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Showing papers in "Review of Scientific Instruments in 1987"


Journal ArticleDOI
TL;DR: In this article, the principle of inertial sliding of a platform on a periodically accelerated support is exploited for the design of a piezoelectric finepositioning device, which provides step sizes of 0.04-0.2 μ, speeds of up to 0.2 mm/s, and practically unlimited translation range.
Abstract: The principle of inertial sliding of a platform on a periodically accelerated support is exploited for the design of a piezoelectric fine‐positioning device. The device provides step sizes of 0.04–0.2 μ, speeds of up to 0.2 mm/s, and practically unlimited translation range. It is powered by a sawtooth electric waveform of 60–300‐V amplitude and useable for loads of up to 1 kg and probably even more. Mechanical parts and driver electronics are extremely simple, reliable, and easy to operate.

306 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe how CT is used to measure the volume fraction of pore space occupied by up to three discrete phases, such as oil, water, and gas.
Abstract: The medical x‐ray computerized tomography (CT) scanner has proved to be a useful tool for studies of fluid flow in porous media, with particular applications in reservoir engineering and enhanced oil recovery. This paper explains how CT is used to measure the volume fraction of pore space occupied by up to three discrete phases, such as oil, water, and gas. The image processing system, x‐ray transparent high‐pressure flow equipment, choice of fluid dopants, and x‐ray energies are described for scanning of core flood experiments. Examples are given of tertiary miscible carbon dioxide displacements in Berea sandstone.

232 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic depth profiles near the surfaces of ferromagnets and superconductors were determined by measuring the spin-dependent reflectivities of a well-collimated (0.01°) beam of cold neutrons from surfaces of a few cm2.
Abstract: A description is given of the prototype polarized neutron reflectometer installed at the intense pulsed neutron source. This instrument is designed for determining the magnetic depth profiles near the surfaces of ferromagnets and superconductors, by measuring the spin‐dependent reflectivities of a well‐collimated (0.01°) beam of cold neutrons from surfaces of a few cm2. Magnetic profiles can be determined with the spatial resolution of 40 A, over thicknesses up to 5000 A. Variations of the magnetic flux of the order of 10−5 G cm2 can be detected.

223 citations


Journal ArticleDOI
TL;DR: In this article, a new type of time-of-flight photoelectron spectrometer was proposed for the study of cold metal and semiconductor cluster anions prepared in a supersonic molecular beam.
Abstract: Design considerations and initial results are presented for a new type of time‐of‐flight photoelectron spectrometer which is particularly suited to the study of cold metal and semiconductor cluster anions prepared in a supersonic molecular beam. The desired cluster is extracted from the molecular beam, mass‐selected after an initial time‐of‐flight, and decelerated as it enters the photoelectron spectrometer. Photoelectrons ejected from the cluster by an ArF excimer laser are collected with >98% efficiency in an intense pulsed magnetic field of carefully controlled divergence. This divergent field parallelizes the photoelectron trajectories and maps smoothly onto a low, uniform magnetic field which guides the electrons along a 234‐cm flight tube leading to a microchannel‐plate detector. The strong magnetic fields and simple, open design provide excellent rejection of stray photoelectrons in a clean, ultrahigh‐vacuum environment. The UPS spectrum of Si20− is given as an example.

218 citations


Journal ArticleDOI
TL;DR: In this paper, an ac technique is described for measuring low-frequency resistance fluctuation spectra with improved sensitivity over dc methods achieved by avoiding preamplifier 1/f noise.
Abstract: An ac technique is described for measuring low‐frequency resistance fluctuation spectra with improved sensitivity over dc methods achieved by avoiding preamplifier 1/f noise. The technique, easily implemented with decade resistors and a lock‐in amplifier, allows the current noise of low‐resistance (r<10 kΩ) specimens to be measured to frequencies below 1 mHz. Use of a center‐tapped, four‐probe specimen geometry allows discrimination between specimen and contact noise and eliminates noise due to bath temperature variations. The technique is demonstrated in use to determine the dependence of the 1/f noise of Cr films on film area. Measurements with simultaneous direct and alternating currents provide means to study the noise of nonlinear devices and frequency‐dependent conductors.

182 citations


Journal ArticleDOI
TL;DR: In this paper, the frequency-dependent specific heat of a liquid over a frequency range exceeding five decades, 0.01-3000 Hz, was measured using a planar heater.
Abstract: We have developed a technique to measure the frequency‐dependent specific heat of a liquid over a frequency range exceeding five decades, 0.01–3000 Hz. The measurement is not performed adiabatically, but rather relies on heat diffusion from a thin, planar heater immersed in the liquid sample. The spectrometer has been used to study organic liquids near the glass transition.

170 citations


Journal ArticleDOI
TL;DR: A high-resolution, time-resolving soft x-ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics as discussed by the authors.
Abstract: A high‐resolution, time‐resolving soft x‐ray multichannel spectrometer (SOXMOS) that permits the simultaneous measurement of emission in two different spectral ranges has been developed and tested extensively for tokamak plasma diagnostics. The basic instrument is a high‐resolution, interferometrically adjusted, extreme grazing incidence Schwob–Fraenkel duochromator. The instrument is equipped with two multichannel detectors that are adjusted interferometrically and scan along the Rowland circle. Each consists of an MgF2 coated, funneled microchannel plate, associated with a phosphor screen image intensifier that is coupled to a 1024‐element photodiode array by a flexible fiber‐optic conduit. The total wavelength coverage of the instrument is 5–340 A with a measured resolution (FWHM) of about 0.2 A when equipped with a 600‐g/mm grating, and 5–85 A with a resolution of about 0.06 A using a 2400‐g/mm grating. The simultaneous spectral coverage of each detector varies from 15 A at the short wavelength limit to 70 A at the long wavelength limit with the lower dispersion grating. The minimum readout time for a full spectral portion is 16 ms, but several individual lines can be measured with 1‐ms time resolution by selected pixel readout. Higher time resolution can be achieved by replacing one multichannel detector with a single channel electron multiplier detector. Examples of data from the PLT and TFTR tokamaks are presented to illustrate the instrument’s versatility, high spectral resolution, and high signal‐to‐noise ratio even in the 10‐A region.

165 citations


Journal ArticleDOI
TL;DR: In this paper, a continuous and stopped flow EPR spectrometer based on a new loop gap resonator operating at the X band is described, where very small amounts of material are consumed in both stopped and continuous flow modes of operation, and dead times on the order of 4 ms for stopped flow and 1 ms for continuous flow are realized with a very narrow age distribution in the sample compartment, and the dead times and, hence, sample age are highly reproducible and independent of viscosity.
Abstract: A continuous and stopped flow EPR spectrometer based on a new loop gap resonator operating at X band is described. The important features of the instrument are: (1) very small amounts of material are consumed in both stopped and continuous flow modes of operation, (2) dead times on the order of 4 ms for stopped flow and 1 ms for continuous flow are realized with a very narrow age distribution in the sample compartment, and (3) the dead times and, hence, sample age are highly reproducible and independent of viscosity due to the use of a positive displacement syringe ram. The performance of the instrument is evaluated using the decay of ascorbate radical generated by Ce(iv) oxidation and reduction of nitroxides by ascorbic acid.

142 citations


Journal ArticleDOI
TL;DR: In this article, a time-of-flight diagnostic for analysis of relatively low-energy ion beams is described, which can provide an alternative to magnetic analysis of ion beams for the determination of ion charge state and beam composition.
Abstract: A time‐of‐flight diagnostic for analysis of relatively low‐energy ion beams is described. The system incorporates several novel features which improve its performance in a number of ways. The technique is simple and can provide an alternative to magnetic analysis of ion beams for the determination of ion charge state and beam composition.

130 citations


Journal ArticleDOI
TL;DR: In this paper, a valve for production of jet-cooled species in a pulsed, long path length (1.2 cm) expansion was described, which produces 150-600μs-duration pulses at repetition rates up to 60 Hz from a nozzle with variable slit width.
Abstract: We describe a valve for production of jet‐cooled species in a pulsed, long‐path‐length (1.2‐cm) supersonic expansion. The valve produces 150–600‐μs‐duration pulses at repetition rates up to 60 Hz from a nozzle with variable slit width, and is suitable for use with corrosive gases and vapors.

119 citations


Journal ArticleDOI
TL;DR: In this article, the design, construction, and performance of a new high-sensitivity dc SQUID magnetometer, covering a circular area of 93mm diameter, is described.
Abstract: The design, construction, and performance of a new high‐sensitivity dc SQUID magnetometer, covering a circular area of 93‐mm diameter, is described. The device, now used routinely in our brain research, comprises seven asymmetric first‐order gradiometers, located on a spherical surface of 125‐mm radius and with the symmetry axis tilted 30° with respect to the vertical. The pickup coil diameter is 20 mm, and the channels are separated by 36.5 mm from each other in a hexagonal array. The overall field sensitivity of the system, measured inside our magnetically shielded room, is 5 fT/(Hz)1/2, mainly limited by the thermal noise in the radiation shields of the Dewar. The optimization of the coil configuration and the measurement system is discussed in detail, and a system to determine automatically the position and orientation of the Dewar with respect to certain fixed points on the subject’s head is described. Finally, some examples of measurements carried out with the new device are given.

Journal ArticleDOI
TL;DR: In this paper, a programmable apparatus for removing surface active trace impurities from surfactant solutions has been constructed and tested, which takes advantage of the contaminants' stronger surface activity and considerably lower content in comparison with the main surface component.
Abstract: Generally, surfactants contain trace impurities that will falsify their adsorption properties enormously. To carry out reliable experiments with surfactant solutions necessitates removing those trace impurities beforehand. A programmed apparatus for removing surface‐active trace impurities from surfactant solutions has been constructed and tested. It takes advantage of the contaminants’ stronger surface activity and considerably lower content in comparison with the main surfactant component. Surface‐active material of the solution to be purified is allowed to adsorb at its surface. After considerable reduction of the solution surface area, the adsorbed material is sucked off from the surface in a definite manner by using a fine capillary. The single operating steps are repeated periodically and automatically until the solution reaches the state of ‘‘surface chemical purity.’’ The apparatus can be utilized for a wide range of different conditions given by the individual surfactant properties simply by changing the operating parameters. The instrument favorably and effectively provides that peculiar grade of surfactant purity necessary for all kinds of fundamental surfactant research and characterization.

Journal ArticleDOI
TL;DR: In this paper, the authors describe a photon counting readout system for microchannel-plate spectrometers that uses a delay line and timing circuit for the wavelength coordinate and a wedge-wedge charge division system for the orthogonal spatial coordinate.
Abstract: We describe a photon‐counting readout system for microchannel‐plate spectrometers that uses a delay line and timing circuit for the wavelength coordinate and a wedge–wedge charge division system for the orthogonal spatial coordinate. A novel zigzag layout allows these two anode patterns to coexist on a common planar substrate and share the charge from each photoevent, thereby simultaneously localizing the photon in each of its two dimensions. Unlike wedge‐and‐strip or resistive anode encoders, the delay line offers a spatial resolution that is relatively independent of the format length. Unlike discrete anode systems, the delay line readout system’s complexity is also independent of the field of view size. These facts make the delay line readout system advantageous in large format detectors. We have assembled a testbed detector having a delay line propagation speed of 2.2 mm/ns and a time resolution of 33 ps FWHM. Ultraviolet testing shows a Gaussian event distribution having a 70 μm FWHM width; the readout system blur contribution is less than 50 μm FWHM.

Journal ArticleDOI
TL;DR: In this article, two innovations have been applied to improve a method developed earlier for the production of field-ion tips, which produces sharper, smaller tips with low-aspect ratio shanks to fulfill the specific needs of scanning tunneling microscopy.
Abstract: Two innovations have been applied to improve a method developed earlier for the production of field‐ion tips. The new technique produces sharper, smaller tips with low‐aspect ratio shanks to fulfill the specific needs of scanning tunneling microscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors used an extraordinary mode reflectometer for determining the density profile of a plasma, but the fact that this mode reflects where its frequency equals the local plasma frequency restricts its use to the region of the density gradient.
Abstract: The use of an ordinary mode reflectometer has already proved to be a good means for determining the density profile of a plasma, but the fact that this mode reflects where its frequency equals the local plasma frequency restricts its use to the region of the density gradient. The extraordinary mode reflectometry investigated here permits the observation of the scrape‐off layer as well as the near‐axis region and in certain conditions also the high magnetic field side of the density profile. It is also shown that this mode requires a range of frequency sweep for measuring a given density profile smaller than the ordinary mode. On the Petula‐B tokamak, the density profile has been measured in 200 μs, its evolution when applying the lower hybrid current drive could be also followed. Since the measurement is particularly sensitive near the reflection point of the wave, it could be used to determine precisely the position of magnetic islands and the fluctuation amplitudes. In addition, the access and place occupied in the vacuum chamber being very small, this diagnostic should be compatible with reactor conditions.

Journal ArticleDOI
TL;DR: In this article, a servomechanism driven variable neutral density filter was proposed to obtain the relative change in the reflectance (transmittance) spectrum of the signal from the detector.
Abstract: We report a new type of normalization procedure for modulation spectroscopy experiments in order to obtain the relative change in the reflectance (transmittance) spectrum ΔR/R(ΔT/T). Our new technique utilizes a servomechanism driven variable neutral density filter which keeps the dc component of the signal from the detector constant by varying the intensity of the light striking the sample. This method is particularly useful for photoreflectance measurements which can have background problems due to scattered pump light and/or photoluminescence. Advantages for other modulation spectroscopies, particularly in the region of the fundamental band gap of semiconductors, also will be discussed.

Journal ArticleDOI
TL;DR: In this article, a pulsed EPR spectrometer is described for the study of relaxation times of dilute solutions of samples in common solvents as a function of temperature both above and below room temperature.
Abstract: A pulsed EPR spectrometer is described. This spectrometer is designed for the study of relaxation times of dilute solutions of samples in common solvents as a function of temperature both above and below room temperature. Resolution of pulse widths and spacings is 1 ns. Both continuous wave (cw) and pulsed electron spin‐echo studies can be done on the same sample on the same spectrometer. Details of component choices and timing synchronization are provided. Phase alternation sequences for eliminating unwanted echoes are described. Examples of performance of the spectrometer are presented.

Journal ArticleDOI
TL;DR: In this paper, the design and construction of a long path cell for absorption measurements at temperatures ranging from 215-470 K and at pressures from vacuum to 10 atm are described.
Abstract: The design and construction of a long path cell for absorption measurements at temperatures ranging from 215-470 K and at pressures from vacuum to 10 atm are described. The cell consists of three concentric stainless-steel tubes; the innermost tube is 6.5-in. in internal diameter, has a volume of about 47 l, and contains White-type optics, six thermocouples, and a gas input tube; and the outermost tube provides a vacuum Dewar around the inner assembly. The optical design and temperature control system for the long path temperature variable cell are examined. The long path cell is applicable for analyzing temperature and pressure dependence of spectra and reaction rates of gases, and the cell has flow and photolysis capabilities for studying transient species and photochemically initiated reactions. A diagram of the cell is provided.

Journal ArticleDOI
TL;DR: In this article, a delay differential equation is used to understand the behavior of feedback and estimate the necessary gain and time constant for the best performance of the scanning tunneling microscope (STM).
Abstract: The theories of the feedback and vibration isolation systems have been developed to illuminate the essential points in the design and operation of the scanning tunneling microscope (STM). By analyzing a delay differential equation, we can understand the behavior of feedback and estimate the necessary gain and time constant for the best performance of the STM. Design considerations for a vibration isolation system consisting of spring suspension and magnetic damping are discussed with theoretical optimization.

Journal ArticleDOI
TL;DR: In this article, the amplitude modulated sinusoidal carrier disturbance was used to produce highly stable droplet streams over a previously unattainable range of wavenumbers, and a decrease in the speed variation of the drops within the stream, which is a result of the amplitude modulation, was demonstrated over a range of non-dimensions from 4 to 4.
Abstract: A recent discovery about a well‐studied phenomenon leads to the formation of ultracoherent streams of liquid drops A remarkably straightforward, although previously unreported, method of drop generation from capillary streams, which involves the imposition of an amplitude modulated sinusoidal carrier disturbance, is discussed The amplitude‐modulated disturbance results in the production of highly stable droplet streams over a previously unattainable range of wavenumbers A decrease in the speed variation of the drops within the stream, which is a result of the amplitude modulation, is demonstrated over a range of nondimensional wavenumbers from 04 to 004 The nondimensional wavenumber is the ratio of stream circumference to disturbance wavelength It is suggested that amplitude modulating the capillary stream’s disturbance may also decrease the diameter variation of the drops

Journal ArticleDOI
TL;DR: HAIFA as discussed by the authors is a modular, multichannel, fiberoptically coupled spectroscopy diagnostic for tokamak plasmas that operates in the visible, measuring Hα radiation, the visible continuum from thermal bremsstrahlung, and selected impurity lines.
Abstract: HAIFA is a modular, multichannel, fiber‐optically coupled spectroscopy diagnostic for tokamak plasmas. It operates in the visible, measuring Hα radiation, the visible continuum from thermal bremsstrahlung, and selected impurity lines. HAIFA is characterized by high modularity and flexibility, good radiation resistance, high noise immunity, and low cost. Details of design, construction, and calibration are given. The analysis of visible bremsstrahlung radiation measurements to deduce the effective ionic charge in a plasma is discussed.

Journal ArticleDOI
TL;DR: In this article, a new method for rapidly acquiring fluorescence spectra from optical probes using an acousto-optic tunable filter (AOTF) was developed, which consists of a piezoelectric transducer bonded to a birefringent crystal.
Abstract: A new method for rapidly acquiring fluorescence spectra from optical probes using an acousto‐optic tunable filter (AOTF) has been developed. The AOTF consists of a piezoelectric transducer bonded to a birefringent crystal. Acoustic waves are generated in the crystal by an applied radio frequency. For a given radio frequency, only a narrow band of optical frequencies will be diffracted. Unlike normal Bragg diffraction which can only be used with collimated light, the AOTF has a large angular aperture (up to 28 deg) and can therefore be coupled to an uncollimated broadband white light source, photomultiplier tube, or camera. Using the device and a xenon–mercury arc lamp, excitation and emission spectra of the fluorescent pH probe BCECF were acquired in 17 ms (spectral resolution=4 nm). Rapid wavelength switching or modulation of selected wavelengths was achieved at ∼105 Hz. The device is also capable of spectral imaging with a spatial resolution of greater than 100 lines/mm.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the design of a scanning tunneling microscope (STM) which is suitable for surface science work and investigate various concepts in mechanical structure and electronic circuitry of the STM to optimize its performance.
Abstract: This article describes the design of a scanning tunneling microscope (STM) which is suitable for surface science work. Various concepts in mechanical structure and electronic circuitry of the STM have been pursued to optimize its performance. This STM has been designed especially to meet the requirement of in situ sample preparation and sample transfer in ultrahigh vacuum. The electronics of this STM are capable of taking simultaneous images with opposite polarities of tunneling voltages.

Journal ArticleDOI
TL;DR: In this article, a scanning tunneling microscope capable of operating at low temperatures, T=400 mK, and in high magnetic fields, B=8 T, is described. And the authors demonstrate the usefulness of spatially resolved spectroscopy in low temperatures and in higher magnetic fields.
Abstract: A scanning tunneling microscope capable of operating at low temperatures, T=400 mK, and in high magnetic fields, B=8 T, is described. Accompanying electronics, under the control of an IBM PC/AT, provide routine spatially resolved spectroscopy, allowing characterization of properties such as superconducting energy gaps and local density of states on the surface. Data are presented to illustrate the usefulness of spatially resolved spectroscopy at low temperatures and in high magnetic fields.

Journal ArticleDOI
TL;DR: In this paper, the authors describe new surface wave launchers intended to sustain plasma columns with high-frequency (hf) power in the range of 1-300 MHz, which complements the existing surface wave plasma generators (surfatron and surfaguide launchers).
Abstract: We describe new surface wave launchers intended to sustain plasma columns with high‐frequency (hf) power in the range of 1–300 MHz. This frequency range complements that of the existing surface wave plasma generators (surfatron and surfaguide launchers), which are best suited to operate in the microwave domain (≳300 MHz). With the addition of this new type of launchers, called Ro‐box, it is now feasible to achieve a surface wave produced plasma column at applied frequencies ranging from 1 MHz to 10 GHz. The possibility of using the same physical hf coupling mechanism (surface wave propagation) over such a broad frequency band is an unprecedented situation with hf produced plasmas. This is of interest for both fundamental and applied physics, as it allows frequency effect investigations and frequency optimization of plasma processes. The new devices can be made so that the wave‐launching and the impedance‐matching functions are physically separated, leading to a modular design, a feature that facilitates c...

Journal ArticleDOI
TL;DR: In this article, a thermal contact with the sample is made via a grease film and a radiation shield is built into the calorimeter to minimize the effect of temperature gradients.
Abstract: A calorimeter is described in which thermal contact with the sample is made via a grease film. Radiation shields built into the calorimeter minimize the effect of temperature gradients. Used in an adiabatic shield system the apparatus gives results of high precision and accuracy. The new design permits easy sample changing but there is a small specific heat anomaly owing to melting of the grease film. An all‐metal water triple point cell can be installed in place of the sample to check the temperature measuring equipment. The adiabatic shield system used had four independently controlled elements. Experiment showed that a single controlled element is sufficient for discontinuous heating calorimetry. The apparatus could be run in both continuous and discontinuous heating modes. There was no significant difference in results. Measurements on pure copper are reported and the use of this material as a specific heat standard up to 300 K is discussed.

Journal ArticleDOI
TL;DR: In this paper, a laser deflection measurement system was developed which is both fast (τ≊20 ns) and sensitive (δφ≊0.5 μrad).
Abstract: A laser deflection measurement system has been developed which is both fast (τ≊20 ns) and sensitive (δφ≊0.5 μrad). This diagnostic is capable of sensing and discriminating between electrons and neutral particles in a multicomponent plasma, and yields quantitative results. The technique allows continuous measurements in time. Construction is inexpensive and simple to field. This system is, therefore, highly competitive with traditional techniques in diagnosing the development of transient plasmas.

Journal ArticleDOI
TL;DR: In this article, two schemes of coupling radio frequency magnetic fields to the spins inside a metal gasket are described, and the relaxation times T1 and T2 of methanol:ethanol solution have been measured to 52 kbar at room temperature.
Abstract: Techniques are presented for NMR measurements at high pressure in a diamond anvil cell. Two schemes of coupling radio frequency magnetic fields to the spins inside a metal gasket are described. As a demonstration of the techniques, the relaxation times T1 and T2 of methanol:ethanol solution have been measured to 52 kbar at room temperature.

Journal ArticleDOI
TL;DR: In this article, a coherent source of XUV light was developed, which is continuously tunable between 904 and 1024 A, and line tunable to 720 A. It employs the technique of frequency tripling in a pulsed free jet of gas, and requires a single tunable laser system.
Abstract: We have developed a coherent source of XUV light, which is continuously tunable between 904 and 1024 A, and line tunable to 720 A. It employs the technique of frequency tripling in a pulsed free jet of gas, and requires a single tunable laser system. Spectra of the relative XUV output vs wavelength in the 904–1024‐A range are presented for the tripling gases Ar, Kr, Xe, CO, and N2. Also listed are relative outputs obtained by tripling at resonantly enhanced lines between 720 and 900 A in Kr, Xe, and CO. Possible improvements to the source are discussed, and examples of its application are given.

Journal ArticleDOI
TL;DR: In this paper, the operation of a Proca and Green type 30° parallel plate electrostatic energy analyzer is modeled in a new manner that permits high-resolution heavy ion beam probe measurements of fluctuating plasma potential.
Abstract: The operation of a Proca and Green type 30° parallel plate electrostatic energy analyzer is modeled in a new manner that permits high‐resolution heavy ion beam probe measurements of fluctuating plasma potential. Systematic calibration procedures permit detection of potential changes smaller than 0.01% of the probing beam energy at frequencies up to a megahertz. Most recent applications of beam probes have made use of this new capability.