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Jan 2007

Volume 78, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 78, 011302 (2007); http://dx.doi.org/10.1063/1.2431313 (39 pages)

R. D. Gehrz, T. L. Roellig, M. W. Werner, G. G. Fazio, J. R. Houck, F. J. Low, G. H. Rieke, B. T. Soifer, D. A. Levine, and E. A. Romana
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Invited Article: A unified evaluation of iterative projection algorithms for phase retrieval

S. Marchesini

Rev. Sci. Instrum. 78, 011301 (2007); http://dx.doi.org/10.1063/1.2403783 (10 pages) | Cited 65 times

Online Publication Date: 25 January 2007

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Iterative projection algorithms are successfully being used as a substitute of lenses to recombine, numerically rather than optically, light scattered by illuminated objects. Images obtained computationally allow aberration-free diffraction-limited imaging and the possibility of using radiation for which no lenses exist. The challenge of this imaging technique is transferred from the lenses to the algorithms. We evaluate these new computational “instruments” developed for the phase-retrieval problem, and discuss acceleration strategies.
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42.30.Wb Image reconstruction; tomography
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The NASA Spitzer Space Telescope

R. D. Gehrz, T. L. Roellig, M. W. Werner, G. G. Fazio, J. R. Houck, F. J. Low, G. H. Rieke, B. T. Soifer, D. A. Levine, and E. A. Romana

Rev. Sci. Instrum. 78, 011302 (2007); http://dx.doi.org/10.1063/1.2431313 (39 pages) | Cited 34 times

Online Publication Date: 30 January 2007

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The National Aeronautics and Space Administration’s Spitzer Space Telescope (formerly the Space Infrared Telescope Facility) is the fourth and final facility in the Great Observatories Program, joining Hubble Space Telescope (1990), the Compton Gamma-Ray Observatory (1991–2000), and the Chandra X-Ray Observatory (1999). Spitzer, with a sensitivity that is almost three orders of magnitude greater than that of any previous ground-based and space-based infrared observatory, is expected to revolutionize our understanding of the creation of the universe, the formation and evolution of primitive galaxies, the origin of stars and planets, and the chemical evolution of the universe. This review presents a brief overview of the scientific objectives and history of infrared astronomy. We discuss Spitzer’s expected role in infrared astronomy for the new millennium. We describe pertinent details of the design, construction, launch, in-orbit checkout, and operations of the observatory and summarize some science highlights from the first two and a half years of Spitzer operations. More information about Spitzer can be found at http://spitzer.caltech.edu/.
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95.55.Fw Space-based ultraviolet, optical, and infrared telescopes
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Photonic Doppler velocimetry of laser-ablated ultrathin metals

A. R. Valenzuela, G. Rodriguez, S. A. Clarke, and K. A. Thomas

Rev. Sci. Instrum. 78, 013101 (2007); http://dx.doi.org/10.1063/1.2424434 (7 pages) | Cited 12 times

Online Publication Date: 4 January 2007

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Obtaining velocity information from the interaction of a laser pulse on a metal layer provides insight into the rapid dynamics of material removal and plasma plume physics during ablation. A traditional approach involves using a velocity interferometer system for any reflector (VISAR) on a reflective metal surface. However, when the target is a thin metal layer, the cohesion of the surface is quickly lost resulting in a large spread of particle velocities that cannot be easily resolved by VISAR. This is due to material ejection“confusing” the VISAR measurement surface, effectively washing out the spatial fringe visibility in the VISAR interferometer. A new heterodyne-based optical velocimeter method is the photonic Doppler velocimeter (PDV). Because PDV tracks motion in a frequency encoded temporal electro-optical signal, velocity information is preserved and allows for multiple velocity components to be recorded simultaneously. The challenge lies in extracting PDV velocity information at short (nanosecond) laser ablation time scales with rapidly varying heterodyne beats by using electronic, optical, and analytical techniques to recover the velocity information from a fleeting signal. Here we show how we have been able to obtain velocity information on the nanosecond time scale and are able to compare it to hydrodynamic simulations. Also, we examine refinements to our PDV system by increasing the bandwidth, utilizing different probes, and sampling different analysis techniques.
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06.30.Gv Velocity, acceleration, and rotation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Large atom number Bose-Einstein condensate of sodium

K. M. R. van der Stam, E. D. van Ooijen, R. Meppelink, J. M. Vogels, and P. van der Straten

Rev. Sci. Instrum. 78, 013102 (2007); http://dx.doi.org/10.1063/1.2424439 (10 pages) | Cited 15 times

Online Publication Date: 4 January 2007

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We describe the setup to create a large Bose-Einstein condensate containing more than 120×106 atoms. In the experiment a thermal beam is slowed by a Zeeman slower and captured in a dark-spot magneto-optical trap (MOT). A typical dark-spot MOT in our experiments contains 2.0×1010 atoms with a temperature of 320 μK and a density of about 1.0×1011 atoms/cm3. The sample is spin polarized in a high magnetic field before the atoms are loaded in the magnetic trap. Spin polarizing in a high magnetic field results in an increase in the transfer efficiency by a factor of 2 compared to experiments without spin polarizing. In the magnetic trap the cloud is cooled to degeneracy in 50 s by evaporative cooling. To suppress the three-body losses at the end of the evaporation, the magnetic trap is decompressed in the axial direction.
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37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
32.60.+i Zeeman and Stark effects
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

High throughput spectrometer for fast localized Doppler measurements

D. Craig, D. J. Den Hartog, D. A. Ennis, S. Gangadhara, and D. Holly

Rev. Sci. Instrum. 78, 013103 (2007); http://dx.doi.org/10.1063/1.2424450 (6 pages) | Cited 12 times

Online Publication Date: 4 January 2007

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A new custom-built duo spectrometer has been commissioned for fast localized Doppler measurements of plasma ions in the Madison Symmetric Torus. The instrument combines very high optical throughput (transmission efficiency of 6% and etendue of 0.80 mm2 sr divided into two simultaneous measurements) with good resolution (λ/Δλ = 5600). The design is a double grating variant of the Czerny-Turner layout and has been carefully optimized for fast (100 kHz) measurements of the C VI line at 343.4 nm. The instrument is currently being applied for high speed charge exchange recombination spectroscopy measurements.
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07.60.Rd Visible and ultraviolet spectrometers
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
42.79.Dj Gratings

Reflection of attosecond x-ray free electron laser pulses

Stefan P. Hau-Riege and Henry N. Chapman

Rev. Sci. Instrum. 78, 013104 (2007); http://dx.doi.org/10.1063/1.2428271 (3 pages) | Cited 2 times

Online Publication Date: 10 January 2007

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In order to utilize hard x-ray free electron lasers (XFEL’s) when they are extended to attosecond pulse lengths, it is necessary to choose optical elements with minimal response time. Specular grazing-incidence optics made of low-Z materials are popular candidates for reflectors since they are likely to withstand x-ray damage and provide sufficiently large reflectivities. Using linear-optics reflection theory, we calculated the transient reflectivity of a delta-function electric pulse from a homogenous semi-infinite medium as a function of angle of incidence for s- and p-polarized light. We specifically considered the pulse response of beryllium, diamond, silicon carbide, and silicon, all of which are of relevance to the XFEL’s that are currently being built. We found that the media emit energy in a damped oscillatory way, and that the impulse-response times are shorter than 0.3 fs for normal incidence. For grazing incidence, the impulse-response time is substantially shorter, making grazing-incidence mirrors a good choice for deep subfemtosecond reflective optics.
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41.60.Cr Free-electron lasers
42.55.Vc X- and γ-ray lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.85.-m X- and γ-ray instruments
41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity

C. Marengoni, F. Canova, D. Batani, R. Benocci, M. Librizzi, V. Narayanan, M. Gomareschi, G. Lucchini, A. Kilpio, E. Shashkov, I. Stuchebrukhov, V. Vovchenko, V. Chernomyrdin, I. Krasuyk, T. Hall, et al.

Rev. Sci. Instrum. 78, 013105 (2007); http://dx.doi.org/10.1063/1.2356853 (8 pages)

Online Publication Date: 17 January 2007

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We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Discrete retardance second harmonic generation ellipsometry

Christopher J. Dehen, R. Michael Everly, Ryan M. Plocinik, Hartmut G. Hedderich, and Garth J. Simpson

Rev. Sci. Instrum. 78, 013106 (2007); http://dx.doi.org/10.1063/1.2400011 (7 pages) | Cited 2 times

Online Publication Date: 17 January 2007

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A new instrument was constructed to perform discrete retardance nonlinear optical ellipsometry (DR-NOE). The focus of the design was to perform second harmonic generation NOE while maximizing sample and application flexibility and minimizing data acquisition time. The discrete retardance configuration results in relatively simple computational algorithms for performing nonlinear optical ellipsometric analysis. NOE analysis of a disperse red 19 monolayer yielded results that were consistent with previously reported values for the same surface system, but with significantly reduced acquisition times.
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07.60.Fs Polarimeters and ellipsometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.15.Eq Optical system design

Stable, mode-matched, medium-finesse optical cavity incorporating a microcantilever mirror: Optical characterization and laser cooling

J. G. E. Harris, B. M. Zwickl, and A. M. Jayich

Rev. Sci. Instrum. 78, 013107 (2007); http://dx.doi.org/10.1063/1.2405373 (4 pages) | Cited 13 times

Online Publication Date: 22 January 2007

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A stable optical resonator has been built using a 30-μm-wide, metal-coated microcantilever as one mirror. The second mirror was a 12.7-mm-diameter concave dielectric mirror. By positioning the two mirrors 75 mm apart in a near-hemispherical configuration, a Fabry-Pérot cavity with a finesse equal to 55 was achieved. The finesse was limited by the optical loss in the cantilever’s metal coating; diffraction losses from the small mirror were negligible. The cavity achieved passive laser cooling of the cantilever’s Brownian motion.
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42.79.Bh Lenses, prisms and mirrors
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

New developments for an electron impact (e,2e)/(e,3e) spectrometer with multiangle collection and multicoincidence detection

F. Catoire, E. M. Staicu-Casagrande, A. Lahmam-Bennani, A. Duguet, A. Naja, X. G. Ren, B. Lohmann, and L. Avaldi

Rev. Sci. Instrum. 78, 013108 (2007); http://dx.doi.org/10.1063/1.2428275 (8 pages) | Cited 19 times

Online Publication Date: 22 January 2007

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We describe new developments aimed to extend the capabilities and the sensitivity of the (e,2e)∕(e,3e) multicoincidence spectrometer at Orsay University [ Duguet et al., Rev. Sci. Instrum. 69, 3524 (1998) ]. The spectrometer has been improved by the addition of a third multiangle detection channel for the fast “scattered” electron. The present system is unique in that it is the only system which combines three toroidal analyzers all equipped with position sensitive detectors, thus allowing the triple coincidence detection of the three electrons present in the final state of an electron impact double ionization process. The setup allows measurement of the angular and energy distributions of the ejected electrons over almost the totality of the collision plane as well as that of the scattered electron over a large range of scattering angles in the forward direction. The resulting gain in sensitivity ( ∼ 25) has rendered feasible a whole class of experiments which could not be otherwise envisaged. The setup is described with a special emphasis on the new toroidal analyzer, data acquisition hardware, and data analysis procedures. The performances are illustrated by selected results of (e,2e) and (e,3e) experiments on the rare gases.
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07.81.+a Electron and ion spectrometers
34.80.Dp Atomic excitation and ionization
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Optimized end station and operating protocols for reflection extended x-ray absorption fine structure (ReflEXAFS) investigations of surface structure at the European Synchrotron Radiation Facility beamline BM29

Víctor López-Flores, Stuart Ansell, Daniel T. Bowron, Sofía Díaz-Moreno, Silvia Ramos, and Adela Muñoz-Páez

Rev. Sci. Instrum. 78, 013109 (2007); http://dx.doi.org/10.1063/1.2409763 (12 pages) | Cited 6 times

Online Publication Date: 22 January 2007

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The development of the capability to engineer the surface properties of materials to match specific requirements demands high quality surface characterization techniques. The ideal tool should provide chemically specific structural characterization as well as surface sensitivity and depth profiling. Ideally the characterization method should also be applicable to systems both with and without long range order. X-ray absorption spectroscopy fine structure, when using the standard transmission detection system, provides all this information with the significant exception of surface sensitivity. In contrast, by detecting the reflected instead of the transmitted beam, it encompasses all these requirements because when the incident beam impinges onto a sample surface at glancing angles, in conditions close to the total reflection, only the outermost regions of the system under study are sampled. Such a technique provides information about the local structure as a function of depth as well as thin layer structure in the case of layered samples. Although it is potentially the ideal tool to study surface modified materials, experimental difficulties have hampered its widespread use in the fields of surface and materials sciences. As a solution to the experimental challenges, we provide a detailed description of an appropriate experimental station, the sample requirements, the measuring protocols, and software routines needed to optimize the collection of the data. To illustrate the capabilities of the technique the results obtained for a model multilayer sample are presented and analyzed under the total external reflection approximation.
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07.85.Nc X-ray and γ-ray spectrometers
78.70.Dm X-ray absorption spectra
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.66.Bz Metals and metallic alloys

High-temperature multipass cell for infrared spectroscopy of heated gases and vapors

R. Bartlome, M. Baer, and M. W. Sigrist

Rev. Sci. Instrum. 78, 013110 (2007); http://dx.doi.org/10.1063/1.2432249 (6 pages) | Cited 5 times

Online Publication Date: 22 January 2007

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In absorption spectroscopy, infrared spectra of heated gases or condensed samples in the vapor phase are usually recorded with a single pass heated gas cell. This device exhibits two orders of magnitude lower sensitivity than the high-temperature multipass cell presented in this article. Our device is a novel type of compact long path absorption cell that can withstand aggressive chemicals in addition to temperatures up to 723 K. The construction of the cell and its technical features are described in detail, paying special attention to the mechanisms that compensate for thermal expansion and that allow the user to vary the optical path length under any thermal or vacuum condition. The cell may be used with a laser source or implemented within a Fourier transform infrared spectrometer. Its design is compatible with optical arrangements using astigmatic mirrors or spherical mirrors in a Herriott configuration. Here we implement a homebuilt Herriott-type cell with a total optical path length of up to 35 m. In order to demonstrate the feasibility of the cell, methane and water vapor absorption lines showing dissimilar temperature effects on line intensity were recorded with the help of a mid-infrared laser source tunable between 3 and 4 μm. Emphasis is put on lines that are too weak to be recorded with a single pass cell.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
82.80.Dx Analytical methods involving electronic spectroscopy
07.20.Ka High-temperature instrumentation; pyrometers

Photoreflectance spectroscopy with a step-scan Fourier-transform infrared spectrometer: Technique and applications

Jun Shao, Wei Lu, Fangyu Yue, Xiang Lü, Wei Huang, Zhifeng Li, Shaoling Guo, and Junhao Chu

Rev. Sci. Instrum. 78, 013111 (2007); http://dx.doi.org/10.1063/1.2432269 (8 pages) | Cited 15 times

Online Publication Date: 24 January 2007

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We report on a new technique of realizing photoreflectance (PR) spectroscopy with a step-scan Fourier-transform infrared spectrometer. The experimental configuration is briefly described and a detailed theoretical analysis is conducted. The results reveal two distinct features of this PR technique that (i) the PR related signal is enhanced by a factor of at least 100 relative to those of the conventional PR techniques and (ii) the unwanted spurious signal introduced by either diffuse reflected pump beam or pump-beam induced material’s photoluminescence reaching the photodetector of the PR configuration is eliminated without any special consideration of normalization for deducing the final PR spectrum. Applications are given as examples in the study of GaNAs/GaAs single quantum wells and GaInP/AlGaInP multiple quantum wells, respectively, under different pump-beam excitation energy and/or power. The experimental results approve the theoretically predicted features and illustrate the possibility of investigating weak PR features by using high pump-beam power. A brief comparison of this technique with the conventional PR techniques is given, and the extendibility of this technique to long-wavelength spectral regions is pointed out.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
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Quasianamorphic optical imaging system with tomographic reconstruction for electron beam imaging

H. Bender, C. Carlson, D. Frayer, D. Johnson, K. Jones, A. Meidinger, and C. Ekdahl

Rev. Sci. Instrum. 78, 013301 (2007); http://dx.doi.org/10.1063/1.2409770 (8 pages) | Cited 1 time

Online Publication Date: 4 January 2007

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We have developed a quasianamorphic optical tomography system coupled to a streak camera to provide continuous recording of the electron beam profile of an intense, long-pulse induction accelerator. A tomographic reconstruction method based on a maximum-entropy algorithm is used to reconstruct the images. The system has simplified the calculation of beam moments, eliminated ambiguity due to beam motion, and contributed to accelerator tuning.
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07.68.+m Photography, photographic instruments; xerography
42.30.Wb Image reconstruction; tomography
29.40.-n Radiation detectors
29.27.Fh Beam characteristics

Lithium ion sources for investigations of fast ion transport in magnetized plasmas

Y. Zhang, H. Boehmer, W. W. Heidbrink, R. McWilliams, D. Leneman, and S. Vincena

Rev. Sci. Instrum. 78, 013302 (2007); http://dx.doi.org/10.1063/1.2431086 (8 pages) | Cited 12 times

Online Publication Date: 10 January 2007

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In order to study the interaction of ions of intermediate energies with plasma fluctuations, two plasma immersible lithium ion sources, based on solid-state thermionic emitters (Li aluminosilicate) were developed. Compared to discharge based ion sources, they are compact, have zero gas load, small energy dispersion, and can be operated at any angle with respect to an ambient magnetic field of up to 4.0 kG. Beam energies range from 400 eV to 2.0 keV with typical beam current densities in the 1 mA/cm2 range. Because of the low ion mass, beam velocities of 100–300 km/s are in the range of Alfvén speeds in typical helium plasmas in the large plasma device.
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52.25.Fi Transport properties
52.25.Xz Magnetized plasmas
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)

Apparatus for time-resolved and energy-resolved measurement of internal conversion electron emission induced by nuclear resonant excitation with synchrotron radiation

Taizo Kawauchi, Masuaki Matsumoto, Katsuyuki Fukutani, Tatsuo Okano, Shunji Kishimoto, Xiaowei Zhang, and Yoshitaka Yoda

Rev. Sci. Instrum. 78, 013303 (2007); http://dx.doi.org/10.1063/1.2431754 (4 pages) | Cited 2 times

Online Publication Date: 22 January 2007

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A high-energy and large-object-spot type cylindrical mirror analyzer (CMA) was constructed with the aid of electron trajectory simulations. By adopting a particular shape for the outer cylinder, an energy resolution of 7% was achieved without guide rings as used in conventional CMAs. Combined with an avalanche photodiode as an electron detector, the K-shell internal conversion electrons were successfully measured under irradiation of synchrotron radiation at 14.4 keV in an energy-resolved and time-resolved manner.
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29.40.-n Radiation detectors
85.60.Dw Photodiodes; phototransistors; photoresistors
78.47.-p Spectroscopy of solid state dynamics
79.20.Fv Electron impact: Auger emission
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Study of saturation of CR39 nuclear track detectors at high ion fluence and of associated artifact patterns

S. Gaillard, J. Fuchs, N. Renard-Le Galloudec, and T. E. Cowan

Rev. Sci. Instrum. 78, 013304 (2007); http://dx.doi.org/10.1063/1.2400020 (13 pages) | Cited 15 times

Online Publication Date: 24 January 2007

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The occurrence of saturation in CR39 solid state nuclear track detectors has been systematically studied as a function of the incident ion (α particles and laser-accelerated protons) fluence and the etching time. When overexposed (i.e., for fluences above ∼ 108 particles/cm2) and/or overetched, the CR39 detectors enter a saturated regime where direct track counting is not possible anymore. In this regime, optical measurements of saturated CR39 detectors become unreliable as well, since the optical response of the saturated detectors with respect to the ion fluence is highly nonlinear. This nonlinear optical response is likely due to scattering from the surface of irregular clumping patterns which have a diameter ∼ 20 μm, i.e., ten times larger than the diameter of individual tracks. These patterns, which aggregate many individual tracks, are observed to develop in highly saturated regimes. For fluences typical of high energy short pulse laser experiments, saturation occurs, inducing the appearance of artifact ringlike structures. By careful microscopic analysis, these artifact ring patterns can be distinguished from the genuine rings occurring below saturation and characteristic of low energy laser accelerated proton beams.
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29.40.Gx Tracking and position-sensitive detectors

Electron gun using carbon-nanofiber field emitter

Y. Sakai, A. Haga, S. Sugita, S. Kita, S.-I. Tanaka, F. Okuyama, and N. Kobayashi

Rev. Sci. Instrum. 78, 013305 (2007); http://dx.doi.org/10.1063/1.2430650 (6 pages) | Cited 14 times

Online Publication Date: 30 January 2007

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An electron gun constructed using carbon-nanofiber (CNF) emitters and an electrostatic Einzel lens system has been characterized for the development of a high-resolution x-ray source. The CNFs used were grown on tungsten and palladium tips by plasma-enhanced chemical-vapor deposition. Electron beams with the energies of 10<E<20 keV were focused by the electrostatic lens and impinged on a W target for x-ray radiography. Analyzing the recorded x-ray radiographs, the focal spot size of the electron beam extracted from the CNFs was estimated to be D<50 μm in diameter. Superior performance was realized by using CNFs with larger fiber radii (100–500 nm) grown sparsely on the metal tips, which were installed in a holder at the short length L = 0.5 mm.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
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Wire tomography in the H-1NF heliac for investigation of fine structure of magnetic islands

Santhosh T. A. Kumar, Boyd D. Blackwell, and Jeffrey H. Harris

Rev. Sci. Instrum. 78, 013501 (2007); http://dx.doi.org/10.1063/1.2424453 (7 pages) | Cited 3 times

Online Publication Date: 4 January 2007

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Electron beam wire tomography in the H-1NF heliac enables high resolution mapping of vacuum flux surfaces with minimal disruption of the plasma operations schedule. Recent experimental results have proven this technique to be a highly accurate and high resolution method for mapping vacuum magnetic islands. Islands of width as small as δ ∼ 8 mm have been measured, providing estimates of the internal rotational transform of the island. Point-to-point comparison of the mapping results with computer tracing, in conjunction with an image warping technique, enables systematic exploration of magnetic islands and surfaces of interest. Recent development of a fast mapping technique significantly reduced the mapping time and made this technique suitable for mapping at higher magnetic fields. This article presents recent experimental results and associated techniques.
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52.70.La X-ray and γ-ray measurements
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.40.Mj Particle beam interactions in plasmas
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Bipolar pulse generator for intense pulsed ion beam accelerator

H. Ito, K. Igawa, I. Kitamura, and K. Masugata

Rev. Sci. Instrum. 78, 013502 (2007); http://dx.doi.org/10.1063/1.2424455 (5 pages) | Cited 2 times

Online Publication Date: 10 January 2007

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A new type of pulsed ion beam accelerator named “bipolar pulse accelerator” (BPA) has been proposed in order to improve the purity of intense pulsed ion beams. To confirm the principle of the BPA, we developed a bipolar pulse generator for the bipolar pulse experiment, which consists of a Marx generator and a pulse forming line (PFL) with a rail gap switch on its end. In this article, we report the first experimental result of the bipolar pulse and evaluate the electrical characteristics of the bipolar pulse generator. When the bipolar pulse generator was operated at 70% of the full charge condition of the PFL, the bipolar pulse with the first (−138 kV, 72 ns) and the second pulse (+130 kV, 70 ns) was successfully obtained. The evaluation of the electrical characteristics indicates that the developed generator can produce the bipolar pulse with fast rise time and sharp reversing time.
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29.20.-c Accelerators
84.30.Ng Oscillators, pulse generators, and function generators

Diagnosing pure-electron plasmas with internal particle flux probes

J. P. Kremer, T. Sunn Pedersen, Q. Marksteiner, R. G. Lefrancois, and M. Hahn

Rev. Sci. Instrum. 78, 013503 (2007); http://dx.doi.org/10.1063/1.2431084 (9 pages) | Cited 17 times

Online Publication Date: 22 January 2007

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Techniques for measuring local plasma potential, density, and temperature of pure-electron plasmas using emissive and Langmuir probes are described. The plasma potential is measured as the least negative potential at which a hot tungsten filament emits electrons. Temperature is measured, as is commonly done in quasineutral plasmas, through the interpretation of a Langmuir probe current-voltage characteristic. Due to the lack of ion-saturation current, the density must also be measured through the interpretation of this characteristic thereby greatly complicating the measurement. Measurements are further complicated by low densities, low cross field transport rates, and large flows typical of pure-electron plasmas. This article describes the use of these techniques on pure-electron plasmas in the Columbia Non-neutral Torus (CNT) stellarator. Measured values for present baseline experimental parameters in CNT are ϕp = −200±2 V, Te = 4±1 eV, and ne on the order of 1012 m−3 in the interior.
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52.70.Ds Electric and magnetic measurements
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow

A retractable electron emitter for the creation of unperturbed pure electron plasmas

John W. Berkery, Thomas Sunn Pedersen, and Luis Sampedro

Rev. Sci. Instrum. 78, 013504 (2007); http://dx.doi.org/10.1063/1.2431090 (6 pages) | Cited 4 times

Online Publication Date: 30 January 2007

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A retractable electron emitter has been constructed for the creation of unperturbed pure electron plasmas on magnetic surfaces in the Columbia Non-neutral Torus stellarator. The previous method of electron emission using emitters mounted on stationary rods limited the confinement time to 20 ms. A pneumatically driven system that can retract from the magnetic axis to the last closed flux surface in less than 20 ms while filling the surfaces with electrons was designed. The motion of the retractable emitter was modeled with a system of dynamical equations. The measured position versus time of the emitter agrees well with the model and the fastest axis-to-edge retraction was measured to be 20 ms with 40 psig helium gas driving the pneumatic piston.
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52.50.-b Plasma production and heating
52.55.Jd Magnetic mirrors, gas dynamic traps
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.70.-m Plasma diagnostic techniques and instrumentation

New Thomson scattering diagnostic on RFX-mod

A. Alfier and R. Pasqualotto

Rev. Sci. Instrum. 78, 013505 (2007); http://dx.doi.org/10.1063/1.2431769 (7 pages) | Cited 35 times

Online Publication Date: 31 January 2007

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This article describes the completely renovated Thomson scattering (TS) diagnostic employed in the modified Reversed Field eXperiment (RFX-mod) since it restarted operation in 2005. The system measures plasma electron temperature and density profiles along an equatorial diameter, measuring in 84 positions with 7 mm spatial resolution. The custom built Nd:YLF laser produces a burst of 10 pulses at 50 Hz with energy of 3 J, providing ten profile measurements in a plasma discharge of about 300 ms duration. An optical delay system accommodates three scattering volumes in each of the 28 interference filter spectrometers. Avalanche photodiodes detect the Thomson scattering signals and allow them to be recorded by means of waveform digitizers. Electron temperature is obtained using an alternative relative calibration method, based on the use of a supercontinuum light source. Rotational Raman scattering in nitrogen has supplied the absolute calibration for the electron density measurements. During RFX-mod experimental campaigns in 2005, the TS diagnostic has demonstrated its performance, routinely providing reliable high resolution profiles.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.-b Plasma properties
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
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Tomography experiment of an integrated circuit specimen using 3 MeV electrons in the transmission electron microscope

Hai-Bo Zhang, Xiang-Liang Zhang, Yong Wang, and Akio Takaoka

Rev. Sci. Instrum. 78, 013701 (2007); http://dx.doi.org/10.1063/1.2409864 (4 pages) | Cited 6 times

Online Publication Date: 4 January 2007

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The possibility of utilizing high-energy electron tomography to characterize the micron-scale three dimensional (3D) structures of integrated circuits has been demonstrated experimentally. First, electron transmission through a tilted SiO2 film was measured with an ultrahigh-voltage electron microscope (ultra-HVEM) and analyzed from the point of view of elastic scattering of electrons, showing that linear attenuation of the logarithmic electron transmission still holds valid for effective specimen thicknesses up to 5 μm under 2 MV accelerating voltages. Electron tomography of a micron-order thick integrated circuit specimen including the Cu/via interconnect was then tried with 3 MeV electrons in the ultra-HVEM. Serial projection images of the specimen tilted at different angles over the range of ±90° were acquired, and 3D reconstruction was performed with the images by means of the IMOD software package. Consequently, the 3D structures of the Cu lines, via and void, were revealed by cross sections and surface rendering.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.30.Wb Image reconstruction; tomography
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Feedforward control of a closed-loop piezoelectric translation stage for atomic force microscope

Yang Li and John Bechhoefer

Rev. Sci. Instrum. 78, 013702 (2007); http://dx.doi.org/10.1063/1.2403839 (8 pages) | Cited 9 times

Online Publication Date: 11 January 2007

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Simple feedforward ideas are shown to lead to a nearly tenfold increase in the effective bandwidth of a closed-loop piezoelectric positioning stage used in scanning probe microscopy. If the desired control signal is known in advance, the feedforward filter can be acausal: the information about the future can be used to make the output of the stage have almost no phase lag with respect to the input. This keeps in register the images assembled from right and left scans. We discuss the design constraints imposed by the need for the feedforward filter to work robustly under a variety of circumstances. Because the feedforward needs only to modify the input signal, it can be added to any piezoelectric stage, whether closed or open loop.
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07.79.Lh Atomic force microscopes
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