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Review of Scientific Instruments

Issue 9 • Date Sep 2008

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Displaying Results 1 - 25 of 69
  • Issue Cover

    Page(s): c1
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  • Issue Table of Contents

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  • Invited Article: Deep Impact instrument calibration

    Page(s): 091301 - 091301-77
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    Calibration of NASA’s Deep Impact spacecraft instruments allows reliable scientific interpretation of the images and spectra returned from comet Tempel 1. Calibrations of the four onboard remote sensing imaging instruments have been performed in the areas of geometric calibration, spatial resolution, spectral resolution, and radiometric response. Error sources such as noise (random, coherent, encoding, data compression), detector readout artifacts, scattered light, and radiation interactions have been quantified. The point spread functions (PSFs) of the medium resolution instrument and its twin impactor targeting sensor are near the theoretical minimum [∼1.7 pixels full width at half maximum (FWHM)]. However, the high resolution instrument camera was found to be out of focus with a PSF FWHM of ∼9 pixels. The charge coupled device (CCD) read noise is ∼1 DN. Electrical cross-talk between the CCD detector quadrants is correctable to ≪2 DN. The IR spectrometer response nonlinearity is correctable to ∼1%. Spectrometer read noise is ∼2 DN. The variation in zero-exposure signal level with time and spectrometer temperature is not fully characterized; currently corrections are good to ∼10 DN at best. Wavelength mapping onto the detector is known within 1 pixel; spectral lines have a FWHM of ∼2 pixels. About 1% of the IR detector pixels behave badly and remain uncalibrated. The spectrometer exhibits a faint ghost image from reflection off a beamsplitter. Instrument absolute radiometric calibration accuracies were determined generally to ≪10% using star imaging. Flat-field calibration reduces pixel-to-pixel response diffe- rences to ∼0.5% for the cameras and ≪2% for the spectrometer. A standard calibration image processing pipeline is used to produce archival image files for analysis by researchers. View full abstract»

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  • High resolution flat crystal spectrometer for the Shanghai EBIT

    Page(s): 093101 - 093101-4
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    We report on a high resolution flat crystal spectrometer designed for the Shanghai EBIT. Its energy range is from 0.5 to 10 keV. Three crystals can be installed in the vacuum chamber simultaneously, and its effective Bragg angle can be covered from 15° to 75°. A vacuum version charge-coupled device detector is used for detection of photons. An energy resolution under 1 eV was reached in measurements of the 4.5 keV 1 line by using an x-ray generator with a titanium anode. The spectrometer was also tested to operate well on the Shanghai EBIT by observing the lines of tungsten at around 3.2 keV. View full abstract»

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  • Cooling an optical fiber to 4.5 K by indirect thermal contact with a liquid-helium flow and spectroscopic temperature measurements

    Page(s): 093102 - 093102-5
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    We have made it possible to cool a 10-m-long optical fiber to 4.5 K in a compact helium-flow cryostat. The cryostat is vacuum loaded and the cooling principle is based on thermal contact with a copper holder cooled by the liquid-helium flow. To measure the temperature directly, we employed two different spectroscopic methods depending on the temperature regions. One was photon-counting Raman spectroscopy and the other was Brillouin spectroscopy. We used certain devices to improve the cooling efficiency and confirmed that the fiber was uniformly cooled to 4.5 K. View full abstract»

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  • Closed source experimental system for soft x-ray spectroscopy of radioactive materials

    Page(s): 093103 - 093103-5
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    An instrumental and experimental setup for soft x-ray spectroscopy meeting the requirements of a closed source for radioactivity is described. The system consists of a vacuum sealed cell containing the sample, mounted on a tubing system to ensure compatibility with most standard manipulators. The soft x rays penetrate a thin x-ray window separating the interior of the cell from the vacuum in the experimental chamber. Our first results for single crystal PuO2 confirm the feasibility of experiments using the setup. The results are consistent with results of first principles calculations and previously recorded spectra obtained using a standard open source setup. The results show that the closed source experimental system can be used to collect valuable experimental data from radioactive materials. View full abstract»

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  • Electron beam diagnostics for a superconducting radio frequency photoelectron injector

    Page(s): 093301 - 093301-8
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    A superconducting radio frequency (SRF) photoelectron injector is currently under construction by a collaboration of BESSY, DESY, FZD, and MBI. The project aims at the design and setup of a continuous-wave SRF injector including a diagnostics beamline for the ELBE free electron laser (FEL) and to address R&D issues on low emittance injectors for future light sources such as the BESSY FEL. Of critical importance for the injector performance is the control of the electron beam parameters. For this reason a compact diagnostics beamline is under development, serving a multitude of operation settings. In this paper the layout and the rationale of the diagnostics beamline are described. Furthermore detailed information on specific components is given, together with results from laboratory tests and data taking. View full abstract»

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  • Electrophoresis system for high temperature mobility measurements of nanosize particles

    Page(s): 093302 - 093302-4
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    The electrophoretic mobility, which reflects the zeta potential of a solid material, is an important experimental quantity providing information about the electrical double layer at the solid/liquid interface. A new high temperature electrophoresis cell was developed suitable for electrophoretic mobility measurements of dispersed nanosize particles up to 150 °C and 40 bars. Amorphous silica (SiO2) particle size standards were used to test the particle size detection limit of the new instrument at 25, 100, and 150 °C and several pH values. The microscopic detection of the particles was enabled by dark-field illumination, which allowed extending the previously available capabilities and provided higher accuracy of the electrophoretic mobility data. The electrophoretic mobility measurements for SiO2 at temperatures above 100 °C were reported for the first time and indicated a gradual increase in particle electrophoretic response with increasing temperature. The obtained data indicated negatively charged SiO2 surface throughout the pH and temperature ranges studied. View full abstract»

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  • Measurement of the gamma-ray sensitivity and signal-to-noise ratio of a new scattered-electron detector

    Page(s): 093303 - 093303-5
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    A new detector suitable for measuring high intensity pulsed gamma-ray sources and based upon scattered-electron method is proposed. The detector has a relatively flat energy response in the range of 0.4–5 MeV and works in current mode. The performances of the detector under several conditions were studied by Monte Carlo simulation using the MCNP code. A comparison between calculations and measurements performed using the 1.25 MeV line of Co-60 is also addressed. The experimental signal produced by the detector was thus studied and decomposed into its main components in order to establish the signal-to-noise ratio (SNR). The latter is compared to SNR calculated for other type of detectors. View full abstract»

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  • High resolution energy analyzer for broad ion beam characterization

    Page(s): 093304 - 093304-16
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    Characterization of the ion energy distribution function (IEDF) of low energy high current density ion beams by conventional retarding field and deflection type energy analyzers is limited due to finite ion beam emittance and beam space charge spreading inside the analyzer. These deficiencies are, to a large extent, overcome with the recent development of the variable-focusing retarding field energy analyzer (RFEA), which has a cylindrical focusing electrode preceding the planar retarding grid. The principal concept of this analyzer is conversion of a divergent charged particle beam into a quasiparallel beam before analyzing it by the planar retarding field. This allows analysis of the beam particle total kinetic energy distribution with greatly improved energy resolution. Whereas this concept was first applied to analyze 5–10 keV pulsed electron beams, the present authors have adapted it to analyze the energy distribution of a low energy (≤1 KeV) broad ion beam. In this paper we describe the RFEA design, which was modified from the original, mainly as required by the specifics of broad ion beam energy analysis, and the device experimental characterization and modeling results. Among the modifications, an orifice electrode placed in front of the RFEA provides better spatial resolution of the broad ion beam ion optics emission region and reduces the beam plasma density in the vicinity of analyzer entry. An electron repeller grid placed in front of the RFEA collector was found critical for suppressing secondary electrons, both those incoming to the collector and those released from its surface, and improved energy spectrum measurement repeatability and accuracy. The use of finer mesh single- and double-grid retarding structures reduces the retarding grid lens effect and improves the analyzer energy resolution and accuracy of the measured spectrum mean energy. However, a- dditional analyzer component and configuration improvements did not further change the analyzed IEDF shape or mean energy value. This led us to conclude that the optimized analyzer construction provides an energy resolution considerably narrower than the investigated ion beam energy spectrum full width at half maximum, and the derived energy spectrum is an objective and accurate representation of the analyzed broad ion beam energy distribution characteristics. A quantitative study of the focusing voltage and retarding grid field effects based on the experimental data and modeling results have supported this conclusion. View full abstract»

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  • Use of multiwavelength emission from hollow cathode lamp for measurement of state resolved atom density of metal vapor produced by electron beam evaporation

    Page(s): 093305 - 093305-7
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    State resolved atom population of metal vapor having low-lying metastable states departs from equilibrium value. It needs to be experimentally investigated. This paper reports the use of hollow cathode lamp based atomic absorption spectroscopy technique to measure online the state resolved atom density (ground and metastable) of metal vapor in an atomic beam produced by a high power electron gun. In particular, the advantage of availability of multiwavelength emission in hollow cathode lamp is used to determine the atom density in different states. Here, several transitions pertaining to a given state have also been invoked to obtain the mean value of atom density thereby providing an opportunity for in situ averaging. It is observed that at higher source temperatures the atoms from metastable state relax to the ground state. This is ascribed to competing processes of atom-atom and electron-atom collisions. The formation of collision induced virtual source is inferred from measurement of atom density distribution profile along the width of the atomic beam. The total line-of-sight average atom density measured by absorption technique using hollow cathode lamp is compared to that measured by atomic vapor deposition method. The presence of collisions is further supported by determination of beaming exponent by numerically fitting the data. View full abstract»

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  • Development and calibration of a Thomson parabola with microchannel plate for the detection of laser-accelerated MeV ions

    Page(s): 093306 - 093306-9
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    This article reports on the development and application of a Thomson parabola (TP) equipped with a (90×70) mm2 microchannel-plate (MCP) for the analysis of laser-accelerated ions, produced by a high-energy, high-intensity laser system. The MCP allows an online measurement of the produced ions in every single laser shot. An electromagnet instead of permanent magnets is used that allows the tuning of the magnetic field to adapt the field strength to the analyzed ion species and energy. We describe recent experiments at the 100 TW laser facility at the Laboratoire d’Utilization des Lasers Intenses (LULI) in Palaiseau, France, where we have observed multiple ion species and charge states with ions accelerated up to 5 MeV/u (O+6), emitted from the rear surface of a laser-irradiated 50 μm Au foil. Within the experiment the TP was calibrated for protons and for the first time conversion efficiencies of MeV protons (2–13 MeV) to primary electrons (electrons immediately generated by an ion impact onto a surface) in the MCP are presented. View full abstract»

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  • Formation of single pinched plasma point in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge

    Page(s): 093501 - 093501-7
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    Characteristics of cathode plasma jet pinching and x-ray emission from a multipicosecond laser-triggered vacuum discharge are presented. Discharge was created in between a planar Al cathode and a conical point-tip Ti anode (separation: 2–15 mm, circuit inductance of ∼0.53 μH, peak discharge current of ∼3 kA, and rise time of ∼400 ns). For anode-cathode separation of ∼13.5 mm, only a single pinched plasma point was formed in the cathode plasma jet at a distance of ∼9.5 mm from the cathode. Quantitative analysis of the x-ray signals recorded using a pin diode with different filters and viewing different regions of the discharge, shows soft (keV photon energy) x-ray emission from the plasma point with a flux of ∼(3–5)×1010photons/sr, and multi-keV x-ray emission from the Ti anode with (∼4.51 keV) photon flux of ∼1010photons/sr. View full abstract»

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  • Development of a high-brightness and low-divergence lithium neutral beam for a Zeeman polarimetry on JT-60U

    Page(s): 093502 - 093502-5
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    A high-brightness and low-divergence neutral beam is obtained for a Zeeman polarimetry of edge plasmas on JT-60U. The electron density and the pitch angle of the magnetic field line, thus the plasma current density distribution, can be measured by the Zeeman polarimetry using the lithium beam. A thermionic ion source heated by an electron beam is developed in order to obtain the ion beam current extraction over 10 mA. The beam optics is designed after detailed numerical simulation taking the space charge effects into account because a low-divergence angle of the neutral lithium beam leads to a narrow spectrum of the beam emission. It is also necessary to keep the beam radius small for good spatial resolution due to a long beam line of 6.5 m. The newly developed ion gun is operated on a test stand which simulates the diagnostic arrangement on JT-60U. The ion beam current of 10 mA at a beam energy of 10 keV is successfully extracted from the ion source operated at the temperature over 1300 °C and focused by Einzel lens. The full width at half maximum radius of the ion beam at the neutralizer is about 9 mm. A sodium vapor neutralizer neutralizes the collimated ion beam fully at the temperature of 300 °C. The neutral beam profiles are measured at two locations of the beam line at Z=2.3 m (beam monitor position) and Z=6.5 m (plasma region). The half-width at half maximum radius of the neutral beam of 26 mm and the equivalent beam current of 3 mA with the beam divergence angle of 0.2 deg which is the half-angle divergence are obtained. Those parameters satisfy the requirements of the Zeeman polarimetry. Furthermore, a long pulse extraction with a current of 10 mA and duration of 50 s is attained. View full abstract»

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  • A line-of-sight electron cyclotron emission receiver for electron cyclotron resonance heating feedback control of tearing modes

    Page(s): 093503 - 093503-12
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    An electron cyclotron emission (ECE) receiver inside the electron cyclotron resonance heating (ECRH) transmission line has been brought into operation. The ECE is extracted by placing a quartz plate acting as a Fabry–Perot interferometer under an angle inside the electron cyclotron wave (ECW) beam. ECE measurements are obtained during high power ECRH operation. This demonstrates the successful operation of the diagnostic and, in particular, a sufficient suppression of the gyrotron component preventing it from interfering with ECE measurements. When integrated into a feedback system for the control of plasma instabilities this line-of-sight ECE diagnostic removes the need to localize the instabilities in absolute coordinates. View full abstract»

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  • Absolute intensity calibration of the Wendelstein 7-X high efficiency extreme ultraviolet overview spectrometer system

    Page(s): 093504 - 093504-6
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    The new high effiency extreme ultraviolet overview spectrometer (HEXOS) system for the stellarator Wendelstein 7-X is now mounted for testing and adjustment at the tokamak experiment for technology oriented research (TEXTOR). One part of the testing phase was the intensity calibration of the two double spectrometers which in total cover a spectral range from 2.5 to 160.0 nm with overlap. This work presents the current intensity calibration curves for HEXOS and describes the method of calibration. The calibration was implemented with calibrated lines of a hollow cathode light source and the branching ratio technique. The hollow cathode light source provides calibrated lines from 16 up to 147 nm. We could extend the calibrated region in the spectrometers down to 2.8 nm by using the branching line pairs emitted by an uncalibrated pinch extreme ultraviolet light source as well as emission lines from boron and carbon in TEXTOR plasmas. In total HEXOS is calibrated from 2.8 up to 147 nm, which covers most of the observable wavelength region. The approximate density of carbon in the range of the minor radius from 18 to 35 cm in a TEXTOR plasma determined by simulating calibrated vacuum ultraviolet emission lines with a transport code was 5.5×1017 m-3 which corresponds to a local carbon concentration of 2%. View full abstract»

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  • Design and development of detector signal conditioning electronics for SST-1 Thomson scattering system

    Page(s): 093505 - 093505-6
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    An IR enhanced thermoelectrically cooled Si-avalanche photodiode (Si-APD) module is used for detection of scattered photons from plasma electrons. Present design of signal conditioning electronics for the APD has fast (50 MHz) and slow (500 kHz) channels to measure scattered and plasma background light, respectively. We report design analysis for different stages and their performance. The performance of fast channel is analyzed for two different group delays, speed, linearity, and its cross-talk with slow channel. Temperature dependence of APD’s responsivity is studied in the wavelength range of 900–1060 nm. A minimum detection of ∼25 photoelectrons (with S/N=1) in the range of 5 to 25 °C is achieved at an APD gain of 75 in the present design. View full abstract»

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  • Improved operation of the nonambipolar electron source

    Page(s): 093506 - 093506-8
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    Significant improvements have been made to the nonambipolar electron source (NES), a radio frequency (rf) plasma-based electron source that does not rely on electron emission at a cathode surface [B. Longmier, S. Baalrud, and N. Hershkowitz, Rev. Sci. Instrum. 77, 113504 (2006)]. A prototype NES has produced 30 A of continuous electron current, using 2 SCCM (SCCM denotes cubic centimeter per minute at STP) Xe, 1300 W rf power at 13.56 MHz, yielding a 180 times gas utilization factor. A helicon mode transition has also been identified during NES operation with an argon propellant, using 15 SCCM Ar, 1000 W rf, and 100 G magnetic field. This NES technology has the ability to replace hollow cathode electron sources and to enable high power electric propulsion missions, eliminating one of the lifetime restrictions that many ion thrusters have previously been faced with. View full abstract»

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  • Determination of electron-heated temperatures of petawatt laser-irradiated foil targets with 256 and 68 eV extreme ultraviolet imaging

    Page(s): 093507 - 093507-7
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    Measurements of plasma temperature at the rear surface of foil targets due to heating by hot electrons, which were produced in short pulse high intensity laser matter interactions using the 150 J, 0.5 ps Titan laser, are reported. Extreme ultraviolet (XUV) imaging at 256 and 68 eV energies is used to determine spatially resolved target rear surface temperature patterns by comparing absolute intensities to radiation hydrodynamic modeling. XUV mirrors at these two energies were absolutely calibrated at the Advanced Light Source at the Lawrence Berkeley Laboratory. Temperatures deduced from both imagers are validated against each other within the range of 75–225 eV. View full abstract»

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  • Measuring the temperature of microparticles in plasmas

    Page(s): 093508 - 093508-4
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    Temperature sensitive features of particular phosphors were utilized for measuring the temperature Tp of microparticles, confined in the sheath of a rf plasma. The experiments were performed under variation of argon pressure and rf power of the process plasma. Tp has been determined by evaluation of characteristic fluorescent lines. The results for Tp measurements are strongly dependent on rf power and gas pressure. View full abstract»

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  • Design and implementation of a 120 GHz tracking interferometer with near diffraction limited focal spot

    Page(s): 093509 - 093509-7
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    The design and implementation of a 120 GHz monostatic tracking interferometer with near diffraction limited focal spot size, used to measure line-averaged plasma density in the source of a plasma opening switch (POS), is described. Physical dimensions of the switch source place an upper limit on the focal spot size. Focusing quasioptics utilize a standard pyramidal horn and a pair of cylindrical lenses that are easily fabricated. The combination of the two cylindrical lenses transforms the asymmetric and approximately Gaussian beam produced by the pyramidal horn into a small focal spot. The circuit utilizes a tracking receiver configuration to track oscillator frequency drifts, which allow for full heterodyne quadrature operation, while avoiding the added complexity of phase or frequency locking of the sources. In order to reduce system noise in the POS pulsed power environment, all sources and amplifiers are battery powered and other noise-reducing techniques are employed. Finally, an improved Gaussian optics design methodology, which tracks the phase center of the Gaussian beam, is proposed. While not critical to this application, this method may yield improvements in systems with short focal lengths. View full abstract»

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  • Development of a simple 2.45 GHz microwave plasma with a repulsive double hexapole configuration

    Page(s): 093510 - 093510-6
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    A simple and inexpensive 2.45 GHz microwave plasma source with a repulsive double hexapole configuration is described and characterized. In this work, the operation of the source is shown to be flexible in terms of electron density, electron temperature, and plasma uniformity even at low-pressures (approximately millitorr). It allows for easy control of the electron temperature (2–3.8 eV) and density (∼109–1010 cm-3) by removing either of the two hexapoles or by varying the separation distance between the two hexapoles. Characterization was done via information gathered from the usual Langmuir probe measurements for electron temperature and density. The source makes a resonant surface with its repulsive double hexapole magnetic configuration providing an additional longitudinal confinement near the walls midway between the two hexapoles. Magnetic field maps are presented for varying double hexapole distances. Power delivery for various settings is also presented. View full abstract»

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  • A flexible luminescent probe to monitor fast ion losses at the edge of the TJ-II stellarator

    Page(s): 093511 - 093511-9
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    A mobile luminescent probe has been developed to detect fast ion losses and suprathermal ions escaping from the plasma of the TJ-II stellarator device. The priorities for its design have been flexibility for probe positioning, ease of maintenance, and detector sensitivity. It employs a coherent fiber bundle to relay, to the outside of the vacuum chamber, ionoluminescence images produced by the ions that impinge, after entering the detector head through a pinhole aperture, onto a screen of luminescent material. Ionoluminescence light detection is accomplished by a charge-coupled device camera and by a photomultiplier, both of which are optically coupled to the in-vacuum fiber bundle head by means of a standard optical setup. A detailed description of the detector, and the first results obtained when operated close to the plasma edge, are reported. View full abstract»

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  • Effect of soft metal gasket contacts on contact resistance, energy deposition, and plasma expansion profile in a wire array Z pinch

    Page(s): 093512 - 093512-5
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    Soft metal gaskets (indium and silver) were used to reduce contact resistance between the wire and the electrode in an aluminum wire Z pinch by more than an order of magnitude over the best weighted contact case. Clamping a gasket over a Z-pinch wire compresses the wire to the electrode with a greater normal force than possible with wire weights. Average contact resistance was reduced from the range of 100–3000 Ω (depending on wire weight mass) to 1–10 Ω with soft metal gaskets. Single wire experiments (13 μm Al 5056) on a 16 kA, 100 kV Marx bank showed an increase in light emission (97%) and emission volume (100%) of the plasma for the reduced contact resistance cases. The measured increases in plasma volume and light emission indicate greater energy deposition in the ablated wire. Additionally, dual-wire experiments showed plasma edge effects were significantly decreased in the soft metal gasket contact case. The average height of the edge effects was reduced by 51% and the width of the edge effects was increased by 40%, thus the gasket contact case provided greater axial uniformity in the plasma expansion profile of an individual wire. View full abstract»

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  • A simple cell for the analysis of nanoelectromechanical systems under gas pressure

    Page(s): 093701 - 093701-5
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    A simple yet versatile apparatus for optical microscopy investigations of solid-state devices under high gas pressures is presented. Interchangeable high-grade sapphire windows with different thicknesses allow variable choice of trade-off between the maximum operating pressure and maximum spatial resolution. The capabilities of this compact chamber were tested by performing stroboscopic optical interferometry on nanoelectromechanical systems (NEMSs) under capacitive excitation. With a 1.7 mm thick sapphire window, the cell is safe to operate at pressures ranging from vacuum to 5 MPa. Minimal optical wavefront distortion allows NEMSs with linear dimensions of 0.1×1.6 μm2 to be explored. For a sapphire window with a maximum thickness of 6 mm, the safe operating pressure increases up to an estimated 60 MPa; however, the increasing distortions inhibit signal from NEMSs smaller than ∼0.5×1 μm2. The cell can be used for confocal microscopy, microphotoluminescence and electroluminescence, light scattering spectroscopy, and reflectivity. The light weight and compact design of the chamber allow mounting on a precision piezomotion control stage or inside a volume tight apparatus such as cryostats. 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