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Feb 2012

Volume 83, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 021101 (2012); http://dx.doi.org/10.1063/1.3681448 (28 pages)

Judah Levine

The many faces of time and frequency metrology. © Salvador Dalí, Fundació Gala-Salvador Dalí / Artists Rights Society (ARS), New York, 2011.

(Left image)

Rev. Sci. Instrum. 83, 021102 (2012);http://dx.doi.org/10.1063/1.3682002 (7 pages)

Thomas E. Parker

SI second is realized by cesium fountain primary frequency standards such as NIST-F1 shown here. NISTF1 is operated by the National Institute of Standards and Technology in Boulder, Colorado, USA. However, other systems also play a significant role in the accuracy of the SI second as delivered to users (©2005 Geoffrey Wheeler Photography).

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Invited Review Article: The statistical modeling of atomic clocks and the design of time scales

Judah Levine

Rev. Sci. Instrum. 83, 021101 (2012); http://dx.doi.org/10.1063/1.3681448 (28 pages)

Online Publication Date: 23 February 2012

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I will show how the statistical models that are used to describe the performance of atomic clocks are derived from their internal design. These statistical models form the basis for time scales, which are used to define international time scales such as International Atomic Time and Coordinated Universal Time. These international time scales are realized by ensembles of clocks at national laboratories such as the National Institute of Standards and Technology, and I will describe how ensembles of atomic clocks are characterized and managed.
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06.30.Ft Time and frequency

Invited Review Article: The uncertainty in the realization and dissemination of the SI second from a systems point of view

Thomas E. Parker

Rev. Sci. Instrum. 83, 021102 (2012); http://dx.doi.org/10.1063/1.3682002 (7 pages)

Online Publication Date: 23 February 2012

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The uncertainty (accuracy) in the realization and dissemination of the SI second is determined by the characteristics of three major components: (1) primary frequency standards, (2) time scale flywheels that provide a continuously present frequency reference, and (3) frequency transfer systems. Currently these three systems contribute at approximately equal levels in the mid 10−16 range over 20 to 30 days of averaging time to the practical delivery of the SI second to the most demanding users. Any significant improvement in one system requires similar improvements in the other two systems in order for most users to see the full benefits.
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06.20.fa Units
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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

A capillary absorption spectrometer for stable carbon isotope ratio (13C/12C) analysis in very small samples

J. F. Kelly, R. L. Sams, T. A. Blake, M. Newburn, J. Moran, M. L. Alexander, and H. Kreuzer

Rev. Sci. Instrum. 83, 023101 (2012); http://dx.doi.org/10.1063/1.3680593 (14 pages)

Online Publication Date: 6 February 2012

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A capillary absorption spectrometer (CAS) suitable for IR laser isotope analysis of small CO2 samples is presented. The system employs a continuous-wave (cw) quantum cascade laser to study nearly adjacent rovibrational transitions of different isotopologues of CO2 near 2307 cm−1 (4.34 μm). This initial CAS system can achieve relative isotopic precision of about 10 ppm 13C, or ∼1‰ (per mil in delta notation relative to Vienna Pee Dee Belemnite) with 20–100 picomoles of entrained sample within the hollow waveguide for CO2 concentrations ∼400–750 ppm. Isotopic analyses of such gas fills in a 1-mm ID hollow waveguide of 0.8 m overall physical path length can be carried out down to ∼2 Torr. Overall 13C/12C ratios can be calibrated to ∼2‰ accuracy with diluted CO2 standards. A novel, low-cost method to reduce cw-fringing noise resulting from multipath distortions in the hollow waveguide is presented, which allows weak absorbance features to be studied at the few ppm level (peak-to-rms) after 1000 scans are co-added in ∼10 s. The CAS is meant to work directly with converted CO2 samples from a laser ablation-catalytic combustion micro-sampler to provide 13C/12C ratios of small biological isolates currently operating with spatial resolutions ∼50 μm.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.55.Px Semiconductor lasers; laser diodes

The electron spectro-microscopy beamline at National Synchrotron Light Source II: A wide photon energy range, micro-focusing beamline for photoelectron spectro-microscopies

R. Reininger, S. L. Hulbert, P. D. Johnson, J. T. Sadowski, D. E. Starr, O. Chubar, T. Valla, and E. Vescovo

Rev. Sci. Instrum. 83, 023102 (2012); http://dx.doi.org/10.1063/1.3681440 (8 pages)

Online Publication Date: 13 February 2012

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A comprehensive optical design for a high-resolution, high-flux, wide-energy range, micro-focused beamline working in the vacuum ultraviolet and soft x-ray photon energy range is proposed. The beamline is to provide monochromatic radiation to three photoelectron microscopes: a full-field x-ray photoelectron emission microscope and two scanning instruments, one dedicated to angle resolved photoemission spectroscopy (μ-ARPES) and one for ambient pressure x-ray photoelectron spectroscopy and scanning photoelectron microscopy (AP-XPS/SPEM). Microfocusing is achieved with state of the art elliptical cylinders, obtaining a spot size of 1 μm for ARPES and 0.5 μm for AP-XPS/SPEM. A detailed ray tracing analysis quantitatively evaluates the overall beamline performances.
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07.85.-m X- and γ-ray instruments
07.85.Tt X-ray microscopes
29.30.Kv X- and γ-ray spectroscopy
42.15.Dp Wave fronts and ray tracing

Penning traps with unitary architecture for storage of highly charged ions

Joseph N. Tan, Samuel M. Brewer, and Nicholas D. Guise

Rev. Sci. Instrum. 83, 023103 (2012); http://dx.doi.org/10.1063/1.3685246 (8 pages)

Online Publication Date: 15 February 2012

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Penning traps are made extremely compact by embedding rare-earth permanent magnets in the electrode structure. Axially-oriented NdFeB magnets are used in unitary architectures that couple the electric and magnetic components into an integrated structure. We have constructed a two-magnet Penning trap with radial access to enable the use of laser or atomic beams, as well as the collection of light. An experimental apparatus equipped with ion optics is installed at the NIST electron beam ion trap (EBIT) facility, constrained to fit within 1 meter at the end of a horizontal beamline for transporting highly charged ions. Highly charged ions of neon and argon, extracted with initial energies up to 4000 eV per unit charge, are captured and stored to study the confinement properties of a one-magnet trap and a two-magnet trap. Design considerations and some test results are discussed.
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41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles
41.85.Ja Particle beam transport
29.27.Eg Beam handling; beam transport
29.25.-t Particle sources and targets

Precise real-time polarization measurement of terahertz electromagnetic waves by a spinning electro-optic sensor

Naoya Yasumatsu and Shinichi Watanabe

Rev. Sci. Instrum. 83, 023104 (2012); http://dx.doi.org/10.1063/1.3683570 (7 pages)

Online Publication Date: 16 February 2012

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We propose and develop a method to quickly and precisely determine the polarization direction of coherent terahertz electromagnetic waves generated by femtosecond laser pulses. The measurement system consists of a conventional terahertz time-domain spectroscopy system with the electro-optic (EO) sampling method, but we add a new functionality in the EO crystal which is continuously rotating with the angular frequency ω. We find a simple yet useful formulation of the EO signal as a function of the crystal orientation, which enables a lock-in-like detection of both the electric-field amplitude and the absolute polarization direction of the terahertz waves with respect to the probe laser pulse polarization direction at the same time. The single measurement finishes around two periods of the crystal rotations (∼21 ms), and we experimentally prove that the accuracy of the polarization measurement does not suffer from the long-term amplitude fluctuation of the terahertz pulses. Distribution of the measured polarization directions by repeating the measurements is excellently fitted by a Gaussian distribution function with a standard deviation of σ = 0.56°. The developed technique is useful for the fast direct determination of the polarization state of the terahertz electromagnetic waves for polarization imaging applications as well as the precise terahertz Faraday or Kerr rotation spectroscopy.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
42.79.-e Optical elements, devices, and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Hard x-ray monochromator with milli-electron volt bandwidth for high-resolution diffraction studies of diamond crystals

Stanislav Stoupin, Yuri Shvyd'ko, Deming Shu, Ruben Khachatryan, Xianghui Xiao, Francesco DeCarlo, Kurt Goetze, Timothy Roberts, Christian Roehrig, and Alexey Deriy

Rev. Sci. Instrum. 83, 023105 (2012); http://dx.doi.org/10.1063/1.3684876 (6 pages)

Online Publication Date: 17 February 2012

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We report on design and performance of a high-resolution x-ray monochromator with a spectral bandwidth of ΔEX ≃ 1.5 meV, which operates at x-ray energies in the vicinity of the backscattering (Bragg) energy EH = 13.903 keV of the (008) reflection in diamond. The monochromator is utilized for high-energy-resolution diffraction characterization of diamond crystals as elements of advanced x-ray crystal optics for synchrotrons and x-ray free-electron lasers. The monochromator and the related controls are made portable such that they can be installed and operated at any appropriate synchrotron beamline equipped with a pre-monochromator.
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07.85.-m X- and γ-ray instruments

A momentum imaging microscope for dissociative electron attachment

H. Adaniya, D. S. Slaughter, T. Osipov, T. Weber, and A. Belkacem

Rev. Sci. Instrum. 83, 023106 (2012); http://dx.doi.org/10.1063/1.3685244 (7 pages)

Online Publication Date: 23 February 2012

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We describe an experimental approach to image the three-dimensional (3D) momentum distribution of the negative ions arising from dissociative electron attachment (DEA). The experimental apparatus employs a low energy pulsed electron gun, an effusive gas source and a 4π solid-angle ion momentum imaging spectrometer consisting of a pulsed ion extraction field, an electrostatic lens, and a time- and position-sensitive detector. The time-of-flight and impact position of each negative ion are measured event by event in order to image the full 3D ion momentum sphere. The system performance is tested by measuring the anion momentum distributions from two DEA resonances, namely H− from H2O− (2B1) and O− from O2− (2Πu). The results are compared with existing experimental and theoretical data.
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34.80.Ht Dissociation and dissociative attachment

Narrow linewidth tunable external cavity diode laser using wide bandwidth filter

Daniel J. Thompson and Robert E. Scholten

Rev. Sci. Instrum. 83, 023107 (2012); http://dx.doi.org/10.1063/1.3687441 (5 pages)

Online Publication Date: 24 February 2012

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We demonstrate single mode operation of an external cavity diode laser (ECDL) employing an interference filter with multimode bandwidth for mode selection. A cateye reflector maximizes feedback efficiency and reduces susceptibility to intra-cavity optical misalignment. Narrow linewidths of 26 kHz are observed, and the laser can be tuned over 14 nm using a single 785 nm filter, without alteration of the output beam direction. The cateye reflector and filter allow a mechanically rigid design free of significant mechanical resonances, illustrated by comparison of the frequency noise spectrum with that of a common Littrow ECDL design using a diffraction grating and kinematic mount.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Ci Filters, zone plates, and polarizers

Measurement of probe displacement to the thermal resolution limit in photonic force microscopy using a miniature quadrant photodetector

Sambit Bikas Pal, Arijit Haldar, Basudev Roy, and Ayan Banerjee

Rev. Sci. Instrum. 83, 023108 (2012); http://dx.doi.org/10.1063/1.3685616 (12 pages)

Online Publication Date: 24 February 2012

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A photonic force microscope comprises of an optically trapped micro-probe and a position detection system to track the motion of the probe. Signal collection for motion detection is often carried out using the backscattered light off the probe–however, this mode has problems of low S/N due to the small backscattering cross sections of the micro-probes typically used. The position sensors often used in these cases are quadrant photodetectors. To ensure maximum sensitivity of such detectors, it would help if the detector size matched with the detection beam radius after the condenser lens (which for backscattered detection would be the trapping objective itself). To suit this condition, we have used a miniature displacement sensor whose dimensions makes it ideal to work with 1:1 images of micrometer-sized trapped probes in the backscattering detection mode. The detector is based on the quadrant photo-integrated chip in the optical pick-up head of a compact disc player. Using this detector, we measured absolute displacements of an optically trapped 1.1 μm probe with a resolution of ∼10 nm for a bandwidth of 10 Hz at 95% significance without any sample or laser stabilization. We characterized our optical trap for different sized probes by measuring the power spectrum for each probe to 1% accuracy, and found that for 1.1 μm diameter probes, the noise in our position measurement matched the thermal resolution limit for averaging times up to 10 ms. We also achieved a linear response range of around 385 nm with cross talk between axes ≃4% for 1.1 μm diameter probes. The detector has extremely high bandwidth (few MHz) and low optical power threshold–other factors that can lead to its widespread use in photonic force microscopy.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
85.60.Gz Photodetectors (including infrared and CCD detectors)

Development of soft x-ray time-resolved photoemission spectroscopy system with a two-dimensional angle-resolved time-of-flight analyzer at SPring-8 BL07LSU

Manami Ogawa, Susumu Yamamoto, Yuka Kousa, Fumitaka Nakamura, Ryu Yukawa, Akiko Fukushima, Ayumi Harasawa, Hiroshi Kondoh, Yoshihito Tanaka, Akito Kakizaki, and Iwao Matsuda

Rev. Sci. Instrum. 83, 023109 (2012); http://dx.doi.org/10.1063/1.3687428 (7 pages)

Online Publication Date: 27 February 2012

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We have developed a soft x-ray time-resolved photoemission spectroscopy system using synchrotron radiation (SR) at SPring-8 BL07LSU and an ultrashort pulse laser system. Two-dimensional angle-resolved measurements were performed with a time-of-flight-type analyzer. The photoemission spectroscopy system is synchronized to light pulses of SR and laser using a time control unit. The performance of the instrument is demonstrated by mapping the band structure of a Si(111) crystal over the surface Brillouin zones and observing relaxation of the surface photo-voltage effect using the pump (laser) and probe (SR) method.
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07.85.Nc X-ray and γ-ray spectrometers
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
71.20.Mq Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.20.At Surface states, band structure, electron density of states

Compact terahertz passive spectrometer with wideband superconductor-insulator-superconductor mixer

K. Kikuchi, S. Kohjiro, T. Yamada, N. Shimizu, and A. Wakatsuki

Rev. Sci. Instrum. 83, 023110 (2012); http://dx.doi.org/10.1063/1.3687430 (4 pages)

Online Publication Date: 28 February 2012

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We developed a compact terahertz (THz) spectrometer with a superconductor-insulator-superconductor (SIS) mixer, aiming to realize a portable and highly sensitive spectrometer to detect dangerous gases at disaster sites. The receiver cryostat which incorporates the SIS mixer and a small cryocooler except for a helium compressor has a weight of 27 kg and dimensions of 200 mm × 270 mm × 690 mm. In spite of the small cooling capacity of the cryocooler, the SIS mixer is successfully cooled lower than 4 K, and the temperature variation is suppressed for the sensitive measurement. By adopting a frequency sweeping system using photonic local oscillator, we demonstrated a spectroscopic measurement of CH3CN gas in 0.2–0.5 THz range.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
85.25.-j Superconducting devices
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Characteristics of low-energy ion beams extracted from a wire electrode geometry

M. Vasquez, Jr., S. Tokumura, T. Kasuya, S. Maeno, and M. Wada

Rev. Sci. Instrum. 83, 023301 (2012); http://dx.doi.org/10.1063/1.3680105 (6 pages)

Online Publication Date: 2 February 2012

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Beams of argon ions with energies less than 50 eV were extracted from an ion source through a wire electrode extractor geometry. A retarding potential energy analyzer (RPEA) was constructed in order to characterize the extracted ion beams. The single aperture RPEA was used to determine the ion energy distribution function, the mean ion energy and the ion beam energy spread. The multi-cusp hot cathode ion source was capable of producing a low electron temperature gas discharge to form quiescent plasmas from which ion beam energy as low as 5 eV was realized. At 50 V extraction potential and 0.1 A discharge current, the ion beam current density was around 0.37 mA/cm2 with an energy spread of 3.6 V or 6.5% of the mean ion energy. The maximum ion beam current density extracted from the source was 0.57 mA/cm2 for a 50 eV ion beam and 1.78 mA/cm2 for a 100 eV ion beam.
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29.27.Ac Beam injection and extraction
52.25.Fi Transport properties
52.50.Dg Plasma sources
52.80.-s Electric discharges
29.25.Ni Ion sources: positive and negative

The dependence of extracted current on discharge gas pressure in neutral beam ion sources on HL-2A tokamak

H. L. Wei, J. Y. Cao, J. Rao, G. J. Lei, S. F. Jiang, H. Liu, L. M. Yu, W. M. Xie, M. Li, X. F. Yang, G. Q. Zou, D. L. Lu, and X. R. Duan

Rev. Sci. Instrum. 83, 023302 (2012); http://dx.doi.org/10.1063/1.3681446 (4 pages)

Online Publication Date: 7 February 2012

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The discharge gas pressure is a key factor to influence the extracted current of ion source. In this paper, the dependence of extracted current on discharge gas pressure was investigated in detail at different arc discharge currents. The discharge gas pressure with a very broad range (0.1 Pa–2.7 Pa) was scanned for the first time. It is turned out that, with the increasing of discharge gas pressure, the extracted current increases and the arc voltage decreases at different arc currents; however, when the discharge gas pressure exceeds a certain value, the extracted current decreases. For the same discharge gas pressure, the higher the arc current, the higher the arc voltage and the extracted current are. The arc efficiency was also calculated, and its dependence on gas pressure was almost the same with the dependence of extracted current on gas pressure, but at the same discharge gas pressure, the lower the arc current, the higher the arc efficiency is and the lower the extracted current is.
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52.55.Fa Tokamaks, spherical tokamaks
52.50.Gj Plasma heating by particle beams
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.50.Dg Plasma sources
52.25.Fi Transport properties

Simulations of ionization in a hot cavity surface ion source

M. Turek, A. Droździel, K. Pyszniak, D. Mączka, and B. Słowiński

Rev. Sci. Instrum. 83, 023303 (2012); http://dx.doi.org/10.1063/1.3685247 (9 pages)

Online Publication Date: 15 February 2012

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A new numerical Monte Carlo method based model of a hot cavity surface ionization ion source is presented in this paper. The model, intended to support the studies on ionization phenomena in a widely used class of ion sources, takes into account geometry of the ion source and extraction system, ionizer temperature and other features. The results of ion source efficiency calculations for various configurations of the extraction field are reviewed. The dominant role of the ionizer region near the extraction opening is described. Simulated dependences of ionization efficiency on the working parameters like ionizer length and temperature, ionization potential of the substance, and extraction voltage are discussed. A good agreement of the experimental data (e.g., influence of ionizer temperature, current-voltage curve) and the predictions of the model is found. It is also shown that the contribution to the ionization yield from impact of thermionic electrons accelerated by the extraction field may be significant, especially for the substances of small surface ionization coefficient. The simulation results are compared to the predictions of different theoretical models of the ion source—the obtained simulation data are in accordance both with a well-known Kirchner formula and the so called spherical ionizer model.
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29.25.Ni Ion sources: positive and negative
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
05.10.Ln Monte Carlo methods
back to top Nuclear Physics, Fusion and Plasmas

Improved chopping of a lithium beam for plasma edge diagnostic at ASDEX Upgrade

M. Willensdorfer, E. Wolfrum, R. Fischer, J. Schweinzer, M. Sertoli, B. Sieglin, G. Veres, F. Aumayr, and the ASDEX Upgrade Team

Rev. Sci. Instrum. 83, 023501 (2012); http://dx.doi.org/10.1063/1.3682003 (7 pages)

Online Publication Date: 6 February 2012

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The lithium beam diagnostic at ASDEX Upgrade routinely delivers electron density profiles in the plasma edge by lithium beam impact excitation spectroscopy. An accurate background subtraction requires a periodically chopped lithium beam. A new, improved chopping system was developed and installed. It involves a voltage modulation for the extractor electrode and the beam deflection plates. The modulation of the extractor electrode reduces the unused portion of lithium ions and improves the stability of the beam with respect to its position. Furthermore, the data indicate an extended emitter lifetime. The extractor chopping was also found to be insensitive to sparks. The deflection chopping experiments demonstrated beam chopping in the kilohertz range. The significantly higher modulation frequency of the deflection chopping improves background subtraction of fast transient events. It allows a more accurate density measurements in the scrape off layer during impurity injections and edge localized modes.
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52.70.Nc Particle measurements
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Vy Impurities in plasmas
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
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Measurement of ion and electron temperatures in plasma blobs by using an improved ion sensitive probe system and statistical analysis methods

K. Okazaki, H. Tanaka, N. Ohno, N. Ezumi, Y. Tsuji, and S. Kajita

Rev. Sci. Instrum. 83, 023502 (2012); http://dx.doi.org/10.1063/1.3681778 (5 pages)

Online Publication Date: 7 February 2012

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We have measured ion temperature as well as electron temperature in plasma blobs observed in a linear plasma device by using an improved ion sensitive probe. Current–voltage characteristics of the ion sensitive probe inside and outside plasma blobs were re-constructed with a conditional sampling method. It is clearly found that both ion and electron temperatures in plasma blobs decrease more slowly in a cross-field direction than those in a bulk plasma without plasma blobs.
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52.70.Ds Electric and magnetic measurements
52.75.-d Plasma devices
52.25.Fi Transport properties
02.50.-r Probability theory, stochastic processes, and statistics

Tracer-encapsulated solid pellet injection system

Shigeru Sudo and Naoki Tamura

Rev. Sci. Instrum. 83, 023503 (2012); http://dx.doi.org/10.1063/1.3681447 (6 pages)

Online Publication Date: 10 February 2012

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The method of tracer-encapsulated solid pellet (TESPEL) is now flourishing in various fields. The original purpose to study impurity transport without giving substantial perturbation on the plasma is implemented successfully for years. In addition to this, TESPEL is being intensively applied to study thermal (especially non-local) transport, high energy particles with the use of TESPEL ablation cloud, and spectroscopy from the viewpoint of atomic data. It is now further growing up to the utilization of multiple tracer methods which was not planned at the initial phase of the project. The proof-of-principle experiment using triple tracers has been successfully implemented. This opens a way to compare the Z dependence or mass dependence of impurity transport. In this article, as TESPEL is used in a variety of fields, the TESPEL injection system is summarized together with the method of TESPEL production, TESPEL storage disk, TESPEL guide system, and the differential pumping system. Also, the observation system for TESPEL flight and TESPEL ablation is explained.
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82.80.-d Chemical analysis and related physical methods of analysis

Electric field-perturbation measurement of the interaction between two laser-induced plasmas

C. Sánchez-Aké, F. Bredice, and M. Villagrán-Muniz

Rev. Sci. Instrum. 83, 023504 (2012); http://dx.doi.org/10.1063/1.3683453 (6 pages)

Online Publication Date: 13 February 2012

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The interaction between two ns-laser-induced plasmas in air at the early-stage of expansion has been analyzed by using a method based on the direct measurement of the perturbation of an externally applied electric field. In this experimental method, the plasmas were produced by focusing two laser beams between the plates of a parallel-plane-charged capacitor. These plasmas produce a perturbation in the electric field of the capacitor which can be measured as a voltage change across a resistor connected to the ground plate. It was found that for delays shorter than 5 ns, the interaction between plasmas is mainly due to the interaction of the dipole-charge distribution of each plasma. For longer time delays, the shielding effect was dominant.
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52.20.-j Elementary processes in plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Collection of solid and gaseous samples to diagnose inertial confinement fusion implosions

M. A. Stoyer, C. A. Velsko, B. K. Spears, D. G. Hicks, G. B. Hudson, T. C. Sangster, and C. G. Freeman

Rev. Sci. Instrum. 83, 023505 (2012); http://dx.doi.org/10.1063/1.3685250 (9 pages)

Online Publication Date: 16 February 2012

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Collection of representative samples of debris following inertial confinement fusion implosions in order to diagnose implosion conditions and efficacy is a challenging endeavor because of the unique conditions within the target chamber such as unconverted laser light, intense pulse of x-rays, physical chunks of debris, and other ablative effects. We present collection of gas samples following an implosion for the first time. High collection fractions for noble gases were achieved. We also present collection of solid debris samples on flat plate collectors. Geometrical collection efficiencies for Au hohlraum material were achieved and collection of capsule debris (Be and Cu) was also observed. Asymmetric debris distributions were observed for Au and Be samples. Collection of Be capsule debris was higher for solid collectors viewing the capsule through the laser entrance hole in the hohlraum than for solid collectors viewing the capsule around the waist of the hohlraum. Collection of Au hohlraum material showed the opposite pattern: more Au debris was collected around the waist than through the laser entrance hole. The solid debris collectors were not optimized for minimal Cu backgrounds, which limited the conclusions about the symmetry of the Cu debris. The quality of the data limited conclusions on chemical fractionation effects within the burning, expanding, and then cooling plasma.
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52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)
28.52.Cx Fueling, heating and ignition
28.52.Fa Materials
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Lp Plasma production and heating by shock waves and compression

A technique for measuring the propagation of a supersonic radiation front in foam via spatially resolved spectral imaging of a tracer layer

J. M. Taccetti, P. A. Keiter, N. Lanier, K. Mussack, K. Belle, and G. R. Magelssen

Rev. Sci. Instrum. 83, 023506 (2012); http://dx.doi.org/10.1063/1.3685621 (7 pages)

Online Publication Date: 21 February 2012

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We present a technique for measuring the propagation of a supersonic radiation front in low-density foam, where the lack of motion of the objects in its wake makes it difficult to determine its location. We illuminate a thin tracer foil embedded in the foam with a broadband x-ray source, and measure its changing absorption of these x rays as it ionizes. We record both spatial and spectral information of the heated tracer, and thus obtain its ionization state as a function of distance along the front propagation direction. We extrapolate this information to determine the state of the foam and the location of the radiation front. We present the experimental configuration used to test this technique at the Omega laser facility along with experimental results.
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47.40.Ki Supersonic and hypersonic flows
29.25.Rm Sources of radioactive nuclei
32.30.Rj X-ray spectra

First measurement of electron temperature from signal ratios in a double-pass Thomson scattering system

H. Tojo, A. Ejiri, J. Hiratsuka, T. Yamaguchi, Y. Takase, K. Itami, and T. Hatae

Rev. Sci. Instrum. 83, 023507 (2012); http://dx.doi.org/10.1063/1.3685612 (4 pages)

Online Publication Date: 22 February 2012

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This paper presents an experimental demonstration to determine electron temperature (Te) with unknown spectral sensitivity (transmissivity) in a Thomson scattering system. In this method, a double-pass scattering configuration is used and the scattered lights from each pass (with different scattering angles) are measured separately. Te can be determined from the ratio of the signal intensities without knowing a real chromatic dependence in the sensitivity. Note that the wavelength range for each spectral channel must be known. This method was applied to the TST-2 Thomson scattering system. As a result, Te measured from the ratio (Te,r) and Te measured from a standard method (Te,s) showed a good agreement with 〈|Te,r − Te,s|/Te,s〉 = 7.3%.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties

Continuous wave cavity ring down spectroscopy measurements of velocity distribution functions of argon ions in a helicon plasma

Saikat Chakraborty Thakur, Dustin McCarren, Jerry Carr, Jr., and Earl E. Scime

Rev. Sci. Instrum. 83, 023508 (2012); http://dx.doi.org/10.1063/1.3687429 (8 pages)

Online Publication Date: 27 February 2012

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We report continuous wave cavity ring down spectroscopy (CW-CRDS) measurements of ion velocity distribution functions (VDFs) in low pressure argon helicon plasma (magnetic field strength of 600 G, Te ≈ 4 eV and n ≈ 5 × 1011 cm−3). Laser induced fluorescence (LIF) is routinely used to measure VDFs of argon ions, argon neutrals, helium neutrals, and xenon ions in helicon sources. Here, we describe a CW-CRDS diagnostic based on a narrow line width, tunable diode laser as an alternative technique to measure VDFs in similar regimes but where LIF is inapplicable. Being an ultra-sensitive, cavity enhanced absorption spectroscopic technique; CW-CRDS can also provide a direct quantitative measurement of the absolute metastable state density. The proof of principle CW-CRDS measurements presented here are of the Doppler broadened absorption spectrum of Ar II at 668.6138 nm. Extrapolating from these initial measurements, it is expected that this diagnostic is suitable for neutrals and ions in plasmas ranging in density from 1 × 109 cm−3 to 1 × 1013 cm−3 and target species temperatures less than 20 eV.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
back to top Microscopy and Imaging

A new TriBeam system for three-dimensional multimodal materials analysis

McLean P. Echlin, Alessandro Mottura, Christopher J. Torbet, and Tresa M. Pollock

Rev. Sci. Instrum. 83, 023701 (2012); http://dx.doi.org/10.1063/1.3680111 (6 pages)

Online Publication Date: 3 February 2012

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The unique capabilities of ultrashort pulse femtosecond lasers have been integrated with a focused ion beam (FIB) platform to create a new system for rapid 3D materials analysis. The femtosecond laser allows for in situ layer-by-layer material ablation with high material removal rates. The high pulse frequency (1 kHz) of ultrashort (150 fs) laser pulses can induce material ablation with virtually no thermal damage to the surrounding area, permitting high resolution imaging, as well as crystallographic and elemental analysis, without intermediate surface preparation or removal of the sample from the chamber. The TriBeam system combines the high resolution and broad detector capabilities of the DualBeamTM microscope with the high material removal rates of the femtosecond laser, allowing 3D datasets to be acquired at rates 4–6 orders of magnitude faster than 3D FIB datasets. Design features that permit coupling of laser and electron optics systems and positioning of a stage in the multiple analysis positions are discussed. Initial in situ multilayer data are presented.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
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