temperature. An overall accuracy of 15% is estimated for the total power injected into TFTR. Contributions to this error are uncertainties in the beam neutralization efficiency, reionization and beam scrape-off in the drift duct, and fluctuations in the temperature of the supply water.
Photoacoustic calorimetry: a new cell design and improved analysis algorithms
Authors: Melton Lynn A. , Ni Tuqiang , Lu Qingzheng
Published: July 2002

A new cell design has been developed for use in photoacoustic calorimetry. In contrast to previous designs, this cell has a hundred-fold better sensitivity (signal/energy absorbed), allows measurements to be made on optically thick solutions, allows greater laser pulse energy to be used (with consequent increase in signal levels), allows greater time resolution of transient decays in the time regime below 100 ns, and reduces the effects of reflections. The determination of photophysical parameters by use of photoacoustic calorimetry requires iterative reconvolution, and improved algorithms for these processes are presented.