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Review of Scientific Instruments

Issue 1 • Date Jan 1983

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Displaying Results 1 - 25 of 28
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Measurement of low‐temperature specific heat

    Page(s): 1 - 11
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    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. View full abstract»

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  • Technique for determining second‐sound attenuation near the superfluid transition in 4He

    Page(s): 12 - 15
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    A procedure has been developed to measure the attenuation of second sound in liquid helium at temperatures near Tλ. The decay rate of a second‐sound resonance in a high‐Q cavity is determined, and data for more than one harmonic is obtained allowing the separation of the attenuation due to bulk fluid from losses at the cavity walls. This method has proven particularly successful near Tλ, where the second‐sound velocity is strongly dependent on temperature and a high degree of temperature stability is needed. Results are given for the temperature range 40 μK≪Tλ‐T≪40 mK at saturated vapor pressure. With minor modifications the apparatus can be used for measurements at elevated pressure and over a much wider range of temperatures. View full abstract»

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  • Inductive technique for measuring critical current densities in thin‐film superconductors

    Page(s): 16 - 20
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    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. View full abstract»

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  • Procedures for determining the critical parameters of fluids

    Page(s): 21 - 25
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    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. View full abstract»

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  • New approach to the measurement of the thermal conductivity of electrical conductors

    Page(s): 26 - 28
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    A novel method for measuring the thermal conductivity of an electrical conductor is described. The heat flow is radial, giving important advantages for high‐temperature studies. It is an electrical method and is, therefore, most suited to resistive materials which have a high temperature coefficient of resistance, such as semiconductors. Since the outside temperature of the sample need not be determined directly, and the sample is best kept thin, the method holds promise for studies of liquids, especially where convection problems have occurred in the past. In many of these aspects, the proposed method works best where the conventional axial guarded heat flow method fails. View full abstract»

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  • Self‐emissive probes

    Page(s): 29 - 34
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    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. View full abstract»

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  • Multipoint Thomson scattering

    Page(s): 35 - 40
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    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. View full abstract»

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  • Ion‐extraction performance of the circular magnetic‐multipole bucket ion source applied for the neutral beam injection system of the Heliotron E machine

    Page(s): 41 - 45
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    The ion‐beam extraction performance of the 30‐kV–35‐A circular magnetic‐multipole bucket ion source applied for the neutral beam injection system of the Heliotron E fusion machine has been investigated with special reference to ion‐beam optics. By using the numerical simulation code for the cylindrical ion‐extraction system, the computational beam‐divergence angles have been compared with the experimental data. The experiments show that the applied three‐electrode beam optics are satisfactorily stable against source‐plasma variation and that the minimum beam‐divergence angle is less than 1.15 deg. The obtained optimal perveance of the ion source is nearly 6.3×10-6 (A/V3/2), and the experimental optics behavior is in reasonable agreement with the numerical prediction. On the basis of the experiments, the effect of the edge angle of the first beam‐forming, high‐potential electrode is also discussed. The experiment suggests that the obtuse angle (∼73°) for that edge is preferable to the acute angle (∼30°). View full abstract»

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  • Electron beam probe for charge neutralization studies of heavy ion beams

    Page(s): 46 - 49
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    The design and operation of an electron beam probe for ion beam diagnostics is described. Advantages of this method for the analysis of space‐charge neutralization studies are discussed and examples of its applications to heavy ion beams are shown. View full abstract»

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  • Reduction of the impurity concentration of an intense hydrogen ion beam

    Page(s): 50 - 55
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    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%. View full abstract»

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  • Extraction of volume‐produced H- ions from a multicusp source

    Page(s): 56 - 61
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    H- ions formed by volume processes are extracted from a multicusp ion source. It is shown that a permanent magnet filter together with a small positive bias voltage on the plasma grid can produce a very significant reduction in electron drain as well as a sizable increase in H- ions available for extraction. A further reduction in electron current is achieved by installing a pair of ceramic magnets at the extraction aperture. The combined arrangement improves the ratio of extracted H- ion current to electron current to about unity. View full abstract»

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  • New operation mode of a microchannel plate for the detection of low‐energy positive ions

    Page(s): 62 - 64
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    The gain characteristics of a microchannel plate (MCP) operated in the reflection mode are measured for positive ions with energies between 100 and 300 eV. Singly charged alkali ions emitted thermionically are used as the incident ions. The gain in the reflection mode is found to be higher than that in the conventional transmission mode. A preacceleration for the penetrating ions into the channels is responsible for the high gain obtainable. This result suggests the potential usefulness of a MCP operated in the reflection mode for the detection of low‐energy positive ions. View full abstract»

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  • Multiplexers for acquiring data in molecular beam laser depletion experiments

    Page(s): 65 - 67
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    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. View full abstract»

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  • Spectrometer for momentum‐resolved bremsstrahlung spectroscopy

    Page(s): 68 - 75
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    A spectrometer for momentum‐resolved and polarization‐dependent bremsstrahlung spectroscopy (inverse photoemission) in the vacuum UV range is described and the performance of the apparatus is discussed. A Seya–Namioka monochromator combined with a position‐sensitive channel plate device for parallel detection of a wavelength range of 165 Å is used as a photon detector and covers an energy regime from 10 to 40 eV with a resolution of 5 Å. Due to the polarization‐dependent reflectivity of the gold‐coated gratings, the monchromator is also inherently an analyzer for the polarization of the detected light. A space‐charge‐limited Pierce‐type electron gun comprising a BaO dispenser cathode is used as an electron source with 0.1‐Å-1 momentum resolution. The overall energy resolution of the apparatus is 0.3 eV at 20 eV photon energy. The sensitivity is 1.8×104 counts per Coulomb and eV for the unoccupied s, p bands of a polycrystalline gold sample. View full abstract»

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  • Fast chopper for time‐resolved resonant fluorescence spectroscopy

    Page(s): 76 - 79
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    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. View full abstract»

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  • Application of a personal computer for control and data acquisition in an Auger electron spectrometer

    Page(s): 80 - 84
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    A digital system was designed to control a Varian Auger spectrometer to perform automatic data acquisition and data reduction. It is based on the Apple II personal computer. The advantages of the system are: low cost, simple design and construction of interface circuits, and great flexibility and power for different setups. A detailed description is given for the interface circuits, the analog‐to‐digital converter, and the digital‐to‐analog converters. Finally, it is discussed how to make changes in the original design to suit different needs. View full abstract»

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  • Laser interferometer for measuring microwave‐induced motion in eye lenses in vitro

    Page(s): 85 - 89
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    A system was designed to optically measure the physical motion induced by a microwave pulse on a rat eye lens immersed in saline. After consideration of several possible techniques, a Michelson interferometer using a HeNe laser and normal reflection from the lens surface was constructed. The system uses wavefronts matched to the curved lens surface, a vibrating reference mirror for calibration and signal discrimination, a sample chamber mechanically isolated from the microwave waveguide, and a fast photodetector and signal averager. A rotatable half‐wave plate and two polarizers were used to smoothly vary the intensity of the reference beam while maintaining the spatial integrity of its wavefronts. The system was able to measure motion down to 2 nm and performed successfully in the microwave pulse exposure experiments. View full abstract»

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  • Interferometric measurements of very small electrostrictive strains

    Page(s): 90 - 92
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    Electrostrictive dilatations in the order of 10-13 m are measured in dielectric crystals by an interferometric method based on the Michelson interferometer. The electrostriction constants γ1111 of quartz, diamond, and LiF are found to be (-0.6±0.2), (+0.17±0.03), and (-7.9±0.8) 10-21m2/V2, respectively. View full abstract»

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  • Visualization of evaporative convection in minute drops by laser shadowgraphy

    Page(s): 93 - 96
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    A very simple optical procedure is developed to investigate the morphology of natural convection and the dynamic behavior of drops evaporating on a plate by means of a laser shadowgraphic system. This method is the only nonintrusive means of visualizing flow patterns in a time‐varying ‘‘lens’’ shaped system. Its uniqueness and superiority are discussed. View full abstract»

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  • New pulsed laser data‐acquisition system

    Page(s): 97 - 99
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    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. View full abstract»

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  • Computer‐controlled method for removal of stray magnetic fields

    Page(s): 100 - 103
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    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. View full abstract»

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  • Rapid‐sampling system for dusts and gases

    Page(s): 104 - 108
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    The Bureau of Mines has developed a system for the rapid grab sampling of heterogeneous mixtures of gases and dusts during the preignition and postignition stages of dust explosions. The combustion chamber in which the explosion occurs is first fitted with a hypodermic sampling needle with its inlet end at the desired sampling point within the chamber and its sharp, injecting end protruding outside of the chamber. Rapid sampling (approximately 25 to 50 ms) is achieved with a double‐acting, air‐pressure‐actuated cylinder. The forward stroke of the cylinder thrusts the rubber septum seal of an evacuated glass sampling tube onto the protruding needle which punctures the septum, filling the tube with gas and dust from the combustion chamber. The return stroke of the cylinder reseals the sampling tube by returning the mechanism to its original position. The initial time of sampling and the duration of sampling are independently variable and controlled by a microprocessor. Results obtained with a trimodal distribution of coal dust show no significant size discrimination at least up to 70 μm. Data obtained from laboratory‐scale coal dust explosion tests are also presented. Such data provide valuable insights into the basic phenomena involved in explosions. View full abstract»

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  • Localized metallic melting and hole boring by laser guided discharges

    Page(s): 109 - 113
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    We demonstrate a new technique for localized melting and boring of materials using discharges guided by laser induced breakdown of atmospheric pressure air. This technique has important applications to a novel method for machining and welding materials, since the melting location can be controlled by adjusting the path of the focused laser beam. These experiments have demonstrated several features of localized metallic melting by laser guided discharges: (1) the melted spot can be scanned by changing only the position of the laser focal spot on the metal sample; (2) the melted spot diameter and profile depend upon the relative timing of the laser pulse and the discharge; (3) defocusing the laser beam has an effect upon the melted spot pattern; and (4) hole boring has been accomplished in aluminum foils which cover the stainless‐steel electrode. View full abstract»

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  • Laser system for two pulse and multiple position Thomson scattering

    Page(s): 114 - 115
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    We developed a special laser system for two pulse (about 100 ms interval) and multiple position (10 different points) Thomson scattering. A special feature of this laser system is that the beam quality is improved by adjusting the condition of the cavity wall. For two pulses, the power supplies are doubled and thyristor switches are used. View full abstract»

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Aims & Scope

Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Editor
Albert T. Macrander
Argonne National Laboratory