By Topic

Review of Scientific Instruments

Issue 9 • Date Sep 1989

Filter Results

Displaying Results 1 - 25 of 51
  • JET polari‐interferometer

    Page(s): 2825 - 2834
    Save to Project icon | PDF file iconPDF (1631 KB)  

    A multichannel far‐infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195‐μm DCN laser. The instrument is of the Mach–Zehnder type, with a heterodyne detection system. The modulation frequency (100 kHz) is produced by diffraction from a rotating grating. There are six vertical and two oblique channels. The latter rely on retroreflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8 μm. The various subsystems are described, with emphasis on features necessitated by (a) large path lengths, (b) remote handling requirements, (c) fluctuations in atmospheric humidity, and (d) unmanned automatic operation. Typical measurements, along with real‐time and off‐line data analysis, are presented. The phase‐shift measurement is made with an accuracy of (1)/(20) of a fringe, corresponding to a line‐integrated electron density of 5×1017 m-2. Comparison with other electron density diagnostics are shown. The introduction of additional optics allows measurements of the Faraday effect and a determination of the poloidal magnetic field distribution. The signal processing and data analysis are described. Errors introduced by the calibration procedure, birefringence of the probing beams, toroidal field pickup, the flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5% and a time resolution of 1–10 ms. The poloidal magnetic field is deduced with an accuracy of ±15%. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two‐dimensional plasma‐electron temperature measurements

    Page(s): 2835 - 2837
    Save to Project icon | PDF file iconPDF (462 KB)  

    A system to measure the two‐dimensional cold‐electron temperature profile in a magnetic confinement laboratory plasma is described. Using a digital storage CCD camera, image intensifier, and optical transmission filters, a two‐dimensional helium‐line emission‐ratio measurement shows plasma features which are not possible to resolve using only a single detector or an array of detectors. The system is especially useful for nonaxisymmetric magnetic geometries, where the three‐dimensional equilibria make interpretation of more standard measurements difficult. Other two‐dimensional plasma‐profile measurements including density and ionization source measurements are also possible using the system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Statistical method for efficient determination of electron temperature from pulse height analysis of soft x rays in Heliotron E

    Page(s): 2838 - 2846
    Save to Project icon | PDF file iconPDF (1552 KB)  

    A pulse‐height‐analysis (PHA) technique of soft x rays is applied to Heliotron E experiments. The primary interest of this measurement is the determination of the electron temperature. Since the number of photons measured in a PHA system is extremely restricted owing to a finite processing rate of the system, it is most important to use the full amount of information involved in the spectral data. The statistical estimator from the maximum‐likelihood method is efficiently used for this purpose. The estimated temperature is in good coincidence with the temperature by the electron‐cyclotron‐emission measurement, which is calibrated by the laser Thomson scattering. A check of reliability of the estimated electron temperature is developed from a statistical test of goodness of fit. The identification of impurity lines buried in a thermal spectrum is also discussed in the spectra accumulated through several or several tens of plasma discharges. The line emissions from Si, Cl, Ca, and Ti are identified. A systematic error in the estimated temperature due to the impurity lines is evaluated. The contributions from Cl and Ti cannot be neglected in the temperature estimation from a spectrum accumulated through several currentless ECH plasmas in Heliotron E. A removal of those contributions to the temperature estimation is successfully demonstrated. The electron temperature with several percent uncertainty is obtained by PHA every 10 ms during a Heliotron E discharge. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Observation of soft x‐ray radiation from Heliotron E plasmas by the absorption method for the measurement of electron temperatures

    Page(s): 2847 - 2856
    Save to Project icon | PDF file iconPDF (1458 KB)  

    An absorption method of soft x ray is applied to Heliotron E plasmas for measurement of the electron temperature. Nitrogen gas is used as an absorber for convenience, owing to its accurate, uniform, and easily controllable density. The general feature of the absorption method for measurement of the electron temperature is discussed using a model with two parameters: the generalized thickness of the absorber and the electron temperature. The energy resolution of this method is not sufficient as a general method for spectral analysis. Hence, it is necessary to assume in advance such a model spectrum as consists of bremsstrahlung, recombination radiation, and impurity line radiation. Since the spectrum is always assumed before the analysis, we should try to find the origins of deformation of the energy spectrum and to correct the contribution. The effect of line emission from impurity ions to the estimated electron temperature is evaluated as a function of the electron temperature and the energy of the line relative to the generalized absorber thickness used in the measurement. An actual spectrum is measured by a pulse‐height analysis (PHA) of the soft x ray. The one clear line, from chlorine, is not significant in the present determination of the electron temperature by the absorption method. Another possible line from iron at energy less than 1 keV is included in the analysis. Using a convenient method for determination of local emissivity from a chord‐integrated emissivity, the electron temperature is determined from the local emissivity. The observed broad electron‐temperature profile might be an artifact due to recombination radiation of the highly ionized ion diffused out of the hot core of the plasma. It is confirmed that the absorption method gives absolute measurement of the electron temperature at the plasma center, when additional information on impurity lines are given by PHA. The estimated temperature is consistent with the PHA meas- urement. The absorption method combined with PHA provides an easy and inexpensive measurement of the electron temperature compared with a system fully constructed by PHA. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • USX and SX radiation measurement of tokamak plasma by microchannel plate

    Page(s): 2857 - 2860
    Save to Project icon | PDF file iconPDF (624 KB)  

    A new method is described for the measurement of soft x‐ray (SXR) and ultrasoft x‐ray (USXR) radiation of fusion plasmas. The system applies the microchannel plate (MCP) detector and can be used to measure the emitted radiation along 12 chords in different energy ranges. The operation of the MCP in the measurement is discussed in detail. Some results are included which demonstrate the capabilities of the device. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An elliptical spectrograph/fiber‐array/streak camera system for remote time‐resolved spectral measurements in the x‐ray region

    Page(s): 2861 - 2867
    Save to Project icon | PDF file iconPDF (1433 KB)  

    An elliptical spectrograph and a scintillator/fiber‐array detection system have been developed to provide time‐resolved measurements of the x‐ray spectra from a Z‐pinch plasma. The elliptical spectrograph (1.2‐m focal distance, eccentricity=0.9586) observes the 1‐keV region, covering a range of λ/2d=0.5–0.9. The detector consists of a thin scintillator butt‐coupled to a fiber optic array which transmits the signal to a streak camera in a remote location. This system provides continuous time history with temporal resolution of ∼3 ns, and a spectral resolving power of ∼165. The detection scheme is limited to spectral lines with intensities greater than ∼106 W/sr‐eV. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Discrimination between particle and radiation losses by using a time‐of‐flight type neutral particle energy analyzer

    Page(s): 2868 - 2872
    Save to Project icon | PDF file iconPDF (738 KB)  

    A time‐of‐flight type neutral particle energy analyzer can discriminate between neutral particle loss and radiation loss from a plasma by use of the difference between their times of flight. The energy distribution of hydrogen atoms which are emitted from the plasma can be estimated from the time evolution of the detector signal. The energy distribution of radiated photons can be obtained by using several filters which transmit different ranges of the photon energy. With this method the ratio of the particle and radiation losses emitted from the same plasma volume and within the same detector solid angle can be obtained. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Photodetachment technique for measuring H- velocities in a hydrogen plasma

    Page(s): 2873 - 2878
    Save to Project icon | PDF file iconPDF (988 KB)  

    This article reports work in progress on laser diagnostics of negative‐ion transport velocity in H-‐ion volume sources. The plasma dynamics after the laser shot is discussed in detail, and the effect of the potential perturbation on the H- velocities is evaluated. A method of evaluation of the H- transport velocity from single‐laser‐beam photodetachment experiments is proposed. To substantiate this method, two‐laser‐beam photodetachment experiments have been effected. The velocities thus determined are pressure dependent; they correspond to H- energies in the range 0.23–0.08 eV. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modified perveance law for neutral‐beam ion sources

    Page(s): 2879 - 2882
    Save to Project icon | PDF file iconPDF (494 KB)  

    The perveance law for ion sources is modified based on experimental data gained during the conditioning phase of three multiaperture ion sources for neutral‐beam injection into TEXTOR. The ion sources are modified JET PINIs with a three‐grid accel‐decel extraction system designed for 55 kV, 88 A, 4.8 MW, operated in hydrogen. Results show that best agreement of the perveance law with the experimental data is achieved when the measured ion species mixture is used and, additionally, when the total width of the first acceleration gap, usually determined by the geometrical distance d1 between grid 1 and grid 2 and thickness D1 of grid 1, is enlarged by a third distance term r2, taking the effect of distortion of the electrical field lines at the decel grid into account. At perveance matched conditions, i.e., minimum beam divergence, the optimum value is found to be r2 =0.8r2, where r2 is the aperture radius of the decel grid. The species fractions were measured by optical and magnetic spectrometry. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A method to measure magnetic field perturbations in plasma devices

    Page(s): 2883 - 2887
    Save to Project icon | PDF file iconPDF (917 KB)  

    Magnetic field perturbations with specific spatial geometry can be detected in the presence of a large magnetic field ‘‘background’’ using printed circuit pickup coils which have the advantages of large effective area, near dc frequency response, precise geometry, thin profile, and low cost. The design and construction techniques to produce these coils are presented. A printed circuit coil has been used to detect the magnetic field from the perturbed plasma current distribution in the TEXT tokamak due to current in an external helical (m=7,n=3) winding. The measured sensitivity of this coil, ΔBcoil/Btotal, is ∼3×10-6. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultranarrow bandwidth VUV‐XUV laser system

    Page(s): 2888 - 2892
    Save to Project icon | PDF file iconPDF (797 KB)  

    An ultrahigh‐brightness laser system has been developed to study the spectroscopy and dynamics of molecules and clusters in the vacuum ultraviolet (VUV) extreme ultraviolet (XUV) spectral region. The laser utilizes pulse amplification of a single‐mode ring dye laser, frequency doubling, and four‐wave mixing in a pulsed jet. Pulse energies of ≫100 mJ in the visible and ≫1011 photons/pulse in the VUV‐XUV have been obtained. The bandwidth of the laser has been measured to be 91 MHz in the visible and 210 MHz in the XUV. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impedance monitor to protect the thyratron in metal vapor lasers

    Page(s): 2893 - 2895
    Save to Project icon | PDF file iconPDF (430 KB)  

    It is found that the appearance of high reverse‐voltage spikes on the thyratron anode in the discharge of metal vapor lasers due to high laser impedances can easily be monitored by a dc current meter in series with the bypass inductor of the discharge circuit. Experiments are demonstrated using a copper vapor laser. Results show that the proposed impedance monitor is effective, reliable, and economical. The meter deflection corresponding to acceptable, well‐behaved thyratron operation can be obtained easily by the residual ionization‐control method using a clean laser tube. By keeping the deflection within a specified limit, the lifetime of thyratron can greatly be extended. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Stable current supply with protection circuits for a lead‐salt laser diode

    Page(s): 2896 - 2901
    Save to Project icon | PDF file iconPDF (1199 KB)  

    A high‐stability, high‐level (1.3‐A) current source circuit of modest cost is described, suitable for powering lead‐salt laser diodes or other semiconductor devices, especially expensive, delicate, or rare experimental samples requiring the protection features this current supply offers. The supply features circuits to shut off current to the laser or other device smoothly and quickly (in less than 90 μs) if there is an overvoltage, overcurrent, main battery supply failure, or elevated temperature condition, to protect the laser or device from any of these potentially damaging conditions. Spectral data of a lead‐salt laser emitting in the 1840‐cm-1 region are presented to demonstrate the use of the current supply. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Concurrent pump‐probe and streak camera measurements with a single mode‐locked Nd:YAG laser: A picosecond absorption/emission spectrometer

    Page(s): 2902 - 2914
    Save to Project icon | PDF file iconPDF (2557 KB)  

    A description is presented of a laser system that can be used for two concurrent and independent types of picosecond spectroscopic measurements. Two data‐collection sybsystems, (1) a picosecond pump‐probe transient absorption/emission spectrometer and (2) a streak camera system for time‐dependent measurements of absorption and emission, have been developed as independent work stations within an integrated system based on a single mode‐locked Nd:YAG laser oscillator which concurrently supplies each subsystem with picosecond pulses. The electronic links among the two work stations and the laser are discussed. In addition to applications involving pump‐probe absorption and pulsed laser‐induced emission measurements, this system can be used for picosecond‐pulsed preparation‐pump‐probe absorption and preparation‐pump emission experiments. Examples of data collected with each subsystem are presented to illustrate the complementary nature of the information that can be obtained with this versatile laser system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficiency and resolution of a new readout system for electro‐optical devices

    Page(s): 2915 - 2919
    Save to Project icon | PDF file iconPDF (845 KB)  

    Results of a new experiment investigating fiber‐coupled, astronomical CCD cameras as imaging systems for electro‐optic devices are described. These results indicate that single‐electron detection is achievable at 10‐kV energy and that the resolution can exceed 35‐μm FWHM. A system using such a camera to read a matched, high‐resolution phosphor is described, and characterizations of the various component efficiencies are given. It is concluded that this system offers formidable competition to microchannel plate intensified systems with respect to dynamic range, absolute sensitivity, and cost. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Signal processing for an infrared array detector

    Page(s): 2920 - 2923
    Save to Project icon | PDF file iconPDF (636 KB)  

    A broadband detection scheme for a time‐resolved infrared absorption spectrometer, based on a multielement mercury‐cadmium‐telluride (MCT) array, has been successfully implemented. The spectrometer achieves a resolution on the 10‐ns time scale despite the much larger time constant characteristic of the MCT elements. Our signal‐collection circuitry takes advantage of the slow decay by integrating the detector response to pulsed IR radiation. The dynamic range is 100–1 and the resultant noise level is near the detector limit. Data acquisition for the 120 elements is fast enough to allow scan rates of 30–40 Hz. The completed electronics are sufficiently compact to be situated local to the array detector, and the design is relatively inexpensive to construct using commonly found electronic components. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A high‐speed photomultiplier gating circuit for luminescence measurements

    Page(s): 2924 - 2928
    Save to Project icon | PDF file iconPDF (753 KB)  

    A high‐speed, normally on, gating circuit has been developed for linear‐focused photomultipliers such as the EMI 9816. The gate is capable of attenuating photomultiplier response by ≫5000:1 with a turn‐off and turn‐on time of 60 and 40 ns, respectively. The circuit is compact enough to fit in a standard photomultiplier housing and has low enough power consumption to run off the photomultiplier high‐voltage supply. The high speed and high extinction efficiency make this gate suitable for pulse rejection in low‐light level, submicrosecond, time‐resolved luminescence measurements. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Digital parallel acquisition in frequency domain fluorimetry

    Page(s): 2929 - 2936
    Save to Project icon | PDF file iconPDF (1233 KB)  

    The analog electronics commonly found in frequency domain fluorometers are limited to collecting only a single frequency at a time, and can be a source of systematic errors. We have developed an instrument in which most of the analog electronics are replaced with a computer‐controlled digital‐acquisition system. The computer is used for the direct collection of multifrequency data; filtering and calculation of the phase and modulation ratio are done by the software. From these values, fluorescence lifetimes can be determined. This new approach reduces most of the systematic errors due to the analog electronics’ hardware and allows for reconfiguration of the instrument with only minor changes of the software. This digital‐acquisition system is not a simple substitution of an analog element, but it provides a new function and new capabilities for frequency domain fluorometers. We have used this digital approach to build a ‘‘parallel’’ phase fluorometer which simultaneously collects and processes several modulation frequencies. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new nonclipped correlator for photon count spectroscopy

    Page(s): 2937 - 2939
    Save to Project icon | PDF file iconPDF (336 KB)  

    A circuit for photon count spectroscopy and its interface to a digital signal processor (DSP) are described. The complete circuit is housed in a standard IBM‐PC board and, as it contains its own processor and memory, has a background mode of operation that releases the host system for being used in other tasks while the correlator is running. The basic autocorrelation routine executed by the DSP on data collected by the count circuit is also discussed. The use of the DSP lends the system great flexibility allowing for a high degree of customization while keeping performance to a level comparable to that of large dedicated units. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High‐brightness and high‐resolution RHEED system

    Page(s): 2940 - 2944
    Save to Project icon | PDF file iconPDF (904 KB)  

    A RHEED system, consisting of a high‐resolution (75‐μm FWHM) and high‐brightness (10‐μA) electron gun, and a phosphor screen with high resolution and good linearity, was developed. The system is based on concepts from projection television. The results show that this setup is particularly useful for obtaining quantitative RHEED patterns. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A high‐resolution low‐energy electron diffraction instrument

    Page(s): 2945 - 2948
    Save to Project icon | PDF file iconPDF (678 KB)  

    A high‐resolution LEED system with optimum operating parameters for use below 100 eV has been designed and tested. A field‐emission‐based electron gun with an angular divergence of  2 mrad, and a large sample detector distance of 150 mm provide the major improvements in resolution. Measured beam widths (Δk/2π FWHM) for both specular and nonspecular beams are approximately 0.002 Å-1 in the energy range of 50–100 eV. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel method for accurate g measurements in electron‐spin resonance

    Page(s): 2949 - 2952
    Save to Project icon | PDF file iconPDF (731 KB)  

    In high‐accuracy work, electron‐spin‐resonance (ESR) g values are generally determined by calibrating against the accurately known proton nuclear magnetic resonance (NMR). For that method—based on leakage of microwave energy out of the ESR cavity—a convenient technique is presented to obtain accurate g values without needing conscientious precalibration procedures or cumbersome constructions. As main advantages, the method allows the easy monitoring of the positioning of the ESR and NMR samples while they are mounted as close as physically realizable at all time during their simultaneous resonances. Relative accuracies on g of ≊2×10-6 are easily achieved for ESR signals of peak‐to‐peak width ΔBpp≲0.3 G. The method has been applied to calibrate the g value of conduction electrons of small Li particles embedded in LiF—a frequently used g marker—resulting in gLiF Li=2.002 293±0.000 002. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A sensitive and inexpensive susceptometer for the study of high‐temperature superconductors

    Page(s): 2953 - 2957
    Save to Project icon | PDF file iconPDF (838 KB)  

    A moving‐sample susceptometer based on a Hartshorn inductance bridge is described. This instrument makes it possible to measure magnetic susceptibility as a function of temperature. The lower limit of detection is approximately 50 parts per million of powdered YBa2Cu3Ox superconductor contained in a 5‐mg sample, corresponding to approximately 10-6 emu/g. Measurements can be conducted in the 4.2–300 K temperature range. The apparatus can be built inexpensively of commonly available parts. Construction, operation, and possible applications are discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Computer‐assisted data acquisition on Josephson junctions

    Page(s): 2958 - 2963
    Save to Project icon | PDF file iconPDF (1010 KB)  

    An automatic digital data‐acquisition system for the test and characterization of superconducting Josephson tunnel junctions is presented. The key feature is represented by the high degree of interaction of the measurement system with the device under test. This is accomplished by an iterated sequence of data acquisitions, automatic analysis, and subsequent modifications of the control signals in the device. In this way, the basic calibration and the value of the relevant quantities involved with the Josephson junction are automatically determined. A connection with a host computer makes possible more complex data analysis, while the full control of the experiment by a dedicated computer allows the operator to perform nonroutine procedures. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Eddy current shielding and heating: Reduction of dissipation for very low‐temperature experiments in the presence of magnetic field ripple

    Page(s): 2964 - 2968
    Save to Project icon | PDF file iconPDF (906 KB)  

    We have studied eddy current heating and shielding for conducting materials in a cylindrical geometry, and we have performed numerical calculations as a function of the important parameters. Results are presented in graphical form. Eddy current heating in OFHC copper at low temperatures and means of suppressing it have been studied in a Bitter magnet in a field of 15 T. Results show that it is possible to use conducting materials for experiments in high magnetic fields at temperatures below 1 K. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
Albert T. Macrander
Argonne National Laboratory