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Review of Scientific Instruments

Issue 11 • Date Nov 1982

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Displaying Results 1 - 25 of 38
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Method for measuring specific heats in intense magnetic fields at low temperatures using capacitance thermometry

    Page(s): 1647 - 1652
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    A drift method is described for measuring specific heats in intense magnetic fields at low temperatures. Capacitance thermometry is used, and an automated data‐collection system utilizes the imbalance of a transformer‐ratio‐arm bridge to process the capacitance data. The zero‐field specific heat must be known, and measurement of the in situ drift in zero‐field calibrates the thermal link. Additional calibration of the link is required if the link’s magnetothermal conductivity effects are significant, and a specific example of a copper‐wire link is presented. The method resolves complex structure in the specific heat near a steep λ‐type anomaly, as illustrated by measurements on a chromite spinel at 7.5 T. The uncertainty in the method is estimated to be ≂±7%. View full abstract»

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  • Application of light polarization technique to the generalized line‐reversal method for gaseous temperature measurements

    Page(s): 1653 - 1656
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    The light polarization technique was applied to the generalized line‐reversal method in order to improve the inherently restricted resolution characteristics found in the conventional method using a chopper or a knife wedge, which discriminate the reference lamp light from the gaseous emission either temporally or spatially, respectively. In the proposed method, each of the lights was linearly and perpendicularly polarized and was detected through the same spatiotemporal optical path. The applicability of this method to measure the hot gaseous temperature was confirmed experimentally in a shock tube MHD power generation system. View full abstract»

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  • Dilatometry at low temperatures

    Page(s): 1657 - 1660
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    A dilatometer has been constructed for the routine measurement of thermal expansion coefficients in the temperature range of 0.1–10 K. Using a SQUID detector, the dilatometer provides a resolution of 2×10-4 Å. As a test of this apparatus, the linear thermal expansion coefficient of high‐purity copper has been measured between 0.2 and 9 K. View full abstract»

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  • Fabrication of ultrashort niobium variable‐thickness bridges

    Page(s): 1661 - 1662
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    A simple technique for the fabrication of niobium variable‐thickness bridges of length ∼0.1 μm is described. The bridges are found to operate as ideal Josephson junctions over a wide temperature range. View full abstract»

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  • Electrical properties of an input–output cable for Josephson applications

    Page(s): 1663 - 1666
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    The electrical properties of an 80 signal line microstrip cable for transmitting signals between room‐temperature electronics and cryogenic electronics were calculated and verified. The impedance, propagation velocity, skin effect losses, dielectric losses, forward wave cross talk, and backward wave cross talk were investigated for a copper and polyimide microstrip cable. An effective method of reducing forward wave cross talk was discovered. The microstrip cable has a high signal line density, 19.7 lines/cm, and a high bandwidth, dc‐1 GHz. View full abstract»

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  • High repetition rate mini TEA CO2 laser using a semiconductor preionizer

    Page(s): 1667 - 1669
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    A mini TEA CO2 laser using a semiconductor preionizer is described. The laser will operate at a pulse repetition frequency greater than 5 kHz. At a pulse repetition frequency of 1 kHz a mean power output of 35 W can be maintained over extended periods. Burst mode operation of 104 shots at a pulse repetition frequency of 1.5 kHz can produce mean power in excess of 50 W. View full abstract»

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  • High‐precision tunable infrared reflectometer

    Page(s): 1670 - 1672
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    This report describes a double‐bounce reflectometer operating between 1 and 4 μm. This reflectometer uses the Nernst glower as a source in conjunction with a liquid N2‐cooled InSb detector. Data collection was best accomplished with a noise eliminating sample‐and‐hold system and a low‐noise straight ac amplifier in conjunction with a computer. The reflectometer was evaluated using two samples with different metallic coatings, one aluminum and the other gold. Average absolute reflectance values of 95.059±0.025% for the aluminum sample and 98.088±0.017% for the gold sample were obtained at 3.79 μm at 45° incidence angle. The precision of the reflectometer was better than 0.03% for measurements made over a period of several days. View full abstract»

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  • Observations of sonoluminescence using image intensification

    Page(s): 1673 - 1676
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    A high‐gain image intensifier system has been applied to the study of the light emitted when cavitation occurs in a liquid (sonoluminescence). Observations of sonoluminescence from several different magnetostrictive oscillators show that spatial and temporal distributions can be recorded in a few seconds in cases where recording on conventional film would not be possible. In the present experiments, the spectral transmission properties of the optics precluded recording of the light in ultraviolet. The spatial details of the cavitation process would not be available from photomultiplier records. View full abstract»

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  • Fast transient digitizer system using a TV camera for the measurement of optically induced spin polarization

    Page(s): 1677 - 1681
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    A fast digitizer for single transient analysis is described which is composed of a microcomputer‐based image processor and a TV camera attached to a 1‐GHz oscilloscope. Oscilloscope traces are viewed by a TV camera and displayed on a TV screen in a digitized form. The corrected data can be accumulated at 1.5 s intervals. The system has been used successfully for measurements of nanosecond single transients in a study of optically induced spin polarization. Hardware design, software, and experimental performance are described. View full abstract»

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  • S-100/Z80 microprocessor‐based scanning microdensitometer and signal processing system

    Page(s): 1682 - 1684
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    A S‐100/Z80 8‐bit microprocessor‐based system which is used to digitize, reduce, and smooth picosecond data is described. Utilizing real‐time signal sampling combined with a software‐controlled signal averaging, the system uses, to the maximum extent, all of the information obtainable from the microdensitometer. The versatility of the system, in terms of both the hardware and software, minimized the need for extensive in‐house interfacing and makes it possible to scan a film containing six spectra (6×40K raw data points) in 16 min. The use of a LS1 stepping motor controller chip is described. View full abstract»

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  • Plasma target output from a magnetically augmented, gas‐injected, washer‐stack plasma gun

    Page(s): 1685 - 1692
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    This article describes a new washer‐stack gun design developed for the application of plasma target production for the startup of neutral‐beam trapping in a fusion research magnetic confinement system. The gun is a Mo anode type that is D2 injected and has an auxiliary pulsed magnet for control of plasma‐flux mapping. One of the principal features of 2–10‐ms duration pulses for gun operation in a suitable magnetic field is the formation of an arc column along magnetic field lines from the gun’s central cathode electrode to the vacuum chamber walls (at common anode potential). The primary power output from a 5.0‐cm‐i.d. gun is typically carried along this arc column by a stream of approximately 2000 A of 50–250‐eV electrons. This primary stream of relatively low‐density energetic electrons efficiently ionizes the injected gas, forming a quasi‐dc source of denser secondary plasma of ∼1013/cm3 at a few eV, which is able to flow or diffuse away along a somewhat larger column of magnetic field lines. In plasma‐target production tests on a test stand, a gun operated at a D2 gas flow of 22 Torr ls-1 yielded 250 A of equivalent plasma flow. View full abstract»

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  • Comparison of two types of antennas for plasma heating

    Page(s): 1693 - 1695
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    The ability of a quadrupole coil, an antenna, of new design for the production of high‐energy protons in a plasma has been compared experimentally with that of a conventional wraparound coil. The energies of the protons in the escape cone of a magnetic bottle were measured by a Faraday cup. The antennas were placed alternately midway between the two solenoids and operated in resonance under similar conditions. Proton energies of 380 eV were attained with the new quadrupole coil, a value more than twice that obtained by the wraparound coil. Thus, the new coil is judged superior for the purpose of ion cyclotron resonance heating. View full abstract»

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  • Low‐energy neutral atom spectrometer

    Page(s): 1696 - 1708
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    The design, calibration, and performance of a low‐energy neutral atom spectrometer are described. Time‐of‐flight analysis is used to measure the energy spectrum of charge‐exchange deuterium atoms emitted from the PLT tokamak plasma in the energy range from 20 to 1000 eV. The neutral outflux is gated on a 1‐μs time scale by a slotted rotating chopper disc, supported against gravity in vacuum by magnetic levitation, and is detected by secondary electron emission from a Cu–Be plate. The energy dependent detection efficiency has been measured in particle beam experiments and on the tokamak so that the diagnostic is absolutely calibrated, allowing quantitative particle fluxes to be determined with 200‐μs time resolution. In addition to its present application as a plasma diagnostic, the instrument is capable of making a wide variety of measurements relevant to atomic and surface physics. View full abstract»

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  • Graphical analysis method for a retarding potential analyzer and its application to the real‐time measurements of ion temperature in space plasmas

    Page(s): 1709 - 1713
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    In order to obtain the ion temperature from a voltage‐to‐current characteristic of a retarding potential analyzer (RPA) in a drifted density (106 1/cc), low‐temperature (1 eV) plasma such as an ionospheric plasma, optimum fitting procedures using the digital computer have been used. But these methods must take a lot of time to search the parameters. A graphical method using the sampling of a RPA curve has been developed to obtain the ion temperature quickly. Many diagrams were drawn by calculation to determine the ion temperature. This method is suitable not only for the processing of a large quantity of data but also for the in‐flight data analysis aboard a sounding rocket. By the use of feedback control circuits, ion temperature data could be obtained at a ratio of several tens per second in the ionosphere, where the mass of the ion M varies slowly. The accuracy of this method and the effect of variations of M, angle of attack Θa, and drift velocity v0 is discussed. Also the efficacy of this method is confirmed. This method was examined in the ionosphere aboard a rocket whose velocity was about 2 km/s. The ion temperature data obtained are compared with those obtained by the usual optimum fitting procedure. View full abstract»

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  • Supersonic nozzle beam source of atomic oxygen produced by electric discharge heating

    Page(s): 1714 - 1718
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    An atmospheric pressure supersonic nozzle beam source of atomic oxygen is described. Dissociation of molecular oxygen is accomplished by injection into a flow of helium and/or argon which has been heated in a commercial plasma torch. Dissociation efficiencies approaching unity are achieved with beam velocities in the range of 1.5–4.0 km s-1. Production of rare gas metastable and electronically excited oxygen species are minimized by the source design. View full abstract»

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  • Infrared laser spectroscopy of molecular beams using a room‐temperature beam detector: Application to the study of translational freezing in free‐jet expansions

    Page(s): 1719 - 1723
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    A simple and inexpensive alternative to the liquid He bolometer for observing laser induced vibrational excitation in molecular beams is reported. A room‐temperature pyroelectric detector is used to directly measure the increase in molecular energy resulting from laser excitation. With this detector, line broadening effects have been used to study translational freezing in free‐jet expansions. View full abstract»

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  • High‐pressure–low‐temperature apparatus for NMR study of phase transitions

    Page(s): 1724 - 1726
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    An apparatus has been developed for nuclear‐magnetic‐resonance (NMR) measurement of relaxation times in solids at hydrostatic pressures to 7 kbar and temperatures down to 77 K. Sample temperature can be controlled accurately with ±2 mK stability allowing measurement of dynamic phenomena very near phase transitions. The high‐pressure vessel is equipped with additional electrical feedthroughs so that dielectric measurements can be carried out concurrently, providing additional information on ferroelectric phase transitions. View full abstract»

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  • Balanced cavity scheme for saturation transfer dispersion electron paramagnetic resonance

    Page(s): 1727 - 1729
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    Dispersion electron paramagnetic resonance (EPR) suffers from high AM noise levels due to discrimination of FM noise from the klystron by the high Q cavity. If the EPR cavity is placed in one arm of a magic tee, and a similar cavity in the other arm, then this noise can be removed by arranging the two (correlated) noise components to cancel. Signal‐to‐noise ratio improvements of a factor of 40 are easily attainable. Only minor modifications to commercial instruments are required. View full abstract»

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  • Phase‐locked heterodyne receiver and its application to lower hybrid wave detection by microwave scattering

    Page(s): 1730 - 1737
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    The frequency stabilized, low‐noise heterodyne receiver is developed for microwave scattering measurements in a plasma. Its application to the observation of a lower hybrid wave (LHW) externally excited in a linear test plasma is demonstrated. The frequency fluctuation of 70 GHz klystrons employed for scattering measurements is stabilized by the phase‐locked loop. The frequency resolution of the receiver is about 10 kHz and its noise equivalent power is about 7×10-19 W/Hz, corresponding to the minimum detectable density fluctuation ñe/n¯e=6×10-5 under present experimental conditions. By the scattering of 70 GHz millimeter waves using this heterodyne receiver, LHW externally excited by the helical antenna can be detected. The spatial intensity distribution and the wave number spectrum of the scattered power are obtained. These observations make clear not only the magnitude, but also the direction of the wave number of the excited wave. The observed wave numbers in the several scattering positions over the plasma cross section are almost in the radial direction but not always consistent with the theoretical expectations. Their magnitudes are close to those determined from the auxiliary measurements using an electrostatic probe. The density fluctuation obtained from the absolute value of the scattered power is about ñe/n¯e=5×10-4. The theoretical estimation gives ñe/n¯e=2×10-3. View full abstract»

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  • Zero‐field pulsed spin echo spectrometer for the study of ferromagnetic materials

    Page(s): 1738 - 1742
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    Complete description of a pulsed nuclear‐magnetic‐resonance spectrometer operating in the frequency range 100–600 MHz is presented. The spectrometer is suitable for investigating hyperfine fields in ferromagnetic materials and has some novel features. High sensitivity, simplicity of operation, and ease of tuning over the entire frequency interval are some significant characteristics of the spectrometer. View full abstract»

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  • Frequency‐modulated coil sensor for magnetic suspensions

    Page(s): 1743 - 1745
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    A FM coil sensor using digital electronics is described here for use as a position transducer in a magnetic suspension. This is similar to the Q‐coil method of Beams et al. [Rev. Sci. Instrum. 33, 151 (1962)] as used in magnetic suspensions except that a different parameter is being controlled. The circuits are presented and their operating characteristics are discussed. View full abstract»

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  • Slot‐effect electrometers with monopolar electrets

    Page(s): 1746 - 1748
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    Slot‐effect electrometers with monopolar electrets as active elements are, in several aspects, superior to similar electrometers with bipolar electrets. In particular, the sensitivity of electrometers with monopolar electrets does not depend on the electret thickness and on the electret–electrode gap. Therefore, monopolar foil electrets can be used in such meters, and the electrometers can be constructed with less precision than when bipolar electrets are used. Two prototype electrometers are described: one with a disk‐shaped electret, the other with a cylindrical electret. The sensitivity of the former is 1000 V or 10-7 C per full‐scale deflection, that of the latter is 100 V or 10-9 C per full‐scale deflection. View full abstract»

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  • Automatic capacitance–voltage (C–V) plotter for solar cells

    Page(s): 1749 - 1753
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    An instrument is described which measures the capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of solar cells in the dark and under illumination and other semiconductor junction devices in the capacitance range of 2–200 000 pF. The instrument is also provided with the facility for DLTS measurements. View full abstract»

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  • Movable target assembly for diode sputtering system

    Page(s): 1754 - 1756
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    A decrease in the energy of sputtered atoms may be accomplished by either altering the gas pressure or the target‐substrate distance. Increased gas pressure is sometimes accompanied by a deterioration in the quality of the deposited film. To offset this negative aspect, a movable cathode assembly with external control and direct measurement of separation distance has been designed and employed for the rf sputtering of SiC. View full abstract»

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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