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Mar 2011

Volume 82, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 82, 031301 (2011); http://dx.doi.org/10.1063/1.3567309 (15 pages)

Farideh Honary, Steve R. Marple, Keith Barratt, Peter Chapman, Martin Grill, and Erling Nielsen
Shown in the top half of the figure is the Ny-Ålesund imaging riometer. The tower in the background is not part of the antenna array; it was used by Amundsen to moor the Norge airship. Inset is a three-dimensional visualization of the 49 beams generated from the filled phased array. In the lower half is shown the Mills cross antenna array from the Advanced Rio-Imaging Experiment in Scandinavia (ARIES). Inset is a three-dimensional visualization of one of the 556 imaging beams; the pencil beam is constructed from the cross-correlation of two perpendicular fan beams.
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Invited Article: Digital beam-forming imaging riometer systems

Farideh Honary, Steve R. Marple, Keith Barratt, Peter Chapman, Martin Grill, and Erling Nielsen

Rev. Sci. Instrum. 82, 031301 (2011); http://dx.doi.org/10.1063/1.3567309 (15 pages) | Cited 2 times

Online Publication Date: 22 March 2011

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The design and operation of a new generation of digital imaging riometer systems developed by Lancaster University are presented. In the heart of the digital imaging riometer is a field-programmable gate array (FPGA), which is used for the digital signal processing and digital beam forming, completely replacing the analog Butler matrices which have been used in previous designs. The reconfigurable nature of the FPGA has been exploited to produce tools for remote system testing and diagnosis which have proven extremely useful for operation in remote locations such as the Arctic and Antarctic. Different FPGA programs enable different instrument configurations, including a 4 × 4 antenna filled array (producing 4 × 4 beams), an 8 × 8 antenna filled array (producing 7 × 7 beams), and a Mills cross system utilizing 63 antennas producing 556 usable beams. The concept of using a Mills cross antenna array for riometry has been successfully demonstrated for the first time. The digital beam forming has been validated by comparing the received signal power from cosmic radio sources with results predicted from the theoretical beam radiation pattern. The performances of four digital imaging riometer systems are compared against each other and a traditional imaging riometer utilizing analog Butler matrices. The comparison shows that digital imaging riometer systems, with independent receivers for each antenna, can obtain much better measurement precision for filled arrays or much higher spatial resolution for the Mills cross configuration when compared to existing imaging riometer systems.
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94.80.+g Instrumentation for space plasma physics, ionosphere, and magnetosphere
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
84.40.Ba Antennas: theory, components and accessories
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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Secondary ion counting for surface-sensitive chemical analysis of organic compounds using time-of-flight secondary ion mass spectroscopy with cluster ion impact ionization

K. Hirata, Y. Saitoh, A. Chiba, K. Yamada, Y. Takahashi, and K. Narumi

Rev. Sci. Instrum. 82, 033101 (2011); http://dx.doi.org/10.1063/1.3541799 (5 pages) | Cited 1 time

Online Publication Date: 4 March 2011

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We report suitable secondary ion (SI) counting for surface-sensitive chemical analysis of organic compounds using time-of-flight (TOF) SI mass spectroscopy, based on considerably higher emission yields of SIs induced by cluster ion impact ionization. A SI counting system for a TOF SI mass spectrometer was developed using a fast digital storage oscilloscope, which allows us to perform various types of analysis as all the signal pulses constituting TOF SI mass spectra can be recorded digitally in the system. Effects of the SI counting strategy on SI mass spectra were investigated for C8 and C60 cluster ion impacts on an organically contaminated silicon wafer and on polytetrafluoroethylene targets by comparing TOF SI mass spectra obtained from the same recorded signals with different SI counting procedures. Our results show that the use of a counting system, which can cope with high SI yields, is necessary for quantitative analysis of SI mass spectra obtained under high SI yield per impact conditions, including the case of cluster ion impacts on organic compounds.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.80.Rt Time of flight mass spectrometry
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
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Active control of the pointing of a multi-terawatt laser

G. Genoud, F. Wojda, M. Burza, A. Persson, and C.-G. Wahlström

Rev. Sci. Instrum. 82, 033102 (2011); http://dx.doi.org/10.1063/1.3556438 (6 pages)

Online Publication Date: 7 March 2011

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The beam pointing of a multi-terawatt laser is stabilized on a millisecond time scale using an active control system. Two piezo mirrors, two position sensing detectors, and a computer based optimization program ensure that both near- and far-field are stable, even during single shot operation. A standard deviation for the distribution of laser shots of 2.6 μ rad is achieved.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors

Optical cell for combinatorial in situ Raman spectroscopic measurements of hydrogen storage materials at high pressures and temperatures

Jason R. Hattrick-Simpers, Wilbur S. Hurst, Sesha S. Srinivasan, and James E. Maslar

Rev. Sci. Instrum. 82, 033103 (2011); http://dx.doi.org/10.1063/1.3558693 (6 pages)

Online Publication Date: 10 March 2011

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An optical cell is described for high-throughput backscattering Raman spectroscopic measurements of hydrogen storage materials at pressures up to 10 MPa and temperatures up to 823 K. High throughput is obtained by employing a 60 mm diameter × 9 mm thick sapphire window, with a corresponding 50 mm diameter unobstructed optical aperture. To reproducibly seal this relatively large window to the cell body at elevated temperatures and pressures, a gold o-ring is employed. The sample holder-to-window distance is adjustable, making this cell design compatible with optical measurement systems incorporating lenses of significantly different focal lengths, e.g., microscope objectives and single element lenses. For combinatorial investigations, up to 19 individual powder samples can be loaded into the optical cell at one time. This cell design is also compatible with thin-film samples. To demonstrate the capabilities of the cell, in situ measurements of the Ca(BH4)2 and nano-LiBH4–LiNH2–MgH2 hydrogen storage systems at elevated temperatures and pressures are reported.
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87.64.kp Raman
88.30.R- Hydrogen storage

Laser ablation with resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for determining aromatic lignin volatilization products from biomass

Calvin Mukarakate, Adam M. Scheer, David J. Robichaud, Mark W. Jarvis, Donald E. David, G. Barney Ellison, Mark R. Nimlos, and Mark F. Davis

Rev. Sci. Instrum. 82, 033104 (2011); http://dx.doi.org/10.1063/1.3563704 (10 pages) | Cited 10 times

Online Publication Date: 10 March 2011

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We have designed and developed a laser ablation/pulsed sample introduction/mass spectrometry platform that integrates pyrolysis (py) and/or laser ablation (LA) with resonance-enhanced multiphoton ionization (REMPI) reflectron time-of-flight mass spectrometry (TOFMS). Using this apparatus, we measured lignin volatilization products of untreated biomass materials. Biomass vapors are produced by either a custom-built hot stage pyrolysis reactor or laser ablation using the third harmonic of an Nd:YAG laser (355 nm). The resulting vapors are entrained in a free jet expansion of He, then skimmed and introduced into an ionization region. One color resonance-enhanced multiphoton ionization (1+1 REMPI) is used, resulting in highly selective detection of lignin subunits from complex vapors of biomass materials. The spectra obtained by py-REMPI-TOFMS and LA-REMPI-TOFMS display high selectivity and decreased fragmentation compared to spectra recorded by an electron impact ionization molecular beam mass spectrometer (EI-MBMS). The laser ablation method demonstrates the ability to selectively isolate and volatilize specific tissues within the same plant material and then detect lignin-based products from the vapors with enhanced sensitivity. The identification of select products observed in the LA-REMPI-TOFMS experiment is confirmed by comparing their REMPI wavelength scans with that of known standards.
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79.20.Eb Laser ablation
42.62.-b Laser applications
82.80.Rt Time of flight mass spectrometry
64.70.Hz Solid-vapor transitions
64.70.F- Liquid-vapor transitions
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Calibration method to characterize the accuracy of phase-shifting point diffraction interferometer

Ke Liu, Yanqiu Li, and Hai Wang

Rev. Sci. Instrum. 82, 033105 (2011); http://dx.doi.org/10.1063/1.3560072 (6 pages)

Online Publication Date: 11 March 2011

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Characterization of measurement accuracy of the phase-shifting point diffraction interferometer (PS/PDI) is usually performed by two-pinhole null test. In this procedure, the geometrical coma and detector tilt astigmatism systematic errors are almost one or two magnitude higher than the desired accuracy of PS/PDI. These errors must be accurately removed from the null test result to achieve high accuracy. Published calibration methods, which can remove the geometrical coma error successfully, have some limitations in calibrating the astigmatism error. In this paper, we propose a method to simultaneously calibrate the geometrical coma and detector tilt astigmatism errors in PS/PDI null test. Based on the measurement results obtained from two pinhole pairs in orthogonal directions, the method utilizes the orthogonal and rotational symmetry properties of Zernike polynomials over unit circle to calculate the systematic errors introduced in null test of PS/PDI. The experiment using PS/PDI operated at visible light is performed to verify the method. The results show that the method is effective in isolating the systematic errors of PS/PDI and the measurement accuracy of the calibrated PS/PDI is 0.0088λ rms  (λ = 632.8 nm).
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42.87.Bg Phase shifting interferometry
07.60.Ly Interferometers
06.20.fb Standards and calibration
42.25.Fx Diffraction and scattering
02.10.De Algebraic structures and number theory
42.82.Cr Fabrication techniques; lithography, pattern transfer

Performance of Y2O3/Al multilayer coatings for the He-II radiation at 30.4 nm

Go Murakami, Kouichi Sakai, Tatsuro Homma, Kazuo Yoshioka, Ichiro Yoshikawa, Satoshi Ichimaru, and Hisataka Takenaka

Rev. Sci. Instrum. 82, 033106 (2011); http://dx.doi.org/10.1063/1.3560136 (4 pages) | Cited 2 times

Online Publication Date: 11 March 2011

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We briefly report on the performance and stability of periodic multilayer mirrors containing Y2O3 and Al layers designed for normal incidence reflection at the He-II emission line (30.4 nm). We found that Y2O3/Al multilayer coatings had higher reflectivity (24.9%) at 30.4 nm and significantly lower reflectivity (1.3%) at 58.4 nm than the conventional coatings such as Mo/Si. Furthermore, we investigated the temporal stability of the Y2O3/Al multilayer coatings. Our sample was kept under vacuum, dry N2 purge, and normal atmosphere for over three months, and there were no measurable changes in the reflectivity. These results suggest that we can use Y2O3/Al multilayer coatings as standard mirrors for the He-II radiation.
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68.65.Ac Multilayers
81.65.-b Surface treatments
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Measuring gain and noise in active long-range surface plasmon-polariton waveguides

Israel De Leon and Pierre Berini

Rev. Sci. Instrum. 82, 033107 (2011); http://dx.doi.org/10.1063/1.3555337 (10 pages) | Cited 1 time

Online Publication Date: 21 March 2011

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We describe techniques and an experimental setup to measure the gain and noise characteristics of a long-range surface plasmon-polariton amplifier consisting of a symmetric metallic stripe waveguide incorporating optically pumped dye molecules in the solution as the gain medium. The setup is capable of acquiring absolute power measurements at the amplifier's output over a narrow optical bandwidth. This allows independent characterization of the amplifier's gain via measurements of stimulated emission and via measurements of amplified spontaneous emission (ASE) over a narrow optical bandwidth, both obtained during the same experimental run. In addition, the absolute power measurements of ASE quantify directly the amplifier's noise.
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42.81.Cn Fiber testing and measurement of fiber parameters
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Compact magnetospectrometer for pulsed magnets based on infrared quantum cascade lasers

O. Drachenko, S. Winnerl, H. Schneider, M. Helm, J. Wosnitza, and J. Leotin

Rev. Sci. Instrum. 82, 033108 (2011); http://dx.doi.org/10.1063/1.3556441 (6 pages) | Cited 7 times

Online Publication Date: 21 March 2011

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In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron–resonance studies under pulsed magnetic fields up to 60 T.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.55.-f Lasers

A photoelectron velocity map imaging spectrometer for experiments combining synchrotron and laser radiations

P. O’Keeffe, P. Bolognesi, M. Coreno, A. Moise, R. Richter, G. Cautero, L. Stebel, R. Sergo, L. Pravica, Y. Ovcharenko, and L. Avaldi

Rev. Sci. Instrum. 82, 033109 (2011); http://dx.doi.org/10.1063/1.3563723 (8 pages) | Cited 10 times

Online Publication Date: 24 March 2011

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A velocity map imaging/ion time-of-flight spectrometer designed specifically for pump–probe experiments combining synchrotron and laser radiations is described. The in-house built delay line detector can be used in two modes: the high spatial resolution mode and the coincidence mode. In the high spatial resolution mode a kinetic energy resolution of 6% has been achieved. The coincidence mode can be used to improve signal-to-noise ratio for the pump–probe experiments either by using a gate to count electrons only when the laser is present or by recording coincidences with the ion formed in the ionization process.
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07.75.+h Mass spectrometers
07.81.+a Electron and ion spectrometers
07.85.Qe Synchrotron radiation instrumentation

A high-sensitivity angle and energy dipersive multichannel electron momentum spectrometer with 2π angle range

QiGuo Tian, KeDong Wang, Xu Shan, and XiangJun Chen

Rev. Sci. Instrum. 82, 033110 (2011); http://dx.doi.org/10.1063/1.3568744 (7 pages) | Cited 2 times

Online Publication Date: 24 March 2011

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A high-sensitivity angle and energy dispersive multichannel electron momentum spectrometer with simultaneous detection in 2π angle range is presented. A newly designed double half wedge and strip anode position-sensitive detector is employed to collect the ionized and scattered electrons passing through a 90° sector, 2π spherical electrostatic analyzer over azimuthal angle range of about 150° for each. Experimental results on argon are presented to exhibit the performance of the spectrometer.
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29.40.Gx Tracking and position-sensitive detectors

Microfabricated atomic vapor cell arrays for magnetic field measurements

S. Woetzel, V. Schultze, R. IJsselsteijn, T. Schulz, S. Anders, R. Stolz, and H.-G. Meyer

Rev. Sci. Instrum. 82, 033111 (2011); http://dx.doi.org/10.1063/1.3559304 (4 pages) | Cited 5 times

Online Publication Date: 25 March 2011

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We describe a method for charging atomic vapor cells with cesium and buffer gas. By this, it is possible to adjust the buffer gas pressure in the cells with good accuracy. Furthermore, we present a new design of microfabricated vapor cell arrays, which combine silicon wafer based microfabrication and ultrasonic machining to achieve the arrays of thermally separated cells with 50 mm3 volume. With cells fabricated in the outlined way, intrinsic magnetic field sensitivities down to 300 fT/Hz1/2 are reached.
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06.30.Ka Basic electromagnetic quantities
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Vector-magneto-optical generalized ellipsometry

K. Mok, N. Du, and H. Schmidt

Rev. Sci. Instrum. 82, 033112 (2011); http://dx.doi.org/10.1063/1.3568822 (10 pages) | Cited 7 times

Online Publication Date: 25 March 2011

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We present the setup of a variable-angle vector-magneto-optical generalized ellipsometer (VMOGE) in the spectral range from 300 to 1100 nm using an octupole magnet, and demonstrate VMOGE measurements of the upper 3 × 4 submatrix of the Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. New “field orbit” measurements can be performed without physically moving the sample, which is useful to study magnetic multilayer or nanostructure samples. A 4 × 4 matrix formalism is employed to model the experimental VMOGE data. Searching the best match model between experimental and calculated VMOGE data, the magneto-optical dielectric tensor ɛMO of each layer in a multilayer sample system can be determined. In this work, we assume that the nonsymmetric terms of ɛMO are induced by an external magnetic field and depend linearly on the sample magnetization. Comparison with vector magnetometer measurements can provide the anisotropic magneto-optical coupling constants Qx, Qy, Qz.
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07.60.Fs Polarimeters and ellipsometers
85.70.Sq Magnetooptical devices

Formation of subwavelength grating on molybdenum mirrors using a femtosecond Ti:sapphire laser system operating at 10 Hz

Avnish Kumar Sharma, John Smedley, Thomas Tsang, and Triveni Rao

Rev. Sci. Instrum. 82, 033113 (2011); http://dx.doi.org/10.1063/1.3569763 (7 pages) | Cited 3 times

Online Publication Date: 29 March 2011

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We report formation of subwavelength surface grating over large surface area of molybdenum mirror by multiple irradiation of amplified femtosecond laser pulses from a homemade Ti:sapphire oscillator–amplifier laser system in a raster scan configuration. The laser system delivered 2 mJ, 80 fs duration laser pulses at a pulse repetition rate of 10 Hz. Various parameters such as pulse fluence, number of pulses, laser polarization, scan speed, and scan steps were optimized to obtain uniform subwavelength gratings. Energy dispersive x-ray spectroscopy measurements were conducted to analyze the elemental composition of mirror surfaces before and after laser treatment.
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42.62.-b Laser applications
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.79.Bh Lenses, prisms and mirrors

Temperature-insensitive laser frequency locking near absorption lines

Natalie Kostinski, Ben A. Olsen, Robert Marsland, III, Bart H. McGuyer, and William Happer

Rev. Sci. Instrum. 82, 033114 (2011); http://dx.doi.org/10.1063/1.3574221 (4 pages) | Cited 1 time

Online Publication Date: 30 March 2011

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Combined magnetically induced circular dichroism and Faraday rotation of an atomic vapor are used to develop a variant of the dichroic atomic vapor laser lock that eliminates lock sensitivity to temperature fluctuations of the cell. Operating conditions that eliminate first-order sensitivity to temperature fluctuations can be determined by low-frequency temperature modulation. This temperature-insensitive gyrotropic laser lock can be accurately understood with a simple model, that is in excellent agreement with observations in potassium vapor at laser frequencies in a 2 GHz range about the 770.1 nm absorption line. The methods can be readily adapted for other absorption lines.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
32.60.+i Zeeman and Stark effects
03.75.Be Atom and neutron optics
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Determination of the temperature of bremsstrahlung photon generated by ultraintense laser using various thickness attenuators

Shuichi Hasegawa, Ryuta Takashima, Masaru Todoriki, Satoshi Kikkawa, Keita Soda, Kei Takano, Yuji Oishi, Takuya Nayuki, Takashi Fujii, and Koshichi Nemoto

Rev. Sci. Instrum. 82, 033301 (2011); http://dx.doi.org/10.1063/1.3553496 (4 pages)

Online Publication Date: 1 March 2011

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We evaluate the simplified method using the Lambert–Beer law to measure the temperature of bremsstrahlung photon generated by an ultraintense laser. Analytical values are compared to the results of the Monte Carlo calculation of GEANT4 and they agreed very well on the condition of the appropriate distance between the attenuator and the detector. We performed the experiment to measure the temperature of bremsstrahlung x-ray emitted from a metal target irradiated by a Ti:sapphire laser with 76 mJ, 72 fs, 2.2 × 1018 W/cm2. For a Cu target of 30 μm thick, the photon temperature was reasonably determined to be 0.18 MeV, which is in good agreement with previous studies.
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07.20.Dt Thermometers
41.50.+h X-ray beams and x-ray optics
42.62.-b Laser applications
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

Spatially resolved measurements of electron cyclotron resonance ion source beam profile characteristics

Lauri Panitzsch, Michael Stalder, and Robert F. Wimmer-Schweingruber

Rev. Sci. Instrum. 82, 033302 (2011); http://dx.doi.org/10.1063/1.3553013 (7 pages) | Cited 2 times

Online Publication Date: 7 March 2011

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Simulations predict that the concentric rings and the triangular structures in the profiles of strongly focused ion beams that are found in different experiments should be dominated by ion species with the same or at least similar m/q-ratio. To verify these theoretical predictions we have tuned our ECR ion source to deliver a beam consisting of multiple ion species whose particular m/q-depending focusing ranges from weakly focused to overfocused. We then recorded spatially resolved charge-state distributions of the beam profile at characteristic positions in the plane perpendicular to the beam line. The results validate theoretical predictions and are summarized in this paper. To achieve the required beam profile characteristics we moved the extraction along the beam line to achieve stronger focusing than by only changing the extraction voltage. To fit the regions of interest of the beam profile into the transmission area of the sector magnet, we steered the beam by moving the extraction in the plane perpendicular to the beam axis. The results of both investigations, beam focusing and beam steering by using a 3D-movable extraction, are also reported in this paper. A brief overview of the new beam monitor extensively used during these measurements, the Faraday cup array, is also given.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
41.85.Lc Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles

A Mott polarimeter operating at MeV electron beam energies

V. Tioukine, K. Aulenbacher, and E. Riehn

Rev. Sci. Instrum. 82, 033303 (2011); http://dx.doi.org/10.1063/1.3556593 (8 pages) | Cited 4 times

Online Publication Date: 14 March 2011

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We have developed a Mott electron polarimeter for the Mainzer microtron (MAMI) accelerator in Mainz, Germany. At beam energies ranging between 1.0 and 3.5 MeV two double focusing magnet spectrometers collect elastically backscattered electrons from gold targets. In spite of the small spectrometer acceptance, a sufficient statistical efficiency is achieved to provide very fast measurements if beam currents typical for experiments at MAMI are being used. High reproducibility is achieved, demonstrating that the results of asymmetry measurements are independent of the primary beam current in a range from 0.004 to 45 μA at a level of <1% relative variation. Compared to low energy polarimeters of similar construction an improvement of a factor 2–3 in absolute accuracy seems possible.
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29.27.Eg Beam handling; beam transport
29.20.dg Cyclotrons
41.85.-p Beam optics
41.75.Fr Electron and positron beams

Improvement of four anode rods ion source

F. W. Abdel Salam, H. El-Khabeary, M. M. Ahmed, and A. M. Abdel Reheem

Rev. Sci. Instrum. 82, 033304 (2011); http://dx.doi.org/10.1063/1.3554637 (5 pages)

Online Publication Date: 17 March 2011

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In this work, an improved form of a saddle field ion source has been designed and constructed. It consists of four anode rods made from copper and two copper cathode discs. The two cathode discs are placed symmetrically on both sides of the four anode rods. The electrical discharge and output ion beam characteristics were measured at different pressures using argon gas. The optimum distance between each two anode rods was determined. Also the optimum distance between the four anode rods and any cathode disc was obtained. It was found that the optimum distance between each two anode rods equal to 6 mm, while the optimum distance between the four anode rods and any cathode disc equal to 16 mm, where a stable discharge current and maximum output ion beam current can be obtained. The effect of negative extraction voltage applied to both the extractor electrode and Faraday cup on the output ion beam current was studied. The sputter yield of copper and aluminum targets using argon ions of different energies was determined.
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29.25.Ni Ion sources: positive and negative
52.80.-s Electric discharges

A Freon-filled bubble chamber for neutron detection in inertial confinement fusion experiments

M. C. Ghilea, D. D. Meyerhofer, and T. C. Sangster

Rev. Sci. Instrum. 82, 033305 (2011); http://dx.doi.org/10.1063/1.3554649 (6 pages) | Cited 1 time

Online Publication Date: 18 March 2011

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Neutron imaging is one of the main methods used in inertial confinement fusion experiments to measure the core symmetry of target implosions. Previous studies have shown that bubble chambers have the potential to obtain higher resolution images of the targets for a shorter source-to-target distance than typical scintillator arrays. A bubble chamber for neutron imaging with Freon 115 as the active medium was designed and built for the OMEGA laser system. Bubbles resulting from spontaneous nucleation were recorded. Bubbles resulting from neutron–Freon interactions were observed at neutron yields of 1013 emitted from deuterium–tritium target implosions on OMEGA. The measured column bubble density was too low for neutron imaging on OMEGA but agreed with the model of bubble formation. The recorded data suggest that neutron bubble detectors are a promising technology for the higher neutron yields expected at National Ignition Facility.
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52.57.Fg Implosion symmetry and hydrodynamic instability (Rayleigh-Taylor, Richtmyer-Meshkov, imprint, etc.)
52.57.Bc Target design and fabrication
52.70.Nc Particle measurements
back to top Nuclear Physics, Fusion and Plasmas

A high-power spatial filter for Thomson scattering stray light reduction

J. P. Levesque, K. D. Litzner, M. E. Mauel, D. A. Maurer, G. A. Navratil, and T. S. Pedersen

Rev. Sci. Instrum. 82, 033501 (2011); http://dx.doi.org/10.1063/1.3549142 (5 pages) | Cited 1 time

Online Publication Date: 2 March 2011

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The Thomson scattering diagnostic on the High Beta Tokamak-Extended Pulse (HBT-EP) is routinely used to measure electron temperature and density during plasma discharges. Avalanche photodiodes in a five-channel interference filter polychromator measure scattered light from a 6 ns, 800 mJ, 1064 nm Nd:YAG laser pulse. A low cost, high-power spatial filter was designed, tested, and added to the laser beamline in order to reduce stray laser light to levels which are acceptable for accurate Rayleigh calibration. A detailed analysis of the spatial filter design and performance is given. The spatial filter can be easily implemented in an existing Thomson scattering system without the need to disturb the vacuum chamber or significantly change the beamline. Although apertures in the spatial filter suffer substantial damage from the focused beam, with proper design they can last long enough to permit absolute calibration.
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52.55.Fa Tokamaks, spherical tokamaks
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b Plasma properties
52.80.-s Electric discharges
06.20.fb Standards and calibration

In situ spectral calibration method for the impurity influx monitor (divertor) for ITER using angled physical contact fibers

A. Iwamae, H. Ogawa, T. Sugie, and Y. Kusama

Rev. Sci. Instrum. 82, 033502 (2011); http://dx.doi.org/10.1063/1.3559117 (4 pages)

Online Publication Date: 2 March 2011

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The in situ calibration method for the impurity influx monitor (divertor) is experimentally examined. The total reflectance of the optical path from the focal point of the Cassegrain telescope to the first mirror is derived using a micro retroreflector array. An optical fiber with angled physical contact (APC) connectors reduces the return edge reflection. APC fibers and a multimode coupler increase the signal-to-noise ratio by about one order compared to that of triple-branched fibers and enable measurement of the wavelength dependence of the total reflectance of the optical system even after potential deterioration of mirror surfaces reduces reflectance.
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06.20.fb Standards and calibration
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Rk Power exhaust; divertors
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Bh Lenses, prisms and mirrors
07.60.Rd Visible and ultraviolet spectrometers

Development of radially movable multichannel Reynolds stress probe system for a cylindrical laboratory plasma

Yoshihiko Nagashima, Shigeru Inagaki, Kunihiro Kamakaki, Hiroyuki Arakawa, Takuma Yamada, Shunjiro Shinohara, Yoshinobu Kawai, Masatoshi Yagi, Akihide Fujisawa, Sanae -I. Itoh, Kimitaka Itoh, and Yuichi Takase

Rev. Sci. Instrum. 82, 033503 (2011); http://dx.doi.org/10.1063/1.3557384 (5 pages) | Cited 1 time

Online Publication Date: 2 March 2011

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A new radially movable multichannel azimuthal probe system has been developed for measuring azimuthal and radial profiles of electrostatic Reynolds stress (RS) per mass density of microscale fluctuations for a cylindrical laboratory plasma. The system is composed of 16 probe units arranged azimuthally. Each probe unit has six electrodes to simultaneously measure azimuthal and radial electric fields for obtaining RS. The advantage of the system is that each probe unit is radially movable to measure azimuthal RS profiles at arbitrary radial locations as well as two-dimensional structures of fluctuations. The first result from temporal observation of fluctuation azimuthal profile presents that a low-frequency fluctuation (1–2 kHz) synchronizes oscillating Reynolds stress. In addition, radial scanning of the probe system simultaneously demonstrates two-dimensional patterns of mode structure and nonlinear forces with frequency f = 1.5  kHz and azimuthal mode number m = 1.
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52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena

New measurement system for on line in core high-energy neutron flux monitoring in materials testing reactor conditions

B. Geslot, L. Vermeeren, P. Filliatre, A. Legrand Lopez, L. Barbot, C. Jammes, S. Bréaud, L. Oriol, and J.-F. Villard

Rev. Sci. Instrum. 82, 033504 (2011); http://dx.doi.org/10.1063/1.3554439 (7 pages) | Cited 3 times

Online Publication Date: 10 March 2011

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Flux monitoring is of great interest for experimental studies in material testing reactors. Nowadays, only the thermal neutron flux can be monitored on line, e.g., using fission chambers or self-powered neutron detectors. In the framework of the Joint Instrumentation Laboratory between SCK-CEN and CEA, we have developed a fast neutron detector system (FNDS) capable of measuring on line the local high-energy neutron flux in fission reactor core and reflector locations. FNDS is based on fission chambers measurements in Campbelling mode. The system consists of two detectors, one detector being mainly sensitive to fast neutrons and the other one to thermal neutrons. On line data processing uses the CEA depletion code DARWIN in order to disentangle fast and thermal neutrons components, taking into account the isotopic evolution of the fissile deposit. The first results of FNDS experimental test in the BR2 reactor are presented in this paper. Several fission chambers have been irradiated up to a fluence of about 7 × 1020 n/cm2. A good agreement (less than 10% discrepancy) was observed between FNDS fast flux estimation and reference flux measurement.
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28.20.-v Neutron physics
28.41.-i Fission reactors

Fusion neutron detector for time-of-flight measurements in z-pinch and plasma focus experiments

D. Klir, J. Kravarik, P. Kubes, K. Rezac, E. Litseva, K. Tomaszewski, L. Karpinski, M. Paduch, and M. Scholz

Rev. Sci. Instrum. 82, 033505 (2011); http://dx.doi.org/10.1063/1.3559548 (7 pages) | Cited 3 times

Online Publication Date: 11 March 2011

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We have developed and tested sensitive neutron detectors for neutron time-of-flight measurements in z-pinch and plasma focus experiments with neutron emission times in tens of nanoseconds and with neutron yields between 106 and 1012 per one shot. The neutron detectors are composed of a BC-408 fast plastic scintillator and Hamamatsu H1949-51 photomultiplier tube (PMT). During the calibration procedure, a PMT delay was determined for various operating voltages. The temporal resolution of the neutron detector was measured for the most commonly used PMT voltage of 1.4 kV. At the PF-1000 plasma focus, a novel method of the acquisition of a pulse height distribution has been used. This pulse height analysis enabled to determine the single neutron sensitivity for various neutron energies and to calibrate the neutron detector for absolute neutron yields at about 2.45 MeV.
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29.40.-n Radiation detectors
52.58.Lq Z-pinches, plasma focus, and other pinch devices
85.60.Ha Photomultipliers; phototubes and photocathodes
06.20.fb Standards and calibration
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