bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of the plasma generator for a long pulse 10×40 neutral beam
Authors: Pincosy P. A. , Ehlers K. W. , Lietzke A. F. , Owren H. M. , Paterson J. A. , Pyle R. V. , Vella M. C.
Published: July 2002

Users of fusion devices have identified heating requirements for positive ion based neutral beams to include energies of 80 or 120 kV with pulse length up to 30 s. Additional requirements are low beam divergence (0.3°×1.0°; 1/e half angles), low impurity (less than 1%), high species (over 80% atomic), and cathode lifetime exceeding 5 h of beam operation. Accelerator design remains as an engineering problem, whereas most of the performance goals have required development of the plasma generator. Problems of concern which relate to the performance goals are the heat dissipation, magnetic field configuration, and cathode placement. The plasma generator was tested on TS IIA (the plasma generator testing facility) which does not have beam extraction capability but is used to evaluate efficiency, operating conditions, arc notching characteristics, species, plasma uniformity, and cathode conditioning. The source, consisting of the plasma generator mounted on the long pulse accelerator was mounted on NBETF (Neutral Beam Engineering Test Facility) for beam testing. During beam operation the back-streaming electrons add power to the source and affect the arc operation. Source durability and stability were studied at 80 kV and 40 A of accelerator current (deuterium). The arc efficiency was higher than the value used for the design. Power loading from back-streaming electrons was much less than the design level. With feedback control, plasma density and accel current were constant to ±2% during 30-s shots. The beam atomic fraction of 84%–88% (deuterium) was slightly higher than measured on TS IIA. Cathode durability was tested by operating over 500, 30-s full shots at 80 kV and 40 A of deuterium. Arc conditioning was found to be an important phase to avoid filament damage.
Effect of the filament-induced magnetic field on the spatial distribution of primary electrons in magnetic multicusp source
Authors: Kaneko Osamu , Oka Yoshihide , Sakurai Keiichi , Kuroda Tsutomu
Published: July 2002

The influence of the filament on the discharge characteristics of the multicusp source (bucket source) is studied experimentally and theoretically. It is found that the magnetic field which is produced by the filament itself plays an important role to determine the trapped region of primary electrons by coupling with the magnetic multicusp field. Experimentally, arc efficiency varies drastically when only the direction of the filament current is changed. The measurements of the spatial profiles of the electron density and the temperature show that the plasma production occurs at the periphery of the chamber in the case of poor arc efficiency. Theoretical calculation also shows that in this case primary electrons are trapped in the local magnetic mirror of the multicusp field. The trapping condition depends on the magnetic field geometry around the filament, and, therefore, it is sensitive to the location of filament in the magnetic multicusp field as well as the strength and the direction of filament current.
High time resolution ion temperature profile measurements on PBX
Authors: Gammel G. , Kaita R. , Fonck R. , Jaehnig K. , Powell E.
Published: July 2002

Ion temperature profiles with a time resolution of 2–5 ms have been measured on the Princeton Beta Experiment tokamak (PBX) by charge-exchange recombination spectroscopy (CXRS) and a neutral particle charge-exchange analyzer (NPA). The sightlines of both diagnostics crossed the trajectory of a near-perpendicular heating beam, which enhanced the local neutral density (∝ signal strength) and provided spatial resolution. The time resolution of these two independent techniques is sufficient to see sawtooth oscillations and other magneto- hydrodynamic activity. Effects of these phenomena on the toroidal rotation velocity profile, vφ(r), are clearly observed by CXRS. For example, a sharp drop in the central vφ occurs at the sawtooth crash, followed by a linear rise during the quiescent phase. The NPA results are compared with those from CXRS.
Cable parameter estimation based on impedance measurements at one end
Authors: Roberts M. J.
Published: July 2002

A technique has been developed for estimating, based on impedance measurements made from only one end, the distributed parameters that characterize the input impedance and voltage transfer function of a nearly lossless, four-conductor cable used as a two-wire transmission line. This technique was used to infer the transfer function of the cable in order to compensate for its filtering effect in measuring the noise voltage and current of a remotely located resistor used as a Johnson noise thermometer.
New dielectric method for the measurement of physical adsorption of gases at high pressure
Authors: Bose T. K. , Chahine R. , Marchildon L. , St-Arnaud J. M.
Published: July 2002

A new method for the measurement of gas adsorption at high pressure is described in detail. The method is based on dielectric virial coefficients and it takes advantage of the dielectric technique for the accurate measurement of the compressibility factor of gases at high pressure. The method is simple, self-sufficient, easy to use, and permits precise measurement of the density of nonideal gases. Adsorption measurements of methane on BPL-activated carbon as a function of pressure at 25 °C are reported.
Novel high-pressure isolation cell capable of reaching 120 atm mounted in an ultrahigh-vacuum chamber
Authors: Rucker T. G. , Franck K. , Colomb D. , Logan M. A. , Somorjai G. A.
Published: July 2002

A high-pressure cell and manipulator mounted inside an UHV surface analysis chamber has been built which can reach 1800 psi. With this apparatus, catalytic reactions on small surface area (∼1 cm2) single crystals and polycrystalline surfaces are monitored, and the effect of reactant pressure, surface composition, and surface structure are correlated with catalytic activity. This article describes in detail the apparatus and typical experimental procedure.
Improved oscillating buoy viscometer
Authors: Ritter Rogers C. , Molloy Janelle A.
Published: July 2002

An improved design of the vertically oscillating buoy viscometer with real-time computer control, evaluation, and plotting is presented. In this method, the optically observed phase lag of the buoy relative to a sinusoidal driving force is a direct and absolute measure of viscosity. Construction features of the new version improve reassembly precision and give three-axis positioning of the sphere, as well as an 80-fold improvement in the signal-to-noise ratio for small amplitudes of the buoy motion. Design of the ‘‘crossed coil’’ system is discussed and the magnetic and mechanical faults which lead to various kinds of motional instability are considered. Boundary layer corrections are now computer corrected as are temperature variations. The evaluation of ‘‘intrinsic viscosity’’ as a measure of molecular ellipticity is discussed and one measurement set is presented.
Simple, inexpensive double ac Hall measurement system for routine semiconductor characterization
Authors: Chu Peter , Niki Shigeru , Roach J. W. , Wieder H. H.
Published: July 2002

A simple, comparatively inexpensive Hall-effect measurement apparatus is described in which the magnetic field and sample current are sine waves at different frequencies. The current for the electromagnet is obtained directly from the 60-Hz power line, providing magnetic fields ≊0.1 T(rms). The sample current frequency is 200 Hz and the Hall voltage is detected at the sum frequency, 260 Hz, by a lock-in amplifier. Such double ac Hall measurements eliminate most thermoelectric and thermomagnetic errors associated with dc measurements. The same apparatus can be used to measure the sample resistivity at 200 Hz. Hall voltages as small as 10 μV were measured.
Mutual inductance bridge for the measurement of superconducting transition temperatures and magnetic susceptibility
Authors: Gotszalk Ryszard , Lisowski Michal/
Published: July 2002

An ac inductance bridge for the measurement of low temperatures is described. Instead of a resistive divider, an inductive voltage divider was used in the bridge. Good noise immunity of the system, a low noise value of 0.5 nV, the resolution of 4×10−6, and the comparison accuracy of 2×10−5 have been obtained. The described measuring device may be used for the determination of fixed points on provisional temperature scale EPT-76, for the investigation of superconductive transition zone of fine metals, and for the measurement of low temperatures, using paramagnetic salt sensors.
Externally heated copper vapor laser using a carbon heater
Authors: Hwang In Heon , Cha Byung Heon , Nam Sung Mo
Published: July 2002

An externally heated copper vapor laser using a carbon tubular heater is described. A recrystallized alumina tube of 20-mm inner diameter is used as the laser tube, which is located inside the tubular heater. When the heating power of the carbon heater is 3 kW, the temperature of the laser tube is 1600 °C. The average laser output power is measured to be 1.2 W at a laser tube temperature of 1500 °C when the charging voltage to the energy storage capacitor is 5 kV, the pulse repetition rate is 5 kHz, and the Ne gas fill pressure is 10 Torr.
Optics mount with 180° angle of view from both sides
Authors: Houtman H.
Published: July 2002

A simple design for a stable, general-purpose optics mount is described, with independent, self-locking angular adjustments about two orthogonal axes. Requiring only simple machining and readily available parts, the design allows unrestricted access for incident and transmitted beams.
Silicon photodiode detector for fluorescence EXAFS
Authors: Bouldin Charles E. , Forman Richard A. , Bell Michael I.
Published: July 2002

A large-area silicon diode is used as a fluorescence detector for extended x-ray absorption fine-structure (EXAFS) measurements. A direct comparison of this diode detector relative to a gas ionization fluorescence detector is made. Advantages of the diode detector include: higher signal for a given photon flux (due to higher quantum efficiency), vacuum and cryogenic compatibility, freedom from microphonic noise, good linearity, extremely wide dynamic range, operation without high voltage or gas connections, very simple electronics, and low cost. A brief comparison with other detection methods for fluorescence EXAFS is given. Use of photodiodes for transmission EXAFS is discussed.
Scanning laser acoustic microscope with digital data acquisition
Authors: Rudd E. P. , Mueller R. K. , Robbins W. P. , Skaar T. , Soumekh B. , Zhou Z. Q.
Published: July 2002

A scanning laser acoustic microscope (SLAM) is described. The SLAM achieves a resolution of about 10 μm and is capable of imaging subsurface features at depths up to several millimeters, using appropriate reconstruction algorithms. The various components of the apparatus, both acousto-optical and electronic, are described. A major feature of the SLAM is a digital data-acquisition system capable of storing and processing the complex acoustic field in images with 256×256-pixel resolution. An array processor enables most floating-point operations to be completed in a few seconds. Examples of acoustic images obtained from a test sample are presented.
In situ calibration of electrical double probes in magnetized plasmas
Authors: Höthker Klaus , Bieger Wolfgang , van Nieuwenhove Rudi
Published: July 2002

We present a procedure to perform in situ calibration of electrical double probes in magnetized plasmas as far as the density is concerned. The procedure does not rely on assumptions of the transport of particles perpendicular to the magnetic field. The comparison of the density as measured by a calibrated probe and by a lithium beam diagnostic in the scrape-off layer of the tokamak TEXTOR gives good agreement.
Four-frame gated optical imager with 120-ps resolution (invited)
Authors: Young P. E. , Hares J. D. , Kilkenny J. D. , Phillion D. W. , Campbell E. M.
Published: July 2002

In this article we describe the operation and applications of a framing camera capable of four separate two-dimensional images with each frame having a 120-ps gate width. Fast gating of a single frame is accomplished by using a wafer image intensifier tube in which the cathode is capacitively coupled to an external electrode placed outside of the photocathode of the tube. This electrode is then pulsed relative to the microchannel plate by a narrow (120-ps), high-voltage pulse. Multiple frames are obtained by using multiple gated tubes which share a single bias supply and pulser with relative gate times selected by the cable lengths between the tubes and the pulser. A beam-splitter system has been constructed which produces a separate image for each tube from a single scene. Applications of the framing camera to inertial confinement fusion experiments are discussed.
UHV transport system for laser irradiation studies
Authors: Helms A. L. , Schiedt W. A. , Bernasek Steven L. , Biwer Bruce M.
Published: July 2002

The design of a UHV sample transfer system is described. The transfer system allows irradiation of samples under vacuum in a laboratory physically removed from the location of the surface analysis system. Design considerations and advantages of this design are discussed.
CAMAC module for high-speed synchronous transfer of 32-bit binary data
Authors: Stoelting Mark , Marchant Roy , Smith Owen I.
Published: July 2002

In this work we report the design of a CAMAC module for the synchronous transfer of 32-bit binary data to an external device at rates up to 5 MHz. The module is capable of handling a data vector of up to 8192 words. The length and contents of the data vector are fully programmable by a sequence of simple calls to the CAMAC crate controller. The update rate, from 2 to 61438 cycles of an external clock, may be programmed similarly. The external clock frequency is limited to 10 MHz by the programmable interval timer employed in the circuitry. The use of this module to control a frequency synthesizer used in Fourier transform mass spectrometry is described.
X-ray luminosity time-of-flight spectrometer for laser-produced plasmas
Authors: Naik P. A. , Gupta P. D. , Kumbhare S. R.
Published: July 2002

A simple and compact x-ray luminosity time-of-flight spectrometer for measurements of the velocity distribution of highly charged ions in laser-produced plasmas is presented. The spectrometer is based on making time- and space-resolved measurements of x-ray line emission from these ions in the expansion zone. Design, operation, and performance of this system are described. The spectrometer is useful in studying processes of interaction between highly charged ions and buffer gases, and nonthermal behavior of laser-produced plasma expansion.
Multichannel boxcar-averaged measurements of plasma parameters made using a digital storage scope
Authors: Sheridan T. E. , Hayes M. A.
Published: July 2002

We present a technique for rapidly acquiring time-resolved, ensemble-averaged Langmuir probe characteristics. Fifty probe characteristics are acquired using a digital storage oscilloscope in the time it would take to acquire a one-probe characteristic using a single-channel boxcar averager. A single Langmuir probe is used, and the probe bias is swept quite slowly, so that the probe is always in equilibrium with the plasma. A method for the automatic extraction of electron temperature, electron density, and the plasma potential from the acquired probe characteristics is described. This technique for acquisition and analysis is applied to the study of plasma decay and the effects of rf excitation in a pulsed, strongly magnetized plasma.
Parallel detection for high-resolution electron energy loss studies in the scanning transmission electron microscope
Authors: Batson P. E.
Published: July 2002

A parallel detection system has been added to the Wien Filter electron spectrometer on the dedicated scanning transmission electron microscope at IBM. The system uses an intensified diode array that is optically coupled to a single-crystal YAG screen by a vacuum window and an f/1.4–22 camera lens. The YAG screen shares the spectrometer image plane with energy selecting slits used for bright field STEM images and for single-channel energy loss analysis. Energy calibration to ±0.05 eV for scans over arbitrary energy ranges is accomplished by combining many parallel spectra having different energy centers. This process can remove channel gain variations, background variations, and nonlinear energy scale effects.
Ripple method: An application of the square-wave excitation method for heat-capacity measurements
Authors: Machado F. L. A. , Clark W. G.
Published: July 2002

An extension of the square-wave excitation method for measuring heat capacity is reported. In particular, attention is focused on the limit where the period of the heat pulse excitation is much smaller than the thermal relaxation time of the calorimeter-sample system. In this limit, one finds that the thermal ripple induced by the heat pulse is inversely proportional to the heat capacity. This technique allows one to do real-time heat-capacity measurements as in the conventional ac technique with the same instrumentation as the square-wave method. The ripple method is demonstrated with a measurement of the heat capacity of strained Al near its superconducting phase transition.
Laser-T-jump apparatus for kinetic studies of ion transport through planar (artificial) lipid membranes
Authors: Stark G. , Brock W. , Awiszus R.
Published: July 2002

Relaxation phenomena associated with ion transport through planar bimolecular lipid membranes may be studied by measurement of current transients which are induced by a temperature jump. The T jump is obtained by absorption of an IR-light pulse from a Nd-glass laser by the membrane and its aqueous environment. The apparatus described allows the detection of characteristic time constants between approximately 10 μs and several seconds. Processes can be resolved if the underlying change of enthalpy exceeds 1 kcal/mol.
Null input current SQUID magnetometer for the measurement of the transition temperature of high-T
c superconducting samples
Authors: Barbanera S. , Castellano M. G. , Foglietti V.
Published: July 2002

In this article we describe a SQUID-based system used to measure the superconducting transition temperature in the range 4.2–300 K. The apparatus has been tested using a high-critical-temperature single crystal of YBa2 Cu3 O7−x (≂ 10−1 mm3 volume). The system is based on mutual inductance variations measurements, performed in a low-frequency ac magnetic field of 2×10−5 T. A feedback loop is closed on the input circuit in order to null out the current flowing in the pickup coil. This is achieved using an electronic scheme which does not involve any modification of the commercial SQUID electronics. Our experiment is performed using a copper wire pickup coil, but the scheme can also be used with a superconducting input circuit, thus allowing measurements in a dc regime. The obtained sensitivity is 5×10−5/√Hz. This figure can be further improved by optimizing the circuit parameters.
Prism laser light-scattering spectrometer
Authors: Chu Benjamin , Xu Renliang , Maeda Tadakazu , Dhadwal H. S.
Published: July 2002

A prism light-scattering spectrometer capable of measuring both the angular distribution of scattered intensity and Rayleigh linewidth is described. The spectrometer employs a unique prism light-scattering cell capable of making small-angle self-beating dynamic light-scattering measurements down to a scattering angle of 2° and is able to achieve an optical coherence factor β∼0.9 routinely, with the theoretical limit for β being 1. The prism light-scattering cell also permits refractive index measurements in the 1.33–1.60 range to a precision of 8×10−7 using a single-axis lateral position sensor. It is a flow cell with potential as a detector for other analytical techniques once the cell volume can be minimized. The apparatus can be controlled by a computer for measurements, as well as acquisition, display, computation, and storage of data.
Novel technique to measure the microwave response of high T
c superconductors between 4.2 and 200 K
Authors: Sridhar S. , Kennedy W. L.
Published: July 2002

We have devised and implemented a novel technique that has the required sensitivity to enable measurements of the complex surface impedance (Zs) of high Tc superconducting materials between 4.2 K and at least 200 K. The essential ideal is to employ a superconducting high-Q cavity resonator operated at an ambient temperature of 4.2 K. The sample, mounted on a sapphire rod, is placed inside the cavity at a high magnetic field location, and is thermally insulated from the cavity walls, enabling external control of the sample temperature between 4.2 and 200 K. The cavity characteristics are dominated by the sample properties—the Pb walls maintained at 4.2 K contribute negligibly. Measurement of the cavity Q and resonant frequency enables the measurement of Zs as a function of the sample temperature. The technique is applicable to both bulk and thin-film materials. We have used this technique with success to measure Zs, at 9.58 GHz, for bulk Y1Ba2Cu3Oy and La1.85Sr0.15CuO4 over a temperature range from 4.2 to 100 K.
Macroparticle distribution and chemical composition of laser deposited apatite coatings
Authors: Bagratashvili V. N. , Antonov E. N. , Sobol E. N. , Popov V. K. , Howdle S. M.
Published: July 2002

We have studied the effect of pulsed laser ablation conditions on the deposition of biocompatible apatite coatings on Ti and Ti–6Al–4V alloy at room temperature. We have made detailed analyses of the spatial distribution of the macroparticles (MP) and of the Ca/P ratio in the coatings. We find that (i) two types of MP are observed, differing in size, shape, and stoichiometry, and (ii) the size distribution of the MP has a maximum depending on the laser fluence and gas pressure in the deposition chamber. Manipulation of the laser deposition conditions allows fine control over both morphology and stoichiometry of coatings. Experimental results are explained on the basis of a theoretical model which includes the analysis of cluster-type ablation mechanisms due to the high pressures of gas evolved in thermal decomposition of the target material under laser irradiation.
New method for accurate calibration of an electron-spin polarimeter
Authors: Hopster H. , Abraham D. L.
Published: July 2002

A new method is described which allows the accurate absolute calibration of an electron-spin polarization analyzer. It is based on measuring spin–orbit-induced scattering asymmetries and simultaneous polarization analysis of the scattered electrons in elastic electron scattering. It is shown how the effective Sherman function of a classical high-energy Mott detector can be determined easily to within better than ±2%. The method is applicable to other types of electron-spin polarization detectors as well.
Acoustic gas density measuring cell
Authors: Haran E. N.
Published: July 2002

Preliminary experiments reported in 1983 suggested that the density of a known gas could be determined, in principle, by measuring the alternating pressure of an acoustic field set up in the gas. A density measuring cell has now been developed that is inherently fast acting (overall response time less than 3 s) and linear to within ±0.3% (of reading). It has been used over an approximately 700:1 density range, from 30 g/m3 to 20 kg/m3. Density determinations near room temperature and pressures from 0.1 to 20 atm were shown to be accurate within ±2% (of reading) up to about 0.1 kg/m3 and within ±0.2% for higher densities.
New lens for a low-voltage scanning electron microscope
Authors: Shao Zhifeng
Published: July 2002

This article introduces the idea of a ‘‘half ’’ pole-piece to modify single pole-piece lenses, enabling them to form an electron probe a few millimeters in front of the pole face. This modified single pole-piece lens has relatively low spherical and chromatic aberration coefficients. If 2 mm is an acceptable working distance, then a 6-Å radius probe can be made using 5-kV electrons.
Tomographic imaging of MHD activity in tokamaks by combining diode arrays and a tangentially viewing pinhole camera
Authors: Holland A. , Fonck R. J. , Powell E. T. , Sesnic S.
Published: July 2002

Two 32-channel side-viewing soft x-ray diode arrays will be installed on PBX-M which will provide profile information in the horizontal and vertical directions with a time resolution up to 1 μs. The information from these arrays can be reconstructed to provide a high time-resolution poloidal emission profile using a maximum-entropy-based technique which incorporates the reconstructed profile from a tangentially viewing soft x-ray pinhole camera. The pinhole camera provides lower time-resolution (about 5 ms) shape information which has been reconstructed with the assumption of toroidal symmetry. The pinhole camera information supplements the information from the diode arrays, allowing a reconstruction which can resolve MHD fluctuations of the equilibrium profile. The pinhole camera information need only be a better approximation to the real emission profile than the assumption of a flat profile since the algorithm uses it as a first-order solution which is perturbed by the information from the diode arrays. The algorithm can also explicitly include the bean-shaped PBX-M vacuum vessel and the vignetting of some detectors by the pusher coil.
Multiframe ion pinhole camera for intense ion beam transport and focusing experiments
Authors: Stygar W. A. , Leeper R. J. , Mix L. P. , Brock E. R. , Bailey J. E. , Hebron D. E. , Johnson D. J. , Lockner T. R. , Maenchen J. , Mehlhorn T. A. , Reyes P.
Published: July 2002

We have developed a new ion pinhole camera to obtain energy density profiles of a focused multiterawatt ion beam as a function of ion energy. Beam ions that are elastically scattered from a thin gold foil are imaged through six baffled pinholes onto six separate areas of a sheet of CR-39 nuclear track detector. Each of the areas is covered by an aluminum range filter and records an image with a different lower bound on the ion energy. Subtracting images with adjacent cutoff energies results in images with upper and lower bounds on the ion energy. Ion images are read from the CR-39 with VERA, a fully automatic, image-processor-based nuclear track counting system. Images of the Particle Beam Fusion Accelerator-II (PBFA-II) proton beam have been obtained and show that the beam has been focused to achieve a horizontal FWHM of 5.7 mm and has delivered 9 kJ/cm2 to a target.
Absolute calibration of a SPRED EUV spectrograph for use on the DIII-D tokamak (abstract)
Authors: Wood R. D. , Allen S. L.
Published: July 2002

We have performed an absolute intensity calibration of a SPRED multichannel EUV spectrograph1 using synchrotron radiation from the NBS SURF-II electron storage ring. The calibration procedure and results for both a survey (450 g/mm) and a high-resolution (2100 g/mm) grating are presented. The spectrograph is currently in use on the DIII-D tokamak with a tangential line-of-sight at the plasma midplane. Data are first acquired and processed by a microcomputer; the absolute line intensities are then sent to the DIII-D database for comparison with data from other diagnostics. Representative absolute line brightnesses for ohmic, L-mode, and H-mode plasma operations will be presented. This work was supported by the U.S. DOE Contracts W-7405-ENG-48 and DE-AC03-84ER51044.
Versatile Raman spectrometer control with the IBM-PC/XT
Authors: Rauch W. , Kelbert K. , Bettermann H.
Published: July 2002

The scan drive of a stepper motor, signal detection and data processing of the recorded Raman signals were controlled by a compatible IBM-PC/XT which was connected to a Jarrell–Ash 25-400 spectrometer. Excitation source fluctuations were eliminated by the simultaneous detection of a small portion of laser light. This reference and the Raman signals were transmitted to the 8-bit parallel port of the IBM by multiplexing. The parallel port was modified to bidirectional data transfer so that control and signal processing required only one port.
Simple, high current LaB6 cathode
Authors: Siegrist K. , Brown M. R. , Bellan P. M.
Published: July 2002

A cathode constructed of a thin, directly heated strip of LaB6 is described. The cathode is simple to construct, requires modest heating power, has high current emission capability and is quite rugged. Construction details will be given and cathode performance data presented. The cathode has been used in tokamak dc current injection experiments.
New high-pressure computer-assisted differential thermal analysis apparatus
Authors: Bartelt Angelika , Schneider Gerhard M.
Published: July 2002

A high-pressure differential thermal analysis apparatus for investigations in the temperature range between 273 and 600 K and at pressures up to 7 kbar is described. The experimental setup and the measuring technique are discussed. Finally, some results on the phase behavior of liquid crystals are presented.
Development of a fiber anemometer for direct measurement of low average velocity inside ducts
Authors: Fujii Tetsu , Buenconsejo N. S. , Koyama Shigeru
Published: July 2002

A fiber anemometer for direct (without traversing) measurement of average velocities, 0<u<40 cm/s, of air in laminar flow inside ducts is developed. Three experimental configurations representing different locations of the fiber, shapes of flow cross section (circular and rectangular), and duct heating are considered. The relationship between average mass velocity and fiber deflection is established by calibration and calculations, which used a local drag coefficient for thin cylinders in laminar cross flow. The effect of velocity profile on the relationship was found to be significant. The effect of fluid temperature was also significant, and the anemometer is capable of measuring the average mass velocity only in connection with a thermometer. For the present applications, however, the uncertainty of the method due to these effects was found to be small.
Impulse excitation amplifier for Fourier transform mass spectrometry
Authors: Mclver Robert T. , Hunter Richard L. , Baykut Gökhan
Published: July 2002

In Fourier transform mass spectrometry (FTMS), static electric and magnetic fields are used to store gaseous ions in an analyzer cell. Typically, the ions can be stored for several minutes if the pressure in the analyzer cell is below 10−8 Torr. While they are stored, the ions move in circular cyclotron orbits having a radial frequency given by w=qB/m, where q/m is the charge-to-mass ratio of an ion, and B is the magnetic field strength. With most FTMS instruments, a mass spectrum of the stored ions is obtained by using a rapid radio frequency (rf) sweep, or ‘‘chirp,’’ to accelerate the ions. The chirp excitation signal produces an oscillatory electric field perpendicular to the magnetic field, and as the frequency of the oscillatory electric field approaches the cyclotron frequency of an ion, the ion is accelerated to a larger cyclotron orbit. In this article the theory of operation, design, and performance of an alternative excitation method called ‘‘impulse excitation’’ is described. Impulse excitation is different from chirp excitation because the ions are accelerated by a very short, high-voltage pulse rather than an oscillatory, radio frequency signal. One of the advantages of impulse excitation is that all the ions in the analyzer cell are accelerated simultaneously in less than a microsecond. This gives more stable FTMS signals and more reliable isotope ratios. An impulse excitation amplifier is inexpensive to build and far less complex than the hardware needed for chirp excitation.
Synthesis of metal hydrides and i
n s
i
t
u resistance measurements in a high-pressure diamond anvil cell
Authors: Hemmes H. , Driessen A. , Kos J. , Mul F. A. , Griessen R. , Caro J. , Radelaar S.
Published: July 2002

We have constructed a diamond anvil cell and a cryogenic system for high-pressure experiments at temperatures down to 1.5 K. A new mechanism is used to apply the force, and the body of the cell contains a heat-exchanger for use with liquid helium or liquid nitrogen. With the press, a maximum force of 30 000 N can be applied to the diamonds. The force can be changed at any temperature from outside the cryostat. We describe a technique to load metal samples with hydrogen at high pressures and do in situ resistance measurements. With this technique, we have synthesized stoichiometric PdH and PdD at a pressure of ∼4 GPa. We also have measured the pressure dependence of their superconducting transition temperatures. For PdH we find Tc=8.8 K and ∂ ln Tc/∂P=−6.8×10−2 GPa−1, and for PdD we find Tc=11.05 K and ∂ ln Tc/∂P=−5.0×10−2 GPa−1.
An experimental technique for measurements of capillary waves
Authors: Målo/y Knut Jo/rgen , Feder Jens , Jo/ssang Torstein
Published: July 2002

An experimental method has been developed for the measurements of wave profiles at liquid interfaces. An oscillating string was used to generate interface waves, which gave rise to oscillations of a laser beam reflected from the interface. These oscillations were detected using a lock-in amplifier technique, which allowed us to measure the derivative of the surface wave profile at any given phase in the wave period. We discuss in detail experiments on the water-air interface. From the observed form of the capillary waves, we deduce the surface tension and the viscosity. The dispersion relation of capillary waves has been observed, and we found a spatial damping coefficient and wave number consistent with results obtained by dynamic light scattering and mechanical methods. Our technique is to a large extent insensitive to mechanical and optical noise and determines the capillary waveform reliably and reproducibly.
A phase-locked loop for driving vibrating tube densimeters
Authors: Wood Robert H. , Buzzard Charles W. , Majer Vladimir , Inglese Americo
Published: July 2002

A phase-locked loop has been developed for use in driving vibrating tube densimeters. This circuit allows reliable density measurements under high-noise conditions with lower drive power to the vibrating tube. The design and operation of the instrument is discussed.
Improved sequencing system for sampling clean gases to obtain particle size distributions with a diffusion battery and a condensation nucleus counter
Authors: Wu Jin Jwang , Cooper Douglas W. , Miller Robert J.
Published: July 2002

Experience with the combination of a diffusion battery and a condensation nucleus counter (CNC) showed the need for lowering the background counts due to particle generation within the sample sequencing mechanism of one commercial switching valve. An improved sample sequencing system was developed, based on a modular series of gas-operated solenoid valves. It produced fewer spurious particle counts and allowed very accurate and flexible sample durations to be preset.
Extremely low-noise potentiometry with a scanning tunneling microscope
Authors: Pelz J. P. , Koch R. H.
Published: July 2002

Novel ac biasing and detection techniques have been developed to allow a scanning tunneling microscope (STM) to measure spatial variations in electric potential on metallic surfaces with sub-μV sensitivity. When implemented with a room-temperature STM operating with minimal electrical shielding and no vibration isolation, the voltage sensitivity was limited by the thermal (Johnson) noise of the tunneling resistance.
Method for fabricating a simple low-cost position-sensitive photodetector
Authors: Burns Michael J.
Published: July 2002

We describe a very simple method for making a low-cost wide-band position-sensitive photodetector (PSD) and preamplifier circuit. The detector is most suitable for experiments where a laser is used to measure the deflection (linear or angular) of some part of the experimental apparatus. The response of the photodetector is exponential for static beam position changes and linear for oscillating position. The static deflection exponential behavior can be linearized with a logarithmic preamplifier circuit. The detector can also be used as a low-cost laser beam intensity monitor with only a few percent beam loss and approximately 100 dB of dynamic range. We have fabricated PSDs and beam-power monitors capable of operating at wavelengths from 0.2 to 1 μm and by a suitable change of components this range should be extendable from 0.1 up to 22 μm.
Time-of-flight spectrometer for an ECR ion source
Authors: Whaley D. R. , Goodman T. P. , Getty W. D.
Published: July 2002

A time-of-flight ion spectrometer using electrostatic grids for ion gating is described. The spectrometer was built to monitor the charge state distribution of endloss ions passing from the midplane region of an ECR-heated, simple magnetic-mirror plasma experiment. Design considerations of the spectrometer are presented as well as the gating pulse circuit and signal amplifier circuit. An example of a time-averaged spectrum is included to illustrate the achievable resolution of the spectrometer. Also a method is described to determine the ion energy distribution of a given charge state in the ion endloss.
Composite dilatometer for polymer thin films
Authors: Parsons Alan T. , Balik C. M.
Published: July 2002

A dilatometer is described for measuring volume changes in polymer thin films over a temperature range of 30–150 °C. The dilatometer is made entirely of glass, except for a stainless steel base and an aluminum clamp, which allow the sample chamber to be reusable. The dilatometer has the capability to measure volume changes in a 0.2 cm3 sample to within 0.13%. Polymer volume data reduction is discussed as well as the calibration procedures for this dilatometer.
Fiber-optic fluorescence array to study free convection in porous media
Authors: Perkins Richard A. , Jones Michael C.
Published: July 2002

A 64-point fiber-optic fluorescence array is integrated into a heated-packed bed to study free convection in porous media. The array consists of 64 individual fluorescence coupler-detector modules. The array modules are designed for rhodamine 6G dye and allow real-time measurement of tracer concentrations to about 40 ppb. The coupler-detectors are inexpensive and allow a single fiber to carry both the excitation light and the emitted fluorescence light between the detectors and the remote probe terminations at known locations within the bed. Dilute pulses of tracer dye are injected into the packed bed and the dye concentration at each of the 64 fiber-optic probe terminations is monitored as a function of elapsed time. The tracer concentration as a function of time and position allows the fluid movement to be followed within the porous medium.
Coded-aperture x- or γ-ray telescope with least-squares image reconstruction. II. Computer simulation
Authors: Kohman Truman P.
Published: July 2002

A novel design of coded-aperture x- or γ-ray telescope is described in a companion article [Kohman, Rev. Sci. Instrum. 60, 3396 (1989)] A fortran computer program xgrtel developed for simulation of its operation is described briefly and illustrated with a representative simulation of the imaging of a synthetic object field with a small system; details are presented in supporting material. The simulation is displayed graphically, and significant results from numerous other simulations are presented. These explore the effects of various instrument parameters, object characteristics, etc., and indicate the overall imaging performance. Under appropriate circumstances excellent imaging, limited only by pixel-size resolution and statistics of counting, is achieved. The point-spread function contains no side-lobes, ghost images, or excess noise when the least-squares reconstruction method is used with random-coded apertures, which yield just as good results as uniformly redundant-array apertures. Disadvantages of the design are increased size and mass, possible detector-background enhancement by the limiter structure, and relatively large amount of computer time required for large systems.
Parallel plane gradient system for NMR experiments
Authors: Frollo I.
Published: July 2002

A multiconductor parallel plane gradient system has been designed and constructed for the purpose of magnetic resonance experiments. The stress is laid upon the analysis of the optimal geometrical configuration of the parallel conductive strips, the four-conductor back current pass and the introduction of basic equations for the multiconductor gradient system calculation. The influence of the length and the number of conductors on the linearity of the gradient magnetic field contours have been discussed. The proposed gradient system was used in experimental MR equipment for the imaging of small biological objects.
Construction of a prototype MOS electrometer
Authors: Cover Keith S.
Published: July 2002

A parametric metal-oxide-silicon (MOS) electrometer, which offers the possibility of an electrometer with an input bias current lower, and an input resistance higher than any presently available has been constructed. The design of the electrometer permits the use of thicker silicon dioxide gate insulation than is possible with MOS field-effect-transistors (MOSFET) electrometers; thus reducing gate leakage currents. It also has a unique feedback configuration which eliminates any leakage current through the feedback loop. The electrometer is a solid-state analog of the vibrating-capacitor electrometer with MOS capacitors replacing the vibrating capacitor. The design and construction of a prototype which demonstrates the feasibility of the MOS electrometer is described.
Utilization of high speed x-ray topography for determining diffusion coefficients of point defects in nearly perfect crystals
Authors: Hondoh T. , Goto A. , Hoshi R. , Ono T. , Anzai H. , Kawase R. , Pimienta P. , Mae S.
Published: July 2002

A new method for determining diffusion coefficients of point defects using synchrotron radiation topography (SRT) is described. Since the method is based on dynamical observations of dislocation motion in a thick specimen with a low dislocation density, advantage of the SRT is fully utilized. It is shown by typical observations on ice crystals that an absolute value of the diffusion coefficient is determined by a simple analysis of the climb motion of the dislocations.
NIKOS II—a system for noninvasive coronary angiography with synchrotron radiation (abstract)
Authors: Dix W.-R. , Graeff W. , Heuer J. , Engelke K. , Jabs H. , Kupper W. , Stellmaschek K. H.
Published: July 2002

During the last years attempts have been underway at several synchrotron radiation laboratories1–4 to employ the abrupt change of absorption at the iodine K edge (33.17 keV) to the imaging of coronary arteries. The subtraction of two images taken with photon energies just above and below the edge strongly surpresses background contrast like bone and soft tissue and allows for amplification of iodinated structure contrast. At HASYLAB, for these studies, a beamline at a bending magnet was only available until 1987. At this beamline the system NIKOS I was tested to obtain information on its essential components like monochromator and detector by in-vivo investigations of dogs.

The basic feature which differs from the approaches in other laboratoriesis simultaneous registration of two stationary beams in a two-line detector without any beam switching. Based on the experience with this system during the last year all its components have been improved and changed to dimensions capable of taking a 12-cm-wide image of the human heart. At present the new system NIKOS II is under testing at the new wiggler beamline HARWI. The new monochromator comprises two pairs of a thin Si Laue case crystal and a Ge Bragg crystal, each, with inherent focussing of the beam to a horizontal line focus of about 0.5 mm height and 12 cm width. The advantage of the Laue crystals which are optimized in thickness (30 μm) for maximum reflectivity, is the low heat absorption and the full use of the white beam in the production of two monochromatic beams. The crystals are cooled in a stream of helium. Compared to the NIKOS I version5 the detector was changed in the following points: The two detection lines are enlarged to 125 mm width and the phosphor at the entrance is exchangeable to be either made of powderlike Gd2O2S:Tb or of single crystals like CdWO4 or CaF2:Eu separated by thin walls for optimum spatial resolution. The numerical aperture of the glass fiber optics guiding the light via image intensifiers to the photodiode arrays is higher. The gain of the intensifiers is raised to 1000.

Now two photodiode arrays are needed for the simultaneous readout of the two entrance lines. The readout time is halved by reading the odd and even number diodes by two ADCs per array. All these measures will increase the detective quantum efficiency from 0.2 to 0.6. The performance of the new system will be tested again by investigations of dogs before moving to investigations on humans, expected at the end of this year.
Construction of a new apparatus for angle- and energy-resolved measurements of photoelectrons and photoions
Authors: Masuoka T. , Horigome T. , Koyano I.
Published: July 2002

A new apparatus for the study of photoionization processes has been designed and constructed. The main capabilities of the apparatus include measurements of angle-resolved photoelectrons, as well as time-of-flight measurements of photoions in coincidence with total, energy selected, or threshold electrons.
Computer-based controller and averager for the Balle-Flygare spectrometer
Authors: Chuang C. , Hawley C. J. , Emilsson T. , Gutowsky H. S.
Published: July 2002

A computer-based controller/averager has been built for the Balle-Flygare pulsed nozzle, Fourier transform, microwave spectrometer. We have integrated gas and microwave pulse control, digitizing and averaging, signal processing, and mirror and frequency control into an IBM PC-AT, allowing the computer to coordinate all processes in the spectrometer. Multiple free induction decays (FIDs) are recorded for a single gas pulse without delay between digitizing sequences by continuously clocking the FID’s into multiple segments of digitizer memory. The averager fits into one of the AT’s expansion slots and has the unique feature of sharing 16 kbyte of static memory with the CPU. This gives the computer immediate access to the current average since it is already in the computer’s memory. The averaging is very fast so that the nozzle and vacuum pump remain the limiting factors for the repetition rate. Programming features are described. The spectrometer is now easier and faster to run. The increased speed and multiple FIDs per gas shot improve the signal-to-noise ratio, thus improving the chances of finding weak transitions. It is possible now to make automated searches for new transitions.
A new correlation method for improvement in selectivity of bulk trap measurements from capacitance and voltage transients
Authors: Dmowski K.
Published: July 2002

A new correlation method for improvement in the selectivity of bulk trap measurements from both capacitance and voltage transients is proposed. It relies on using, for deep-level transient spectroscopy, one of the new weighting functions instead of a weighting function originally proposed by Lang. The proposed method is an extension of Lang’s DLTS method. Analytical expressions for correlation signals are derived. Finally, a comparative analysis of results obtained for the proposed method with those obtained for Lang’s method and the method utilizing an exponential weighting function is made.
Miniature high pressure cell for transport property measurements down to 2 K
Authors: Reghu M. , Vaidyanathan R. S. , Prasad V. , Subramanyam S. V.
Published: July 2002

A miniature high-pressure cell for electrical and galvanomagnetic measurements down to 2 K has been designed and fabricated. The Bridgman anvils are made of either tungsten carbide, or reinforced alumina, for pressures up to 8 and 4 GPa, respectively. This cell is calibrated both at high pressures and at low temperatures. The pressure clamped at room temperature is not found to vary significantly when cooled down to liquid helium temperatures.