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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Sensitivity calibration of an imaging extreme ultraviolet spectrometer-detector system for determining the efficiency of broadband extreme ultraviolet sources

S. Fuchs, C. Rödel, M. Krebs, S. Hädrich, J. Bierbach, A. E. Paz, S. Kuschel, M. Wünsche, V. Hilbert, U. Zastrau, E. Förster, J. Limpert, and G. G. Paulus

Rev. Sci. Instrum. 84, 023101 (2013); http://dx.doi.org/10.1063/1.4788732 (5 pages)

Online Publication Date: 4 February 2013

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We report on the absolute sensitivity calibration of an extreme ultraviolet (XUV) spectrometer system that is frequently employed to study emission from short-pulse laser experiments. The XUV spectrometer, consisting of a toroidal mirror and a transmission grating, was characterized at a synchrotron source in respect of the ratio of the detected to the incident photon flux at photon energies ranging from 15.5 eV to 99 eV. The absolute calibration allows the determination of the XUV photon number emitted by laser-based XUV sources, e.g., high-harmonic generation from plasma surfaces or in gaseous media. We have demonstrated high-harmonic generation in gases and plasma surfaces providing 2.3 μW and μJ per harmonic using the respective generation mechanisms.
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07.60.Rd Visible and ultraviolet spectrometers
42.72.-g Optical sources and standards
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.79.Pw Imaging detectors and sensors
06.20.fb Standards and calibration

A new high intensity and short-pulse molecular beam valve

B. Yan, P. F. H. Claus, B. G. M. van Oorschot, L. Gerritsen, A. T. J. B. Eppink, S. Y. T. van de Meerakker, and D. H. Parker

Rev. Sci. Instrum. 84, 023102 (2013); http://dx.doi.org/10.1063/1.4790176 (8 pages)

Online Publication Date: 6 February 2013

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In this paper, we report on the design and performance of a new home-built pulsed gas valve, which we refer to as the Nijmegen Pulsed Valve (NPV). The main output characteristics include a short pulse width (as short as 20 μs) combined with operating rates up to 30 Hz. The operation principle of the NPV is based on the Lorentz force created by a pulsed current passing through an aluminum strip located within a magnetic field, which opens the nozzle periodically. The amplitude of displacement of the opening mechanism is sufficient to allow the use of nozzles with up to 1.0 mm diameter. To investigate the performance of the valve, several characterizations were performed with different experimental methods. First, a fast ionization gauge was used to measure the beam intensity of the free jet emanating from the NPV. We compare free jets from the NPV with those from several other pulsed valves in current use in our laboratory. Results showed that a high intensity and short pulse-length beam could be generated by the new valve. Second, the NPV was tested in combination with a skimmer, where resonance enhanced multiphoton ionization combined with velocity map imaging was used to show that the NPV was able to produce a pulsed molecular beam with short pulse duration (∼20 μs using 0.1% NO/He at 6 bars) and low rotational temperature (∼1 K using 0.5% NO/Ar at 6 bars). Third, a novel two-point pump-probe method was employed which we label double delay scan. This method allows a full kinematic characterization of the molecular beam, including accurate speed ratios at different temporal positions. It was found that the speed ratio was maximum (S = 50 using 0.1% NO/He at 3 bars) at the peak position of the molecular beam and decreased when it was on the leading or falling edge.
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89.20.Kk Engineering
89.20.Bb Industrial and technological research and development
FREE

A quantum cascade laser absorption spectrometer devoted to the in situ measurement of atmospheric N2O and CH4 emission fluxes

I. Mappé, L. Joly, G. Durry, X. Thomas, T. Decarpenterie, J. Cousin, N. Dumelie, E. Roth, A. Chakir, and P. G. Grillon

Rev. Sci. Instrum. 84, 023103 (2013); http://dx.doi.org/10.1063/1.4790376 (8 pages)

Online Publication Date: 12 February 2013

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This paper describes a Quantum Cascade Laser Absorption Spectrometer, called “QCLAS” that was developed to monitor in situ greenhouse gases like N2O and CH4, at high temporal resolution and with a high accuracy. The design of the laser sensor is reported as well as its performances in terms of precision error and field deployment capabilities. Finally, to demonstrate the efficiency and the robustness of QCLAS and its suitability for gas emission monitoring and for the determination of fluxes, we report the results from a field campaign, that took place in the Wallis and Futuna Islands in 2011, to investigate the impact of environmental intensive pig farming.
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42.55.Px Semiconductor lasers; laser diodes
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

A polychromator-type near-infrared spectrometer with a high-sensitivity and high-resolution photodiode array detector for pharmaceutical process monitoring on the millisecond time scale

Kodai Murayama, Takuma Genkawa, Daitaro Ishikawa, Makoto Komiyama, and Yukihiro Ozaki

Rev. Sci. Instrum. 84, 023104 (2013); http://dx.doi.org/10.1063/1.4790413 (8 pages)

Online Publication Date: 13 February 2013

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In the fine chemicals industry, particularly in the pharmaceutical industry, advanced sensing technologies have recently begun being incorporated into the process line in order to improve safety and quality in accordance with process analytical technology. For estimating the quality of powders without preparation during drug formulation, near-infrared (NIR) spectroscopy has been considered the most promising sensing approach. In this study, we have developed a compact polychromator-type NIR spectrometer equipped with a photodiode (PD) array detector. This detector is consisting of 640 InGaAs-PD elements with 20-μm pitch. Some high-specification spectrometers, which use InGaAs-PD with 512 elements, have a wavelength resolution of about 1.56 nm when covering 900–1700 nm range. On the other hand, the newly developed detector, having the PD with one of the world's highest density, enables wavelength resolution of below 1.25 nm. Moreover, thanks to the combination with a highly integrated charge amplifier array circuit, measurement speed of the detector is higher by two orders than that of existing PD array detectors. The developed spectrometer is small (120 mm × 220 mm × 200 mm) and light (6 kg), and it contains various key devices including the high-density and high-sensitivity PD array detector, NIR technology, and spectroscopy technology for a spectroscopic analyzer that has the required detection mechanism and high sensitivity for powder measurement, as well as a high-speed measuring function for blenders. Moreover, we have evaluated the characteristics of the developed NIR spectrometer, and the measurement of powder samples confirmed that it has high functionality.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
82.80.Bg Chromatography
85.60.Dw Photodiodes; phototransistors; photoresistors

Cascaded two-photon spectroscopy of Yb atoms with a transportable effusive atomic beam apparatus

Minsoo Song and Tai Hyun Yoon

Rev. Sci. Instrum. 84, 023105 (2013); http://dx.doi.org/10.1063/1.4790849 (5 pages)

Online Publication Date: 14 February 2013

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We present a transportable effusive atomic beam apparatus for cascaded two-photon spectroscopy of the dipole-forbidden transition (6s2 1S0↔ 6s7s 1S0) of Yb atoms. An ohmic-heating effusive oven is designed to have a reservoir volume of 1.6 cm3 and a high degree of atomic beam collimation angle of 30 mrad. The new atomic beam apparatus allows us to detect the spontaneously cascaded two-photons from the 6s7s1S0 state via the intercombination 6s6p3P1 state with a high signal-to-noise ratio even at the temperature of 340 °C. This is made possible in our apparatus because of the enhanced atomic beam flux and superior detection solid angle.
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37.20.+j Atomic and molecular beam sources and techniques
03.75.Pp Atom lasers
32.80.-t Photoionization and excitation
42.62.Fi Laser spectroscopy

Time-of-flight electron spectrometer for a broad range of kinetic energies

Alexander Kothe, Jan Metje, Martin Wilke, Alexandre Moguilevski, Nicholas Engel, Ruba Al-Obaidi, Clemens Richter, Ronny Golnak, Igor Yu. Kiyan, and Emad F. Aziz

Rev. Sci. Instrum. 84, 023106 (2013); http://dx.doi.org/10.1063/1.4791792 (7 pages)

Online Publication Date: 20 February 2013

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A newly constructed time-of-flight electron spectrometer of the magnetic bottle type is characterized for electron detection in a broad range of kinetic energies. The instrument is designed to measure the energy spectra of electrons generated from liquids excited by strong laser fields and photons in the range of extreme ultra violet and soft X-rays. Argon inner shell electrons were recorded to calibrate the spectrometer and investigate its characteristics, such as energy resolution and collection efficiency. Its energy resolution ΔE/E of 1.6% allows resolving the Ar 2p spin orbit structure at kinetic energies higher than 100 eV. The collection efficiency is determined and compared to that of the spectrometer in its field-free configuration.
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07.81.+a Electron and ion spectrometers
06.20.fb Standards and calibration

Continuously tunable optical multidimensional Fourier-transform spectrometer

P. Dey, J. Paul, J. Bylsma, S. Deminico, and D. Karaiskaj

Rev. Sci. Instrum. 84, 023107 (2013); http://dx.doi.org/10.1063/1.4792378 (7 pages)

Online Publication Date: 21 February 2013

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A multidimensional optical nonlinear spectrometer (MONSTR) is a robust, ultrastable platform consisting of nested and folded Michelson interferometers that can be actively phase stabilized. The MONSTR provides output pulses for nonlinear excitation of materials and phase-stabilized reference pulses for heterodyne detection of the induced signal. This platform generates a square of identical laser pulses that can be adjusted to have arbitrary time delays between them while maintaining phase stability. This arrangement is ideal for performing coherent optical experiments, such as multidimensional Fourier-transform spectroscopy. The present work reports on overcoming some important limitations on the original design of the MONSTR apparatus. One important advantage of the MONSTR is the fact that it is a closed platform, which provides the high stability. Once the optical alignment is performed, it is desirable to maintain the alignment over long periods of time. The previous design of the MONSTR was limited to a narrow spectral range defined by the optical coating of the beam splitters. In order to achieve tunability over a broad spectral range the internal optics needed to be changed. By using broadband coated and wedged beam splitters and compensator plates, combined with modifications of the beam paths, continuous tunability can be achieved from 520 nm to 1100 nm without changing any optics or performing alignment of the internal components of the MONSTR. Furthermore, in order to achieve continuous tunability in the spectral region between 520 nm and 720 nm, crucially important for studies on numerous biological molecules, a single longitudinal mode laser at 488.5 nm was identified and used as a metrology laser. The shorter wavelength of the metrology laser as compared to the usual HeNe laser has also increased the phase stability of the system. Finally, in order to perform experiments in the reflection geometry, a simple method to achieve active phase stabilization between the signal and the reference beams has been developed.
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07.60.Ly Interferometers
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Slab coupled optical fiber sensor calibration

B. Whitaker, J. Noren, S. Chadderdon, W. Wang, R. Forber, R. Selfridge, and S. Schultz

Rev. Sci. Instrum. 84, 023108 (2013); http://dx.doi.org/10.1063/1.4789766 (6 pages) | Cited 1 time

Online Publication Date: 22 February 2013

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This paper presents a method for calibrating slab coupled optical fiber sensors (SCOS). An automated system is presented for selecting the optimal laser wavelength for use in SCOS interrogation. The wavelength calibration technique uses a computer sound card for both the creation of the applied electric field and the signal detection. The method used to determine the ratio between the measured SCOS signal and the applied electric field is also described along with a demonstration of the calibrated SCOS involving measuring the dielectric breakdown of air.
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42.81.Pa Sensors, gyros
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.20.fb Standards and calibration
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Photoacoustic absorption spectrometer for highly transparent dielectrics with parts-per-million sensitivity

Niklas Waasem, Stephan Fieberg, Janosch Hauser, Gregory Gomes, Daniel Haertle, Frank Kühnemann, and Karsten Buse

Rev. Sci. Instrum. 84, 023109 (2013); http://dx.doi.org/10.1063/1.4792724 (8 pages)

Online Publication Date: 26 February 2013

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A sensitive photoacoustic absorption spectrometer for highly transparent solids has been built and tested. As the light source an optical parametrical oscillator pumped by a nanosecond pulse laser with 10 Hz repetition rate is employed, covering the complete wavelength range from 407 to 2600 nm. A second-harmonic-generation unit extends the range of accessible wavelengths down to 212 nm. A lead-zirconate-titanate piezo transducer, directly coupled to the sample, detects the photoacoustically generated sound waves. Absorption spectra of lithium triborate, lithium niobate, and alpha barium borate crystals with absorption coefficients down to 10−5 cm−1 are presented.
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43.38.Fx Piezoelectric and ferroelectric transducers
84.30.Ng Oscillators, pulse generators, and function generators
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Plasma electron source for the generation of wide-aperture pulsed beam at forevacuum pressures

E. Oks, V. Burdovitsin, A. Medovnik, and Yu. Yushkov

Rev. Sci. Instrum. 84, 023301 (2013); http://dx.doi.org/10.1063/1.4789771 (4 pages)

Online Publication Date: 1 February 2013

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This article reports on design and application of wide-aperture pulsed beam source, based on hollow cathode discharge. The source is intended for electron beam generation in pressure range 2–15 Pa. Multi-aperture extraction system, used in a source, provided beam cross-section uniformity of 10% on diameter 40 mm. The limiting values of the current density, pulse duration, and accelerating voltage are 350 mA/cm2, 250 μs, and 10 kV, respectively. These parameters are sufficient for surface modification of various materials, including non-conducting matters.
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52.50.Dg Plasma sources
52.25.Fi Transport properties
52.80.Hc Glow; corona
41.75.Fr Electron and positron beams

Conceptual design and scaled experimental validation of an actively damped carbon tie rods support system for the stabilization of future particle collider superstructures

C. Collette, D. Tshilumba, L. Fueyo-Rosa, and I. Romanescu

Rev. Sci. Instrum. 84, 023302 (2013); http://dx.doi.org/10.1063/1.4789783 (7 pages)

Online Publication Date: 4 February 2013

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This paper presents a simple solution to increase the stability of the large superstructures supporting the final electromagnets of future linear particle collider. It consists of active carbon fiber tie rods, fixed at one end on the structure and at the other end to the detector through active tendons. In the first part of the paper, the solution has been tested on a finite element model of one half of the CLIC_ILD final focus structure. With a reasonable design, it is shown numerically that the compliance can be decreased by at least a factor 4, i.e., that the structure is 4 times more robust to technical noise at low frequency. Two additional features of the active rods are that they can also actively damp the structural resonances and realign the superstructures. The second part of the paper presents a successful experimental validation of the concept, applied to a scaled test bench, especially designed to contain the same modal characteristics as the full scale superstructure.
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29.20.Ej Linear accelerators
02.70.Dh Finite-element and Galerkin methods

Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

Sumit Som, Sudeshna Seth, Aditya Mandal, Saikat Paul, and Anjan Duttagupta

Rev. Sci. Instrum. 84, 023303 (2013); http://dx.doi.org/10.1063/1.4789784 (5 pages)

Online Publication Date: 6 February 2013

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Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9–27 MHz with amplitude and phase stability of 100 ppm and ±0.20, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages (“Dee” voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.
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29.20.dg Cyclotrons
29.27.-a Beams in particle accelerators
06.20.fb Standards and calibration

First successful ionization of Lr (Z = 103) by a surface-ionization technique

Tetsuya K. Sato, Nozomi Sato, Masato Asai, Kazuaki Tsukada, Atsushi Toyoshima, Kazuhiro Ooe, Sunao Miyashita, Matthias Schädel, Yusuke Kaneya, Yuichiro Nagame, Akihiko Osa, Shin-ichi Ichikawa, Thierry Stora, and Jens Volker Kratz

Rev. Sci. Instrum. 84, 023304 (2013); http://dx.doi.org/10.1063/1.4789772 (5 pages)

Online Publication Date: 20 February 2013

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We have developed a surface ionization ion-source as part of the JAEA-ISOL (Isotope Separator On-Line) setup, which is coupled to a He/CdI2 gas-jet transport system to determine the first ionization potential of the heaviest actinide lawrencium (Lr, Z = 103). The new ion-source is an improved version of the previous source that provided good ionization efficiencies for lanthanides. An additional filament was newly installed to give better control over its operation. We report, here, on the development of the new gas-jet coupled surface ion-source and on the first successful ionization and mass separation of 27-s 256Lr produced in the 249Cf + 11B reaction.
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34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)
32.50.+d Fluorescence, phosphorescence (including quenching)

Development of a cold-neutron imaging detector based on thick gaseous electron multiplier

M. Cortesi, R. Zboray, A. Kaestner, and H.-M. Prasser

Rev. Sci. Instrum. 84, 023305 (2013); http://dx.doi.org/10.1063/1.4793225 (7 pages)

Online Publication Date: 26 February 2013

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We present the results of our recent studies on a cold-neutron imaging detector prototype based on THick Gaseous Electron Multiplier (THGEM). The detector consists of a thin Boron layer, for neutron-to-charged particle conversion, coupled to two THGEM electrodes in cascade for charge amplification and a position-sensitive charge-readout anode. The detector operates in Ne/(5%)CF4, at atmospheric pressure, in a stable condition at a gain of around 104. Due to the geometrical structure of the detector elements (THGEM geometry and charge read-out anode), the image of detector active area shows a large inhomogeneity, corrected using a dedicated flat-filed correction algorithm. The prototype provides a detection efficiency of 5% and an effective spatial resolution of the order of 1.3 mm.
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29.40.Gx Tracking and position-sensitive detectors

A new kind of low-inductance transformer type magnetic switch (TTMS) with coaxial cylindrical conductors

Yu Zhang and Jinliang Liu

Rev. Sci. Instrum. 84, 023306 (2013); http://dx.doi.org/10.1063/1.4791926 (8 pages)

Online Publication Date: 27 February 2013

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As important devices for voltage boosting and switching, respectively, pulse transformer and magnetic switch are widely used in pulsed power technology. In this paper, a new kind of transformer type magnetic switch (TTMS) with coaxial cylindrical conductors is put forward to combine the functions of voltage boosting and switching in one power device. As a compact combination device of discrete pulse transformer and magnetic switch, the compact TTMS decreases the required volume of magnetic cores in a large scale. The primary windings of the TTMS have a parallel combination structure so that the TTMS which only has 3 turns of secondary windings has a step-up ratio at 1:9. Before the magnetic core saturates, the TTMS has low unsaturated inductances of windings and good pulse response characteristics, so it can be used to substitute the Marx generator to charge the pulse forming line (PFL) at the ranges of several hundred kV and several hundred ns. After the core saturates, the cylindrical conductors can decrease the saturated inductance of the secondary windings of TTMS to a level less than 400 nH. As a result, the proposed TTMS can be used as the boosting transformer and main switch of helical Blumlein PFL to form the quasi-square voltage pulse on the 160 Ω load with a short pulse rise time only at 60 ns.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
85.70.-w Magnetic devices
84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Influence of gold coating and interplate voltage on the performance of chevron micro-channel plates for temporally and spatially resolved single particle detection

A. L. Hoendervanger, D. Clément, A. Aspect, C. I. Westbrook, D. Dowek, Y. J. Picard, and D. Boiron

Rev. Sci. Instrum. 84, 023307 (2013); http://dx.doi.org/10.1063/1.4793402 (8 pages)

Online Publication Date: 28 February 2013

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We present a study of two different sets of Micro-Channel Plates used for time and space resolved single particle detection. We investigate the effects of the gold coating and that of introducing an interplate voltage between the spatially separated plates. We find that the gold coating increases the count rate of the detector and the pulse amplitude as previously reported for non-spatially resolved setups. The interplate voltage also increases count rates. In addition, we find that a non-zero interplate voltage improves the spatial accuracy in determining the arrival position of incoming single particles (by ∼20%) while the gold coating has a negative effect (by ∼30%).
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29.40.-n Radiation detectors
42.79.Ls Scanners, image intensifiers, and image converters
85.60.Ha Photomultipliers; phototubes and photocathodes
back to top Nuclear Physics, Fusion and Plasmas

Single exposure three-dimensional imaging of dusty plasma clusters

Peter Hartmann, István Donkó, and Zoltán Donkó

Rev. Sci. Instrum. 84, 023501 (2013); http://dx.doi.org/10.1063/1.4789770 (5 pages)

Online Publication Date: 1 February 2013

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We have worked out the details of a single camera, single exposure method to perform three-dimensional imaging of a finite particle cluster. The procedure is based on the plenoptic imaging principle and utilizes a commercial Lytro light field still camera. We demonstrate the capabilities of our technique on a single layer particle cluster in a dusty plasma, where the camera is aligned and inclined at a small angle to the particle layer. The reconstruction of the third coordinate (depth) is found to be accurate and even shadowing particles can be identified.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Pure ion current collection in ion sensitive probe measurement with a metal mesh guard electrode for evaluation of ion temperature in magnetized plasma

Tung-Yuan Hsieh, Eiichirou Kawamori, and Yasushi Nishida

Rev. Sci. Instrum. 84, 023502 (2013); http://dx.doi.org/10.1063/1.4790175 (4 pages) | Cited 1 time

Online Publication Date: 6 February 2013

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This paper presents a new design of ion sensitive probe (ISP) that enables collection of pure ion current for accurate measurement of the perpendicular ion temperature in magnetized plasmas. The new type of ISP resolves a longstanding issue widely observed in ISP type measurements, namely, that the current-voltage characteristic is smeared by an unexpected electron current in the standard ISP model. The new ISP is equipped with a fine scale metal mesh on the sensor entrance to prevent electrons from flowing to the sensor, a phenomenon considered to be caused by the space-charge effect. The new ISP successfully measured the ion temperature of electron cyclotron resonance plasmas.
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52.70.Ds Electric and magnetic measurements
07.20.Dt Thermometers

Core-ion temperature measurement of the ADITYA tokamak using passive charge exchange neutral particle energy analyzer

Santosh P. Pandya, Kumar Ajay, Priyanka Mishra, Rajani D. Dhingra, and J. Govindarajan

Rev. Sci. Instrum. 84, 023503 (2013); http://dx.doi.org/10.1063/1.4791998 (9 pages)

Online Publication Date: 20 February 2013

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Core-ion temperature measurements have been carried out by the energy analysis of passive charge exchange (CX) neutrals escaping out of the ADITYA tokamak plasma (minor radius, a = 25 cm and major radius, R = 75 cm) using a 45° parallel plate electrostatic energy analyzer. The neutral particle analyzer (NPA) uses a gas cell configuration for re-ionizing the CX-neutrals and channel electron multipliers (CEMs) as detectors. Energy calibration of the NPA has been carried out using ion-source and ΔE/E of high-energy channel has been found to be ∼10%. Low signal to noise ratio (SNR) due to VUV reflections on the CEMs was identified during the operation of the NPA with ADITYA plasma discharges. This problem was rectified by upgrading the system by incorporating the additional components and arrangements to suppress VUV radiations and improve its VUV rejection capabilities. The noise rejection capability of the NPA was experimentally confirmed using a standard UV-source and also during the plasma discharges to get an adequate SNR (>30) at the energy channels. Core-ion temperature Ti(0) during flattop of the plasma current has been measured to be up to 150 eV during ohmically heated plasma discharges which is nearly 40% of the average core-electron temperature (typically Te(0) ∼ 400 eV). The present paper describes the principle of tokamak ion temperature measurement, NPA's design, development, and calibration along with the modifications carried out for minimizing the interference of plasma radiations in the CX-spectrum. Performance of the NPA during plasma discharges and experimental results on the measurement of ion-temperature have also been reported here.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.25.Ya Neutrals in plasmas
52.55.Fa Tokamaks, spherical tokamaks
07.20.Ka High-temperature instrumentation; pyrometers
07.20.Dt Thermometers

Identification and control of plasma vertical position using neural network in Damavand tokamak

H. Rasouli, C. Rasouli, and A. Koohi

Rev. Sci. Instrum. 84, 023504 (2013); http://dx.doi.org/10.1063/1.4791925 (12 pages)

Online Publication Date: 21 February 2013

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In this work, a nonlinear model is introduced to determine the vertical position of the plasma column in Damavand tokamak. Using this model as a simulator, a nonlinear neural network controller has been designed. In the first stage, the electronic drive and sensory circuits of Damavand tokamak are modified. These circuits can control the vertical position of the plasma column inside the vacuum vessel. Since the vertical position of plasma is an unstable parameter, a direct closed loop system identification algorithm is performed. In the second stage, a nonlinear model is identified for plasma vertical position, based on the multilayer perceptron (MLP) neural network (NN) structure. Estimation of simulator parameters has been performed by back-propagation error algorithm using Levenberg–Marquardt gradient descent optimization technique. The model is verified through simulation of the whole closed loop system using both simulator and actual plant in similar conditions. As the final stage, a MLP neural network controller is designed for simulator model. In the last step, online training is performed to tune the controller parameters. Simulation results justify using of the NN controller for the actual plant.
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52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
07.05.Dz Control systems
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)

2D divertor heat flux distribution using a 3D heat conduction solver in National Spherical Torus Experiment

K. F. Gan, J-W. Ahn, J.-W. Park, R. Maingi, A. G. McLean, T. K. Gray, X. Gong, and X. D. Zhang

Rev. Sci. Instrum. 84, 023505 (2013); http://dx.doi.org/10.1063/1.4792595 (8 pages)

Online Publication Date: 21 February 2013

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The divertor heat flux footprint in tokamaks is often observed to be non-axisymmetric due to intrinsic error fields, applied 3D magnetic fields or during transients such as edge localized modes. Typically, only 1D radial heat flux profiles are analyzed; however, analysis of the full 2D divertor measurements provides opportunities to study the asymmetric nature of the deposited heat flux. To accomplish this an improved 3D Fourier analysis method has been successfully applied in a heat conduction solver (TACO) to determine the 2D heat flux distribution at the lower divertor surface in the National Spherical Torus Experiment (NSTX) tokamak. This advance enables study of helical heat deposition onto the divertor. In order to account for heat transmission through poorly adhered surface layers on the divertor plate, a heat transmission coefficient, defined as the surface layer thermal conductivity divided by the thickness of the layer, was introduced to the solution of heat conduction equation. This coefficient is denoted as α and a range of values were tested in the model to ensure a reliable heat flux calculation until a specific value of α led to the constant total deposited energy in the numerical solution after the end of discharge. A comparison between 1D heat flux profiles from TACO and from a 2D heat flux calculation code, THEODOR, shows good agreement. Advantages of 2D heat flux distribution over the conventional 1D heat flux profile are also discussed, and examples of 2D data analysis in the study of striated heat deposition pattern as well as the toroidal degree of asymmetry of peak heat flux and heat flux width are demonstrated.
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28.52.Fa Materials
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
02.30.Nw Fourier analysis

Performance of an inverted ion source

M. C. Salvadori, F. S. Teixeira, L. G. Sgubin, W. W. R. Araujo, R. E. Spirin, E. M. Oks, and I. G. Brown

Rev. Sci. Instrum. 84, 023506 (2013); http://dx.doi.org/10.1063/1.4793377 (5 pages)

Online Publication Date: 27 February 2013

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Whereas energetic ion beams are conventionally produced by extracting ions (say, positive ions) from a plasma that is held at high (positive) potential, with ion energy determined by the potential drop through which the ions fall in the beam formation electrode system, in the device described here the plasma and its electronics are held at ground potential and the ion beam is formed and injected energetically into a space maintained at high (negative) potential. We refer to this configuration as an “inverted ion source.” This approach allows considerable savings both technologically and economically, rendering feasible some ion beam applications, in particular small-scale ion implantation, that might otherwise not be possible for many researchers and laboratories. We have developed a device of this kind utilizing a metal vapor vacuum arc plasma source, and explored its operation and beam characteristics over a range of parameter variation. The downstream beam current has been measured as a function of extraction voltage (5–35 kV), arc current (50–230 A), metal ion species (Ti, Nb, Au), and extractor grid spacing and beamlet aperture size (3, 4, and 5 mm). The downstream ion beam current as measured by a magnetically-suppressed Faraday cup was up to as high as 600 mA, and with parametric variation quite similar to that found for the more conventional metal vapor vacuum arc ion source.
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52.50.Dg Plasma sources
29.25.Ni Ion sources: positive and negative

Development of a polarization resolved spectroscopic diagnostic for measurements of the vector magnetic field in the Caltech coaxial magnetized plasma jet experiment

T. Shikama and P. M. Bellan

Rev. Sci. Instrum. 84, 023507 (2013); http://dx.doi.org/10.1063/1.4793403 (7 pages)

Online Publication Date: 28 February 2013

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In the Caltech coaxial magnetized plasma jet experiment, fundamental studies are carried out relevant to spheromak formation, astrophysical jet formation/propagation, solar coronal physics, and the general behavior of twisted magnetic flux tubes that intercept a boundary. In order to measure the spatial profile of the magnetic field vector for understanding the underlying physics governing the dynamical behavior, a non-perturbing visible emission spectroscopic method is implemented to observe the Zeeman splitting in emission spectra. We have designed and constructed a polarization-resolving optical system that can simultaneously detect the left- and right-circularly polarized emission. The system is applied to singly ionized nitrogen spectral lines. The magnetic field strength is measured with a precision of about ±13 mT. The radial profiles of the azimuthal and axial vector magnetic field components are resolved by using an inversion method.
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52.75.-d Plasma devices
07.55.Ge Magnetometers for magnetic field measurements
back to top Microscopy and Imaging

A cryogenic scattering-type scanning near-field optical microscope

Honghua U. Yang, Erik Hebestreit, Erik E. Josberger, and Markus B. Raschke

Rev. Sci. Instrum. 84, 023701 (2013); http://dx.doi.org/10.1063/1.4789428 (6 pages)

Online Publication Date: 1 February 2013

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Scattering-type scanning near-field optical microscopy (s-SNOM) provides few nanometer optical spatial resolution and is compatible with nearly any form of linear and nonlinear optical spectroscopy. We have developed a versatile s-SNOM instrument operating under cryogenic and variable temperature (∼20–500 K) and compatible with high magnetic fields (up to 7 T). The instrument features independent tip and sample scanning and free-space light delivery with an integrated off-axis parabolic mirror for tip-illumination and signal collection with a numerical aperture of N.A. = 0.45. The optics operate from the UV to THz range allowing for continuous wave, broadband, and ultrafast s-SNOM spectroscopy, including different variants of tip-enhanced spectroscopy. We discuss the instrument design, implementation, and demonstrate its performance with mid-infrared Drude response s-SNOM probing of the domain formation associated with the metal-insulator transitions of VO2 (TMIT ≃ 340 K) and V2O3 (TMIT ≃ 150 K). This instrument enables the study of mesoscopic order and domains of competing quantum phases in correlated electron materials over a wide range of controlled electric and magnetic fields, strain, current, and temperature.
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07.79.Fc Near-field scanning optical microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
42.79.Bh Lenses, prisms and mirrors

Design of a high-speed electrochemical scanning tunneling microscope

Y. I. Yanson, F. Schenkel, and M. J. Rost

Rev. Sci. Instrum. 84, 023702 (2013); http://dx.doi.org/10.1063/1.4779086 (9 pages)

Online Publication Date: 5 February 2013

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In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.
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07.79.Cz Scanning tunneling microscopes
02.70.Dh Finite-element and Galerkin methods
07.10.-h Mechanical instruments and equipment
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