bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiparameter matrix signal averaging
Authors: Gethner J. S. , Woodin R. L. , Rabinowitz P. , Kaldor A.
Published: March 2003

A data acquisition technique is described in which entire real-time transient waveforms, which are functions of two independent parameters, are recorded and stored as the elements of a matrix that is indexed by the measured values of the independent parameter signals. In this way parameter variations are explicitly taken into account and useful data are acquired from every experimental repetition, avoiding averaging errors introduced when the system response is highly nonlinear. Additionally, the technique is shown to be amenable to determination of the noise statistics associated with the measurements and to have the capability of distinguishing between random and systematic fluctuations. The application to infrared multiple photon dissociation of UF6 is described, illustrating the general utility of this procedure.
Multichannel light detector system for visible continuum measurements on Alcator C
Authors: Foord M. E. , Marmar E. S. , Terry J. L.
Published: March 2003

A spatially resolving visible light detector system has been constructed and used to measure continuum radiation in the wavelength region near 5360 Å on the Alcator C tokamak. The instrument measures the line integral brightnesses from 20 chords through the plasma. For high-electron temperature regimes and relatively line-free wavelength regions, Zeff(r, t) is inferred from Abel inverted brightness profiles. During the steady-state portion of the discharge, Zeff(r) is usually found to be constant within 10% out to r/a = 0.75.
Bolometer for use in a noisy electromagnetic environment
Authors: Miller G. , Ingraham J. C. , Schrank L. S.
Published: March 2003

A bolometer system for measuring energy flux in a noisy electromagnetic environment is described. The system consists of a platinum foil grid, heated by energy flux from a fusion plasma experiment, whose resistance controls the frequency of a 5-MHz oscillator. The information about heating of the foil is thus shifted to a high-frequency band, and noise pickup (which is mainly at lower frequencies) is reduced.
Spot spectroscopy: Local spectroscopic measurements within laser-produced plasmas
Authors: Herbst M. J. , Burkhalter P. G. , Grun J. , Whitlock R. R. , Fink M.
Published: March 2003

Use of a locally embedded tracer in laser-irradiated solid targets yields a localized source of diagnostic x-ray line radiation in the blowoff plasma. This technique potentially eliminates problems of chord integration over regions of varying density and temperature in an inhomogeneous plasma, and reduces complications due to plasma opacity effects in the interpretation of spectra. Spectra obtained in an experimental test of this new technique are of a quality superior to those obtained from standard laser-produced plasmas, and should provide the best tests to date of spectroscopic models for these plasma conditions.
NMR imaging techniques and applications: A review
Authors: Bottomley Paul A.
Published: March 2003

Over the past ten years, a variety of techniques have been proposed and demonstrated that enable the spatial discrimination and mapping of nuclear-magnetic-resonance (NMR) signals in heterogeneous objects. These NMR imaging techniques are currently finding useful application in clinical medicine and physiological chemistry, where their noninvasive, apparently hazard-free nature, and the sensitivity of the NMR signal to the state of biological tissue, are key advantages. This article reviews the historical development, the conceptual basis, and the applications of the various NMR imaging techniques. Qualitative descriptions and illustrations of each technique and an outline of imaging instrumentation are provided. Proton NMR imaging, in medicine, of pathological states such as cancer, imaging of relaxation time, chemical shift and flow parameters, imaging of nuclei other than hydrogen, and potential hazards are discussed and demonstrated with examples.
Gradient control system for nuclear-magnetic-resonance imaging
Authors: Fitzsimmons J. R.
Published: March 2003

A group of circuits are described for generating the gradient control currents needed to implement NMR imaging on a conventional NMR spectrometer and computer. Software control over X, Y, and Z gradients is provided for, and a sample program is included. The gradients generated can be amplitude and frequency controlled, as well as phase locked. A brief summary of the physical requirements and cost is included. The design is sufficiently simple and versatile to permit its application to a variety of spectrometers and computers with little modification.
Design and performance of a frequency-stabilized ring dye laser
Authors: Divens W. G. , Jarrett S. M.
Published: March 2003

A commercial version of a scannable, frequency-stabilized, cw ring dye laser is described. The optical and electronic systems are presented along with the results of long-term stability tests and linewidth measurements. Spectral data obtained using the technique of polarization spectroscopy are also discussed.
High-precision optical switching modulator
Authors: Schneider C. W. , Kucerovsky Z. , Brannen E.
Published: March 2003

The design of an optical switching modulator for general purpose application to light chopping, switching, and merging experiments is presented. This modulator is a motor-driven mirrored chopping wheel arrangement that incorporates several unique features not found in similar commercially available products.
Microprocessor-controlled magneto-optics apparatus
Authors: Bissolotti P. , Borghesi A. , Guizzetti G. , Pedrotti P. , Reguzzoni E.
Published: March 2003

We describe a new apparatus which measures the reflectance and magneto-thermoreflectance at normal incidence in Faraday geometry, with an external magnetic field up to 2.3 T and with circularly polarized light in the spectral range 220–2000 nm. The sample temperature may be changed from 5 to 300 K continuously. The experimental variables (wavelength, polarization, temperature, and magnetic field) are controlled by a low-cost microcomputer which also performs the data acquisition and preprocessing, in which the data fluctuations are reduced with multiscaler and smoothing techniques.
Further study on a magnetically filtered multicusp ion source
Authors: Ehlers K. W. , Leung K. N.
Published: March 2003

An optimized permanent magnet filter geometry has been determined for a multicusp ion source operated with hydrogen gas. By applying a negative bias potential to the plasma grid, energetic secondary electrons are produced which can generate molecular hydrogen ions in the extraction chamber and thus reduce the H+ ion fraction in the extracted beam. Both the atomic species percentage and the ion current density can be improved by the addition of 16-eV electrons into the extraction chamber. It is also observed that once started, the discharge can be maintained with only the extraction chamber and the plasma grid acting as the anode. Thus the total discharge current can pass through the filter in the form of cold electrons.
Automated conductivity profiler for multilayer GaAs–(AlGa)As structures
Authors: Stiles K. R. , Lee J. W.
Published: March 2003

An apparatus for automatic conductivity profiling of GaAs–(AlGa)As multilayer structures is described. The apparatus includes a microprocessor which controls a solenoid valve sequence in order to chemically etch the sample, and a programmable calculator which calculates sample conductance versus number of etch steps from which layer conductivities are calculated. Conductivity profiles of multilayer GaAs–(AlGa)As heterostructure laser material are presented and compared to profiles done by an earlier manual technique.
Aerodynamic levitation of laser-heated solids in gas jets
Authors: Nordine Paul C. , Atkins Robert M.
Published: March 2003

Solid spheres were aerodynamically levitated in gas jets and laser heated to temperatures above 2000 K. Stable levitation in a supersonic jet from a 0.081-cm nozzle was demonstrated with 0.03–0.20 g, 0.24–0.47-cm-diam specimens at a height between 0.7–2.0 cm above the nozzle and ambient pressures between 1.1–18 Torr. A model of supersonic jet levitation accurately predicts height vs pressure over the full range of conditions that were investigated. The efficiency with which jet momentum is converted into levitation force decreases with the jet:specimen diameter ratio and jet Reynolds number. The rate of jet spreading with distance from the nozzle deduced from levitation experiments agrees with that measured by pitot tube traverses of the jet. Pitot tube pressure measurements also reveal a transition from laminar to turbulent supersonic jet flow at nozzle Reynolds numbers just above the maximum values at which stable levitation is observed. Laser heating reduces the jet momentum required for levitation at a given height and increases levitation stability. In experiments with subsonic jets, the required jet momentum flow rate exceeds the specimen weight by ∼2/CD, where CD is the specimen drag coefficient at its terminal free-fall speed under the ambient conditions. Exploratory studies of laser-heated liquid levitation are also reported.
High-pressure cell for pressures up to 8 kbar designed for x-ray absorption measurements
Authors: Werner A. , Hochheimer H. D. , Lengeler B.
Published: March 2003

We have designed a cell for x-ray absorption work at hydrostatic pressures up to 8 kbar using liquids or gases as a pressure medium. This allows a very accurate pressure determination of ±8 bar. The two x-ray windows of the cell consist of Be plates with a thickness of 3 mm. The windows have a cross section of 1×10 mm2. Therefore, the decrease of the signal/noise ratio using this high-pressure cell compared with a measurement without the cell is of the order of 3 for x-ray energies higher than 10 keV or 10 for energies of about 6 keV.
High repetition tokamak CSTN–II
Authors: Ushigusa Kenkichi , Hayashi Takashi , Takamura Shuichi , Okuda Takayoshi
Published: March 2003

By employing a condenser system charging up at high speed with a triac switch, a stable tokamak discharge with a high repetition rate was achieved. A good reproducibility of the tokamak discharge made detailed measurements of spatial distribution of plasma and wave parameters possible, with a sampling technique. Basic studies on waves and particle transport in a tokamak configuration are possible with this system.
Miniature TEA N2 laser with automatically timed UV preionization
Authors: Houtman H. , Meyer J.
Published: March 2003

A novel modification to the Blumlein circuit excitation method is presented which allows for automatically timed UV preionization of the main-glow discharge of a miniature 337-nm N2 TEA laser without the use of time-delayed circuits commonly used in larger transverse discharge lasers. The laser reliably produces subnanosecond, gain-switched output pulses of 65 kW at rates up to 50 Hz, with a stability of a few percent, and efficiency of 0.06%.
Simple, low-jitter, scanning nanosecond delay generator
Authors: Benetti P. , Bonelli A. , Gobbi P. G.
Published: March 2003

We present a simple and inexpensive TTL variable delay generator with nanosecond time step resolution and subnanosecond jitter. Its application is intended for the synchronization of pulsed multilaser systems to be used in resonant ionization spectroscopy studies.
Vibrating cross hair: A novel laser beam alignment device
Authors: Weis A.
Published: March 2003

We describe the construction and performance of a low-cost, easy-to-build laser-beam alignment device (scanner) which allows the simultaneous display of the transverse x–y intensity distributions of two parallel or antiparallel beams. The novel feature of this scanner is that it can measure the relative positions of the two beams simultaneously. This makes it an excellent alignment tool for two-photon experiments. The device is also useful for monitoring the transverse mode quality and for measuring the beam diameter. It serves for beam diameters down to 40 μ.
Inductive technique for measuring critical current densities in thin-film superconductors
Authors: Talvacchio J.
Published: March 2003

A technique and a particular apparatus for an inductive measurement of critical currents as a function of temperature and magnetic field in thin-film superconductors are described. The technique has been found to be particularly useful for high-field A-15 compounds 2 to 3 μm thick. Samples with lower critical current densities would have to be correspondingly thicker to measure over the same broad range of temperature and field. The design of the apparatus is detailed showing that the film can be taken directly from the deposition chamber and mounted without electrical contacts so samples can be changed easily. The principles of operation are developed based on the Critical State Model. These principles are tested by measurements which verify that the measured value of critical curent is independent of the amplitudes and frequency of the small ac magnetic field which is added to a much larger quasistatic field. The inductive measurements are compared with results of transport current measurements on a film which had been etched in a four-point bridge pattern. The two techniques give the same values when a 1-μV criterion is used to define the critical transport current.
Measurement of low-temperature specific heat
Authors: Stewart G. R.
Published: March 2003

The measurement of low-temperature specific heat (LTSH) (0.1 K<T<60 K) has seen a number of breakthroughs both in design concepts and instrumentation in the last 15 years—particularly in small sample calorimetry. This review attempts to provide an overview of both large and small sample calorimetry techniques at temperatures below 60 K, with sufficient references to enable more detailed study. A comprehensive review is made of the most reliable measurements of the LTSH of 84 of the elements to illustrate briefly some of the problems of measurements and analysis, as well as to provide additional references. More detail is devoted to three special areas of low-temperature calorimetry that have seen rapid development recently—(1) measurement of the specific heat of highly radioactive samples, (2) measurement of the specific heat of materials in high magnetic fields (18 T), and (3) measurement of the specific heat of very small (100 μg) samples. The review ends with a brief discussion of the frontier research currently underway on microcalorimetry for nanogram sample weights.
Procedures for determining the critical parameters of fluids
Authors: Okazaki S. , Higashi Y. , Takaishi Y. , Uematsu M. , Watanabe K.
Published: March 2003

An apparatus and procedures to determine the critical parameters and the vapor–liquid coexistence curve in the critical region by observing the disappearance of the vapor–liquid interface are described. The apparatus has the advantage of measuring the saturated vapor and liquid densities with only a single filling of the sample, and the procedures are applicable not only to pure fluids but also to mixtures. Three densities of liquid and eight of vapor on the coexistence curve for trifluoromethane are obtained, and the critical temperature, density, and pressure are also determined.
Self-emissive probes
Authors: Hershkowitz Noah , Nelson Brian , Pew James , Gates David
Published: March 2003

A high-density magnetized plasma is seen to heat small diameter tungsten wire probes to electron emission. The use of these self-emissive probes to determine the plasma potential in a tandem mirror plasma is investigated. A simplified model is presented and comparison is made with conventional emissive probe behavior.
Multipoint Thomson scattering
Authors: Levinton F. M. , Navratil G. A.
Published: March 2003

A new detector system for single shot measurement of electron temperature and density profiles in a magnetically confined plasma has been developed. Preliminary results have been obtained with this multipoint Thomson scattering diagnostic on Torus II, a high beta tokamak. It has a density range of 2×1013 cm−3≲ne≲5×1014 cm−3 in the preionization phase and 5×1014 cm−3≲ne≲2×1015 cm−3 in the tokamak phase. Electron temperatures range from Te≳6 eV in the preionization phase to Te≲80 eV in the tokamak phase. The detector used is a multianode microchannel plate (MCP) with a 25-mm-diam multialkali photocathode. A 10×10 array of anodes collects the current, which has been amplified by as much as 106. Each anode is independent, so the MCP can be viewed as a parallel array of 100 independent photomultiplier tubes.
Reduction of the impurity concentration of an intense hydrogen ion beam
Authors: Ott W. , Freudenberger K. , Penningsfeld F. P. , Probst F. , Suess R.
Published: March 2003

An effort was made to measure and reduce the impurity content of an intense hydrogen beam used for neutral injection heating of a stellarator plasma. Originally, the hydrogen ion beam contained 5% water and water-like ions. A simple and very useful method to reduce the contamination turned out to be evaporation of titanium on the inner surfaces of the ion source, which reduced the low-Z impurity content to 0.6%.
Multiplexers for acquiring data in molecular beam laser depletion experiments
Authors: Melamed N. T. , Zomp J. M.
Published: March 2003

Multiplexers are described for use with two- or four-channel signal averagers. The multiplexers in conjunction with a signal averager allow accurate comparisons of two or four repetitive signals even in the presence of considerable drift and noise. The multiplexers can be used in a variety of ways. As an example, their use with boxcar integrators is described and compared with signal averagers.
Computer-controlled method for removal of stray magnetic fields
Authors: Buncick M. C. , Hubbell H. H. , Birkhoff R. D. , Warmack R. J. , Becker R. S.
Published: March 2003

An 8085-based microprocessor system was developed to monitor and control the magnetic field in a three-axis, Helmholtz-coil cage for an electron energy-loss apparatus. The nulling field produced by the coils is monitored by three RFL Industries Model 101 magnetometers, and the coil current is provided by three Kepco PCX21-1MAT power supplies. The computer reads the magnetometers and provides the appropriate reference voltage to each supply to null the field in each direction. The static field is typically nulled to 5 μG with this system.
Single photon timing system for picosecond fluorescence lifetime measurementsa)
Authors: Turko Bojan T. , Nairn John A. , Sauer Kenneth
Published: March 2003

A single-photon timing system is described which is capable of extracting fluorescence lifetimes as short as 25 ps. The system is an improved version of an earlier apparatus. The new system uses a synchronously pumped, mode-locked dye laser with 10-ps pulses operating at 82-MHz repetition rate. A fast photodetector and a leading-edge discriminator were developed to use with this light source. Also, a special rate reduction circuit was built to eliminate large oscillations in fluorescence decay spectra due to the excessive stop rates that overload commercial time-to-amplitude converters.
Fast chopper for time-resolved resonant fluorescence spectroscopy
Authors: Broer M. M. , Levey C. G. , Yen W. M.
Published: March 2003

A fast mechanical chopper system is designed for use with a pulsed YAG laser in time-resolved resonant fluorescence measurements. The firing of the laser is synchronized with the position of the chopping wheel in order to block a photomultiplier from laser scatter. With an optical mapping technique, which does not require tight focusing of the fluorescence on the chopper blade, a turn-on time of 2 μs is obtained with a 100-μm spectrometer slit aperture.
New pulsed laser data-acquisition system
Authors: Singer K. D. , Merlin M. S. , Grossman C. H. , Garito A. F.
Published: March 2003

A new pulsed laser data-acquisition system which can perform the normal operations of boxcar integrators is described. The system is based on a CAMAC standard photocurrent charge-sensitive integrator which is coupled to a laboratory minicomputer. The charge-sensitive integrator is triggered by a gate pulse which is optically synchronized to the laser output. This greatly reduces asynchronous noise. Details of the hardware configuration, the trigger gate circuit, and data averaging software are presented. Flexibility of hardware and software allow for other applications, such as multichannel analysis and other real time data processing.
Simple calibrator for optical reflective sensor
Authors: Sridharan G.
Published: March 2003

We describe a calibrator used to evaluate the response of an optical reflective sensor as a function of the reflector distance. It is easy to fabricate and assemble.
Improved active magnetic suspension
Authors: Sridharan G.
Published: March 2003

A new technique for an active magnetic suspension is proposed here. The salient feature is that the floated ferromagnetic body is magnetized directly by a feedback controller so as to maintain it in stable suspension beneath a rare-earth cobalt magnet. This results in a large load-bearing capacity and a high stiffness coefficient. Consequently, stability is ensured even under large perturbations.
An inexpensive alternate to level-sensing automatic filling systems for liquid nitrogen
Authors: Mihe J-P. , Slavin A. J. , Londry F. A.
Published: March 2003

This note describes an overflow sensor used as the level controller for automatic filling systems for liquid nitrogen. It serves as an inexpensive and reliable alternative to level-sensing devices in applications where the container is to be refilled to the top at regular intervals.
Correction for chromatic aberration in microscope projection photolithography
Authors: Brady M. J. , Davidson A.
Published: March 2003

We have measured the ultraviolet dispersion of several microscope objectives and we find that all of them are limited by axial chromatic aberration when used for polychromatic exposure of photoresist. We show how to measure and correct for the ultraviolet focus shift, and estimate the corrected resolution. Certain lenses are able to produce micron features over millimeter fields.
Polychromatic laser light source
Authors: Henze C. P. , Case S. K.
Published: March 2003

We show that a commercial dye laser can be modified to allow rapid wavelength tuning via an applied voltage. By controlling the laser with a minicomputer, an arbitrarily specified continuous or discrete spectral output can be obtained.
Portable, fast-response gas sensor for measuring methane and ethane and propane in liquefied natural gas spills
Authors: Bingham G. E. , Kiefer R. D. , Gillespie C. H. , McRae T. G. , Goldwire H. C. , Koopman R. P.
Published: March 2003

We have developed a four-band, IR radiometer for measuring methane and ethane plus propane in the 1% to 100% gas per volume of air range in liquefied natural gas spills. The instrument is a small and lightweight open-cell, pyroelectric detector-based sensor designed for field use. It compensates for attenuation because of dense fog and is sufficiently hardened to allow continuous operation in the transient flame front of an ignited natural gas cloud. The sensor transmits five determinations of the gas concentration each second to a data-collection station on an interrupt-driven, serial data link. It has an operational power requirement of 15 W at 12 V dc.
Spectrum analyzer of exponentially decaying signals
Authors: Atanasov R. D.
Published: March 2003

An analyzer of exponentially decaying time signals is described. It is simple for technical realization and has good selectivity.
Effect of sample and magnetometer dimensions on the flux detected by a SQUID magnetometer
Authors: Osterman D. P. , Williamson S. J.
Published: March 2003

From the Green’s function for the magnetic scalar potential inside an infinitely long superconducting shield, an expression is obtained for the flux within a circular pickup coil due to a cylindrical sample of arbitrary dimensions. Using this expression, the dependence of SQUID output on sample dimensions and pickup coil and shield radii is derived. The predictions are found to be in good agreement with experimental measurements.
Instrumentation for low-energy electron diffraction
Authors: Lagally M. G. , Martin J. A.
Published: March 2003

Recent developments in instrumentation for low-energy electron diffraction (LEED) are reviewed. After a summary of the major types of measurements in LEED, the properties of LEED instruments that are important in performing these measurements are described. A detailed discussion is presented on the major components of a LEED diffractometer. LEED is compared briefly to some other techniques that are sensitive to surface structure.
Backscattered electron imaging with scanning Auger electron spectroscopy
Authors: Thomas J. H.
Published: March 2003

Microbeam Auger elemental mapping of surfaces is both time consuming and, for topographically rough surfaces, difficult to interpret. Backscattered electron imaging can provide maps where intensity is a function of atomic number Z. Using a coaxial detector, and moderate primary beam energy, qualitative elemental maps are easily obtained. These maps are used to identify regions for point quantitative analysis by Auger electron spectroscopy. The analysis of heavy-metal defects in metallurgical-grade silicon is presented to demonstrate the application of this potentially powerful technique.
Technique to increase the H+ ion fraction in a multicusp source
Authors: Ehlers K. W. , Leung K. N.
Published: March 2003

It is possible to filter out the primary ionizing electrons from the ion extraction region of a multicusp source by installing the filament inside the dipole fields of the permanent magnets and thereby enhance the H+ ion species in the extracted beam. An optimum position of the filament has been determined such that a quiescent plasma together with a uniform plasma density profile across the extraction plane can be obtained.
Prototype module of a long pulse ion induction Linac
Authors: Kawasaki Sunao , Kubota Yusuke , Miyahara Akira , Yamamoto Keiichi
Published: March 2003

A module of an induction Linac is developed, being aimed at application to ion acceleration. A proton beam of 30 mA is extracted from a reflex discharge ion source and accelerated up to 20 keV, directly by the applied inductive field in a 0.5–1.0 μs pulse.
Plasma spectral analysis using an image dissecting detector
Authors: Weber Paul G.
Published: March 2003

We describe the adaptation of an image dissecting detector to a visible/near-ultraviolet radiation spectrometer used in laboratory plasma diagnostics. The detector has advantages in terms of sensitivity, fast scanning capability, and versatility over other detectors. We demonstrate several plasma diagnostics applications for the system.
Ratemeter with dead-time correction
Authors: Janka K. , Kulmala V.
Published: March 2003

A theoretically ideal and simple dead-time correction system for analog ratemeters is presented. It is based on the use of a correction amplifier controlled by the durations of measured pulses and it allows pulses with varied and unknown durations. A possible application area is the concentration measurement of monodispersive (or limited size distributed) particles using single particle optical counters. Experimental measurements of aerosol particle concentrations with a single particle optical counter shows that a significant extension in the measurement range is achieved.
Simple, thyristor-driven triggering circuit for trigatron gaps
Authors: Kubota Yusuke , Kunibe Toshizu
Published: March 2003

A convenient thyristor-driven triggering circuit for trigatron gaps has been developed. For simplicity, the electric power of the circuit is fed from the high-voltage terminals of the gap through a voltage divider. This circuit could trigger the trigatron gap successfully over the voltage range from 8 to 30 kV.
Technique for junction depth measurement of silicon solar cells
Authors: Biswas D. , Roy J. B.
Published: March 2003

A new technique for junction depth measurements of silicon solar cells is described. The technique essentially consists of repeated anodization and etching of the surface layer followed by electrical measurements. The advantages of the technique are discussed and illustrative results are presented.
100-microsecond-resolved EXAFS technique for studying protein dynamics
Authors: Huang H. W. , Liu W. H. , Teng T. Y. , Wang X. F.
Published: March 2003

We have built a microcomputer-controlled x-ray absorption spectrometer which is capable of measuring 100-μs-resolved extended x-ray absorption fine structure (EXAFS) of dynamic systems. The spectrometer integrates the x-ray absorption signals over a time interval τ at any time t measured from the time of sample excitation. A series of absorption data of different t is measured for a given x-ray energy. The process is repeated for as many different x-ray energies as required. The lower limit on τ is determined by the concentration of sample and the intensity of synchrotron radiation. The system was recently tested at Stanford Synchrotron Radiation Laboratory using a carboxymyoglobin sample. We present the raw data here to demonstrate the feasibility of this spectrometer.
Single-ring magnetic cusp ion source
Authors: Brainard J. P. , O’Hagan J. B.
Published: March 2003

The single-ring cusp ion source discussed in this paper was developed to provide a dc ion beam in a nonpumped D–T neutron generator. The source operates at 0.25 Pa and produces a uniform-density beam through an aperture of 1.3-cm diameter. At the standard operating voltage of 150 V and arc current of 10 A, the atomic ion content of the 200-mA deuterium ion beam is about 60%, and the ion impurity level is less than 0.5%. The ion output of the source was examined at arc currents of up to 40 A and found to be a linear function; in addition, very high D+ yields were realized. With the aid of a shielded Langmuir probe, we have determined such plasma properties as electron energy, plasma potential, floating potential, and current density throughout the volume of the source. It was observed that the plasma is effectively confined by the magnetic field and there is evidence of an electron energy filtering mechanism similar to that found in multicusp ion sources. Electron energy on the filament side of the cusp has been determined to be about 75 eV and on the aperture side about 12 eV. Since the electron impact cross section for ionizing diatomic deuterium is maximum at 75 eV and the cross section for dissociating D+2 to D+ is greatest near 12 eV, we believe that a very effective two-step ionization process accounts for the high D+ yield of the single-ring magnetic cusp source. Plasma potentials measured have values close to the voltage of the anode, and the floating potentials are seen to be directly related to electron energy values. The floating potential is near cathode voltage where electron energies are high, and close to anode voltage where electron energies are low.
High-intensity lithium-ion source
Authors: Weber Paul G.
Published: March 2003

This high-intensity lithium-ion source is a modified duopigatron. The arc discharge between the cathode and anode in a working gas, typically helium or hydrogen, expands through an aperture in the anode into an expansion cup containing lithium vapor, which is subsequently ionized. Results of spectroscopy and mass analysis are reported. Total continuous output at low accelerating potentials has exceeded 15 mA/cm2 while operating at 10% of the maximum arc current capability.
Design of a high-resolution angle-resolving electron energy analyzer
Authors: Kevan S. D.
Published: March 2003

An angle-resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≲1/4° has been designed, constructed, and tested. A novel input lens allows independent control over both the energy and angular resolution. A series of tests has been performed which indicates that the analyzer operates at the theoretical resolution limit for the lowest values used.
Electromagnetically driven closed-circle-type CO2 laser
Authors: Ono S. , Teii S.
Published: March 2003

The electromagnetic force has been used instead of a mechanical blower to drive the gas mixtures in a closed-circle-type CO2 laser tube for cooling and refreshment of the gas. A gas flow velocity has been obtained up to 0.8 m/s by applying a magnetic field B=1.67 kG externally to the discharge current I=40 mA at a fixed gas pressure P=10 Torr. The laser output obtained by moving the gas for the gas mixture ratio of CO2:N2:He=2:1:7 is larger than that without moving the gas by a factor of 3 for up to 1 h of continuous operation.
Resolution of closely spaced fluorescence decays—the luminescence background of the RCA 8850 photomultiplier and other sources of error
Authors: Libertini Louis J. , Small Enoch W.
Published: March 2003

The RCA 8850 photomultiplier has a wavelength-dependent luminescence background when used in the UV below 320 nm. We show that this luminescence gives rise to an additional decay in the deconvoluted fluorescence and, unless corrected for, seriously interferes with the resolution of closely spaced fluorescence decays. A much lower luminescence background is found for the RCA C31000M photomultiplier, which is identical to the 8850 except that it has a fused silica rather than a Pyrex window. Use of the C31000M improves the resolution of known mixtures, but the recovered lifetimes are still somewhat in error. We believe that this residual error is due to additional low-amplitude components in the fluorescence which cannot be resolved. An approach is presented which minimizes the effects of these contaminant decays on an analysis. Using this method, the decays of mixed compounds with lifetimes of 8.8 and 12.8 ns, of 10.1 and 12.8 ns, and of 8.8 and 10.1 ns are accurately resolved.
Sampling correlator for fluorescence decay measurements using free-running, cw laser excitation
Authors: Pelletier M. J. , Harris J. M.
Published: March 2003

An alternative means of measuring fluorescence lifetimes by time correlation is described which avoids the inefficiency of direct multiplication of the high-frequency signals. The process of sampled correlation is used, whereby samples of the input signals are gathered in pairs, the time delay between which is precisely varied. The product of the samples is computed during the long time period between the gathering of sample pairs. In this scheme, the burden of fast response is placed on the sampler while the multiplier can be a slow device of high efficiency. Furthermore, the time delay between samples can be conveniently controlled by electronic means. The sampling correlation approach to fluorescence lifetime measurements is evaluated in light of the noise power spectrum of a free-running ion laser, used for sample excitation.
Normally on fast-gain switch for photomultiplier tubes
Authors: Ballard S. G.
Published: March 2003

A normally on gain switch for photomultiplier tubes is described. Even using inexpensive side-window tubes, on/off ratios exceeding 104 can be obtained, with switching times of less than 50 ns. The system is used to measure weak delayed luminescences down to 200 ns after an intense actinic flash. Detectability is ultimately limited by tube afterpulsing.
Ion cyclotron resonance bridge detector for frequency sweep
Authors: Pitsakis Michael N. , Wobschall Darold C.
Published: March 2003

An electronic ion cyclotron resonance detection system was designed and constructed. The ions are excited by sweeping the frequency of the electric field (3–300 kHz) using a sweep frequency generator with a nonlinear sweep voltage in order to maintain an approximately constant mass resolution. Ion detection is accomplished by a bridge with a phase-sensitive detector as a demodulator. The required reference signal for the phase-sensitive detector is generated by a circuit with a transfer function which approximates that of the ICR signal in order to obtain an accurate phase match between the signal source and the detector. The device is capable of detecting a minimum concentration of 50 ions/cm3 over a mass range of 15 to 1500 amu.
Cryostat for semiautomatic measurement of heat capacity and elastic moduli between 1.6 and 400 K
Authors: Hirao Kazuyuki , Soga Naohiro
Published: March 2003

An adiabatic cryostat system for the measurement of either heat capacity or elastic moduli was constructed. The vacuum system, electronic equipment to achieve the adiabatic conditions, and instruments for measurements are described. The cube resonance method used for measurement of elastic moduli is shown. Test measurements on the heat capacity of α-Al2O3 show agreement within ±1% of the literature values. The results of heat capacity and elastic moduli measurements on optical fiberglass are described and compared with other data.
Loop tracer with waveform storage for ferroelectric hysteresis observation
Authors: Fukami Tatsuo , Yanagisawa Hidenobu , Tsuchiya Hidetoshi
Published: March 2003

The present paper describes a loop tracer devised for ferroelectrics that can record hysteresis phenomena instantaneously. Digital technology has been applied to the conventional Sawyer–Tower circuit to provide a new system. Owing to its fast operation, it is easy to observe the loop of aged specimens without changing their electrical state, as well as to follow the depolarizing process dynamically when an ac voltage is applied.
Positive displacement vacuum-sweep dispenser for small particles
Authors: Sherman P. M. , Glass D. R. , Postman D.
Published: March 2003

A dispenser was developed for feeding small particles into a laboratory burner at a very constant flow rate. A positive displacement of a continuously replaced volume of particles is employed combined with a sonic ejector. The combination meets the requirements for good chemical measurements. The system also satisfies the requirements for laser-Doppler anemometry.
Apparatus for continuous, fast, and precise measurements of position and velocity of a small spherical particle
Authors: Venkataraman T. S. , Eidson William W. , Cohen Leonard D. , Farina James D. , Acquista Charles
Published: March 2003

The position and velocity of optically levitated glass spheres (radii 10–20 μm) moving in a gas are measured accurately, rapidly, and continuously using a high-speed rotating polygon mirror. The experimental technique developed here has repeatable position accuracies better than 20 μm. Each measurement takes less than 1 μs and can be repeated every 100 μs. The position of the levitated glass spheres can be manipulated accurately by modulating the laser power with an acoustic optic modulator. The technique provides a fast and accurate method to study general particle dynamics in a fluid.
High-precision, wide-range, dual-axis, angle monitoring system
Authors: Schuda Felix J.
Published: March 2003

A system is described that uses a helium–neon laser and lateral effect photodiodes to monitor the θ and φ angles of a test mirror. Accuracies of 0.01 arcsec are achieved short term in a laboratory environment. A bandwidth of 900 Hz allows simultaneous real-time angle monitoring on both coarse (10 000 arcsec) and fine (300 arcsec) angular ranges.
Microcomputer-controlled system used in time-resolved EXAFS technique
Authors: Liu W. H. , Wang X. F. , Teng T. Y. , Huang H. W.
Published: March 2003

A microcomputer-controlled system was built to measure 100-μs-resolved EXAFS (extended x-ray absorption fine structure) of dynamic systems. We designed a charge integrator to integrate x-ray absorption signals and a gate circuit to control the time and interval of integration. Since the x-ray source is synchrotron radiation pulses, it is important to time the integration interval with the synchrotron radiation pulse clock. An Apple II microcomputer is used for the circuit control as well as the data acquisition. The computer is also interfaced with a CAMAC crate to operate the monochromator and other standard EXAFS instruments in synchrotron radiation laboratories. The electronic design of this system is described in this paper.
Inexpensive programmable gating unit for transient waveform recorders for NMR
Authors: Shenoy R. K. , Peemoeller H. , Kydon D. W.
Published: March 2003

In order to use transient waveform recorders to digitize the Meiboom and Gill modified Carr–Purcell pulse sequence response in samples with spin-spin relaxation times of the order of seconds the memory of the recorders must be used effectively. The programmable gate, described in this paper, permits selective sampling of the spin-echo envelope. The selective sampling capability of the gate is particularly useful for recording multicomponent signals which are commonly found in heterogeneous biological samples.
Tuning and matching the TM1 cavity
Authors: Matus L. G. , Boss C. B. , Riddle A. N.
Published: March 2003

The cylindrical resonant cavity operating in the TM010 mode is increasingly being used to generate a microwave-induced plasma (MIP) for elemental analysis by atomic emission spectrometry. In this study, the concepts of tuning and impedance matching for the Beenakker type TM010 resonant cavity are discussed. Proper placement and penetration depth of an antenna coupling probe appear to be a preferable approach to matching the TM010 microwave resonant cavity to a microwave generator. This approach precludes the use of external matching devices that add complexity to the system. In our system, a long probe penetrating 92% into the cavity well and positioned 14 mm from the center of the cavity allowed operation of a critically coupled argon plasma at 13–15 W as recorded from the generator’s calibrated power meter. Additionally, a detector is described that permits measurement of the electric field inside the cavity. The electric field inside the cavity decreases substantially upon ignition of a burning plasma. Aided with a tesla coil, a minimum electric field of 150 V cm−1 allows ignition of an argon plasma. After ignition, the electric field typically reduces to 30 V cm−1 and is not strongly affected by increases in input power. The effect of impedance matching and the electric field caused by increasing the input power to the cavity is also examined.
Measuring the electrical resistance of metals to 40 GPa in the diamond-anvil cell
Authors: Reichlin Robin L.
Published: March 2003

A four-probe technique is described for measuring the electrical resistance of metals in a diamond-anvil cell at pressures up to 40 GPa. The pressure range for electrical resistance measurements was extended by developing insulating gaskets that provide the necessary support for the diamonds and the electrical leads at the diamond edges. The various gasket materials and construction methods that were tested fall into two categories: (1) gaskets made entirely of insulating materials, and (2) gaskets made of metal coated with insulating materials. Gaskets developed in each category were used successfully in making resistance measurements up to 40 GPa. The most reliable gaskets were composites of sheet mica and MgO powder. This report describes the testing and development of the gaskets and presents electrical resistance data obtained for iron and beryllium to 40 GPa.
Hydriding system for moderately severe conditions of pressure and temperatures
Authors: Elton J. , Oesterreicher H.
Published: March 2003

A hydriding system capable of pressures up to 1000 atm and temperatures up to 550 °C is described. A pressure generator in which H is outgassed from a metal hydride is used to produce the highest pressures. With this unit one can rather accurately determine the hydrogen uptake in metal hydrides at elevated temperatures and pressures by employing the virial equation of state out to the fourth virial coefficient.
Temperature control for liquid-helium cryostats below 4.2 K
Authors: Escorne M. , Mauger A.
Published: March 2003

We report the operational characteristics of a membrane type of manostat and of a throttle valve system which we have constructed to regulate the pressure P above the liquid-helium bath. The choice of the manostat rather than the other device depends on the nature of the experiments to be performed: in the membrane type of manostat, the temperature is determined with an accuracy limited by the fluctuations ΔT around the mean value T. With throttle valves, the accuracy is limited by the drift of T in time. The performance of both devices prove to be sufficiently good as they stand, since the departure from T in the course of the experiments is lower than 10−2 K in the whole range 1.4<T<4.2 K, being well inside this limit below 2 K. The need for expensive and complex electronic regulations to improve the temperature control is thus exceptional.
Fast cold-trap desorption spectrometers useful in normal vacua
Authors: Milner C. J.
Published: March 2003

A cold trap used as a desorption spectrometer is, after a certain cold time, heated, and the pressure adjacent to it is monitored as a function of the increasing trap temperature. The temperature at which a peak pressure is observed is characteristic of the chemical species of the desorbing molecules. In the ultrahigh-vacuum range, where desorption spectrometry has become established, the temperature at peak usually depends greatly on other factors also, in particular on the substrate surface. This paper: (1) demonstrates that, on the contrary, under lower, ‘‘normal,’’ vacuum conditions, such temperatures at peak are usually within a few kelvins of values predictable from vapor–pressure data, and (2) describes a form of cold-trap system which displays narrow (15 K) and sharp (to 1–2 K) peaks during temperature rise at 100 K/s. The trap consists of a shallow cup or saucer pressed from a 25-μm brass sheet, forming part of the vacuum wall. Pouring 0.3 ml of liquid nitrogen into the saucer cools it and keeps it cold for ∼15 s. Sharp, narrow peaks are secured by placing a constriction in the vacuum connection very close to the trap surface. A leak-detection limit of 50 μl Pa/s (concentration limit 1:100 000) is claimed.
Fast-response dual-beam UV-absorption ozone photometer suitable for use on stratospheric balloons
Authors: Proffitt Michael H. , McLaughlin Richard J.
Published: March 2003

Various types of ozone detectors are currently in use, each with different advantages and compromises in response time, portability, sensitivity, accuracy, need for repeated calibration, and expense. We describe here a new dual-beam UV-absorption instrument for balloon-borne measurements of atmospheric ozone. It has two identical absorption chambers, each alternating between reference mode (ozone free) and sample mode by means of a four-port valve and ozone scrubber. The ratio of the absorption signals, along with the known lengths and ozone absorption cross section, yield the ozone concentration. The dual-beam feature cancels the effects of lamp intensity fluctuations, while the mode alternation compensates for mechanical changes and also provides continuous measurements. The absorption measurement requires no calibration and, hence, is independent of gas flow rate. The response time is 1 s and, for this measurement duration, the minimum ozone concentration detectable by this instrument (one standard deviation) is 1.5×1010 molecules/cm3 (0.6 ppbv at STP). The overall uncertainty of a 1-s measurement at the ozone maximum (22 km) is 3.6%, where 2% of this is the accuracy of the ozone cross section. The size and weight are suitable for launch by small balloons, but the cost of the instrument precludes its use as a disposable unit.
Inverse Helmholtz pairs
Authors: Murgatroyd P. N. , Bernard Bruce E.
Published: March 2003

Pairs of coils, disposed like a Helmholtz pair but connected in opposition, are used to create a region of nearly uniformly varying magnetic field. Optimum configurations for pairs of ideal filamentary coils are calculated. For pairs having a large winding cross section, such as those used in the Davisson–Beams gyromagnetic ratio experiment, optimum shapes of sections are derived which give the maximum field gradient either for given total ampere turns or for given power dissipation.