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Review of Scientific Instruments

Issue 11 • Date Nov 1984

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Displaying Results 1 - 25 of 44
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Fast scanning heterodyne receiver for the measurement of the time evolution of the electron temperature profile on the Tokamak Fusion Test Reactor

    Page(s): 1739 - 1743
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    Two fast scanning heterodyne receivers, swept between 75–110 and 110–170 GHz in 2 ms every 4 ms, were developed to measure the electron cyclotron emission on the horizontal midplane of the Tokamak Fusion Test Reactor (TFTR) plasma. An absolute, in situ calibration technique enables the determination of the profile of the plasma electron temperature from the cyclotron emission intensity. The 4‐ms repetition rate of the receiver allowed the resolution of ‘‘sawtooth’’ fluctuations of temperature, whose period was 10–100 ms, in profiles with central temperatures of 1–2.5 keV. View full abstract»

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  • Neutralization of multi‐MeV light negative ions by plasma neutralizers

    Page(s): 1744 - 1747
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    A hollow cathode discharge fed plasma neutralizer has been built and was used to neutralize 3‐MeV Li-, C-, and Si- ions. Initial results indicate that the performance of an unoptimized plasma neutralizer is better than gas stripping. Since hollow cathodes produce plasma targets with high efficiency, this type of plasma neutralizer can improve the overall efficiency of a neutral beam line. View full abstract»

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  • Barium ion beam probe for magnetic field, diamagnetism, and space potential measurement in plasmas

    Page(s): 1748 - 1755
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    A diagnostic has been developed to simultaneously determine the magnetic field and space potential in fusion‐like plasmas. Initial tests have demonstrated the ability to measure an absolute change of 17 G in the magnetic field strength; under the same test conditions a 6‐V change in space potential could have been detected. The spatial resolution in these tests is a volume of 0.25 cm3. The magnetic field is determined by a measurement of the Zeeman resonance absorption pattern with a frequency scanning narrow‐band laser of an energetic (≪50 keV), low current (∼10 μA) barium ion beam. The laser is injected tangentially to the ion beam to take advantage of the narrow Doppler spread in the direction of the beam. Space potentials are determined by a measurement of the Doppler shift due to a change in beam energy E=E0-eφ. The diagnostic will be used initially on the TRW STM device to measure diamagnetic depression of the ELMO rings in STM. View full abstract»

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  • Absolute and angular efficiencies of a microchannel‐plate position‐sensitive detector

    Page(s): 1756 - 1759
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    This paper presents a characterization of a commercially available position‐sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position‐encoding anode. The work includes measurement of absolute efficiencies of H+, He+, and O+ ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector. View full abstract»

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  • Metal ion source using rf discharge combined with sputtering

    Page(s): 1760 - 1762
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    An ion source capable of producing a wide variety of ion species from elemental materials is described. Ion beams of metals can be produced by sputtering a disk, made of the materials to be ionized, placed on the cathode. In order to raise the rate of ionization of the sputtered materials an rf discharge is superimposed on the dc sputtering. Ions of refractory metals, such as Nb, can be easily produced without using halides. View full abstract»

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  • Large capacity As2 source for molecular beam epitaxy

    Page(s): 1763 - 1766
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    Molecular beam epitaxy (MBE) is a crystal growth technique capable of growing ultrathin layered heterostructures for basic studies, and devices such as modulation doped field‐effect transistors (MODFET’s), heterojunction lasers, heterojunction bipolar transistors (HBT’s), and superlattices. By using a dimeric arsenic source to grow GaAs and AlGaAs layers, the crystalline quality of these devices and structures may be improved, ultimately improving device performance. The design of a novel large capacity effusion cell (capable of producing about 700 μm GaAs growth) for cracking tetrameric arsenic into dimeric arsenic and the results of its use are described. View full abstract»

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  • Novel ion acceleration tube design

    Page(s): 1767 - 1770
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    This paper describes a 280‐kV constant‐gradient positive‐ion acceleration tube in which the interelectrode voltage is established with a voltage divider chain of resistors that is mounted inside the vacuum of the tube. A single glass pipe serves as the vacuum envelope, flat aluminum disks are used for the tube electrodes, and resistance‐paint‐coated plastic cylinders compose the voltage divider chain. These construction features simplify tube construction and keep manufacturing costs low. During high‐voltage tests, interelectrode voltage was estimated to deviate less than ±6% from uniformity, heat was adequately dissipated from the vacuum‐mounted resistors, and the maximum design acceleration voltage of 280 kV was held. Furthermore, preliminary ion acceleration trials yielded from 0.7 μA of N+2 at 50 kV to 1.5 μA at 280 kV. The accelerated‐beam cross section, as viewed on a ground quartz screen, remained stationary during those trials, indicating that the tube configuration provided adequate shielding of the beam from asymmetric charges on the interior insulating walls of the tube. View full abstract»

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  • Pulsed laser‐induced thermal desorption from surfaces: Instrumentation and procedures

    Page(s): 1771 - 1776
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    Instrumentation and procedures for performing pulsed laser‐induced thermal desorption experiments are described. The influence of various instrumental parameters on the measured desorption signals is discussed. Proper conditioning of the desorption flux is shown to be a critical factor for obtaining desorption signals undistorted by the finite pumping speed of the apparatus. Instrumental effects are illustrated using data for pulsed laser desorption of CO from clean copper surfaces. View full abstract»

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  • Low‐cost CO2 laser beam profile monitor

    Page(s): 1777 - 1778
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    Construction and performance of a low‐cost easy‐to‐build CO2 laser beam profile monitor are described. Its specifications correspond to those of commercial devices. In this monitor a small slit covered by a temperature dependent fluorescent surface is imaged on a photodiode. A rotating mirror scans the spatial intensity distribution over the slit. This allows one to avoid an expensive photodiode array. The signal‐to‐noise ratio is improved by repetitive sampling with a low‐cost digital processing unit. The dynamic range of measurement is 7 to 1 and the linearity is 10% within this range. View full abstract»

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  • Numerical calculation of the temperature evolution and profile of the field ion emitter in the pulsed‐laser time‐of‐flight atom probe

    Page(s): 1779 - 1784
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    The temperature evolution and profile of metal field ion emitters under pulsed laser irradiation are solved numerically using an implicit alternating direction method. The temperature profile along the emitter axis at selected times and the temperature evolution curve at the emitter apex during and after the pulsed‐laser irradiation have been obtained. This numerical result shows that the emitter can cool down from the peak temperature by ∼20 K in less than 5 ns, and the heated region is very much localized to the irradiated part of the emitter. The cooling rate is higher for specimens of larger thermal diffusivity, and also if the laser pulse width is narrower and the laser heating is better localized. The peak temperature of the tip apex reached depends almost linearly on the incident flux of the laser beam. View full abstract»

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  • Dynamic observation of surfaces by scanning Auger electron microscopy: A motion picture technique

    Page(s): 1785 - 1787
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    The dynamic observation of surfaces has been developed by using a scanning Auger electron microscope (SAM). The images of Auger and secondary electrons are photographed continuously with a 16‐mm movie camera. Each frame is photographed for very short time exposures of 24 to 48 s for the Auger and 3 s for the secondary electrons. Particular logic circuits to control the system were made providing for the rejection of the secondary electrons ejected by the ions and for the photons from the filament of the ion gun which greatly degrade the images. View full abstract»

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  • Real‐time area‐tracker records cellular volume changes from video images

    Page(s): 1788 - 1790
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    High‐contrast TV images of living cells are recorded from a light microscope. The video line signal is converted to binary and used to gate a 12.5‐MHz clock driving a counter. After completion of each video frame the accumulated counts (proportional to the dark image area) are written onto a stack (FIFO) before the counter is reset. Thus, area information is actualized at a rate of 50 values per second and can be read out at speeds suitable for computer interfacing and (after D/A conversion) oscilloscope displays or paper chart recording. With two counting channels the time course of two areas of distinctly different gray shades can be recorded at once. View full abstract»

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  • Laser‐heated miniature pedestal growth apparatus for single‐crystal optical fibers

    Page(s): 1791 - 1796
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    We have designed and built a single‐crystal fiber growth apparatus. The apparatus employs novel optical, mechanical, and electronic control systems that enable the growth of high optical quality single‐crystal fibers. We have grown oriented single‐crystal fibers of four refractory oxide materials, Al2O3, Cr:Al2O3, Nd:YAG, and LiNbO3. These materials exhibit similar growth characteristics and yield fibers of comparable quality. Fibers as small as 20 μm in diameter and as long as 20 cm have been grown. Measured optical losses at 1.06 μm for a 10‐cm‐long, 170‐μm‐diam Cr:Al2O3 fiber were 0.074 dB/cm. View full abstract»

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  • Manual/automated I–V system for analyzing solar cells

    Page(s): 1797 - 1803
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    A measurement system for the current–voltage characterization of solar cells has been developed. The instrument is based on an Intel 8088 microprocessor, which allows for enhanced data collection and storage, as well as automated measurement control. A high‐power analog supply makes measurements in the range of -10 to +10 V and -0.75 to 0.75 A possible, and provides the capability for sinking currents up to 1 A at +10‐V output. Measured data may be transferred to an IBM personal computer for immediate display, and for consequent analysis (to obtain the characteristic parameters). The system provides a rapid, effective I–V curve measurement and analysis method for many devices, and experimental solar cells in particular. View full abstract»

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  • Simple carrier modulation system for minimizing low‐frequency noise modulation of synchrotron orbital radiation

    Page(s): 1804 - 1808
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    An analysis of the frequency distribution of noise of two synchrotrons (CHESS and SSRL) indicates significant increases of noise at frequencies below 10 Hz. Noise energy distributions above 10 Hz and extending through 200 Hz indicate significant regions of noise distributions relatively independent of frequency, presumably ‘‘white noise.’’ We report tests of two carrier modulation systems in which the ratio (or difference) of a reference signal and measure signal is computed. In one case, the reference and measure sample are alternated at equal intervals, for example, where difference spectroscopy is required. In another version, the measure signal is periodically interrupted by the reference signal at a duty ratio of 10%–15%, thereby maintaining high efficiency of measure signal detection. When using a 10‐Hz oscillator for reference and measure samples, the improvement as observed on beam line A‐3 at CHESS over the ‘‘single‐ended’’ signal is 10‐ to 20‐fold in the nonscanning mode. In the case of a vibrating reed modulator, the signal‐to‐noise ratio at a count rate of 6×105 per s is equal to the statistical limit to within the error of calculation. The improvement over a conventional fluorescence signal to ionization chamber output ratio F/I0 is over tenfold. Application of these modulation techniques to a variety of detectors is included. View full abstract»

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  • A simple high‐performance high‐resolution electron energy‐loss spectroscopy system

    Page(s): 1809 - 1813
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    A simple spherical analyzer combination suitable for use in high‐resolution electron energy‐loss spectroscopy (HREELS) is described. The system is designed to be intrinsically insensitive to extraneous magnetic fields. The problems presented by the control of the spectrometer are also discussed and the advantages of Fourier filtering demonstrated. View full abstract»

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  • Three‐circle goniometer for electron‐paramagnetic‐resonance measurements

    Page(s): 1814 - 1816
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    A three‐circle goniometer for a large‐hole electron‐paramagnetic‐resonance (EPR) cavity is described which, by a very simple operation, enables us to rotate the crystal around arbitrary direction parallel to the static magnetic field, by rotating a sample holder about a redundant (or the third) axis accommodated in a spur and crown gear. By comparing not only the observed resonance field with the calculated one, but also the absorption intensity with the transition probability, the quantitative determination of the concentration of the unpaired electron center in a single crystal is possible. View full abstract»

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  • Stand‐alone pulse‐echo‐overlap facility for ultrasonic wave transit time measurements

    Page(s): 1817 - 1822
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    A completely stand‐alone pulse‐echo‐overlap system which can be easily built using commercially available integrated circuits is described. The system uses a broadband pulse to excite the transducer. The equipment is relatively cheap and yet the sensitivity of the transit time (and, hence, velocity of sound measurement), is made high by making use of a digital frequency synthesizer of 0.01‐Hz resolution, specially constructed for this purpose. Except for the oscilloscope the instrument does not require any other equipment for its operation. View full abstract»

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  • Continuous gaseous ammonia analyzer by gas titration method

    Page(s): 1823 - 1826
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    A new instrument for simply and rapidly determining an ammonia concentration in a gaseous mixture has been developed. The principle is based on the fact that ammonia reacts with NO exactly at 1:1 mole ratio in the presence of an appropriate catalyst: NH3+NO+ 1/4 O2=N2+ (3)/(2) H2O. A sample gas containing NH3 is mixed with NO and made to contact with a catalyst capable of promoting reaction of NH3 and NO to form N2 and H2O in an oxidative atmosphere at an elevated temperature, preferably, 300°–400 °C. The catalyst capable of conducting the reaction is composed of TiO2 and at least one of the oxides of V, Fe, Cu, W, Mo. The concentration of NH3 is determined by measuring concentrations of NO before and after the reaction and calculating the consumption of NO. For the analysis of NO in the gas, a chemiluminescence‐type analyzer can be preferably used. According to the present method, ammonia in a sample gas can be analyzed within a few minutes without any influence of various coexisting gas components. View full abstract»

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  • Dynamic measurement of ultramicro amounts of gases with an ionization gauge

    Page(s): 1827 - 1830
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    A nude ionization gauge adjacent to the closed ion‐source chamber of a quadrupole mass spectrometer is a sensitive detector of the total amount of gas introduced for dynamic analysis. Linear relations between the amount of gas and the area of the ionization gauge pulse record were found for eight gases. For relatively unreactive gases, linearity extended to the smallest samples that could be detected, approximately 10-10 atm cm3. Validity of the dynamic method of analysis was established by demonstrating that the same response was obtained for pulsed and for continuous sample introductions from calibrated leak sources of each of the eight gases. View full abstract»

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  • Versatile zone refiner for liquids and low‐melting solids

    Page(s): 1831 - 1833
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    A versatile zone‐refining apparatus which employs liquid nitrogen as the refrigerant to maintain the compound to be purified in the solid state while appropriately spaced resistance heaters generate the moving liquid zones to purify compounds whose melting point lies between 200 and 350 K is described. As much as 0.750 kg of substance can be purified at one time to a purity better than 99.95 mole %. View full abstract»

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  • High‐power electron‐beam controlled switches

    Page(s): 1834 - 1840
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    The application of an electron‐beam controlled diffuse discharge to high‐power (≫109 W), repetitive opening switches is analytically formulated under a set of assumptions. Basic physics considerations are combined with energy transfer requirements to obtain analytical estimates of the e‐beam controlled switch parameters for given circuit requirements. The switch design is optimized by minimizing the switch pressure subject to the constraint of system efficiency. The result of this optimization is that each of the major energy losses—conduction, opening, and electron‐beam production—are roughly equal to each other. This formulation is used to relate the switch parameters to the desired operating characteristics for an arbitrary number of pulses. As an example, the formalism is utilized in outlining the design of a single pulse, high‐power (≂1010 W) inductive storage system. A judicious choice of gas or gas mixture results in desirable changes in the system design or efficiency. View full abstract»

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  • Miniature solenoid for the production of confined magnetic flux

    Page(s): 1841 - 1842
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    For experiments involving SQUID’s it is sometimes desirable to have a small source of confined magnetic field in order to provide a dc or rf flux bias. This has been done by closely winding ♯50 AWG copper wire on a 250‐μm‐diam optical fiber. The resulting solenoid is very small and has excellent mechanical and electrical properties at 4 K. View full abstract»

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  • Microcomputer‐based system for control of applied uniaxial stress and magnetic field

    Page(s): 1843 - 1848
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    A system is described which allows on‐line control of uniaxial stress and magnetic field for the investigation of the magnetic properties of materials under stress. This has been of considerable importance in studies of the properties of samples of steel, in particular the investigation of ferromagnetic hysteresis and the magnetomechanical effect. As a result, exact algorithms for the demagnetization of samples and for obtaining the anhysteretic or ideal magnetization curve have been devised. 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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Albert T. Macrander
Argonne National Laboratory