Showing papers in "Review of Scientific Instruments in 1980"
TL;DR: In this paper, the design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail.
Abstract: The design, construction, operation, and performance of a spin polarized electron source utilizing photoemission from negative electron affinity (NEA) GaAs are presented in detail. A polarization of 43±2% is produced using NEA GaAs (100). The polarization can be easily modulated without affecting other characteristics of the electron beam. The electron beam intensity depends on the intensity of the exciting radiation at 1.6 eV; beam currents of 20 μA/mW are obtained. The source is electron optically bright; the emittance phase space (energy‐area‐solid angle product) is 0.043 eV mm2 sr. The light optics, electron optics, and cathode preparation including the GaAs cleaning and activation to NEA are discussed in depth. The origin of the spin polarization in the photoexcitation process is reviewed and new equations describing the depolarization of photoelectrons in the emission process are derived. Quantum yield and polarization measurements for both NEA and positive electron affinity surfaces are reported. T...
392 citations
TL;DR: In this article, the theory and design of Rogowski-wound coils used to measure nanosecond electrical curent pulses in the megampere range were described and compared.
Abstract: This paper describes the theory and design of Rogowski‐wound coils used to measure nanosecond electrical curent pulses in the megampere range. The coils have risetimes of less than one nanosecond, microsecond decay times and typical sensitivities in the range of 10−3 to 10−4 V A−1. They operate in large radiation fields, under intense electron bombardment and at high rates of current rise.
129 citations
TL;DR: In this article, an apparatus and technique for loading diamond anvil cells with gases at high pressure was devised. But this was done at room temperature with helium and hydrogen isotopes to initial densities exceeding those of the normal liquids.
Abstract: We devised an apparatus and technique for loading diamond‐anvil cells with gases at high pressure. Cells were filled quickly and conveniently at room temperature with helium and hydrogen isotopes to initial densities exceeding those of the normal liquids. We report preliminary values of 4He and D2 melting points based on the ruby pressure scale and compare them with extrapolations from our earlier melting curves measured to 20 kbar in a piston‐cylinder device. Our filling procedure now makes it possible to use 4He as a pressure medium in diamond cells. The technique is also useful for loading cells with gaseous mixtures.
127 citations
TL;DR: A surface pattern flow visualization technique based on the principle of oxygen quenching of dye fluorescence is demonstrated in this article, which uses visible light excitation and streams of oxygen or nitrogen, which are inexpensive and nontoxic.
Abstract: A surface pattern flow visualization technique is demonstrated based on the principle of oxygen quenching of dye fluorescence. The technique uses visible light excitation and streams of oxygen or nitrogen, which are inexpensive and nontoxic. A sensitive material can be spray coated on shapes of interest to study flow at surfaces.
118 citations
TL;DR: In this article, a high pressure, radio frequency discharge nozzle beam source has been developed for the production of very intense (⩾1018 atoms sr−1 s−1) supersonic beams of oxygen atoms.
Abstract: A high pressure, radio frequency discharge nozzle beam source has been developed for the production of very intense (⩾1018 atoms sr−1 s−1) supersonic beams of oxygen atoms. An efficient impedance matching scheme has been devised for coupling the radio frequency power to oxygen–rare gas mixtures as a function of gas pressure, temperature, and composition. Techniques for localizing the discharge directly behind the orifice of a specially designed quartz nozzle have also been developed. The above combine to yield a beam source which reliably produces a high degree of molecular dissociation in oxygen–rare gas mixtures at pressures up to 350 Torr. Atomic oxygen mean translational energies from 0.14–0.50 eV have been achieved using the seeded beams technique with Mach numbers up to 10 being realized. When helium is used as the carrier gas both O(3PJ) and O(1D2) atoms are present in the beam, while only ground state atoms appear to be present in argon seeded mixtures. This paper describes the design, constructi...
114 citations
TL;DR: The time constant for fluorescent decay of the red R lines of Ruby has previously been shown to be a monotonic function of temperature over a range of more than 200°C.
Abstract: The time constant for fluorescent decay of the red R lines of Ruby has previously been shown to be a monotonic function of temperature over a range of more than 200 °C. An optical thermometer using this effect has been constructed and has a resolution of ±0.3 °C. Improvements in digital signal processing may increase this resolution another factor of 16.
95 citations
TL;DR: In this article, the characteristics of a steady state, surface conversion, multiline-cusp negative ion source have been investigated for the production of high energy neutral beams, and a technique for reducing the background electron density at the source exit is also presented.
Abstract: The characteristics of a steady state, surface conversion, multiline‐cusp negative ion source have been investigated for the production of high‐energy neutral beams. With the presence of cesium, this source has been operated at a neutral pressure of 1×10−3 Torr to generate a H− ion current greater than 400 mA. The percentage of impurities in the self‐extracted negative ion beam has been analyzed by a mass spectrometer. A technique for reducing the background electron density at the source exit is also presented.
85 citations
TL;DR: In this article, a simple clamp-type pressure apparatus was used for measurements of magnetic susceptibility and electrical resistivity at low temperatures, which was capable of generating hydrostatic pressures up to 30 kbar at room temperature and at least up to 25kbar at 4.2 K.
Abstract: A design of simple clamp type pressure apparatus utilized for measurements of magnetic susceptibility and electrical resistivity at low temperatures is presented. The cell consists of WC piston and Be–Cu cylinder which was autofrettage processed, and sample cavity consists of a teflon bucket and an electrode plug. In a temperature range from 300 K down to 77 K, pressure was determined by manganin gauge which was calibrated by Bi I→II transition pressure at room temperature and also the temperature dependence of pressure coefficient of manganin resistance was taken into account. As a result, the cell was capable of generating hydrostatic pressures up to 30 kbar at room temperature and at least up to 25 kbar at 4.2 K.
84 citations
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TL;DR: A family of plasma guns supplying highly ionized carbon plasma was described in this paper, where the guns are simple and inexpensive to construct and are pulsed by small capacitor banks of a few hundred joules.
Abstract: A family of plasma guns supplying highly ionized carbon plasma is described The guns are simple and inexpensive to construct and are pulsed by small capacitor banks of a few hundred joules The output consists of 1017–1018 multiply ionized carbon ions traveling at about 107 cm/s Neutral output is very low and arrives well after the ionized carbon The guns and pulsers are very reliable
77 citations
TL;DR: In this paper, a pulse counting mass spectrometer is described which is comprised of a new ion source of cylindrical geometry, with exceptional optical properties (the Baur source), a dual focal plane externally adjustable collector slits, and a 17-stage Allen-type electron multiplier, all housed in a metal 21 cm radius, 90° magnetic sector flight tube.
Abstract: A pulse‐counting mass spectrometer is described which is comprised of a new ion source of cylindrical geometry, with exceptional optical properties (the Baur source), a dual focal plane externally adjustable collector slits, and a 17‐stage Allen‐type electron multiplier, all housed in a metal 21 cm radius, 90° magnetic sector flight tube. Mass discrimination of the instrument is less than 1 per mil per mass unit; the optical transmission is more than 90%; the source sensitivity (Faraday collection) is 4 ma/torr at 250μm emission; and the abundance sensitivity is 3×104. A low blank extrction system is also described which routinely provides precedural blanks at 1600°C of approximately 10,000 atoms of 132Xe. The corresponding blanks for 84Kr, 36Ar, and 20Ne are 70,000, 4×106, and 5×107 atoms respectively.
72 citations
TL;DR: In this paper, a clamp-type high pressure cell for carrying out electrical conductivity measurements on small solid samples of size 1 mm or less at pressures upto 8 GPa (i.e., 80 kbar) and for use down to 77 K has been designed and fabricated.
Abstract: A compact clamp-type high pressure cell for carrying out electrical conductivity measurements on small solid samples of size 1 mm or less at pressures upto 8 GPa (i.e., 80 kbar) and for use down to 77 K has been designed and fabricated. The pressure generated in the sample region has been calibrated at room temperature against the polymorphic phase transitions of Bismuth and Ytterbium. The pressure relaxation of the clamp at low temperatures has been estimated by monitoring the electrical conductivity behavior of lead. Review of Scientific Instruments is copyrighted by The American Institute of Physics.
TL;DR: In this article, an optical diagnostic is reported which measures the parameters of an intense hydrogen or deuterium neutral beam by observation of the Doppler shifted Balmer alpha or beta lines emitted by fast atoms in the beam at several locations in the neutralizer.
Abstract: An optical diagnostic is reported which measures the parameters of an intense hydrogen or deuterium neutral beam by observation of the Doppler shifted Balmer alpha or beta lines emitted by fast atoms in the beam at several locations in the neutralizer. The spectrum of blue shifted and red shifted light emitted along optic axes which lie in planes perpendicular and parallel to the grid rails of the ion source is recorded by an optical multichannel analyzer which is interfaced to a computer. The light is Doppler shifted sufficiently to resolve the three energy components of the beam resulting from the H+, H+2, and H+3 ions accelerated by the ion source. From the Doppler broadening of each peak the beam divergence parallel and perpendicular to the accelerator slots can be measured. A model is presented whereby the energy distribution can be determined from the intensity of each peak. The spectroscopic results for energy distribution are in agreement to within 5% with momentum analysis by a magnetic mass spec...
TL;DR: The electric gun as mentioned in this paper is capable of projecting thin flyer plates with velocities in the range 1-20 km/s. It is used in highexplosives-initiation experiments and is being developed for equation-of-state measurements in the 1-5 TPa range.
Abstract: We have developed a versatile tool for generating planar shock waves. This system, which we call the electric gun, is capable of projecting thin flyer plates with velocities in the range 1–20 km/s. It is presently being used in high‐explosives‐initiation experiments and is being developed for equation‐of‐state measurements in the 1–5 TPa range. We describe the electric gun facilities that are operational at Lawerence Livermore Laboratory and discuss applications of electric gun technology to problems of interest to shock‐wave researchers.
TL;DR: In this paper, a 1.8 cm3 active volume gas-recirculating mini-TEA CO2 laser is described, capable of operating at 500 Hz with an average output of 10 W.
Abstract: A 1.8 cm3 active volume gas‐recirculating mini‐TEA CO2 laser of relatively simple design is described. The laser is capable of operating at 500 Hz with an average output of 10 W. The device is line tunable over ∼50 CO2 laser frequencies, has operated with up to 34 J/l output density and has a nearly diffraction‐limited output.
TL;DR: In this paper, gas pulses having a typical duration of 500-600 μs are produced by a nozzle which uses a fuel injector valve as its primary component, with a typical length of 500 to 600 μs.
Abstract: Gas pulses having a typical duration of 500–600 μs are produced by a nozzle which uses a fuel injector valve as its primary component.
TL;DR: This device, originally designed and constructed for bronchial cancer detection, alternates visual illumination and narrow band excitation radiation in conjunction with a synchronously shuttered PMT at frequencies above the visual flicker fusion threshold to provide parallel operation.
Abstract: A sensitive parallel system for visual examination of a target area with simultaneous detection and measurement of fluorescent emission from the same region is described. This device, originally designed and constructed for bronchial cancer detection, alternates visual illumination and narrow band excitation radiation in conjunction with a synchronously shuttered PMT at frequencies above the visual flicker fusion threshold to provide parallel operation. The signal from the PMT is synchronously amplified using a lock‐in amplifier, the dc output of which is voltage‐to‐frequency converted and amplified to provide an audible tone whose frequency is proportional to the fluorescence sensed.
TL;DR: A new sensitive x-ray monochromator and detector system for performing extended x-rays absorption fine structure (EXAFS) measurements in the laboratory is described, which can provide synchrotronlike photon intensities, flexibility and resolution, with the easy access and control possible only in the laboratories.
Abstract: A new sensitive x‐ray monochromator and detector system for performing extended x‐ray absorption fine structure (EXAFS) measurements in the laboratory is described. The monochromator combines x‐ray focusing optics with rapid elemental tunability. The detection system effectively removes glitches from the data stream, regardless of whether they are due to impurity lines from the x‐ray source or if they are due to random instabilities in the incident beam. Used together with a high intensity rotating anode x‐ray source, this system can provide synchrotronlike photon intensities, flexibility and resolution, with the easy access and control possible only in the laboratory.
TL;DR: In this article, a single-coil triple-tuned NMR probe was designed to simultaneously stimulate 1H, 2H and 13C resonances, which can be applied to design probes for observing resonances of various other nuclei in liquid or solid state.
Abstract: A single‐coil triple‐tuned NMR probe designed to simultaneously stimulate 1H, 2H and 13C resonances is described. Isolation between the 1H and 13C channels is higher that obtained by the cross‐coil system and the 1H decoupling efficiency is significantly increased. The basic idea can be applied to design probes for observing resonances of various other nuclei either in liquid or solid state.
TL;DR: Capacitively coupled transmission line voltage sensors and inductive shunt current sensors used in experiments with a high density gas-embedded z pinch have provided accurate and reliable measurements.
Abstract: Capacitively‐coupled transmission‐line voltage sensors and inductive‐shunt current sensors used in experiments with a high‐density gas‐embedded z pinch have provided accurate and reliable measurements. Design and construction of these sensors is described, and their calibration is discussed in detail.
TL;DR: In this paper, a low energy electron diffraction instrument has been constructed which allows one to visually observe a LEED pattern, record the pattern photographically and obtain immediate, quantitative intensity data from several diffraction beams in 5-10 s.
Abstract: A low‐energy electron diffraction instrument has been constructed which allows one to visually observe a LEED pattern, record the pattern photographically and obtain immediate, quantitative intensity data from several diffraction beams in 5–10 s. The instrument operates at incident beam currents of a few picoamperes eliminating electron beam damage effects. This paper describes the design and construction of this new LEED instrument and reports on the operating parameters of sensitivity, signal‐to‐noise, image distortion, and angular resolution.
TL;DR: Production of uniform (flat top) high energy laser beam profiles with relatively little beam energy loss is possible through the use of a modified kaleidoscope, multiple reflection beam scrambler.
Abstract: Production of uniform (flat top) high energy laser beam profiles with relatively little beam energy loss is possible through the use of a modified kaleidoscope, multiple reflection beam scrambler.
TL;DR: In this article, two novel types of x-ray monochromators which eliminate unwanted higher orders usually present in crystal Monochromatized synchrotron radiation beams have been used successfully in spectroscopic studies.
Abstract: Two novel types of x‐ray monochromators which eliminate unwanted higher orders usually present in crystal monochromatized synchrotron radiation beams have been used successfully in spectroscopic studies. The design of the monochromators is based on the refractive index correction’s dependence on wavelength and relative orientation of crystal surface to reflecting Bragg planes. In addition to the order sorting property, both types of monochromators can be used to decrease or increase the reflected beam cross section by Bragg focusing, and in one type, to determine the polarization state of the diffracted beam.
TL;DR: In this article, an impact facility has been designed and constructed to produce and measure large amplitude one-dimensional compression and shear waves in solids, and the experimental results are presented to show that the impact facility was satisfactorily constructed.
Abstract: An impact facility has been designed and constructed to produce and measure large amplitude one‐dimensional compression and shear waves in solids. Design considerations and experimental details to produce the necessary impact configuration and to measure the particle velocity profiles resulting from compression and shear waves are described. Experimental results are presented to show that the impact facility was satisfactorily constructed. After a brief discussion of shear wave measurements, the experimental measurements made under compression and shear loading in polymethyl methacrylate and polycrystalline aluminum oxide are presented. These results are expected to provide new information on material response at high strain rates.
TL;DR: In this paper, a procedure suitable for laboratory practice is described to prepare large-area self-supporting silicon thin crystals with (100), (110) and (111) orientations.
Abstract: 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 A in thickness can be produced. Variation in the thickness across the sample can be as low as ±60 A as measured by 4He+ backscattering spectrometry.
TL;DR: In this article, a high performance research-oriented secondary ion mass spectrometer (SIMS) based on a double focusing mass analyzer has been designed, constructed, and evaluated.
Abstract: A high‐performance research‐oriented secondary ion mass spectrometer (SIMS), based on a double‐focusing mass spectrometer, has been designed, constructed, and evaluated. This instrument is relatively free of some of the instrumental limitations associated with conventional molecular SIMS instrumentation such as energy and mass discrimination. Theoretical design considerations and its construction are discussed. Its performance has been evaluated in various operational modes using a variety of samples and some important instrumental parameters are reported. Finally, the novel and outstanding high‐mass capability of this SIMS instrument is demonstrated.
TL;DR: In this article, a stopped flow apparatus is described to study fast reactions in solution up to 1.2 kbar with a half life of 20 ms. The reaction course is followed optically.
Abstract: A stopped flow apparatus is described to study fast reactions in solution up to 1.2 kbar. The reaction course is followed optically. The apparatus is capable of measuring reactions with a half life of 20 ms.
TL;DR: In this article, a low-impedance manganin stress gauge was used for planar impact experiments performed with a 102mm gas gun on high-explosive samples.
Abstract: We describe new techniques that permit the use of low‐impedance manganin stress gauges in chemically reacting shock waves in the 1.0–40.0 GPa range. The rugged, small, and fast response gauge has reproducibility better than 2% when used in conjunction with a pulsed bridge circuit and adjustable, current‐regulated power supplies. Techniques are presented for fabricating the transducer package, calibrating the bridge circuit and oscilloscopes, designing the drive system, and reducing the data. Data are presented for planar impact experiments performed with a 102‐mm gas gun on high‐explosive samples. In particular, we directly measured the Chapman‐Jouquet pressure in the explosive RX03‐BB [92.5% triaminotrinitrobenzene (TATB)/7.5% polychlorotrifluoroethylene (Kel‐F binder)] as 28.2±0.6 GPa. These new developments open the possibility of applying low‐impedance manganin gauges in chemically reactive hydrodynamic flows such as the evolution of a shock wave into a detonation wave.
TL;DR: In this article, the authors measured the self-diffusion coefficients and average concentration of fluorescent molecules in a volume determined by a focussed laser beam, and provided an independent measurement of the beam profile.
Abstract: Central to the application of fluorescence correlation spectroscopy, to measure the self‐diffusion coefficients and average concentration of fluorescent molecules in a volume determined by a focussed laser beam, is the determination of the focal spot size. As the focal spot size in the sample plane is varied by displacing either the focusing lens or sample position along the beam axis, the diffusion time and average number of molecules vary in a parabolic manner. Analysis of the parameters of the parabola leads to estimates of the beam radius at the waist. The results agree with theoretical predictions and provide an independent measurement of the beam profile.
TL;DR: A feedforward tracking technique is described and its application to single frequency millimeter-wave interferometry and Doppler-shift scattering measurements on tokamak plasmas is described.
Abstract: Superheterodyne stimulus‐response measurements can be made with high dynamic range, but are often sensitive to oscillator frequency drift and noise. The usual techniques for reducing this sensitivity often become impractical at millimeter‐wave frequencies and above. This paper describes a feedforward tracking technique and its application to single frequency millimeter‐wave interferometry and Doppler‐shift scattering measurements on tokamak plasmas. Swept frequency transmission measurements can also be made with high dynamic range using this technique.
TL;DR: In this paper, an apparatus is described which combines laser Doppler velocimetry and optical plethysmography for a rapid, multi-parameter characterization of blood flow in cutaneous tissues.
Abstract: 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.