bluuebunny/crossref_metadata_2025 huggingface dataset:
Photopyroelectric thin-film instrumentation and impulse-response detection. Part II: Methodology
Authors: Power Joan F. , Mandelis Andreas
Published: July 2002

Frequency-modulation time-delay spectrometry (FM-TDS) has been implemented in photopyroelectric measurements of thermal diffusivity, on a series of well-characterized samples. The strategy of FM-TDS is sample excitation by a fast linear frequency sweep, whose autocorrelation function is mathematically equivalent to a Dirac delta function. The method permits the fast recovery of high-quality frequency and impulse-response information. Impulse responses recovered in the time-delay domain showed good agreement with a Green’s function model of transient heat conduction. The present work demonstrates that the FM-TDS measurement strategy yields photothermal information equivalent to that obtainable from a pulsed laser system, with much lower excitation power.
Rail-gap switches triggered by semiconductor edge discharges
Authors: Seddon N. , Dickinson P. H.
Published: July 2002

A method of triggering multichannel rail-gap switches is described. The method involves producing a glow discharge between a strip of semiconductor material and one of the rail-gap electrodes, the trigger discharge is arranged to extend to the full length of the rail electrode. This trigger technique has been used to trigger a small rail-gap switch and has been shown to be capable of producing high arc densities in the switch. It is expected that the trigger will be suitable for use with long lifetime rail-gap switches.
Simple balance technique for determining the transition temperature of high T
c superconducting powders
Authors: Takamori Takeshi , Dove Derek B.
Published: July 2002

A simple technique is described that permits the measurement of the transition temperature of high Tc superconductors in powder form. The method employs a modification of a single-pan balance and has sensitivity for measurements on powder amounts as low as a few mg.
Electronic controller for motorized micrometers
Authors: Keen G. R. , O’Neill J. A. , Paul G. L.
Published: July 2002

A low-cost electronic controller for motorized micrometers has been developed. The circuit provides a variable off period at the end of the micrometer travel and is intended for applications where high reliability over many traverses, but not necessarily precise positioning, is required. Two methods of triggering the controller are described, one using mechanical switching, the other optical switching.
Improved control and averaging system for microwave Fourier transform spectroscopy
Authors: Andresen U. , Kleibömer B.
Published: July 2002

A control and averaging system for microwave Fourier transform spectroscopy is described, in which data acquisition and accumulation are performed in parallel to obtain a maximum repetition rate of 75 kHz. Details of circuitry as well as examples of performance are given.
Two-dimensional photon counter for x-ray imaging
Authors: Collett Brian , Podolsky Richard J.
Published: July 2002

This paper characterizes an imaging x-ray detector formed by coupling a gadolinium oxysulphide phosphor to the input of an optical imaging photon detector. The device is small, light, easy to use, and features a direct digital readout. It exhibits fairly high efficiency (40%–80%) and high resolution (160 μm-width point spread function) near the center of its 40-mm active area. There is a small amount of pincushion distortion which seems to be associated with a loss in resolution toward the edge of the active area. The device has very low noise and can be used at x-ray fluxes down to about 0.1 x-ray/mm2/s without loss of accuracy but it is count rate limited at 105 x rays/s over the active area and so is not usable in high-flux situations such as are often found at synchrotrons. We have used the device to record good diffraction patterns from striated rabbit muscle in 30 min on a rotating anode x-ray generator: less than one tenth the time needed under similar conditions when using film.
Endoscopic fluorescence detector
Authors: Lenz Peter
Published: July 2002

This instrument, working in conjunction with standard clinical endoscopes, detects the fluorescence of hematoporphyrin derivative accumulated in tumors. At the same time, the operator receives a conventional image of the target and a signal indicating the intensity of fluorescence. Owing to the simultaneous measurement of fluorescence and backscattered excitation light as a reference, the dependence of this signal on the target vascularization, the target-endoscope distance, and the viewing angle is strongly reduced over a wide range of these parameters.
Simple design for measurement of optical spectra in nuclear-magnetic-resonance tubes
Authors: Dixon Dabney White , Woehler Scott E.
Published: July 2002

A design is presented which permits measurement of optical spectra directly in nuclear-magnetic-resonance (NMR) tubes. Samples which are optically thick at the wavelength of interest can be accommodated. The design is particularly useful for experiments in which removal of aliquots for concentration measurements is not feasible (e.g., samples with reagents which are very air or water sensitive).
Low power, 3.2-cm, efficient microwave electron cyclotron resonant ion source
Authors: Mahoney L. , Dahimene M. , Asmussen J.
Published: July 2002

Design improvements in a microwave (2.45-GHz) plasma disk ion source have resulted in a compact, efficient, and low power ion source capable of delivering ion beam current densities in excess of 10 mA/cm2 . The ion source has been designed for a 3.2-cm-diam double graphite extraction grid set. Ion beam extraction was studied using argon and oxygen discharges with input gas flows of 1–5 standard cubic centimeters per minute (sccm) and input powers under 150 W. Ion beam currents of 20 to over 40 mA were obtained at extraction potentials of 1600 V. Double Langmuir probe measurements were made for argon, and by using a free-fall diffusion model, extracted beam current densities were shown to be consistent with measured discharge electron and ion densities. These experiments demonstrate the ability of microwave plasma technology to produce high beam current densities for both inert and chemically reactive gases. The compact electron cyclotron resonant microwave ion source shows significant improvements in efficiency, lifetime, and ion beam current densities over earlier designs and over similar size conventional broad beam dc and rf ion sources.
Rotational and translational cooling of molecular ions produced in a slot nozzle
Authors: Milkman I. Wysong , Choi J. C. , Hardwick J. L. , Moseley J. T.
Published: July 2002

Excimer laser drilling has been used to cut a 20-μm by 5-mm slot in the end of a closed Pyrex tube. The slot nozzle thus formed is suitable for production of a corona-excited supersonic expansion. The performance of the device has been characterized by recording the spectrum of the N+2B–X(0, 0) band at high resolution with the optical axis parallel to the slot and with the axis perpendicular to the slot (simulating a standard pinhole nozzle expansion) for comparison. The spectral lines recorded parallel to the slot nozzle are found to have a Doppler width such that a spin doubling of 0.06 cm−1 is resolved, while the pinhole-type spectrum resolves spin doubling of 0.09 cm−1. The slot nozzle also enhances the intensity of the spectrum, reducing recording time from 10 to 2 min, while maintaining the same approximate rotational temperature of 20–40% K.
Picosecond time-resolved laser spectrometer with expanded delay range
Authors: Johnson Carey K. , Bostick James M. , Mounter Sarah A. , Ratzlaff Kenneth L. , Schloemer David E.
Published: July 2002

We have developed a pump-probe picosecond spectrometer capable of time-resolved studies spanning nine decades in time, from the picosecond to the millisecond regimes. The system operates at repetition rates up to 2 kHz with ∼40-ps time resolution. Pump and probe beam average powers are ∼10 mW. The system is capable of studies of molecular dynamics in complex systems such as proteins, where internal motions span a wide range of time scales.
High-pressure cell and its inner capsule for optical studies of liquids
Authors: Hara Kimihiko , Morishima Isao
Published: July 2002

A portable optical cell for high-pressure studies of liquids and solutions up to 800 MPa is described. Convenient methods for isolating a sample from pressure-transmitting fluid as well as for loading a sample capsule are presented. Techniques are also discussed for sealing window plugs. This system is used for studies of high-pressure flash photolysis.
Design of a pulsed valve for high-pressure NH3 injection into supersonic beam/mass spectrometry
Authors: Pang Ho Ming , Lubman David M.
Published: July 2002

A novel design of a pulsed valve for high-pressure injection of NH3 for supersonic jet expansions is presented. This valve can operate up to 200-atm reservoir pressure at 180 °C with a pulse width down to 100 μs. This valve has been designed so that the solenoid core is not in contact with the carrier fluid so that it can be used with highly polar corrosive liquids or supercritical fluids. The ability to use supercritical NH3 as a means of injecting small thermally labile biological molecules into supersonic jet expansions for analysis by resonant two-photon ionization in a time-of-flight mass spectrometer is demonstrated.
Emissive probe measurement of electron temperature in high-pressure plasmas (≥1 mTorr)
Authors: Shindo Haruo , Konishi Masayoshi , Tamaru Takeshi
Published: July 2002

A new method was investigated to determine the electron temperature with the emissive probe. The basis of the method is the use of a functional relationship between the floating potential and the heating voltage of the emissive probe. A new expression for the change of the floating potential was obtained as functions of the heating voltage and the electron temperature. This expression enabled us to determine the electron temperature from the measured floating potential. An experimental verification of the present method was made at relatively high pressures (above 1 mTorr). It was shown that the electron temperatures measured by the present method were consistent with those obtained by Langmuir characteristics and that the error in them did not exceed 10%. It was emphasized, further, that the method is very attractive because the circuit required is the same as that used in potential measurement.
Determination of the structure of magnetic islands on TFTR (invited)
Authors: Fredrickson E. D. , McGuire K. , Cavallo A. , Grek B. , Hattori K.-I. , Johnson D. , Morris A. W.
Published: July 2002

The Mirnov coil array, the horizontal soft x-ray camera, and the ECE (electron cyclotron emission) grating polychromator are used to unfold the structure of m≥2 coherent magnetic fluctuations (assumed to be tearing modes) observed in TFTR. The modes are found predominantly in the enhanced confinement, or supershot, regime, and when present seriously degrade confinement. The poloidal and toroidal mode numbers (m and n) are determined with the Mirnov coil array. The radial structure is found by calculating the theoretical radial eigenmode (based on the calculated current-density profile) and scaling the resulting linear eigenmode with the measured fluctuation amplitude at the plasma edge. The presence of rotating magnetic islands is detected as fluctuations on both the chord-averaged soft-x-ray emissivity measurements and the fast grating polychromator electron temperature measurements. The ECE and soft-x-ray systems are used to identify coherent modes as islands and confirm estimates of the islands’ location inferred from the Mirnov coil data and calculated current-density profiles.
Two-color interferometer system for Alcator C-MOD
Authors: Irby J. H. , Marmar E. S. , Sevillano E. , Wolfe S. M.
Published: July 2002

High densities with sharp, fast rising profiles are expected during pellet injection in Alcator C-MOD. Consideration of interferometer systems other than far infrared will be needed to avoid refractive effects and make profile measurements during pellet injection possible. CO2 wavelengths are proving to be the most interesting from the standpoint of density measurements, with the necessary vibration subtraction provided by a coaxial He:Ne system. We will describe the two-color interferometer as it is presently designed and present results from simulations made of the system to determine noise levels, minimum measurable density, and optimal number and location of chords. Ray tracing results both with and without pellet injection will be compared. Possible fringe counting schemes will also be discussed.
Simple method for analog measurement of amplitude probability functions of stationary signals
Authors: Castellano A. , Palamá G. F. , Guerci J. C.
Published: July 2002

An apparatus for the measurement of the amplitude density function and cumulative distribution function of stationary signals is described. The apparatus proposed does not require the use of the multichannel analyzer methods of amplitude sampling and analysis but employs only instruments in general use in research laboratories.
Apparatus for i
n-s
i
t
u measurements of changes in the electrical resistivity accompanying phase changes in metastable metallic alloys
Authors: Kelton K. F. , Holzer J. C.
Published: July 2002

A new apparatus for making in-situ measurements of changes in the electrical resistivity accompanying phase transformations and structural relaxation of rapidly quenched metallic alloys is presented. Measurements may be made in vacuum or inert gas. In inert gas, the sample temperature is raised to the annealing temperature within 3–4 min with no appreciable overshoot; the long-term thermal stability is better than ±0.2 K. The measurement circuit is stable to better than 5 ppm over 24 h. The apparatus is simple, convenient to use, and flexible for changes in the experimental design.
Frequency locking a single-mode TEA CO2 laser
Authors: van Goor F. A. , Sobolewski A.
Published: July 2002

The frequency of a single-mode TEA CO2 laser has been locked on a CF4 absorption feature. Because of the very low repetition rate use has been made of a computer to control the cavity length of the TEA CO2 laser. A stability of about ±5 MHz during long periods could be achieved with this method.
Modular magnetically coupled high-speed stirrer for hermetically sealed chemical reactors
Authors: Ritter Joseph J.
Published: July 2002

A research scale, magnetically coupled, hermetically sealed stirrer module is described. The unit is capable of providing efficient, high shear stirring within chemical reactors with the rigorous exclusion of atmospheric contaminants.
Limitations of the computerized ELZONE particle sizing system
Authors: Lin Shu-Hui , Briedis Daina M.
Published: July 2002

The Particle Data computerized ELZONE system is a popular particle analyzer for liquid suspensions. Several limitations have been discovered in its ‘‘firmware’’ (a program stored permanently in read only memory) for quantitative volume and numbers distribution analysis. To enhance the versatility of the ELZONE firmware for user-specific applications, independent data manipulation is recommended and discussed in this note.
Correctness of the calibration procedure for the computerized ELZONE particle sizing system
Authors: Lin Shu-Hui , Briedis Daina M.
Published: July 2002

A time-saving calibration procedure unique to the Particle Data ELZONE Particle Data Analyzer and a modification to this calibration procedure are discussed. The modified calibration procedure is more straightforward than the original method, and the fundamentals of its application are clearly described. Consistency of two procedures is shown. Data from calibrations using standard particles of three sizes for different electrolytes are presented to verify the correctness of both calibration techniques.
Ultrahigh-vacuum apparatus for surface spectroscopy and characterization at cryogenic temperatures
Authors: Chia Victor K. F. , Veirs D. Kirk , Rosenblatt Gerd M.
Published: July 2002

An ultrahigh-vacuum apparatus is described that enables the study of molecular adsorbates on well-defined single crystals at controlled temperatures from 14 to 900 K. Sample cooling is achieved with a closed-cycle helium refrigerator coupled to the sample holder via a flexible copper cable. This configuration maintains a 3-K temperature differential from the 11-K cryocold head to the sample and damps vibrations from the cyrocold head. The cyrogenic sample manipulator allows X, Y, Z translations, tilt, and rotation of an arm holding the sample through an arc of 270° about the vertical central axis of the vacuum chamber. The sample, mounted 12.7 cm from the central axis, may also be rotated 90° about a vertical axis through the sample. Rotation of the sample about a working circle radius of 12.7 cm allows the sample to be accessed for surface cleaning, characterization, and study by instrumentation whose physical size does not allow access by sample rotation about the chamber central axis alone. In our application, unenhanced surface Raman spectroscopy, low-energy electron diffraction, and Auger spectroscopy are carried out while maintaining a controlled sample temperature. Laser entry ports at two incident angles permit the sutdy of substrates with differing optical properties. Unenhanced surface Raman spectra of nitrogen physisorbed on a silver (111) surface are presented.
Signal generator for simulation of laser doppler velocimetry experiments
Authors: Amaré J. C. , Rebolledo M. A.
Published: July 2002

In this paper an electronic simulation system for laser Doppler velocimetry (LDV) is presented. This simulation system provides a light beam with an intensity that varies with time, as the scattered intensity does in a differential LDV experiment, where a laser whose Gaussian profile intensity has been turned into a uniform intensity profile is used. Several experiments with the simulation system are presented to illustrate its applications.
Data-acquisition system for a thermal desorption spectrometer
Authors: Kubota Yusuke , Kodaira Junichi
Published: July 2002

A data-acquisition system for a thermal desorption spectrometer (TDS), based on a 16-bit personal computer, has been fabricated. The special features of this system are that calibration of a quadrupole mass spectrometer in the TDS is automatically done and that two mass peaks with same mass number can be separated easily for hydrocarbon-rich materials.
New oxide cathode assembly for a duoplasmatron
Authors: Massoletti D. J.
Published: July 2002

An oxide cathode assembly has been designed for long life and serviceability in a duoplasmatron ion source using deuterium gas; with cathode lifetimes on the order of 250 h with an arc discharge power of 5 kW.
Shape of β spectrum obtained with thin detectors
Authors: Ouseph P. J. , Davis C. L. , O’Bryan M. Ray
Published: July 2002

The β spectrum of Tl obtained using a 200-μm detector is distorted with a prominent peak centered around 97 keV. The features of this spectrum can be reproduced by a Monte Carlo procedure. The minimum ionizing nature of the electrons with energy higher than about 300 keV is responsible for the prominent peak. This combined with the energy deposited by the lower-energy electrons leads to the observed experimental spectrum.
Spherical sector electrostatic analyzers for measurements of energy and angular distributions
Authors: DeSerio Robert
Published: July 2002

A method is presented for three-dimensional trajectory calculations of charged particles in a spherical sector electrostatic analyzer. The particle motion in the entrance and exit fringe fields for particular geometries is included. With the initial conditions as input (the analyzer voltages and the particle position and velocity as it enters the analyzer field), the trajectory calculation provides the following information: (1) the position of the particle as it exits the analyzer; (2) the velocity direction of the particle as it exits the analyzer; and (3) the radial extrema of the particle trajectory within the analyzer sectors. Functions (3) determine whether the particle strikes the analyzer electrodes, while functions (1) and (2) can by used for predicting the particle’s position at any point after exiting the analyzer. Functions (2), here given for the first time, are especially useful for quantifying the response of the analyzer for position-sensitive detection of narrow angular distributions. These functions can be expressed as a Taylor series expansion in five variables which are simply related to the initial conditions. The expansion coefficients are given for a commercially available electron analyzer (Comstock Inc., 129 Valley Ct., Oak Ridge, TN 39812). The utility of the approach is demonstrated for determining its focusing properties, energy response, and energy-angle response.
Gordon coupler for K-band EPR loop gap resonator
Authors: Oles T. , Hyde James S. , Froncisz W.
Published: July 2002

A Gordon-type coupler is described for a three-loop two-gap resonator for electron paramagnetic resonance (EPR) spectroscopy at 19 GHz. Dimensions and microwave characterization of the resonator also are provided. The resonator is particularly intended for aqueous samples in ‘‘flat cell’’ geometry. The range of coupling is sufficient to match flat cells of optimum thickness for best sensitivity. The coupling is based on overlap of evanescent fields of the loop gap resonator and transmission line.
Integrated desorption mass spectrometry: A new technique for surface chemistry
Authors: Dubois Lawrence H.
Published: July 2002

Integrated desorption mass spectrometry is a simple yet powerful technique for studying the gas-phase products of complex surface chemical reactions. Data is collected by summing a series of complete mass spectra obtained with a quadrupole mass spectrometer controlled by a personal-computer-based multichannel scalar card. Signal-to-background levels are extremely high as the spectra are recorded and summed during the entire desorption process. Accurately measured cracking patterns can be used to determine the chemical identity of individual compounds or mixtures of desorbing species. The desorption of trace impurities can also be detected readily. The advantages of this technique as well as several examples are discussed.
Liquid-membrane coupling response of submersible electrostatic acoustic transducer
Authors: Cantrell John H. , Yost William T.
Published: July 2002

A mathematical model of the liquid-membrane coupling response of the submersible electrostatic acoustic transducer (ESAT) [Rev. Sci. Instrum. 50, 31 (1979)] is presented. The model predicts that the ESAT responds to an incident ultrasonic wave of frequency ω and a constant displacement amplitude ξ0 with an output that is proportional to 2ξ0[1+(σω/Z)2]−1/2, where σ is the membrane areal density and Z is the acoustic impedance of the immersion fluid. Measurements taken over the frequency range from 1 to 11 MHz are in good agreement with the model.
Improved microwave test fixture for brittle substrate materials
Authors: McGregor Douglas S. , Weichold Mark H.
Published: July 2002

A microwave test fixture has been designed and built to hold brittle substrate materials, such as GaAs, without inducing damage. The substrate pressure is adjustable and easily controlled by the use of compression springs. Tests have shown that the holder does not damage GaAs substrates, and produces repeatable and reliable measurements.
New method for recording the onset temperature of superconductivity of high-temperature superconductors
Authors: Lin Dr. Shui Wai , Berger Dr. Lev I.
Published: July 2002

A most inexpensive, relatively fast, and accurate method of recording the onset temperature (Tc) of superconductivity of a sample is described in detail. A well-characterized sample of YBa2Cu3O6.5 and a newly synthesized material of composition TmBa2Cu3O6.5 were used to demonstrate the advantage of this new technique of recording the Tc of a sample. The reproducibility of the measurements was 99%.
Instrumentation for the study of the kinetic energy distribution and mass composition of particles produced by pulsed laser evaporation of solid materials
Authors: Shi L. , Frankena H. J. , Mulder H.
Published: July 2002

Equipment has been designed for the study of the energy distribution and mass composition of particles, particularly positive ions, emitted from solids upon irradiation with laser pulses from a TEA CO2 laser (power densities in the order of 108 W/cm2). The equipment for the mass/energy analysis consists of a quadrupole mass spectrometer (QMS) and a modified cylindrical mirror analyzer (CMA) which can measure parallel ion beams. This paper describes the equipment, the basic construction, and the operation principles of the experimental setup. The system performance and experimental procedures are described on the basis of some preliminary experimental results. The results indicate that the analyzer described in this paper is capable of measuring the mass composition and the energy distribution of particles, particularly positive ions, supplied either in a pulsed or in a continuous manner. It is useful in studying charged particles in processes involving multispecies plasmas, like those occurring in thin film deposition through evaporation of targets by means of a pulsed laser.
High performance x-ray area detector suitable for small-angle scattering, crystallographic, and kinetic studies
Authors: Widom J. , Feng H.-P.
Published: July 2002

An x-ray area detector has been constructed that has the following capabilities: lower noise and/or higher spatial resolution than previous opto-electronic designs; higher spatial resolution and no significant countrate limitations as compared to multiwire designs; and capability of acquiring millisecond- or microsecond-wide snapshots of a kinetically evolving x-ray pattern. An important feature of the present detector is that all key components are commercially produced; this detector can readily be duplicated in other laboratories.
X-ray optical properties of molybdenum-carbon, molybdenum-silicon, and nickel-carbon multilayers
Authors: Yamashita K. , Tsunemi H. , Kitamoto S. , Hatsukade I. , Ueno Y. , Ohtani M.
Published: July 2002

We have fabricated multilayer reflectors of molybdenum-carbon, molybdenum-silicon, and nickel-carbon for x rays of 1–200 Å with an electron beam evaporation method in ultrahigh vacuum. The multilayers were deposited on flat and figured substrates of float glass and superpolished glass with a surface roughness of 2–3 Å (rms). The thickness of a layer pair and the number of layer pairs were 30–100 Å and 10–20, respectively. The x-ray characteristics of these multilayer reflectors were evaluated in the 1.5–200 Å region with characteristic x rays (Cu-Kα, Si-Kα, Al-Kα, and C-Kα) and monochromatized synchrotron radiation. Peak reflectivities of molybdenum-carbon were found to be 70% at Cu-Kα and 40% at Al-Kα in grazing incidence and those of molybdenum-silicon to be more than 30% in the 150–170 Å band in near-normal incidence. On the basis of these experimental results, the x-ray optical properties of multilayers are discussed.
A new pulse laser energy meter
Authors: Yuan Yipeng
Published: July 2002

This article describes a new laser energy meter that converts light pressure to electromotive force. This meter has a sensitivity of 18.9 μV/J. For single-pulse laser beam energy of a transverse, electric, atmospheric CO2 laser device, the measurement range is from 100 mJ to several joules. It is suitable to measure the energy of laser beam with ultrashort pulse to picosecond durations. The meter features fast response, short recovery time, and no interruption of the laser beam.
A stabilizer for single microscopic particles in a quadrupole trap
Authors: Richardson C. B.
Published: July 2002

Light scattered from a single particle suspended in a quadrupole trap is focused on the detector array in a charged coupled diode (CCD) camera. The video signals obtained from two successive rows of sensors framing the center of the image are compared and the difference used to control a superposed vertical field, holding the particle at trap center. The system is effective for liquid and solid particles in the size range from 1 to 10 μm trapped in vacuum or vapor.
Measurement of dispersion relation of waves in a tandem mirror plasma by the Fraunhofer-diffraction method
Authors: Mase A. , Jeong J. H. , Itakura A. , Ishii K. , Miyoshi S.
Published: July 2002

The Fraunhofer diffraction measurements from a tandem mirror plasma are reported. The successful use of a new multichannel detector array permits a detailed study of k−ω spectra of long-wavelength waves with a few plasma shots. The observed dispersion relations are in good agreement with those of drift wave including a Doppler shift due to E×B rotation velocity.
Effect of changes in viewing window transmission on high-temperature Thomson scattering data
Authors: McNeill D. H.
Published: July 2002

Unmonitored changes in the transmission of viewing windows owing to deposited films can produce errors in Thomson scattering temperature measurements. This effect is illustrated by a recent run on the Tokamak Fusion Test Reactor (TFTR) where apparent errors of over 25% in peak temperatures of 9 keV owing to carbon films were noted. Since coatings can also be removed by hydrogen discharges, the transmission of a window may change with time, resulting in variable errors in the temperature. It is proposed that these changes be monitored by calibration in situ with the aid of a low-pressure hydrogen glow discharge.
A digital phase shifter for multiple pulse NMR
Authors: Gerstein B. C. , Han Jin-Woo , Hwang Son-Jong , Hong-Jun Pan , Skank Harold
Published: July 2002

An eight bit digital phase shifter is described which is suitable for multiple pulse NMR of solids in terms of settling time (≂2 μs) and phase resolution (1.406°). The unit incorporates an 8-bit Merrimac digital phase shifter model PSDW-84-1, and an amplification-damping-pulse shaping circuit to solve the problem of variable attenuation as a function of phase setting. Results of multiple quantum spin counting and homonuclear dipolar decoupling experiments on ensembles of strongly dipolar coupled spin 1/2 systems are used to demonstrate the capability of the unit.
Ion optical and beam energy properties of the electron beam ion source
Authors: Schmieder Robert W.
Published: July 2002

Various figures of merit describing the performance of ion sources in general are derived for the electron beam ion source (EBIS), which emits ions of very high charge but very low kinetic energy. These relations show the functional dependence of the performance on the experimental source parameters and give values typical of these sources. It is shown that the EBIS is potentially useful not only for injection into accelerators and for atomic physics experiments, but also can supply sufficient energy flux for modification and processing of solid surfaces.
A multipurpose miniature diamond anvil cell
Authors: Sterer E. , Pasternak M. P. , Taylor R. D.
Published: July 2002

A new multipurpose miniature diamond anvil high-pressure cell (DAC) has been constructed. The circular DAC has an overall 22-mm diam. and 15-mm height and is comprised of a gasket, opposing diamond anvils each mounted on backing plates, and force rings (platens). The pressure is generated by six Allen-type screws. Pressures up to 38 GPa were achieved with this miniature cell. Design features, mode of operation, and performance are described. A particular application to cryogenic and room temperature 119Sn Mössbauer spectroscopy is presented.
An inexpensive multichannel scaler for Mössbauer experiment with simultaneous display
Authors: Rao K. Raghavendra , Rajagopal E.
Published: July 2002

A completely stand-alone multichannel scaler system which can be easily built using commercially available integrated circuits is described. The multichannel scaler is interfaced to an 8-bit Intel-8085 based microcomputer through a peripheral interface adapter (PIA) Intel 8255. The inherent data latching property of PIA is made use of in the present study. The multiscaler interface system developed has decided advantages: it displays 1024 channels simultaneously, needs no attention of the microprocessor during data acquisition, has less hardware complexity, irrespective of the kind of microprocessor chosen, and has a minimal dead time (approximately 2%) and triple precision storage. Further, the method of Mössbauer data acquisition described in our note results in a higher rate of collection and subsequent lower rate of processing.
Gain of a secondary electron multiplier with ring-shaped continuous dynodes in a magnetic field
Authors: Inaba Seiki
Published: July 2002

The gain of a secondary electron multiplier has been measured in the magnetic field perpendicular to ring-shaped continuous dynodes. It has the maximum value at the magnetic flux density of about 80 G.
An inexpensive x-ray source based on an electron cyclotron
Authors: Garner H. R. , Ohkawa T. , Howald A. M. , Leonard A. W. , Peranich L. S. , D’Aoust J. R.
Published: July 2002

X rays have been produced using an electron cyclotron operated at a frequency of 2.45 GHz. This cyclotron was designed such that it would operate near the relativistic detuning limit of approximately 150 keV. The design and equipment needed are simple and inexpensive. The accelerator consists of a cylindrical cavity operated in the TE111 mode. This tuned cavity is closely coupled to and powered by a magnetron from a microwave oven.
SQUID holder with high magnetic shielding
Authors: Rigby K. W. , Marek D. , Chui T. C. P.
Published: July 2002

We discuss a SQUID holder designed for high magnetic shielding. We show how to estimate the attenuation of the magnetic field from the normal magnetic modes for an approximate geometry. The estimate agrees satisfactorily with the attenuation measured with a commercial rf SQUID installed in the holder. The holder attenuates external magnetic fields by more than 109 at the SQUID input. With the SQUID input shorted, the response to external fields is 10−5 Φ0/G.
Time-resolved temperature measurement of a pinched plasma using the dispersive x-ray analysis of the continuum emission
Authors: Venneri F. , Gerdin G.
Published: July 2002

The dispersive analysis of the x-ray continuum is employed to determine the electron temperature of a dense pinched plasma. A curved crystal spectrometer was used to obtain the desired dispersion, and two or more p-i-n (doubly diffused silicon) diodes were used to monitor the time-resolved emission. The dispersive technique is inherently more accurate than filtering techniques and simpler to implement than laser scattering techniques. In an experimental verification of the technique, the time-resolved temperature of a plasma focus pinch was measured under various conditions, and was found to be consistent with density observations and MHD calculations. It was possible to observe the cooling effect of radiation emission from seeded plasma focus discharges. The elliptical crystal spectrometer is shown to be well suited to the analysis of the x-ray emission from a pinched plasma source.
Time-resolved voltage measurements in terawatt magnetically insulated transmission lines
Authors: Savage M. E. , Mendel C. W. , Grasser T. W. , Simpson W. W. , Zagar D. M.
Published: July 2002

We have developed two voltage diagnostics that circumvent many of the difficulties of measuring voltage in magnetically insulated transmission lines driven by terawatt (megavolt and megampere) electrical pulsers. Two versions of simple vacuum capacitive probes use strong magnetic fields to deflect electrons from the anode-mounted displacement current collector. We then introduce the electron launching voltage monitor as a novel way to measure voltage. This device uses a relationship between anode electric field and electron current launched from a cathode-mounted perturbation. The electron launching voltage monitor has a large number of advantages over methods commonly used to measure voltage, including large signal level, tolerance to poor vacuum, and nanosecond temporal response. This article shows designs for all these monitors, and presents data from experiments done on the SuperMite pulser at Sandia National Laboratories.
Calibration of constant-temperature hot-wire anemometers for very low velocities in air
Authors: Tewari S. S. , Jaluria Y.
Published: July 2002

The measurement of the extremely small velocities that arise in several important heat transfer processes, such as those associated with natural and mixed convective flows, by means of a hot-wire anemometer is generally complicated because of the nonuniform temperature field that exists in these circumstances and because of the sensitivity of the anemometer output to the orientation of the wire sensor with respect to the flow. This article describes an apparatus to calibrate constant-temperature hot-wire anemometers for measurements in air, with variable ambient temperature, and for different orientations of the flow with respect to the sensor. The utility of the technique is demonstrated by calibrating an anemometer by this method and using it to measure the flow velocities in a particular natural convection circumstance.
Long life buncher grids for heavy ion particle accelerators
Authors: Mitchel G. R. , McGregor J. E.
Published: July 2002

We have designed and implemented a rugged, simple double-ribbon buncher grid that has greatly increased the mean time between failure over wire mesh designs. This grid is used to prebunch several microamperes of beams of heavy ions such as 127I or 79Br at 200 keV, for injection into a MP Tandem Accelerator, itself the injector for the Chalk River Superconducting Cyclotron.
Low accelerating voltage SEM imaging and metrology using backscattered electrons
Authors: Postek Michael T.
Published: July 2002

An approach to measure semiconductor structures for nondestructive submicrometer metrology in the scanning electron microscope (SEM) at low accelerating voltage is described utilizing the collection and measurement of only the backscattered electron signal rather than the more commonly used secondary electron signal. In this technique, the backscattered electron signal is collected using a high-efficiency microchannel-plate electron detector system with the front face of the detector biased negatively to reject the low-energy secondary electrons thus collecting only the backscattered electrons. The advantage of using the backscattered electron signal is discussed, as well as a comparison to measurements using the secondary electron signal. The potential of this technique for application to accurate SEM metrology and standards development is also discussed.
The scanning tunneling microscope as a high-gain, low-noise displacement sensor
Authors: Bocko Mark F.
Published: July 2002

We consider the capabilities of the tunneling probe of the scanning tunneling microscope as a displacement sensor as distinguished from its better established application to surface imaging. Electromechanical transducers that operate on this principle can achieve very large gain and a noise temperature equal to the minimum required by quantum mechanics for any linear amplifier. We present a two-port network representation of the tunneling transducer, including noise, that allows us to discuss the differences between the tunneling transducer and more conventional electromechanical transducers and to draw analogies between a tunneling transducer and a transistor. We present a simple equivalent circuit for the tunneling transducer including two uncorrelated noise generators, the tunneling current shot noise and the fluctuating force that the tunneling probe exerts on a test mass. In practice the fluctuating ‘‘back action’’ force spectral density is exceedingly small. We give an example of a system in which a tunneling transducer is used to monitor the motion of a very small mechanical harmonic oscillator. A transducer gain of approximately 108 should be achieved in this system that makes negligible the noise contribution of conventional following electronics. The contribution to the noise of the tunneling transducer itself should be near the quantum limit and the most significant remaining source of noise is the mechanical oscillator’s Brownian motion. The tunneling transducer represents a new approach for measuring mechanical displacements and may profoundly influence transducer technology in applications from gravity wave detectors down to measurements on single molecules.
Low-energy neutral particle analysis by a time-of-flight method on JFT-2M
Authors: Miura Y. , Okano F.
Published: July 2002

A time-of-flight method is used to measure the energy spectrum of charge exchange atoms emitted from the JFT-2M plasma in the energy range below 1000 eV/amu. The neutral flux is chopped in bunches of about 0.8 μs by a slotted cylinder. The rotating cylinder is driven by a turbomolecular pump. After the flight of 1.5 m the particles are detected by a secondary particle detector. This is an electron multiplier modified from a photomultiplier which can be gated for an intense photon. The signal from the electron multiplier is digitized at a sampling time of 0.2 μs. To get good statistics of the arrival time distribution (ATD), eight or nine ATDs are averaged. Then the energy spectrum of charge exchange neutrals is measured by a 2 ms interval. The fast change (≤2–6 ms) of energy spectra at the L/H and H/L transition is also reported. The average energy defined by ∫E(dΓ/dE)dE/∫(dΓ/dE)dE increases by about 100 eV at the H transition like the increase of the ECE electron temperature at the edge. The neutral flux defined by ∫(dΓ/dE)dE decreases like the divertor Hα/Dα signal. In the energy distribution of the flux, the number of particles whose energy less than about 400 eV decrease by the H transition but those greater than 500 eV do not change or increase. The flux at 200 eV in the H phase is two times lower than that in the L phase.
Nova two beam automated target inserter
Authors: Holliday M. A. , Selchow N. J.
Published: July 2002

To improve overall laser experiments system efficiency and provide an accurate, repeatable reentrant plasma diagnostic platform, an in-vacuum automated robotic target inserter was designed and built. The instrument combines accurate target acquisition and deployment as well as linear positioning of the laser target in the two beam chamber. The linear translation system can extend unsupported over 4 ft in length with ∓0.01 mm resolution with repeatability of less than ∓10 μm. Any one of three laser targets can be selected from a control computer and be automatically inserted to target chamber center in less than 20 s. The system is modular by design in that the two degree-of-freedom end effector can easily be removed or replaced. Plasma diagnostics that can be installed on the linear positioning component of the instrument include imaging x-ray spectrometers, pinhole cameras, and reentrant imaging targets such as those used for x-ray backlighting. The flexibility in control of this system is based on its programmability and closed loop feedback inputs from optical motor encoders and position control switches integrated into the target array and linear translation system.
Room-temperature liquid dielectrics for high-energy x-ray tomography
Authors: Lepert S.
Published: July 2002

The purpose of this study considers the possibility to use room-temperature liquid dielectrics for computed x-ray tomography (250-keV average energy). For this application, the most important consequence of a device, using a room-temperature liquid dielectric as detector in the ionization chambers, will be the lowering of the cost by removing some present technological constraints (cryogenics, high pressure). The studied liquids are tetramethylsilane (C4H12Si, TMS), tetramethylgermanium (C4H12Ge, TMGe), and tetramethyltin (C4H12Sn, TMSn). Experimental results are presented to characterize these room-temperature liquid dielectrics with x rays. The liquid, which has the most interesting characteristics for x-ray detection (low dark current, high ionization current, high ionic mobility, low average energy to generate electron-ion pairs), is tetramethylgermanium. Its use in an industrial tomographic device is then possible.
A microwave cavity for measurement of the mass of hydrogen pellets
Authors: So/rensen H. , Hansen J. E. , Michelsen P. , Sass B. , Weisberg K-V. , Knudsen O. , Michelsen E.
Published: July 2002

A description is given of a nondestructive method utilizing a microwave cavity for measuring the mass of high-speed pellets of solid hydrogen. The cavity is designed for use on a multishot pellet injector, where eight pellets are fired successively with trajectories being parallel and symmetrical around the injector axis. The cavity is cylindrical with the axis coinciding with the injector axis. When a pellet passes through the cavity through holes of 15–16 mm diameter, the change in resonant frequency is proportional to the pellet mass. As a result of the cylindrical symmetry the sensitivity will be identical for all pellets. The frequency shift is measured directly and is converted to a signal proportional to the size of the pellet. The cavity was calibrated with pellets of H2 and D2 containing around 6×1020 atoms and with velocities between 1200 and 1500 m/s. The sensitivity was found to be 300±15 mV/1020 atoms in both cases. This is in fair agreement with estimates made from the dielectric constants of solid H2 and D2. The cavity is built together with two optical detectors for time of flight measurements to form an integrated diagnostic unit.
Measurement of neutral density profile in TEXT using a diagnostic neutral beam
Authors: Bengtson Roger D. , Valanju P. M. , Ouroua A. , Rowan William L.
Published: July 2002

We use a diagnostic neutral beam, a scanning neutral particle energy analyzer, and Hα measurements to estimate the neutral density profile from the edge to the center of the TEXT tokamak. The diagnostic neutral beam provides a spatially localized density of neutrals. The plasma neutral density is measured from the ratio of the signals seen with and without the beam. The Hα measurements provide neutral profiles in the edge region and the global particle confinement time τp. The shapes of the observed neutral energy spectra put a lower bound on the central neutral density. Results are compared with estimates of NUT and general agreement is found. Error estimates are given.
Mirnov loop array for field-reversed configurations
Authors: Tuszewski M.
Published: July 2002

An array of 64 magnetic pick-up loops has been used for stability studies of large field-reversed configurations in the FRX-C/LSM device. This array of external BΘ loops proved reliable, could resolve signals of a few Gauss, and allowed the detection of several plasma instabilities.
Status of the Alcator C-MOD scanning two-dimensional Thomson scattering diagnostic
Authors: Watterson Reich , Chen Kuo-in
Published: July 2002

The detailed study of noncircular tokamak discharges will require measurements of local Te and ne over a two-dimensional region. A novel scanning Thomson scattering system is under construction for use on the Alcator C-Mod device. A multipulse (50 Hz pulse rate) Nd:YAG laser (1 J, 15 nS) will be used to scan the plasma major radius within a 14 cm range during a 160 mS period with a spatial step size of 2 cm. The laser beam sweep, which is limited by the size of the diagnostic ports, will cover ∼50% of the plasma discharge cross section. The scattered laser light spectra at various positions along the vertical laser beam path will be analyzed by a set of up to 11 (initial operation is planned for six) Wadsworth spectrometers. A prototype spectrometer with associated light collection optics has been tested and the total Thomson system optical transmission has been measured to be ∼12–15%. System details and performance measurements will be presented.