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Oct 2012

Volume 83, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 83, 101301 (2012); http://dx.doi.org/10.1063/1.4750234 (26 pages)

N. L. Kugland, D. D. Ryutov, C. Plechaty, J. S. Ross, and H.-S. Park

Proton imaging is widely used to reveal electric and magnetic field structures in high energy density plasmas. Even for smooth parent structures, strongly deflected protons can form images with strange shapes or singular lines of very high intensity (i.e. caustics).

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Invited Article: Relation between electric and magnetic field structures and their proton-beam images

N. L. Kugland, D. D. Ryutov, C. Plechaty, J. S. Ross, and H.-S. Park

Rev. Sci. Instrum. 83, 101301 (2012); http://dx.doi.org/10.1063/1.4750234 (26 pages) | Cited 3 times

Online Publication Date: 4 September 2012

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Proton imaging is commonly used to reveal the electric and magnetic fields that are found in high energy density plasmas. Presented here is an analysis of this technique that is directed towards developing additional insight into the underlying physics. This approach considers: formation of images in the limits of weak and strong intensity variations; caustic formation and structure; image inversion to obtain line-integrated field characteristics; direct relations between images and electric or magnetic field structures in a plasma; imaging of sharp features such as Debye sheaths and shocks. Limitations on spatial and temporal resolution are assessed, and similarities with optical shadowgraphy are noted. Synthetic proton images are presented to illustrate the analysis. These results will be useful for quantitatively analyzing experimental proton imaging data and verifying numerical codes.
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52.70.Nc Particle measurements
52.35.Tc Shock waves and discontinuities
52.40.Kh Plasma sheaths
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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

A compact and efficient strontium oven for laser-cooling experiments

M. Schioppo, N. Poli, M. Prevedelli, St. Falke, Ch. Lisdat, U. Sterr, and G. M. Tino

Rev. Sci. Instrum. 83, 103101 (2012); http://dx.doi.org/10.1063/1.4756936 (6 pages) | Cited 1 time

Online Publication Date: 1 October 2012

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Here we describe a compact and efficient strontium oven well suited for laser-cooling experiments. Novel design solutions allowed us to produce a collimated strontium atomic beam with a flux of 1.0 × 1013 s−1 cm−2 at the oven temperature of 450 °C, reached with an electrical power consumption of 36 W. The oven is based on a stainless-steel reservoir, filled with 6 g of metallic strontium, electrically heated in a vacuum environment by a tantalum wire threaded through an alumina multi-bore tube. The oven can be hosted in a standard DN40CF cube and has an estimated continuous operation lifetime of 10 years. This oven can be used for other alkali and alkaline earth metals with essentially no modifications.
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07.20.Hy Furnaces; heaters

A high resolution ultraviolet Brillouin scattering set-up

F. Bencivenga, A. Battistoni, D. Fioretto, A. Gessini, J. R. Sandercock, and C. Masciovecchio

Rev. Sci. Instrum. 83, 103102 (2012); http://dx.doi.org/10.1063/1.4756690 (7 pages)

Online Publication Date: 3 October 2012

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We report on a high resolution inelastic UV scattering table-top setup conceived for Brillouin measurements. The system is based on a tandem 1+1 pass scanning Fabry-Perot interferometer of Sandercock type. Special optics were used in order to adapt such an interferometric device, nowadays only used at visible or IR wavelength, to the UV range. The advantages with respect to other UV Brillouin scattering instruments are the larger resolving power and the improved contrast in the low frequency spectral region. To corroborate these features we provide a comparison between data obtained using the described system and those from existing UV Brillouin scattering instruments.
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07.60.Ly Interferometers
07.60.Rd Visible and ultraviolet spectrometers
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Simple and versatile heterodyne whole-field interferometer for phase optics characterization

D. M. Silva, E. A. Barbosa, and N. U. Wetter

Rev. Sci. Instrum. 83, 103103 (2012); http://dx.doi.org/10.1063/1.4757396 (7 pages)

Online Publication Date: 5 October 2012

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A wavefront sensor for thermally induced lens and passive lens characterization based on low-coherence digital speckle interferometry was developed and studied. By illuminating the optical setup with two slightly detuned red diode lasers, whole-field contour interference fringes were generated according to the resulting synthetic wavelength. For fringe pattern visualization the optical setup used the light transmitted through a ground glass plate as object beam. The performance of the sensor was investigated and its versatility was demonstrated by measuring the thermal lens induced in an Er-doped glass sample pumped by a 1.76-W diode laser emitting at 976 nm and by evaluating the wavefront distortion introduced by an ophthalmic progressive lens.
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07.60.Ly Interferometers
42.25.Hz Interference
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.79.Bh Lenses, prisms and mirrors

In situ triaxial magnetic field compensation for the spin-exchange-relaxation-free atomic magnetometer

Jiancheng Fang (房建成) and Jie Qin (秦杰)

Rev. Sci. Instrum. 83, 103104 (2012); http://dx.doi.org/10.1063/1.4756046 (7 pages) | Cited 1 time

Online Publication Date: 9 October 2012

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The spin-exchange-relaxation-free (SERF) atomic magnetometer is an ultra-high sensitivity magnetometer, but it must be operated in a magnetic field with strength less than about 10 nT. Magnetic field compensation is an effective way to shield the magnetic field, and this paper demonstrates an in situ triaxial magnetic field compensation system for operating the SERF atomic magnetometer. The proposed hardware is based on optical pumping, which uses some part of the SERF atomic magnetometer itself, and the compensation method is implemented by analyzing the dynamics of the atomic spin. The experimental setup for this compensation system is described, and with this configuration, a residual magnetic field of strength less than 2 nT (±0.38 nT in the x axis, ±0.43 nT in the y axis, and ±1.62 nT in the z axis) has been achieved after compensation. The SERF atomic magnetometer was then used to verify that the residual triaxial magnetic fields were coincident with what were achieved by the compensation system.
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07.55.Ge Magnetometers for magnetic field measurements

A von Hamos x-ray spectrometer based on a segmented-type diffraction crystal for single-shot x-ray emission spectroscopy and time-resolved resonant inelastic x-ray scattering studies

J. Szlachetko, M. Nachtegaal, E. de Boni, M. Willimann, O. Safonova, J. Sa, G. Smolentsev, M. Szlachetko, J. A. van Bokhoven, J.-Cl. Dousse, J. Hoszowska, Y. Kayser, P. Jagodzinski, A. Bergamaschi, B. Schmitt, et al.

Rev. Sci. Instrum. 83, 103105 (2012); http://dx.doi.org/10.1063/1.4756691 (7 pages) | Cited 7 times

Online Publication Date: 9 October 2012

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We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV–9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.
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07.85.Nc X-ray and γ-ray spectrometers
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cp X-ray diffraction

Practical axial optical trapping

A. H. Mack, D. J. Schlingman, L. Regan, and S. G. J. Mochrie

Rev. Sci. Instrum. 83, 103106 (2012); http://dx.doi.org/10.1063/1.4757862 (11 pages)

Online Publication Date: 12 October 2012

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We describe a new method for calibrating optical trapping measurements in which tension is applied in the direction of the laser beam to a molecule tethered between a surface and an optically trapped bead. Specifically, we present a generally-applicable procedure for converting from the measured scattering intensity and the measured stage displacement to applied tension and bead-coverslip separation, using measurements of the light intensity scattered from an untethered, trapped bead. Our calibration accounts for a number of effects, including aberrations and the interference of forward-reflected bead-scattered light with the trapping beam. To demonstrate the accuracy of our method, we show measurements of the DNA force-versus-extension relation using a range of laser intensities, and show that these measurements match the expected extensible wormlike-chain (WLC) behavior. Finally, we also demonstrate a force-clamp, in which the tension in a tether is held fixed while the extension varies as a result of molecular events.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.25.Fx Diffraction and scattering
42.25.Hz Interference
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Time-resolved multiple probe spectroscopy

G. M. Greetham, D. Sole, I. P. Clark, A. W. Parker, M. R. Pollard, and M. Towrie

Rev. Sci. Instrum. 83, 103107 (2012); http://dx.doi.org/10.1063/1.4758999 (5 pages)

Online Publication Date: 18 October 2012

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Time-resolved multiple probe spectroscopy combines optical, electronic, and data acquisition capabilities to enable measurement of picosecond to millisecond time-resolved spectra within a single experiment, using a single activation pulse. This technology enables a wide range of dynamic processes to be studied on a single laser and sample system. The technique includes a 1 kHz pump, 10 kHz probe flash photolysis-like mode of acquisition (pump–probe–probe–probe, etc.), increasing the amount of information from each experiment. We demonstrate the capability of the instrument by measuring the photolysis of tungsten hexacarbonyl (W(CO)6) monitored by IR absorption spectroscopy, following picosecond vibrational cooling of product formation through to slower bimolecular diffusion reactions on the microsecond time scale.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
82.50.Bc Processes caused by infrared radiation
78.47.je Time resolved light scattering spectroscopy

Non-degenerated photoluminescence excitation correlation spectroscopy using an optical sampling technique

Takayuki Hasegawa, Naofumi Masumoto, Tomonori Harada, Takayuki Makino, and Yoshihiro Takagi

Rev. Sci. Instrum. 83, 103108 (2012); http://dx.doi.org/10.1063/1.4759133 (5 pages)

Online Publication Date: 19 October 2012

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We have developed a highly time-resolved photoluminescence spectroscopy based on the excitation correlation method. Successive irradiation of a pair of ultrashort light pulses with different wavelength combinations taken from two sub-picosecond lasers has exposed both temporal and energetic correlation in photoluminescence intensity associated with a nonlinear response of a sample. An optical sampling technique has been introduced successfully in order to avoid consideration of the synchronization control of ultrashort light pulses. We have demonstrated the abilities of this technique by applying to the nonlinear photoluminescence dynamics of organic dye molecules in solution.
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07.60.Rd Visible and ultraviolet spectrometers
78.55.Kz Solid organic materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

A rapid reflectance-difference spectrometer for real-time semiconductor growth monitoring with sub-second time resolution

O. Núñez-Olvera, R. E. Balderas-Navarro, J. Ortega-Gallegos, L. E. Guevara-Macías, A. Armenta-Franco, M. A. Lastras-Montaño, L. F. Lastras-Martínez, and A. Lastras-Martínez

Rev. Sci. Instrum. 83, 103109 (2012); http://dx.doi.org/10.1063/1.4760252 (5 pages)

Online Publication Date: 25 October 2012

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We report on a rapid, 32-channel reflectance-difference (RD) spectrometer with sub-second spectra acquisition times and ΔR/R sensitivity in the upper 10−4 range. The spectrometer is based on a 50 kHz photo-elastic modulator for light polarization modulation and on a lock-in amplifier for signal harmonic analysis. Multichannel operation is allowed by multiplexing the 32 outputs of the spectrometer into the input of the lock-in amplifier. The spectrometer spans a wavelength range of 230 nm that can be tuned to cover E1 and E1 + Δ1 transitions for a number of III–V semiconductors at epitaxial growth temperatures, including GaAs, InAs, AlAs, and their alloys. We present two examples of real-time measurements to demonstrate the performance of the RD spectrometer, namely, the evolution of the RD spectrum of GaAs (001) annealed at 500 °C and the time-dependent RD spectrum during the first stages of the epitaxial growth of In0.3Ga0.7As on GaAs (001) substrates.
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78.66.Fd III-V semiconductors
68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.40.Fy Semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Developing small vacuum spark as an x-ray source for calibration of an x-ray focusing crystal spectrometer

Mostafa Ghomeishi, Mohammad Karami, and Faisal Rafiq Mahamd Adikan

Rev. Sci. Instrum. 83, 103110 (2012); http://dx.doi.org/10.1063/1.4762835 (5 pages)

Online Publication Date: 29 October 2012

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A new technique of x-ray focusing crystal spectrometers’ calibration is the desired result. For this purpose the spectrometer is designed to register radiated copper Kα and Kβ lines by using a flat α-quartz crystal. This experiment uses pre-breakdown x-ray emissions in low vacuum of about 2.5–3 mbar. At this pressure the pinch will not form so the plasma will not radiate. The anode material is copper and the capacity of the capacitor bank is 22.6 nF. This experiment designed and mounted a repetitive triggering system to save the operator time making hundreds of shots. This emission amount is good for calibration and geometrical adjustment of an optical crystal x-ray focusing spectrometer.
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07.85.Nc X-ray and γ-ray spectrometers
52.75.Xx Thermionic and filament-based sources (e.g., Q machines, double- and triple-plasma devices, etc.)
52.58.Lq Z-pinches, plasma focus, and other pinch devices
06.20.fb Standards and calibration

Kr II laser-induced fluorescence for measuring plasma acceleration

W. A. Hargus, Jr., G. M. Azarnia, and M. R. Nakles

Rev. Sci. Instrum. 83, 103111 (2012); http://dx.doi.org/10.1063/1.4754889 (11 pages)

Online Publication Date: 29 October 2012

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We present the application of laser-induced fluorescence of singly ionized krypton as a diagnostic technique for quantifying the electrostatic acceleration within the discharge of a laboratory cross-field plasma accelerator also known as a Hall effect thruster, which has heritage as spacecraft propulsion. The 728.98 nm Kr II transition from the metastable 5d4D7/2 to the 5p4P5/2∘ state was used for the measurement of laser-induced fluorescence within the plasma discharge. From these measurements, it is possible to measure velocity as krypton ions are accelerated from near rest to approximately 21 km/s (190 eV). Ion temperature and the ion velocity distributions may also be extracted from the fluorescence data since available hyperfine splitting data allow for the Kr II 5d4D7/2–5p4P5/2∘ transition lineshape to be modeled. From the analysis, the fluorescence lineshape appears to be a reasonable estimate for the relatively broad ion velocity distributions. However, due to an apparent overlap of the ion creation and acceleration regions within the discharge, the distributed velocity distributions increase ion temperature determination uncertainty significantly. Using the most probable ion velocity as a representative, or characteristic, measure of the ion acceleration, overall propellant energy deposition, and effective electric fields may be calculated. With this diagnostic technique, it is possible to nonintrusively characterize the ion acceleration both within the discharge and in the plume.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.75.Di Ion and plasma propulsion
52.80.-s Electric discharges
52.25.Fi Transport properties
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

X-ray luminescence based spectrometer for investigation of scintillation properties

C. R. Varney, M. A. Khamehchi, Jianfeng Ji, and F. A. Selim

Rev. Sci. Instrum. 83, 103112 (2012); http://dx.doi.org/10.1063/1.4764772 (4 pages)

Online Publication Date: 31 October 2012

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A new x-ray luminescence based spectrometer was developed and installed to examine the scintillation properties of materials while revealing the origins of luminescence and investigating trapping defects. Measurements were performed on a number of undoped and Ce doped yttrium aluminum garnet crystals and various luminescence centers were characterized. The measured x-ray luminescence spectra provide information about the spectral range and the scintillation efficiency and linearity. The efficiency of charge-carriers production due to x ray, their energy transfer to the luminescence centers, and the efficiency of luminescence are all reflected in the efficiency of x-ray luminescence.
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07.85.Nc X-ray and γ-ray spectrometers
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Thermal imaging diagnostics of high-current electron beams

A. Pushkarev, G. Kholodnaya, R. Sazonov, and D. Ponomarev

Rev. Sci. Instrum. 83, 103301 (2012); http://dx.doi.org/10.1063/1.4756689 (6 pages)

Online Publication Date: 8 October 2012

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The thermal imaging diagnostics of measuring pulsed electron beam energy density is presented. It provides control of the electron energy spectrum and a measure of the density distribution of the electron beam cross section, the spatial distribution of electrons with energies in the selected range, and the total energy of the electron beam. The diagnostics is based on the thermal imager registration of the imaging electron beam thermal print in a material with low bulk density and low thermal conductivity. Testing of the thermal imaging diagnostics has been conducted on a pulsed electron accelerator TEU-500. The energy of the electrons was 300–500 keV, the density of the electron current was 0.1–0.4 kA/cm2, the duration of the pulse (at half-height) was 60 ns, and the energy in the pulse was up to 100 J. To register the thermal print, a thermal imager Fluke-Ti10 was used. Testing showed that the sensitivity of a typical thermal imager provides the registration of a pulsed electron beam heat pattern within one pulse with energy density over 0.1 J/cm2 (or with current density over 10 A/cm2, pulse duration of 60 ns and electron energy of 400 keV) with the spatial resolution of 0.9–1 mm. In contrast to the method of using radiosensitive (dosimetric) materials, thermal imaging diagnostics does not require either expensive consumables, or plenty of processing time.
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42.79.Pw Imaging detectors and sensors
41.75.Fr Electron and positron beams

Temperature peaking at beginning of breakdown in 2.45 GHz pulsed off-resonance electron cyclotron resonance ion source hydrogen plasma

O. D. Cortázar, A. Megía-Macías, and A. Vizcaíno-de-Julián

Rev. Sci. Instrum. 83, 103302 (2012); http://dx.doi.org/10.1063/1.4757113 (5 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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An experimental study of temperature and density evolution during breakdown in off-resonance ECR hydrogen plasma is presented. Under square 2.45 GHz microwave excitation pulses with a frequency of 50 Hz and relative high microwave power, unexpected transient temperature peaks that reach 18 eV during 20 μs are reported at very beginning of plasma breakdown. Decays of such peaks reach final stable temperatures of 5 eV at flat top microwave excitation pulse. Evidence of interplay between incoming power and duty cycle giving different kind of plasma parameters evolutions engaged to microwave coupling times is observed. Under relative high power conditions where short microwave coupling times are recorded, high temperature peaks are measured. However, for lower incoming powers and longer coupling times, temperature evolves gradually to a higher final temperature without peaking. On the other hand, the early instant where temperature peaks are observed also suggest a possible connection with preglow processes during breakdown in ECRIS plasmas.
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52.80.Pi High-frequency and RF discharges
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Measurement of parameters in Indus-2 synchrotron radiation source

A. D. Ghodke, Riyasat Husain, Pradeep Kumar, Surendra Yadav, and T. A. Puntambekar

Rev. Sci. Instrum. 83, 103303 (2012); http://dx.doi.org/10.1063/1.4760254 (8 pages) | Cited 1 time

Online Publication Date: 24 October 2012

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The paper presents the measurement of optics parameters in Indus-2 synchrotron radiation source, which include betatron tune, beta function, dispersion function, natural chromaticity, corrected chromaticity, central RF frequency, momentum compaction factor, and linear betatron coupling. Two methods were used for beta function measurement; a conventional quadrupole scan method and a method using the fitting of the orbit response matrix. A robust Levenberg-Marquardt algorithm was used for nonlinear least square fitting of the orbit response matrix. In this paper, detailed methods for the parameter measurements are described. The measured results are discussed and compared with the theoretical values obtained using accelerator simulation code Accelerator Toolbox in MATLAB.
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29.27.Fh Beam characteristics
29.20.df Betatrons
29.20.db Storage rings and colliders
41.85.-p Beam optics
41.75.Fr Electron and positron beams

Variation of anode grid surface morphology and its effect on operation of a triode virtual cathode oscillator

Qifu Xu, Dan Cai, Qiang Zhang, Xuelong Zhao, Qi Zhao, Guoxin Cheng, and Lie Liu

Rev. Sci. Instrum. 83, 103304 (2012); http://dx.doi.org/10.1063/1.4763574 (4 pages)

Online Publication Date: 31 October 2012

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After repeatedly operation of a triode virtual cathode oscillator, the surface morphology of anode grid is studied by a scanning electron microscope. It is found that there are many quasi-periodic sawteeth formed on the anode grid, which are about 300–500 μm in height, ∼200 μm in width, and 150–200 μm in period. The formation of this sawteeth implies that there is possible Rayleigh-Taylor-like instability on the anode grid during the irradiation by high-current relativistic electron beam. These sawteeth enhance the electric field on anode grid, leading to more feasible of anode plasma generation, and more rapidly expansion of that plasma. As a result, the electron transmissivity of anode grid is decreased, the output microwave power of the virtual cathode oscillator is lowered and its operational performance is degraded.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.47.+w Vacuum tubes
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.50.Dg Plasma sources
back to top Nuclear Physics, Fusion and Plasmas

High-resolution charge exchange measurements at ASDEX Upgrade

E. Viezzer, T. Pütterich, R. Dux, R. M. McDermott, and ASDEX Upgrade Team

Rev. Sci. Instrum. 83, 103501 (2012); http://dx.doi.org/10.1063/1.4755810 (11 pages) | Cited 2 times

Online Publication Date: 2 October 2012

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The charge exchange recombination spectroscopy (CXRS) diagnostics at ASDEX Upgrade (AUG) have been upgraded and extended to provide high-resolution measurements of impurity ion temperature, density, and rotation profiles. The existing core toroidal CXRS diagnostic has been refurbished to increase the level of signal, thus enabling shorter exposure times down to 3.5 ms. Additional lines of sight provide more detailed profiles and enable simultaneous measurements of multiple impurities. In addition, a new CXRS system has been installed, which allows for the measurement of poloidal impurity ion rotation in the plasma edge with high temporal (1.9 ms) and spatial resolution (down to 5 mm). A new wavelength correction method has been implemented to perform in situ wavelength calibrations on a shot-to-shot basis. Absolute measurements of the poloidal impurity ion rotation with uncertainties smaller than 1.5 km/s have been obtained. Comparison of all the CXRS measurements provides a consistency check of the diagnostics and good agreement has been found for all of the CXRS systems.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.-m Plasma diagnostic techniques and instrumentation
34.70.+e Charge transfer

Control of current and voltage oscillations in a short dc discharge making use of external auxiliary electrode

A. S. Mustafaev, V. I. Demidov, I. Kaganovich, S. F. Adams, M. E. Koepke, and A. Grabovskiy

Rev. Sci. Instrum. 83, 103502 (2012); http://dx.doi.org/10.1063/1.4757111 (3 pages)

Online Publication Date: 8 October 2012

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A dc discharge with a hot cathode is subject to current and voltage plasma oscillations, which have deleterious effects on its operation. The oscillations can be inhibited by installing an auxiliary electrode, placed outside of anode. By collecting a modest current through a small opening in anode, we show that the discharge becomes stable, in a certain pressure range. This method of avoiding current oscillations can be used, for example, for high current stabilizers.
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52.80.-s Electric discharges
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Ion energy analyzer for measurement of ion turbulent transport

V. Sokolov and A. K. Sen

Rev. Sci. Instrum. 83, 103503 (2012); http://dx.doi.org/10.1063/1.4758070 (4 pages)

Online Publication Date: 18 October 2012

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For local measurement of radial ion thermal transport, we developed a novel time-resolved gridded ion energy analyzer. The turbulent thermal flux is obtained by correlating fluctuations of ion temperature, plasma density and plasma velocity. The simultaneous measurement of the ion current fluctuations from an ion energy analyzer mathIEA(t) and the fluctuation of ion saturation current from a conventional Langmuir probe mathLP(t) allow us to determine local fluctuations of ion temperature mathi(t). To reduce the effect of plasma potential fluctuations in the energy analyzer measurements, we use special a compensative circuit loop.
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41.85.-p Beam optics
42.79.Hp Optical processors, correlators, and modulators
52.70.Ds Electric and magnetic measurements

A novel technique for single-shot energy-resolved 2D x-ray imaging of plasmas relevant for the inertial confinement fusion

L. Labate, P. Köster, T. Levato, and L. A. Gizzi

Rev. Sci. Instrum. 83, 103504 (2012); http://dx.doi.org/10.1063/1.4759135 (9 pages)

Online Publication Date: 23 October 2012

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A novel x-ray diagnostic of laser-fusion plasmas is described, allowing 2D monochromatic images of hot, dense plasmas to be obtained in any x-ray photon energy range, over a large domain, on a single-shot basis. The device (named energy-encoded pinhole camera) is based upon the use of an array of many pinholes coupled to a large area CCD camera operating in the single-photon mode. The available x-ray spectral domain is only limited by the quantum efficiency of scientific-grade x-ray CCD cameras, thus extending from a few keV up to a few tens of keV. Spectral 2D images of the emitting plasma can be obtained at any x-ray photon energy provided that a sufficient number of photons had been collected at the desired energy. Results from recent inertial confinement fusion related experiments will be reported in order to detail the new diagnostic.
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52.70.La X-ray and γ-ray measurements
52.57.-z Laser inertial confinement
28.52.Lf Components and instrumentation
85.60.Gz Photodetectors (including infrared and CCD detectors)

Diagnostics of underwater electrical wire explosion through a time- and space-resolved hard x-ray source

D. Sheftman, D. Shafer, S. Efimov, K. Gruzinsky, S. Gleizer, and Ya. E. Krasik

Rev. Sci. Instrum. 83, 103505 (2012); http://dx.doi.org/10.1063/1.4759492 (7 pages)

Online Publication Date: 23 October 2012

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A time- and space-resolved hard x-ray source was developed as a diagnostic tool for imaging underwater exploding wires. A ∼4 ns width pulse of hard x-rays with energies of up to 100 keV was obtained from the discharge in a vacuum diode consisting of point-shaped tungsten electrodes. To improve contrast and image quality, an external pulsed magnetic field produced by Helmholtz coils was used. High resolution x-ray images of an underwater exploding wire were obtained using a sensitive x-ray CCD detector, and were compared to optical fast framing images. Future developments and application of this diagnostic technique are discussed.
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52.70.La X-ray and γ-ray measurements
52.80.Qj Explosions; exploding wires
52.50.Dg Plasma sources
42.79.Pw Imaging detectors and sensors

Laser schlieren deflectometry for temperature analysis of filamentary non-thermal atmospheric pressure plasma

J. Schäfer, R. Foest, S. Reuter, T. Kewitz, J. Šperka, and K.-D. Weltmann

Rev. Sci. Instrum. 83, 103506 (2012); http://dx.doi.org/10.1063/1.4761924 (8 pages)

Online Publication Date: 25 October 2012

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The heat convection generated by micro filaments of a self-organized non-thermal atmospheric pressure plasma jet in Ar is characterized by employing laser schlieren deflectometry (LSD). It is demonstrated as a proof of principle, that the spatial and temporal changes of the refractive index n in the optical beam path related to the neutral gas temperature of the plasma jet can be monitored and evaluated simultaneously. The refraction of a laser beam in a high gradient field of n(r) with cylindrical symmetry is given for a general real refraction index profile. However, the usually applied Abel approach represents an ill-posed problem and in particular for this plasma configuration. A simple analytical model is proposed in order to minimize the statistical error. Based on that, the temperature profile, specifically the absolute temperature in the filament core, the FWHM, and the frequencies of the collective filament dynamics are obtained for non-stationary conditions. For a gas temperature of 700 K inside the filament, the presented model predicts maximum deflection angles of the laser beam of 0.3 mrad which is in accordance to the experimental results obtained with LSD. Furthermore, the experimentally obtained FWHM of the temperature profile produced by the filament at the end of capillary is (1.5 ± 0.2) mm, which is about 10 times wider than the visual radius of the filament. The obtained maximum temperature in the effluent is (450 ± 30) K and is in consistence with results of other techniques. The study demonstrates that LSD represents a useful low-cost method for monitoring the spatiotemporal behaviour of microdischarges and allows to uncover their dynamic characteristics, e.g., the temperature profile even for challenging diagnostic conditions such as moving thin discharge filaments. The method is not restricted to the miniaturized and self-organized plasma studied here. Instead, it can be readily applied to other configurations that produce measurable gradients of refractive index by local gas heating and opens new diagnostics prospects particularly for microplasmas.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Oblique electron-cyclotron-emission radial and phase detector of rotating magnetic islands applied to alignment and modulation of electron-cyclotron-current-drive for neoclassical tearing mode stabilization

F. Volpe, M. E. Austin, G. Campbell, and T. Deterly

Rev. Sci. Instrum. 83, 103507 (2012); http://dx.doi.org/10.1063/1.4758780 (6 pages) | Cited 2 times

Online Publication Date: 25 October 2012

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A two channel oblique electron cyclotron emission (ECE) radiometer was installed on the DIII-D tokamak and interfaced to four gyrotrons. Oblique ECE was used to toroidally and radially localize rotating magnetic islands and so assist their electron cyclotron current drive (ECCD) stabilization. In particular, after manipulations operated by the interfacing analogue circuit, the oblique ECE signals directly modulated the current drive in synch with the island rotation and in phase with the island O-point, for a more efficient stabilization. Apart from the different toroidal location, the diagnostic view is identical to the ECCD launch direction, which greatly simplified the real-time use of the signals. In fact, a simple toroidal extrapolation was sufficient to lock the modulation to the O-point phase. This was accomplished by a specially designed phase shifter of nearly flat response over the 1–7 kHz range. Moreover, correlation analysis of two channels slightly above and below the ECCD frequency allowed checking the radial alignment to the island, based on the fact that for satisfactory alignment the two signals are out of phase.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.Gw Radio-frequency and microwave measurements
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Fourier transform infrared absorption spectroscopy characterization of gaseous atmospheric pressure plasmas with 2 mm spatial resolution

G. Laroche, J. Vallade, R. Bazinette, P. van Nijnatten, E. Hernandez, G. Hernandez, and F. Massines

Rev. Sci. Instrum. 83, 103508 (2012); http://dx.doi.org/10.1063/1.4761925 (7 pages)

Online Publication Date: 29 October 2012

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This paper describes an optical setup built to record Fourier transform infrared (FTIR) absorption spectra in an atmospheric pressure plasma with a spatial resolution of 2 mm. The overall system consisted of three basic parts: (1) optical components located within the FTIR sample compartment, making it possible to define the size of the infrared beam (2 mm × 2 mm over a path length of 50 mm) imaged at the site of the plasma by (2) an optical interface positioned between the spectrometer and the plasma reactor. Once through the plasma region, (3) a retro-reflector module, located behind the plasma reactor, redirected the infrared beam coincident to the incident path up to a 45° beamsplitter to reflect the beam toward a narrow-band mercury-cadmium-telluride detector. The antireflective plasma-coating experiments performed with ammonia and silane demonstrated that it was possible to quantify 42 and 2 ppm of these species in argon, respectively. In the case of ammonia, this was approximately three times less than this gas concentration typically used in plasma coating experiments while the silane limit of quantification was 35 times lower. Moreover, 70% of the incoming infrared radiation was focused within a 2 mm width at the site of the plasma, in reasonable agreement with the expected spatial resolution. The possibility of reaching this spatial resolution thus enabled us to measure the gaseous precursor consumption as a function of their residence time in the plasma.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
42.79.Wc Optical coatings
42.70.-a Optical materials
42.79.Fm Reflectors, beam splitters, and deflectors
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