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Review of Scientific Instruments

Issue 9 • Date Sep 1980

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Displaying Results 1 - 25 of 31
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Real time digital spectral analysis as a plasma fluctuation diagnostic

    Page(s): 1151 - 1158
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    A real time digital spectral analysis system, applicable to broad band plasma fluctuations, is presented. The system digitally records plasma potential fluctuations on a pair of matched electrostatic probes, and subsequently outputs the cross power spectral density and phase via an on‐line computer graphics display. The spectral analysis system and its experimental accuracy are discussed. Using the Lawrence Berkeley Laboratory ten amp neutral beam ion source, several examples demonstrating the systems application to plasma wave detection are given. View full abstract»

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  • Electron distribution function measurement by harmonically driven electrostatic probes

    Page(s): 1159 - 1162
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    An electron distribution function measurement system, applicable to noisy plasma environments, is presented. The system is based on the harmonic differentiation technique, which utilizes the nonlinearity of the probe current‐voltage characteristic to infer distribution function structure. Measurements couple low noise, phase sensitive detection with digital data acquisistion and analysis, resulting in fast and accurate measurement in noisy environments where active electronic differentiation may prove untenable. The accuracy of the experimental technique and measurement system is discussed. Using a high power arc plasma, an example demonstrating the experimental system is given. View full abstract»

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  • Power transmission characteristics of a two‐stage multiaperture neutral beam source

    Page(s): 1163 - 1167
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    Beam power transmission and grid loading characteristics of a two‐stage neutral beam source are presented. The dependence of power deposition on the target, the grids, and the gas cell was studied over a wide range of extraction perveance values with the accel‐to‐extraction gap field ratio as the other parameter. The results show that the power transmission improves remarkably with increasing field ratio. For sufficiently large field ratios (≈2.5), more than 80% of the input IV power was collected on a target located 4 m downstream and subtending 2 ° half angle to the source. The sum of the grid loading is approximately double that of single‐stage accelerators; the plasma grid loading is the highest, followed by ground grid, accel grid, and extraction grid in that order. View full abstract»

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  • State purification of a fast neon metastable beam by collinear optical pumping

    Page(s): 1168 - 1175
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    An apparatus has been constructed to produce well‐characterized fast beams of rare gas metastable atoms for subsequent scattering experiments. Optical pumping by a collinear laser beam can be used to selectively remove either of the two metastable components from the beam. Laser‐induced‐fluorescence (LIF) techniques can be used to determine the original beam composition and to monitor composition changes resulting from optical absorption. These techniques have been successfully applied to a metastable neon beam produced by near‐resonant charge transfer of Ne+ in Na. A simple model has been developed which accurately reproduces the observed LIF lineshape generated by tuning the laser throught the optical transition frequency. View full abstract»

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  • Experimental techniques for determining the structure of high frequency waves impressed on an intense relativistic electron beam

    Page(s): 1176 - 1182
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    Techniques developed to measure the amplitude, wavelength and azimuthal mode structure of high frequency (a few hundred MHz) waves impressed on an intense relativistic electron beam are described. The details of a wave probe array, two different signal processing schemes and data reduction methods are discussed. Sample data illustrating the use of these techniques, including a multi‐probe wavelength measurement made on a single machine firing are presented. View full abstract»

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  • Optically isolated electronic trigger system for experiments on a subnanosecond time scale with a pulsed Van de Graaff electron accelerator

    Page(s): 1183 - 1189
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    An optically isolated electronic trigger system for a pulsed Van de Graaff electron accelerator, producing an external pretrigger pulse 75 ns before arrival of the electron pulse at the target, is described. The total time jitter between trigger signal and electron pulse is 50 ps. The measurement of optical and electrical transients on a subnanosecond time scale with a sequential sampling oscilloscope is demonstrated. The contribution of various parts of the equipment to the total jitter is discussed. Those contributions to the jitter due to the electron transit time fluctuations in the accelerator assuming a constant acceleration voltage gradient and to the shot noise in the photomultiplier detector of the trigger system are calculated to be 5 ps and 12 to 21 ps respectively. Comparison with the experimental results leads to the conclusion that a considerable part of the total jitter may be attributed to acceleration voltage gradient fluctuations, to accelerator vibrations and possibly to density fluctuations in the insulation gas. Possible improvements of the trigger system are discussed. The apparatus is used for pulse radiolysis experiments with subnanosecond time resolution down to 100 ps in combination with subnanosecond time duration electron pulses. View full abstract»

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  • Synchronized flash light source optical detection for electric field‐jump relaxation experiments

    Page(s): 1190 - 1193
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    An electric field‐jump apparatus is constructed, with a synchronized Xe flash lamp for photometric monitoring of chemical relaxations. The instrument is especially useful for the investigation of linear macromolecules, where the analyzing light beam must be linearly polarized. A video amplifier is used in conjunction with the photomultiplier, providing for fast rise time and low noise of the detection system. View full abstract»

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  • Liquid nitrogen cooled laser rod holder design

    Page(s): 1194 - 1197
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    A reliable Ho:YLF laser system has been successfully developed. Problems encountered in laser‐rod and support‐system design were unique and most difficult to solve. These problems include holding a fragile laser rod having nonisotropic thermal expantion with vacuum tight seals which can be thermally cycled. Experimentally proven solutions are described which should help others in developing new solid‐state laser systems. View full abstract»

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  • Method of characterization of dielectric or semiconductor materials using an optically pumped far infrared waveguide laser

    Page(s): 1198 - 1201
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    A method of measurement of the absorption coefficient of a material is presented using a CO2 optically pumped far infrared waveguide laser which has been specially developed for this purpose. This method permits the elimination of the instability effects due to the basic design concept of the laser. It is used to measure the absorption coefficient of a few mesogeneous substances in order to deduce their order parameters. View full abstract»

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  • Photophoretic spectrometer

    Page(s): 1202 - 1204
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    An instrument is described which measures the spectral dependence of the radiometric (photophoretic) force on a micron‐sized particle in a static configuration. This spectrometer consists of a servo‐stabilized Millikan chamber which can be used as a photophoretic balance over the spectral range from 200 nm to 1000 nm. Spectra may be taken in a vacuum as small as 10-4 torr. The action spectrum of the photophoretic force on a crystallite of CdS is used as an example. The pressure dependence of the force at 500 nm is consistant with a radiometric mechanism. View full abstract»

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  • Fast digital apparatus for capacitance transient analysis

    Page(s): 1205 - 1211
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    The analysis of transient phenomena originating from relaxation processes is a tool for material and device characterization. The time constants of the transients provide information about the energy levels involved, and the transient amplitude is coupled to the density of occupied states. A convenient method for the analysis of exponential transients is the use of correlation‐spectroscopic techniques. An example is deep level transient spectroscopy, a capacitance method for the study of deep impurities in semiconductors. The correlation with a weighting function is in this case conventionally made by hardwired instruments. We demonstrate here how shortcomings of this method can be avoided and higher flexibility can be achieved by separating the signal processing from the data acquisition. The hardware is a high‐resolution capacitance measurement system with a resolution of 0.002 pF in capacitance and 5 μs in time. As a result of the measurement, which is considerably faster than analog methods, a data array describes the response of the sample with regard to time and temperature. Several signal processing routines are applied to the data to filter out specific information. View full abstract»

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  • Preparation of large‐area monocrystalline silicon thin windows

    Page(s): 1212 - 1216
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    A procedure suitable for laboratory practice is described to prepare large‐area self‐supporting silicon thin crystals with (100), (110) and (111) orientations. Windows up to 2 cm in diameter and 2000 Å in thickness can be produced. Variation in the thickness across the sample can be as low as ±60 Å as measured by 4He+ backscattering spectrometry. View full abstract»

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  • Low temperature thermal conductivity measurements under uniaxial compression

    Page(s): 1217 - 1219
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    A new technical method of thermal conductivity measurements of uniaxially compressed samples, at liquid helium temperatures, has been tested. This method allows rigorous guiding and alignment of the sample while the problems linked to the thermal insulation of the sample are also minimized. Good reproducibility of the results was obtained after the sample was taken off and mounted again. View full abstract»

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  • Simple thermal conductivity cell using a miniature thin film printed circuit for analysis of binary gas mixtures

    Page(s): 1220 - 1224
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    We describe a thermal conductivity cell for the measurements of the composition of binary gas mixtures. The main advantage of the cell is that its response is pressure independent in the range 20–100 Torr. The apparatus, of the parallel plate type, uses a very thin printed circuit film as the hot plate in order to achieve a fast response time. The cell was designed and operated to determine the ortho‐para‐composition of hydrogen gas samples but it also works reliably as an analyser of 3He–4He gas mixtures. In both cases the precision of the instrument is better than 10-2 for the mole fraction. View full abstract»

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  • TV‐rate histogram equalization processor for the electron microscope

    Page(s): 1225 - 1230
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    A fast (NTSC TV‐rate), low cost, simple histogram equalization processor is described. In this apparatus, the histogram equalization processing is carried out by the table look‐up method at TV‐rate. The characteristics of the processor, and its applications to the real time and on‐line processing of weak contrast images from the Ultra‐High Voltage Electron Microscope (Osaka University) are described. With this apparatus, equilevel processing, level compression, and level slicing may also be easily carried out. View full abstract»

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  • Design of partial dielectric cavities for wide‐band microwave measurements

    Page(s): 1231 - 1233
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    A novel microwave cavity is presented in which a conducting sample can be excited by a strong microwave field and, simultaneously, its response can be measured over a wide frequency range surrounding the excitation frequency. View full abstract»

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  • Analog measurement of the autocorrelation function of Gaussian noise

    Page(s): 1234 - 1239
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    A new method for measuring the autocorrelation function of stationary, Gaussian distributed, differentiable or nondifferentiable noise is presented. This method does not require real‐time digitizing or analog multiplying and can be easily realized since it is based on the use of either a sampling oscilloscope or a boxcar averager. The method requires the measurement of the ensemble average of the multiple traces generated by internally triggering the oscilloscope or averager on the noise. Expressions for interpreting this average to obtain the autocorrelation function as well as examples of measurements made by this technique are given and discussed. View full abstract»

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  • Constriction resistance measuring system for residential branch circuit connections

    Page(s): 1240 - 1246
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    A constriction resistance measuring system was designed for evaluating the performance of residential branch wiring circuit connections. The measurement system separates the bulk from the constriction resistance by utilizing the nonlinear voltage‐current behavior of a connection. The method overcomes some of the past problems with the nonlinear technique by employing a pulse stimulus current coupled to a high‐speed data acquisition system under computer control. A least squares nonlinear fit program is used to obtain the best fit of the voltage‐current data to an equation which serves as the nonlinear model. The model was verified by simulating connections with a ’’true 4‐wire crossed rod’’ measurement technique. Measurements on connections formed with aluminium and copper conductors agree closely with the parameters predicted by the model. The method is shown to have the ability to accurately measure the constriction resistance of practical connectors in the presence of widely changing values of bulk resistance. A modification of the technique is proposed and shown to have a potential threefold increase in sensitivity. View full abstract»

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  • Microanalytical ultracentrifuge

    Page(s): 1247 - 1252
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    An ultracentrifuge based on the air turbine of a dental drill attains 400,000–600,000 rpm and a centrifugal force 2 to 3 million ×g. It is used for the examination of cell suspentions and homogenates and can be applied to macromolecular solutions. Microcuvettes with volumes ranging from less than 1 mm3 to 0.001 mm3 (suitable for single cells) are of disk and square capillary form and are made of polycarbonate or glass. A special microscope is used to obtain a stopped image of the rotating cuvette. A new method to preserve the centrifugal state of the contents is tested: deep freezing of a rotating cuvette for subsequent freeze‐drying and microscopical examination. Experiments on cells include centrifugal intercellular movement of nuclei and cytoplasmic particles, cell fusion, and homogenization. View full abstract»

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  • Microcomputer‐based laser Doppler velocimeter in marine biology

    Page(s): 1253 - 1257
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    A laser doppler velocimeter (LDV) has been designed and constructed for use in measuring ocean water flow velocity in the immediate vicinity of marine organisms anchored inside a water tunnel. The principal innovation reported here is the use of a microprocessor to produce an ’’intelligent’’ instrument which automatically calculates and displays the flow velocity. The resulting electronics design represents a considerable simplification over existing instruments which generally require the use of a separate autocorrelator and/or multi‐channel analyzer (MCA) plus an external minicomputer. The LDV configuration employed is a crossed‐beam design using a 2‐mW He–Ne laser and inexpensive optics. A 48‐channel 1‐bit clipped autocorrelation function is implemented using a modified TTL design reported previously by Chen and co‐workers. A Motorola 6800 micromodule updates the contents of each channel by direct memory access and displays the resulting correlogram on a CRT monitor. The velocity is periodically calculated (±5%) and displayed by LED digits. View full abstract»

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  • Laser doppler blood flow meter and optical plethysmograph

    Page(s): 1258 - 1262
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    An apparatus is described which combines laser Doppler velocimetry and optical plethysmography for a rapid, multi‐parameter characterization of blood flow in cutaneous tissues. The Doppler parameter is determined by analog computation of the square root of the normalized second moment of the photodiode detector output during illumination by laser light scattered from the illuminated tissue. Incident and scattered light are transmitted by fiber optics to permit convenient sampling of local tissue regions. The instrument is compact, portable, and inexpensive. Data are presented which illustrate the utility of this device, and potential applications are discussed. View full abstract»

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  • High‐field titanium‐wafer vacuum pump

    Page(s): 1263 - 1265
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    A new style of sputter‐ion Penning discharge pump has been designed, built and tested using helium and hydrogen as background gases. This pump has been shown to operate reliably and stably in the magnetic field extremes of 0.5 and 51 kG. Anode potential must exceed 2000 V and still higher potentials assure the ability to efficiently pump noble gases. At 51 kG, the current/pressure ratio for this test pump with ∼1.2 cm3 of total cell volume ranges from 500 to 100 A/Torr for a pressure range of approximately 2×10-7 to 4×10-11 Torr (uncorrected) respectively. View full abstract»

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  • Three‐watt near‐room‐temperature CO waveguide laser

    Page(s): 1265 - 1267
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    We report stable performance of a carbon monoxide waveguide laser which produces 3/4 W with the gas and base near zero °C, and 3 W with flowing chilled gas. Stable output power and frequency spectra are obtained by using low‐thermal‐expansion boron nitride as the waveguide material. View full abstract»

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  • Low‐drift optical‐densitometer

    Page(s): 1267 - 1268
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    A general purpose, optical densitometer has been constructed using inexpensive components. A drift rate of approximately 0.3% per hour, and a measurement accuracy of 0.1%, permit the instrument to detect small changes in the optical transmission of unknown samples. 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