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Mar 2010

Volume 81, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 81, 031101 (2010); http://dx.doi.org/10.1063/1.3327886 (14 pages)

Majid Nabavi

For full-field unsteady pressure measurement, pressure sensitive paint (PSP) is an attractive technique due to its relatively fast response and high spatial resolution. The output of the system is a color image representing the pressure variations.

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

Development of analytically capable time-of-flight mass spectrometer with continuous ion introduction

György Hárs and Gábor Dobos

Rev. Sci. Instrum. 81, 033101 (2010); http://dx.doi.org/10.1063/1.3321346 (8 pages) | Cited 1 time

Online Publication Date: 5 March 2010

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The present article describes the results and findings explored in the course of the development of the analytically capable prototype of continuous time-of-flight (CTOF) mass spectrometer. Currently marketed pulsed TOF (PTOF) instruments use ion introduction with a 10 ns or so pulse width, followed by a waiting period roughly 100 μs. Accordingly, the sample is under excitation in 10−4 part of the total measuring time. This very low duty cycle severely limits the sensitivity of the PTOF method. A possible approach to deal with this problem is to use linear sinusoidal dual modulation technique (CTOF) as described in this article. This way the sensitivity of the method is increased, due to the 50% duty cycle of the excitation. All other types of TOF spectrometer use secondary electron multiplier (SEM) for detection, which unfortunately discriminates in amplification in favor of the lighter ions. This discrimination effect is especially undesirable in a mass spectrometric method, which targets high mass range. In CTOF method, SEM is replaced with Faraday cup detector, thus eliminating the mass discrimination effect. Omitting SEM is made possible by the high ion intensity and the very slow ion detection with some hundred hertz detection bandwidth. The electrometer electronics of the Faraday cup detector operates with amplification 1010 V/A. The primary ion beam is highly monoenergetic due to the construction of the ion gun, which made possible to omit any electrostatic mirror configuration for bunching the ions. The measurement is controlled by a personal computer and the intelligent signal generator Type Tabor WW 2571, which uses the direct digital synthesis technique for making arbitrary wave forms. The data are collected by a Labjack interface board, and the fast Fourier transformation is performed by the software. Noble gas mixture has been used to test the analytical capabilities of the prototype setup. Measurement presented proves the results of the mathematical calculations as well as the future potentiality for use in chemical analysis of gaseous mixtures.
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07.75.+h Mass spectrometers
85.60.Ha Photomultipliers; phototubes and photocathodes

Response-time improved hydrothermal-method-grown ZnO scintillator for soft x-ray free-electron laser timing-observation

Toshihiko Shimizu, Kohei Yamamoi, Elmer Estacio, Tomoharu Nakazato, Kouhei Sakai, Nobuhiko Sarukura, Dirk Ehrentraut, Tsuguo Fukuda, Mitsuru Nagasono, Tadashi Togashi, Atsushi Higashiya, Makina Yabashi, Tetsuya Ishikawa, Haruhiko Ohashi, and Hiroaki Kimura

Rev. Sci. Instrum. 81, 033102 (2010); http://dx.doi.org/10.1063/1.3310276 (4 pages) | Cited 5 times

Online Publication Date: 11 March 2010

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For pump and probe experiments in x-ray free-electron laser (XFEL) facilities, accurate timing synchronization between short-wavelength femtosecond pulses from XFELs and short optical pulses from other light sources is required. For this purpose, the response time of a hydrothermal-method-grown ZnO is improved by over one order of magnitude via intentional iron ion doping. The fluorescence rise- and decay-time constants are measured to be less than 10 and 100 ps, respectively. Owing to its intense fluorescence even for single pulse XFEL excitation, the timing jitter of the soft x-ray pulse and timing electronics are evaluated to be less than 70 ps.
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41.60.Cr Free-electron lasers
42.55.Vc X- and γ-ray lasers
81.10.Dn Growth from solutions
78.70.Ps Scintillation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.55.Et II-VI semiconductors

Absolute spectral radiance responsivity calibration of sun photometers

Qiuyun Xu, Xiaobing Zheng, Zhengqiang Li, Wei Zhang, Xianhua Wang, Jianjun Li, and Xin Li

Rev. Sci. Instrum. 81, 033103 (2010); http://dx.doi.org/10.1063/1.3331459 (7 pages) | Cited 1 time

Online Publication Date: 17 March 2010

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Sun photometers are designed to measure direct solar irradiance and diffused sky radiance for the purpose of atmospheric parameters characterization. A sun photometer is usually calibrated by using a lamp-illuminated integrating sphere source for its band-averaged radiance responsivity, which normally has an uncertainty of 3%–5% at present. Considering the calibration coefficients may also change with time, a regular high precision calibration is important to maintain data quality. In this paper, a tunable-laser-based facility for spectral radiance responsivity calibration has been developed at the Key Laboratory of Optical Calibration and Characterization, Chinese Academy of Sciences. A reference standard radiance radiometer, calibrated against cryogenic radiometer, is used to determine the radiance from a laser-illuminated integrating sphere source. Spectral radiance responsivity of CIMEL CE318–2 sun photometer is calibrated using this new calibration system with a combined standard uncertainty of about 0.8%. As a validation, the derived band-averaged radiance responsivity are compared to that from a Goddard Space Flight Center lamp-based sphere calibration and good agreements (difference <1.4%) are found from 675 to 1020 nm bands.
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07.60.Dq Photometers, radiometers, and colorimeters
06.20.fb Standards and calibration

Pulse stretcher with variable pulse length for excimer laser applications

A. Burkert, J. Bergmann, W. Triebel, and U. Natura

Rev. Sci. Instrum. 81, 033104 (2010); http://dx.doi.org/10.1063/1.3340879 (5 pages) | Cited 2 times

Online Publication Date: 22 March 2010

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Excimer laser systems are often combined with pulse stretchers, e.g., in lithography and Raman spectroscopy to reduce pulse peak intensities. We developed a pulse stretcher which is suited especially for pulse length dependent applications, e.g., in material research. This pulse stretcher is based on imaging and provides identical beam profiles and divergences at different pulse lengths in combination with the possibility of switching between four pulse lengths. Therefore, beam splitters are mounted onto motorized translation stages. These features are important for the characterization and development of improved optical materials for deep-ultraviolet applications. Here, two 193 nm single tube excimer lasers (Lambda Physik: LPX 240i, Cymer: ELS 5600) were evaluated concerning their combinability with an attached pulse stretcher. The wave-front radii of the ELS 5600 are dependent on repetition rate or pulse energy and are changing during warming-up. Without adapted pulse shaping, this can cause destruction of stretcher optics due to moving foci. We found that the LPX 240i could be combined easily with a pulse stretcher using beam shaping with only one cylindrical lens. We could demonstrate that stretched 193 nm laser pulses retard aging of CaF2 crystals.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Highly sensitive frequency metrology for optical anisotropy measurements

Gilles Bailly, Raphaël Thon, and Cécile Robilliard

Rev. Sci. Instrum. 81, 033105 (2010); http://dx.doi.org/10.1063/1.3356731 (5 pages) | Cited 3 times

Online Publication Date: 26 March 2010

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In this paper we present a novel apparatus aimed at measuring very small birefringences and anisotropies and based on frequency metrology and not on polarimetry as usual. In our experiment, a very high finesse resonant cavity is used to convert the phase difference into a resonance frequency difference, which can then be measured with very high accuracy. We describe the setup and present the results of experimental tests, which exhibited a sensitivity δn ≃ 2×10−18, allowing for the measurement of long-predicted magnetoelectro-optical effects in gases. Since the shot-noise limited sensitivity of our apparatus lies well below the state-of-the-art sensitivity, frequency metrology appears as a promising technique for small birefringence measurements.
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42.25.Lc Birefringence
78.20.Ls Magneto-optical effects
FREE

Development of multiwavelength-range fine-resolution spectrometer for hydrogen emissions and its application to large helical device periphery plasmas

K. Fujii, K. Mizushiri, T. Nishioka, T. Shikama, A. Iwamae, M. Goto, S. Morita, S Kado, K. Sawada, and M. Hasuo

Rev. Sci. Instrum. 81, 033106 (2010); http://dx.doi.org/10.1063/1.3356730 (4 pages) | Cited 4 times

Online Publication Date: 26 March 2010

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We developed a spectrometer specialized for simultaneous observation of the hydrogen Balmer-α, -β, -γ lines and the Fulcher-α v′ = v″ = 2 rovibronic transition band. The spectrometer was optimized for the light input coupled by nine optical fibers having 400 μm core diameters. The spectral resolutions were 0.02–0.03 nm for these wavelength ranges at the entrance slit width of 20 μm. The polarization resolved spectra of these emissions from the peripheral region of large helical device (LHD) plasmas were measured simultaneously and showed the polarization dependence coming from the magnetic field in the LHD plasma.
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52.55.-s Magnetic confinement and equilibrium
52.75.-d Plasma devices

Space-resolved extreme ultraviolet spectrometer for impurity emission profile measurement in Large Helical Device

Chunfeng Dong, Shigeru Morita, Motoshi Goto, and Hangyu Zhou

Rev. Sci. Instrum. 81, 033107 (2010); http://dx.doi.org/10.1063/1.3299060 (9 pages) | Cited 17 times

Online Publication Date: 30 March 2010

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A space-resolved extreme ultraviolet (EUV) spectrometer working in 60–400 Å range has been developed to observe impurity emission profiles in core and edge plasmas of Large Helical Device (LHD). A flat focus is made for plane surface detector by using a varied line spacing holographic grating with an angle of incidence of 87°. An excellent spectral resolution of 0.22 Å at 200 Å is then obtained after careful adjustment of the optical components. In the profile measurement of the LHD plasmas, the toroidal resolution is important as well as the radial resolution because the magnetic surfaces of LHD quickly change when the observation chord is tilted at a slightly different toroidal location. Horizontal dispersion is therefore selected for the present spectrometer. As a result, the toroidal resolution of 75 mm is achieved at the plasma position. An enough radial resolution of 10 mm is also obtained at spatial-resolution slit width of 0.2 mm. In order to measure the full radial profile of LHD plasmas the spectrometer is placed at a distance of ∼ 9200 mm away from the plasma center and a backilluminated charge-coupled device with a size of 6.6×26.6 mm2 is set vertical to the horizontal dispersion. Half of the LHD plasma, i.e., ∼ 50 cm, can be measured along the vertical direction at horizontally elongated plasma cross section. A full vertical profile can be obtained by changing the vertical angle of the EUV spectrometer. As an example the full vertical profile of edge C IV (312.4 Å) emission is presented. A wavelength interval of 35–65 Å can be simultaneously observed, which varies according to the wavelength to be measured. A local emission profile of Fe XX (132.67 Å) is also presented after Abel inversion as a typical example of the core EUV emission. Finally, the EUV spectrometer is absolutely calibrated using EUV bremsstrahlung continuum profile in comparison with absolute values of visible bremsstrahlung continuum profile because the bremsstrahlung continuum can be easily detected in high-density discharges of LHD.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Vy Impurities in plasmas
52.55.Jd Magnetic mirrors, gas dynamic traps
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
07.60.Rd Visible and ultraviolet spectrometers

Wavefront-sensor-based electron density measurements for laser-plasma accelerators

G. R. Plateau, N. H. Matlis, C. G. R. Geddes, A. J. Gonsalves, S. Shiraishi, C. Lin, R. A. van Mourik, and W. P. Leemans

Rev. Sci. Instrum. 81, 033108 (2010); http://dx.doi.org/10.1063/1.3360889 (5 pages) | Cited 1 time

Online Publication Date: 31 March 2010

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Characterization of the electron density in laser produced plasmas is presented using direct wavefront analysis of a probe laser beam. The performance of a laser-driven plasma-wakefield accelerator depends on the plasma wavelength and hence on the electron density. Density measurements using a conventional folded-wave interferometer and using a commercial wavefront sensor are compared for different regimes of the laser-plasma accelerator. It is shown that direct wavefront measurements agree with interferometric measurements and, because of the robustness of the compact commercial device, offer greater phase sensitivity and straightforward analysis, improving shot-to-shot plasma density diagnostics.
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29.20.Ej Linear accelerators

Multihit mode direct-detection laser radar system using a Geiger-mode avalanche photodiode

Min Seok Oh, Hong Jin Kong, Tae Hoon Kim, Keun Ho Hong, Byung Wook Kim, and Dong Jo Park

Rev. Sci. Instrum. 81, 033109 (2010); http://dx.doi.org/10.1063/1.3374109 (7 pages) | Cited 7 times

Online Publication Date: 31 March 2010

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In this paper, a direct-detection laser radar system that uses a Geiger-mode avalanche photodiode (GAPD) of relatively short dead time (45 ns) is described. A passively Q-switched microchip laser is used as a laser source and a compact peripheral component interconnect system, which includes a time-to-digital converter (TDC), is set up for fast signal processing. With both the GAPD and the TDC functioning multistop acquisition, the system operates in a multihit mode. The software for the three-dimensional visualization and an algorithm for the removal of noise are developed. It is shown that the single-shot precision of the system is ∼ 10 cm (σ) and the precision is improved by increasing the number of laser pulses to be averaged so that the precision of ∼ 1 cm (σ) was acquired with more than 150 laser pulses scattered from the target. The accuracy of the system is measured to be 12 cm when the energy of the emitted laser pulse varies with a factor of 7.
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42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
85.60.Dw Photodiodes; phototransistors; photoresistors
42.55.Px Semiconductor lasers; laser diodes
42.55.Rz Doped-insulator lasers and other solid state lasers
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Absolute charge calibration of scintillating screens for relativistic electron detection

A. Buck, K. Zeil, A. Popp, K. Schmid, A. Jochmann, S. D. Kraft, B. Hidding, T. Kudyakov, C. M. S. Sears, L. Veisz, S. Karsch, J. Pawelke, R. Sauerbrey, T. Cowan, F. Krausz, et al.

Rev. Sci. Instrum. 81, 033301 (2010); http://dx.doi.org/10.1063/1.3310275 (6 pages) | Cited 8 times

Online Publication Date: 3 March 2010

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We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for the detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC/mm2. The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10–100 pC/mm2 was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference to simplify the transfer of a one-time absolute calibration to different experimental setups.
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29.40.Mc Scintillation detectors
06.20.fb Standards and calibration

A compact high-voltage pulse generator based on pulse transformer with closed magnetic core

Yu Zhang, Jinliang Liu, Xinbing Cheng, Guoqiang Bai, Hongbo Zhang, Jiahuai Feng, and Bo Liang

Rev. Sci. Instrum. 81, 033302 (2010); http://dx.doi.org/10.1063/1.3321494 (7 pages) | Cited 7 times

Online Publication Date: 12 March 2010

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A compact high-voltage nanosecond pulse generator, based on a pulse transformer with a closed magnetic core, is presented in this paper. The pulse generator consists of a miniaturized pulse transformer, a curled parallel strip pulse forming line (PFL), a spark gap, and a matched load. The innovative design is characterized by the compact structure of the transformer and the curled strip PFL. A new structure of transformer windings was designed to keep good insulation and decrease distributed capacitance between turns of windings. A three-copper-strip structure was adopted to avoid asymmetric coupling of the curled strip PFL. When the 31 μF primary capacitor is charged to 2 kV, the pulse transformer can charge the PFL to 165 kV, and the 3.5 Ω matched load can deliver a high-voltage pulse with a duration of 9 ns, amplitude of 84 kV, and rise time of 5.1 ns. When the load is changed to 50 Ω, the output peak voltage of the generator can be 165 kV, the full width at half maximum is 68 ns, and the rise time is 6.5 ns.
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84.32.Hh Inductors and coils; wiring
84.30.Jc Power electronics; power supply circuits
84.30.Ng Oscillators, pulse generators, and function generators
89.20.Kk Engineering

Electronic temperatures, densities, and plasma x-ray emission of a 14.5 GHz electron-cyclotron resonance ion source

A. Gumberidze, M. Trassinelli, N. Adrouche, C. I. Szabo, P. Indelicato, F. Haranger, J.-M. Isac, E. Lamour, E.-O. Le Bigot, J. Mérot, C. Prigent, J.-P. Rozet, and D. Vernhet

Rev. Sci. Instrum. 81, 033303 (2010); http://dx.doi.org/10.1063/1.3316805 (10 pages) | Cited 7 times

Online Publication Date: 12 March 2010

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We have performed a systematic study of the bremsstrahlung emission from the electrons in the plasma of a commercial 14.5 GHz electron-cyclotron resonance ion source. The electronic spectral temperature and the product of ionic and electronic densities of the plasma are measured by analyzing the bremsstrahlung spectra recorded for several rare gases (Ar, Kr, and Xe) as a function of the injected power. Within our uncertainty, we find an average temperature of ≈ 48 keV above 100 W, with a weak dependency on the injected power and gas composition. Charge state distributions of extracted ion beams have been determined as well, providing a way to disentangle the ionic density from the electronic density. Moreover x-ray emission from highly charged argon ions in the plasma has been observed with a high-resolution mosaic-crystal spectrometer, demonstrating the feasibility for high-precision measurements of transition energies of highly charged ions, in particular, of the magnetic dipole (M1) transition of He-like of argon ions.
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52.25.-b Plasma properties
52.70.La X-ray and γ-ray measurements
32.30.Rj X-ray spectra
07.77.Ka Charged-particle beam sources and detectors
29.25.Ni Ion sources: positive and negative

High-voltage testing of a 500-kV dc photocathode electron gun

Ryoji Nagai, Ryoichi Hajima, Nobuyuki Nishimori, Toshiya Muto, Masahiro Yamamoto, Yosuke Honda, Tsukasa Miyajima, Hokuto Iijima, Masao Kuriki, Makoto Kuwahara, Shoji Okumi, and Tsutomu Nakanishi

Rev. Sci. Instrum. 81, 033304 (2010); http://dx.doi.org/10.1063/1.3354980 (5 pages) | Cited 5 times

Online Publication Date: 16 March 2010

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A high-voltage dc photocathode electron gun was successfully conditioned up to a voltage of 550 kV and a long-time holding test for 8 h was demonstrated at an acceleration voltage of 500 kV. The dc photocathode electron gun is designed for future light sources based on energy-recovery linac and consists of a Cockcroft–Walton generator, a segmented cylindrical ceramic insulator, guard-ring electrodes, a support-rod electrode, a vacuum chamber, and a pressurized insulating gas tank. The segmented cylindrical ceramic insulator and the guard-ring electrodes were utilized to prevent any damage to the insulator from electrons emitted by the support-rod electrode.
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85.60.Ha Photomultipliers; phototubes and photocathodes
84.47.+w Vacuum tubes

Time of flight elastic recoil detection analysis with a position sensitive detector

Zdravko Siketić, Iva Bogdanović Radović, Milko Jakšić, and Natko Skukan

Rev. Sci. Instrum. 81, 033305 (2010); http://dx.doi.org/10.1063/1.3356976 (5 pages) | Cited 1 time

Online Publication Date: 16 March 2010

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A position sensitive detection system based on the microchannel plate detector has been constructed and installed at the existing time of flight (TOF) spectrometer in order to perform a kinematic correction and improve the surface time/depth resolution of elastic recoil detection analysis (ERDA) system. The position resolution of the detector has been tested for different types of ions and anode voltages. TOF spectra of recoiled O ions from SiO2 and F from CaF2 were collected in coincidence with position sensitive detector signal. Kinematic correction of TOF spectra improved surface time/depth resolution by ∼ 20% for our system; however even higher improvements could be obtained in larger solid angle TOF-ERDA systems.
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29.40.Gx Tracking and position-sensitive detectors
42.79.Ls Scanners, image intensifiers, and image converters

Useful technique for analysis and control of the acceleration beam phase in the azimuthally varying field cyclotron

Satoshi Kurashima, Takahiro Yuyama, Nobumasa Miyawaki, Hirotsugu Kashiwagi, Susumu Okumura, and Mitsuhiro Fukuda

Rev. Sci. Instrum. 81, 033306 (2010); http://dx.doi.org/10.1063/1.3354981 (7 pages) | Cited 2 times

Online Publication Date: 18 March 2010

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We have developed a new technique for analysis and control of the acceleration beam phase in the cyclotron. In this technique, the beam current pattern at a fixed radius r is measured by slightly scanning the acceleration frequency in the cyclotron. The acceleration beam phase is obtained by analyzing symmetry of the current pattern. Simple procedure to control the acceleration beam phase by changing coil currents of a few trim coils was established. The beam phase width is also obtained by analyzing gradient of the decreasing part of the current pattern. We verified reliability of this technique with 260 MeV 20Ne7+ beams which were accelerated on different tuning condition of the cyclotron. When the acceleration beam phase was around 0°, top of the energy gain of cosine wave, and the beam phase width was about 6° in full width at half maximum, a clear turn pattern of the beam was observed with a differential beam probe in the extraction region. Beam phase widths of ion beams at acceleration harmonics of h = 1 and h = 2 were estimated without beam cutting by phase-defining slits. We also calculated the beam phase widths roughly from the beam current ratio between the injected beam and the accelerated beam in the cyclotron without operating the beam buncher. Both beam phase widths were almost the same for h = 1, while phase compressions by a factor of about 3 were confirmed for h = 2.
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29.20.dg Cyclotrons
29.38.-c Radioactive beams
29.25.-t Particle sources and targets

Ultrashort high quality electron beam from laser wakefield accelerator using two-step plasma density profile

Xiongwei Zhu

Rev. Sci. Instrum. 81, 033307 (2010); http://dx.doi.org/10.1063/1.3360927 (4 pages) | Cited 1 time

Online Publication Date: 23 March 2010

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In this paper, we first use the rf linac injector mechanism to generate ultrashort high quality electron beam from laser wakefield accelerator (LWFA) with two-step plasma density profile successfully. We incorporate the physics principle in the conventional rf linac injector into the LWFA by using two-step plasma density to decrease the wavelength of the wakefield in plasma. Using this mechanism, we observe a ultrashort high quality electron beam (the rms energy spread is 1.9%, and the rms bunch length is 2 fs) in the simulation. The ultrashort intense terahertz coherent radiation (200 MW, 2 fs) can be generated with the proposed laser wakefield accelerator.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.-b Plasma properties
52.40.Mj Particle beam interactions in plasmas
52.65.Rr Particle-in-cell method

An imaging technique for detection and absolute calibration of scintillation light

Alfio Pappalardo, Luigi Cosentino, and Paolo Finocchiaro

Rev. Sci. Instrum. 81, 033308 (2010); http://dx.doi.org/10.1063/1.3360931 (6 pages) | Cited 2 times

Online Publication Date: 31 March 2010

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Show Abstract
Triggered by the need of a detection system to be used in experiments of nuclear fusion in laser-generated plasmas, we developed an imaging technique for the measurement and calibration of the scintillation light yield of scintillating materials. As in such experiments, all the reaction products are generated in an ultrashort time frame, the event-by-event data acquisition scheme is not feasible. As an alternative to the emulsion technique (or the equivalent CR39 sheets) we propose a scintillating screen readout by means of a high performance charge coupled device camera. Even though it is not strictly required in the particular application, this technique allows the absolute calibration of the scintillation light yield.
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25.60.Pj Fusion reactions
42.79.Pw Imaging detectors and sensors
back to top Nuclear Physics, Fusion and Plasmas

The parameters of electron cyclotron resonance/radio-frequency hybrid hydrogen plasma adjusted by substrate arrangements

H. Y. Zhou, L. Wang, X. D. Zhu, B. Ke, F. Ding, X. H. Wen, and Y. N. Wang

Rev. Sci. Instrum. 81, 033501 (2010); http://dx.doi.org/10.1063/1.3302534 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2010

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Hybrid hydrogen plasma was formed by biasing 13.56 MHz radio-frequency (rf) power on a substrate immersed in 2.45 GHz microwave electron cyclotron resonance (ECR) plasma. The influences of the substrate configuration on plasma characteristics were investigated. With increasing rf self-bias voltage, electron temperature, Te, increases obviously in the case of the single-electrode substrate, whereas a slight change in Te was observed with the double-electrode substrate condition. Electron density rises almost with a same magnitude under both two substrate conditions. It exhibited that electron energy and density in ECR-rf hybrid mode could be adjusted independently by controlling rf discharge with favorable substrate configurations.
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52.25.-b Plasma properties
52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges

Zeeman polarimetry measurement for edge current density determination using Li-beam probe on JT-60U

K. Kamiya, T. Fujita, A. Kojima, and H. Kubo

Rev. Sci. Instrum. 81, 033502 (2010); http://dx.doi.org/10.1063/1.3309793 (8 pages) | Cited 3 times

Online Publication Date: 2 March 2010

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Zeeman polarimetry system using Li-beam probe has been developed for the edge current density measurement in the JT-60U tokamak, which measures the polarization angle α (related to the pitch angle of the magnetic field) by means of photoelastic modulators, etalons, and phase sensitive detection using digital lock-in amplifiers with the accuracy in the α of Δα ∼ 0.1°. The diagnostic has 20-channel viewing chords covering the plasma peripheral region of normalized minor radius r/a ∼ 0.8–1 with a spatial resolution of up to ∼ 1 cm. Li-beam injection with beam current of up to ∼ 5 mA has been achieved. A new tuning method of the wavelength for the etalon has been demonstrated, scanning the beam acceleration voltage and keeping a beam current constant during a single shot. The peak wavelength of the etalon is adjusted in the direction to both blue- and redshifts by changing the angle of incidence and increasing the temperature, respectively. Time evolution of the edge current density profile has been determined for the current ramp experiment in the Ohmically heated discharges. In addition, the edge current density profile with the local peak of jped ∼ 0.15–0.25 MA/m2 at r/a ∼ 0.9 has been identified in the H-mode plasma, which is correlated with large pressure gradient in the pedestal region.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Nc Particle measurements

Alignment effects on a neutron imaging system using coded apertures

Isabelle Thfoin, Olivier Landoas, Tony Caillaud, Laurent Disdier, Maxime Vincent, Jean-Luc Bourgade, Bertrand Rossé, Thomas C. Sangster, Vladimir Yu. Glebov, Greg Pien, and William Armstrong

Rev. Sci. Instrum. 81, 033503 (2010); http://dx.doi.org/10.1063/1.3331494 (7 pages) | Cited 4 times

Online Publication Date: 11 March 2010

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A high resolution neutron imaging system is being developed and tested on the OMEGA laser facility for inertial confinement fusion experiments. This diagnostic uses a coded imaging technique with a penumbral or an annular aperture. The sensitiveness of these techniques to misalignment was pointed out with both experiments and simulations. Results obtained during OMEGA shots are in good agreement with calculations performed with the Monte Carlo code GEANT4. Both techniques are sensitive to the relative position of the source in the field of view. The penumbral imaging technique then demonstrates to be less sensitive to misalignment compared to the ring. These results show the necessity to develop a neutron imaging diagnostic for megajoule class lasers taking into account our alignment capabilities on such facilities.
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28.52.Cx Fueling, heating and ignition
89.30.Jj Nuclear fusion power

Fast ion generation in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge

A. Moorti, P. A. Naik, and P. D. Gupta

Rev. Sci. Instrum. 81, 033504 (2010); http://dx.doi.org/10.1063/1.3354983 (5 pages)

Online Publication Date: 16 March 2010

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Ion generation in the cathode plasma jet of a moderate-current ( ∼ 2.3 kA), low-energy ( ≤ 20 J) vacuum spark discharge triggered by ∼ 27 ps, 10 mJ laser pulses is studied using time of flight technique. Fastest ion velocity and velocity corresponding to the peak of the time of flight signals for Al cathode were measured to be ∼ 5.25×108 cm/s (energy of ∼ 143 keV/u) and ∼ 8.1×107 cm/s (energy of ∼ 3.4 keV/u), respectively. Corresponding velocities in the case of ions generated from laser-produced Al plasma (energy of ∼ 550 mJ, intensity of ∼ 1014 W/cm2) were found to be much smaller, viz., ∼ 1.05×108 cm/s (energy of ∼ 5.75 keV/u) and ∼ 2.63×107 cm/s (energy of ∼ 0.36 keV/u), respectively. Study shows efficient acceleration of ions in a current-carrying cathode plasma jet of a small-energy multipicosecond laser-triggered spark discharge as compared with that in a high-energy multipicosecond laser-produced plasma plume.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.75.-d Plasma devices
52.80.-s Electric discharges

Intrashot motional Stark effect calibration technique for lower hybrid current drive experiments

Jinseok Ko, Steve Scott, Syun’ichi Shiraiwa, Martin Greenwald, Ronald Parker, and Gregory Wallace

Rev. Sci. Instrum. 81, 033505 (2010); http://dx.doi.org/10.1063/1.3327821 (6 pages) | Cited 1 time

Online Publication Date: 16 March 2010

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The spurious drift in pitch angle of order several degrees measured by the motional Stark effect (MSE) diagnostic in the Alcator C-Mod tokamak over the course of an experimental run day has precluded direct utilization of independent absolute calibrations. Recently, the underlying cause of the drift has been identified as thermal stress-induced birefringence in a set of in-vessel lenses. The shot-to-shot drift can be avoided by using MSE to measure only the change in pitch angle between a reference phase and a phase of physical interest within a single plasma discharge. This intrashot calibration technique has been applied to the lower hybrid current drive (LHCD) experiments and the measured current profiles qualitatively demonstrate several predictions of LHCD theory such as an inverse dependence of current drive efficiency on the parallel refractive index and the presence of off-axis current drive.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
06.20.fb Standards and calibration

Observation of runaway electron beams by visible color camera in the Experimental Advanced Superconducting Tokamak

Yuejiang Shi, Jia Fu, Jiahong Li, Yu Yang, Fudi Wang, Yingying Li, Wei Zhang, Baonian Wan, and Zhongyong Chen

Rev. Sci. Instrum. 81, 033506 (2010); http://dx.doi.org/10.1063/1.3340909 (7 pages) | Cited 4 times

Online Publication Date: 23 March 2010

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The synchrotron radiation originated from the energetic runaway electrons has been measured by a visible complementary metal oxide semiconductor camera working in the wavelength ranges of 380–750 nm in the Experimental Advanced Superconducting Tokamak [ H. Q. Liu et al., Plasma Phys. Contr. Fusion 49, 995 (2007) ]. With a tangential viewing into the plasma in the direction of electron approach on the equatorial plane, the synchrotron radiation from the energetic runaway electrons was measured in full poloidal cross section. The synchrotron radiation diagnostics provides a direct pattern of the runaway beam inside the plasma. The energy and pitch angle of runaway electrons have been obtained according to the synchrotron radiation pattern. A stable shell shape of synchrotron radiation has been observed in a few runaway discharges.
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52.55.Fa Tokamaks, spherical tokamaks

Design of a digital multiradian phase detector and its application in fusion plasma interferometry

A. Mlynek, G. Schramm, H. Eixenberger, G. Sips, K. McCormick, M. Zilker, K. Behler, and J. Eheberg

Rev. Sci. Instrum. 81, 033507 (2010); http://dx.doi.org/10.1063/1.3340944 (5 pages) | Cited 5 times

Online Publication Date: 25 March 2010

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We discuss the circuit design of a digital multiradian phase detector that measures the phase difference between two 10 kHz square wave TTL signals and provides the result as a binary number. The phase resolution of the circuit is 1/64 period and its dynamic range is 256 periods. This circuit has been developed for fusion plasma interferometry with submillimeter waves on the ASDEX Upgrade tokamak. The results from interferometric density measurement are discussed and compared to those obtained with the previously used phase detectors, especially with respect to the occurrence of phase jumps. It is illustrated that the new phase measurement provides a powerful tool for automatic real-time validation of the measured density, which is important for feedback algorithms that are sensitive to spurious density signals.
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84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
52.55.Fa Tokamaks, spherical tokamaks
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Shock experiments and numerical simulations on low energy portable electrically exploding foil accelerators

A. K. Saxena, T. C. Kaushik, and Satish C. Gupta

Rev. Sci. Instrum. 81, 033508 (2010); http://dx.doi.org/10.1063/1.3327818 (9 pages) | Cited 1 time

Online Publication Date: 26 March 2010

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Two low energy (1.6 and 8 kJ) portable electrically exploding foil accelerators are developed for moderately high pressure shock studies at small laboratory scale. Projectile velocities up to 4.0 km/s have been measured on Kapton flyers of thickness 125 μm and diameter 8 mm, using an in-house developed Fabry–Pérot velocimeter. An asymmetric tilt of typically few milliradians has been measured in flyers using fiber optic technique. High pressure impact experiments have been carried out on tantalum, and aluminum targets up to pressures of 27 and 18 GPa, respectively. Peak particle velocities at the target-glass interface as measured by Fabry–Pérot velocimeter have been found in good agreement with the reported equation of state data. A one-dimensional hydrodynamic code based on realistic models of equation of state and electrical resistivity has been developed to numerically simulate the flyer velocity profiles. The developed numerical scheme is validated against experimental and simulation data reported in literature on such systems. Numerically computed flyer velocity profiles and final flyer velocities have been found in close agreement with the previously reported experimental results with a significant improvement over reported magnetohydrodynamic simulations. Numerical modeling of low energy systems reported here predicts flyer velocity profiles higher than experimental values, indicating possibility of further improvement to achieve higher shock pressures.
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29.20.Ej Linear accelerators
52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Kj Magnetohydrodynamic and fluid equation
52.50.Lp Plasma production and heating by shock waves and compression
52.80.Qj Explosions; exploding wires
82.40.Fp Shock wave initiated reactions, high-pressure chemistry
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