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Nov 2005

Volume 76, Issue 11, Articles (11xxxx)

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Ideal collimation, concentration, and imaging with curved diffractive optical elements

Nándor Bokor and Nir Davidson

Rev. Sci. Instrum. 76, 111101 (2005); http://dx.doi.org/10.1063/1.2127908 (17 pages) | Cited 2 times

Online Publication Date: 17 November 2005

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In this article the design, optimization and characterization of diffractive optical elements formed on a curved surface are reviewed. For such curved diffractive optical elements not only the phase function, but also the surface shape are free parameters that can be used for optimization, yielding much better performances than both flat diffractive optical elements and reflective/refractive optical elements when operating with quasimonochromatic light. We present a new analytic design approach for the surface shape that ensures uniform collimation of a light source with any angular distribution. We demonstrate the usefulness of this design also for ideal (brightness conserving) collimation and concentration of diffuse light, aberration-free imaging, and optical Fourier transform. We present experimental results that confirm our theoretical analysis.
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42.79.Ag Apertures, collimators
42.15.Eq Optical system design
42.87.-d Optical testing techniques
42.15.Fr Aberrations
42.30.Kq Fourier optics
01.30.Rr Surveys and tutorial papers; resource letters
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Large-area, low-noise, high-speed, photodiode-based fluorescence detectors with fast overdrive recovery

S. Bickman and D. DeMille

Rev. Sci. Instrum. 76, 113101 (2005); http://dx.doi.org/10.1063/1.2126575 (7 pages) | Cited 2 times

Online Publication Date: 7 November 2005

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Two large-area, low-noise, high-speed fluorescence detectors have been built. One detector consists of a photodiode with an area of 28 mm×28 mm and a low-noise transimpedance amplifier. This detector has a input light-equivalent spectral noise density of less than 3 pW/math, can recover from a large scattered light pulse within 10 μs, and has a bandwidth of at least 900 kHz. The second detector consists of a 16–mm-diam avalanche photodiode and a low-noise transimpedance amplifier. This detector has an input light-equivalent spectral noise density of 0.08 pW/math, also can recover from a large scattered light pulse within 10 μs, and has a bandwidth of 1 MHz.
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06.60.Ei Sample preparation (including design of sample holders)
75.80.+q Magnetomechanical effects, magnetostriction
61.05.F- Neutron diffraction and scattering

Phase-sensitive lock-in detection of semiconductor waveguide intensity profiles

J. F. Holzman, R. Scollo, H.-J. Lohe, F. Robin, H. Jäckel, and D. Erni

Rev. Sci. Instrum. 76, 113102 (2005); http://dx.doi.org/10.1063/1.2126810 (4 pages) | Cited 3 times

Online Publication Date: 7 November 2005

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A phase-sensitive lock-in detection scheme is employed in the measurement of transverse intensity distributions in semiconductor waveguide structures. A modulated (chopped) sampling beam is scanned across the waveguide, and the photocurrent signal from a 1550-nm signal beam in the waveguide is monitored through phase-sensitive lock-in detection (referenced to the sampling beam chopping frequency). It is determined that the photoinjected free-carrier perturbation by the scanning beam can be successfully mapped onto the local signal intensity, and the transverse intensity profile of the signal beam in the waveguide can be extracted. For the 3-μm-wide waveguide and the 2-μm sampling spot size employed in this investigation, the spatial resolution was limited mainly by the 1.7-μm carrier diffusion length in the semiconductor.
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42.79.Gn Optical waveguides and couplers
85.30.De Semiconductor-device characterization, design, and modeling

Simple procedure to extract speed distributions from ion images with a large background contribution

Andreas Braun and Marcel Drabbels

Rev. Sci. Instrum. 76, 113103 (2005); http://dx.doi.org/10.1063/1.2130941 (10 pages) | Cited 2 times

Online Publication Date: 7 November 2005

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We present a simple and robust procedure that allows extracting with high fidelity speed distributions from ion images that contain a large background contribution. The procedure requires no detailed knowledge about the background and is conveniently applied after performing the inverse Abel transform that reconstructs the three-dimensional velocity distribution from a recorded image.
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02.30.Uu Integral transforms
07.77.Ka Charged-particle beam sources and detectors

Soft x-ray submicron imaging detector based on point defects in LiF

G. Baldacchini, S. Bollanti, F. Bonfigli, F. Flora, P. Di Lazzaro, A. Lai, T. Marolo, R. M. Montereali, D. Murra, A. Faenov, T. Pikuz, E. Nichelatti, G. Tomassetti, A. Reale, L. Reale, et al.

Rev. Sci. Instrum. 76, 113104 (2005); http://dx.doi.org/10.1063/1.2130930 (12 pages) | Cited 28 times

Online Publication Date: 17 November 2005

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The use of lithium fluoride (LiF) crystals and films as imaging detectors for EUV and soft-x-ray radiation is discussed. The EUV or soft-x-ray radiation can generate stable color centers, emitting in the visible spectral range an intense fluorescence from the exposed areas. The high dynamic response of the material to the received dose and the atomic scale of the color centers make this detector extremely interesting for imaging at a spatial resolution which can be much smaller than the light wavelength. Experimental results of contact microscopy imaging of test meshes demonstrate a resolution of the order of 400 nm. This high spatial resolution has been obtained in a wide field of view, up to several mm2. Images obtained on different biological samples, as well as an investigation of a soft x-ray laser beam are presented. The behavior of the generated color centers density as a function of the deposited x-ray dose and the advantages of this new diagnostic technique for both coherent and noncoherent EUV sources, compared with CCDs detectors, photographic films, and photoresists are discussed.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Pw Imaging detectors and sensors

Variable gain detection strategy for time-of-flight multiphoton ionization spectroscopy experiments

M. Pasquini, G. Piani, G. Pietraperzia, W. Demtroeder, M. Giuntini, and M. Becucci

Rev. Sci. Instrum. 76, 113105 (2005); http://dx.doi.org/10.1063/1.2130573 (3 pages) | Cited 7 times

Online Publication Date: 21 November 2005

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This note presents a new, simple approach to measure time-of-flight mass spectra containing ions in a wide concentration range as generated by laser photoionization studies of van der Waals complexes. Real-time control of the gain of the microchannel plate detector, applying to it fast-rising high-voltage pulses like in slice imaging experiments, is suggested. Results are presented for a model system study.
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07.75.+h Mass spectrometers
07.60.Rd Visible and ultraviolet spectrometers
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment
33.80.Eh Autoionization, photoionization, and photodetachment
42.79.Ls Scanners, image intensifiers, and image converters

Time-of-flight system with a movable ion detector for absolute measurement of cyclotron beam energy

S. Okumura, S. Kurashima, N. Miyawaki, K. Yoshida, and M. Fukuda

Rev. Sci. Instrum. 76, 113106 (2005); http://dx.doi.org/10.1063/1.2135285 (6 pages) | Cited 1 time

Online Publication Date: 21 November 2005

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A time-of-flight system for determining the absolute energy of ion beams has been developed for the azimuthally varying field (AVF) cyclotron at Japan Atomic Energy Agency (JAEA). Ion detectors, a microchannel-plate detector and a plastic scintillation detector, were applied to the system in order to achieve high time resolution measurement of the flight time and to cover a wide range of beam intensity in combination with a beam attenuator. The change of the flight length, performed by moving the plastic scintillation detector with flexible bellows, allows determination of the mean beam energy only from the relative measurement of the flight time and the flight length without knowing their absolute values. A maximum movable distance of 2 m yields the difference in the time of flight from 16 to 94 ns for the energy range of ion beams accelerated by the JAEA AVF cyclotron. The time-of-flight system even with the 2 m change in the flight length achieves accurate energy determination of the order of 0.1%, since the relative measurement has an advantage of elimination of the uncertainties in determination of the time zero and the length zero. The time-of-flight measurement with the relative measurement also allows estimation of the beam energy spread without conventional expensive systems such as a magnetic spectrometer. By comparing the widths of the time-of-flight spectra of ions accumulated at different flight lengths, we have estimated the energy spread. In order to reduce the labor process of the coincidence detection of ions in the time-of-flight measurement, we have also accomplished a simple estimation method for mean beam energy determination with a beam bunch, naturally modulated with the acceleration RF of the cyclotron. The mean beam energy has been obtained from the shift of the beam bunch centroids at different flight lengths in the time-of-flight spectrum.
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07.75.+h Mass spectrometers
29.30.Aj Charged-particle spectrometers: electric and magnetic
29.40.Gx Tracking and position-sensitive detectors
29.40.Mc Scintillation detectors
07.77.Ka Charged-particle beam sources and detectors
41.75.-i Charged-particle beams
41.85.Ew Particle beam profile, beam intensity
41.85.Ct Particle beam shaping, beam splitting

Absolute energy reference calorimeter with bismuth telluride thermocouples for laser energy standard

Daiji Fukuda, Shinji Kimura, and Mitiyuki Endo

Rev. Sci. Instrum. 76, 113107 (2005); http://dx.doi.org/10.1063/1.2135286 (7 pages)

Online Publication Date: 21 November 2005

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A highly sensitive calorimeter has been developed for measuring the absolute energy of single laser pulses. The calorimeter, which consists of a solid volume absorber, a copper absorption cavity, and bismuth telluride thermocouples, is operated at room temperature with no vacuum window. The absorption of the laser energy in the calorimeter leads to a temperature increase of the cavity. The time-dependent temporal temperature change was measured as voltage signals with highly sensitive bismuth telluride semiconductor thermocouples. The calorimeter was calibrated by injecting a known Joule heat with a heater on the cavity. The experimental results showed a linear relationship in an energy range from 5 to 100 mJ. The standard deviation of the calibrated sensitivity was less than 0.1%. The systematic errors of the laser energy measurement are estimated to be as small as 0.32%.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
07.20.Fw Calorimeters
06.20.Dk Measurement and error theory

Fabrication of narrow-band self-filtering GaAs photodetector by epitaxy

Jin Shown Shie and Thunter S. D. Hwang

Rev. Sci. Instrum. 76, 113108 (2005); http://dx.doi.org/10.1063/1.2133996 (4 pages)

Online Publication Date: 23 November 2005

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A narrow-band self-filtering (NBSF) GaAs photodiode has been fabricated by the LPE technique, where epilayers of high-low-high N doping were grown on a P-type substrate. By proper control of the thickness and doping concentration of each layer, it can be demonstrated that the fabricated NBSF detector has a spectral bandwidth as narrow as 315 Å at 880 nm peak wavelength. This means over 98% of the blue-side light is suppressible, indicating that the NBSF photodetector is a useful device for many applications where the suppression of high background light is necessary.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Ea III-V semiconductors
42.79.Ci Filters, zone plates, and polarizers

Absolute calibration of extreme ultraviolet optical components with an x-ray-induced fluorescence source

Nobuyoshi Ueda, Hiroaki Nishimura, Shinsuke Fujioka, Noriaki Miyanaga, Yasukazu Izawa, Junya Uegaki, Kazuaki Shimizu, and Takashi Yamada

Rev. Sci. Instrum. 76, 113109 (2005); http://dx.doi.org/10.1063/1.2135287 (4 pages) | Cited 3 times

Online Publication Date: 23 November 2005

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A calibration system for extreme ultraviolet (EUV) optical components has been developed. In the system, x rays from a conventional tube induce fluorescence in source materials, which is detected with a gas flow counter or a charge-coupled device detector. The transmittance of an EUV filter (Zr foil) and the diffraction efficiency of a grazing incidence grating were measured and compared with measurements by other sources and calculations. The measured transmission of a filter for 13.5 nm light was 14.4%±0.6%, which agrees well with 14.55% measured with synchrotron orbital radiation. As for the gratings, the first-order diffraction shows good agreement with the model calculation, while the second order one has a remarkable discrepancy between the measurement and the calculation.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
42.79.Ci Filters, zone plates, and polarizers

Setup for the in situ monitoring of the irradiation-induced effects in optical fibers in the ultraviolet-visible optical range

D. G. Sporea and R. A. Sporea

Rev. Sci. Instrum. 76, 113110 (2005); http://dx.doi.org/10.1063/1.2130932 (5 pages) | Cited 3 times

Online Publication Date: 28 November 2005

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The paper describes a setup for in situ monitoring of the radiation-induced optical absorption and the radiation-induced luminescence, in the UV-visible spectral range (200–800 nm), for large diameter (400 μm) optical fibers. Silica and sapphire optical fibers were irradiated, at room temperature, with gamma rays (dose rate of 0.33 kGy/h, total dose of 34.5 kGy) and protons (dose rate of 100 Gy/s, total dose of 1.8 MGy). At several moments, the irradiation was interrupted and the annealing of the radiation-induced optical absorption was observed at room temperature. The setup also makes possible the monitoring of the optical radiation-induced recovery of the optical absorption (the effect of photobleaching), as the optical fiber can be exposed at the same time to both the ionizing radiation (gamma or protons) and to the radiation of a broadband optical source. The optical absorption and radioluminescence were measured with an optical fiber multichannel spectrometer coupled to an optical fiber multiplexer. The equipment control as well as the data collection and processing were performed using the graphical programming environment LabVIEW. The paper includes several graphs illustrating the evolution of the optical absorption and radiation-induced luminescence during gamma and proton irradiation of optical fibers.
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42.81.Cn Fiber testing and measurement of fiber parameters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
07.05.Hd Data acquisition: hardware and software
61.80.Ed γ-ray effects
61.80.Jh Ion radiation effects
81.40.Gh Other heat and thermomechanical treatments
42.65.-k Nonlinear optics

Cross calibration of new x-ray films against direct exposure film from 1 to 8 keV using the X-pinch x-ray source

K. M. Chandler, S. A. Pikuz, T. A. Shelkovenko, M. D. Mitchell, D. A. Hammer, and J. P. Knauer

Rev. Sci. Instrum. 76, 113111 (2005); http://dx.doi.org/10.1063/1.2135276 (8 pages) | Cited 9 times

Online Publication Date: 28 November 2005

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A cross calibration of readily available x-ray sensitive films has been carried out against the calibrated direct exposure film (DEF) which is no longer being manufactured by Kodak. Four-wire X pinches made from various metal wires were used as x-ray sources for this purpose. Tests were carried out for the Kodak films Biomax MS, Biomax XAR, M100, Technical Pan, and T-Max over the energy range of 1–8 keV (12.4–1.5 Å wavelength). The same hand-development procedures as described by Henke et al. [J. Opt. Soc. Am. B 3, 1540 (1986)] were followed for all films in every test. Sensitivity curves as a function of wavelength for these films relative DEF are presented. These relative calibrations show that Biomax MS is likely to be the best replacement film for DEF for most purposes over the energy range tested here.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.68.+m Photography, photographic instruments; xerography
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements
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Using ultrasonic atomization to produce an aerosol of micron-scale particles

T. D. Donnelly, J. Hogan, A. Mugler, M. Schubmehl, N. Schommer, A. J. Bernoff, S. Dasnurkar, and T. Ditmire

Rev. Sci. Instrum. 76, 113301 (2005); http://dx.doi.org/10.1063/1.2130336 (10 pages) | Cited 5 times

Online Publication Date: 9 November 2005

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A device that uses ultrasonic atomization of a liquid to produce an aerosol of micron-scale droplets is described. This device represents a new approach to producing targets relevant to laser-driven fusion studies, and to rare studies of nonlinear optics in which wavelength-scale targets are irradiated. The device has also made possible tests of fluid dynamics models in a novel phase space. The distribution of droplet sizes produced by the device and the threshold power required for droplet production are shown to follow scaling laws predicted by fluid dynamics.
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82.70.Rr Aerosols and foams
43.35.-c
28.52.Cx Fueling, heating and ignition

Generation of cold low divergent atomic beam of indium by laser ablation

Kamlesh Alti and Alika Khare

Rev. Sci. Instrum. 76, 113302 (2005); http://dx.doi.org/10.1063/1.2130943 (3 pages) | Cited 3 times

Online Publication Date: 17 November 2005

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The formation of low-energy (below 100 m/s), low divergence (without any collimation optics) pulsed indium atomic beam via ablation of thin film by direct illumination (unfocused) from the rear side with second harmonic of Q-switched Nd:YAG laser under high vacuum ( ∼ 10−5 Torr) is reported. Angular divergence of an ablated indium beam was measured for the different laser powers. Axial atomic and ionic velocities were studied as a function of laser energy per pulse using a beam deflection setup.
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37.20.+j Atomic and molecular beam sources and techniques
37.10.De Atom cooling methods
37.10.Gh Atom traps and guides
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

Photocathode microwire monitor for nondestructive and highly sensitive spatial profile measurements of ultraviolet, x-ray, and charged particle beams

Masaki Hori

Rev. Sci. Instrum. 76, 113303 (2005); http://dx.doi.org/10.1063/1.2130931 (6 pages) | Cited 8 times

Online Publication Date: 23 November 2005

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A nondestructive and sensitive monitor consisting of photocathode wire grids arranged in an XY configuration for measuring the spatial profile, divergence, and intensity of pulsed UV, x-ray, and charged particle beams is described. The monitor has been used to measure laser beams at wavelengths λ = 213−532 nm, and antiproton, proton, H− ions, and electron beams of energies E = 50 eV to 5 MeV.
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85.60.Ha Photomultipliers; phototubes and photocathodes
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
41.75.Fr Electron and positron beams
07.85.-m X- and γ-ray instruments

Development of a compact electron-cyclotron-resonance ion source for high-energy carbon-ion therapy

M. Muramatsu, A. Kitagawa, Y. Sakamoto, S. Sato, Y. Sato, Hirotsugu Ogawa, S. Yamada, Hiroyuki Ogawa, Y. Yoshida, and A. G. Drentje

Rev. Sci. Instrum. 76, 113304 (2005); http://dx.doi.org/10.1063/1.2132267 (6 pages) | Cited 12 times

Online Publication Date: 23 November 2005

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Ion sources for medical facilities should have characteristics of easy maintenance, low electric power consumption, good stability, and long operation time without problems (one year or longer). For this, a 10 GHz compact electron-cyclotron-resonance ion source with all-permanent magnets (Kei2 source) was developed. The maximum mirror magnetic fields on the beam axis are 0.59 T at the extraction side and 0.87 T at the gas-injection side, while the minimum B strength is 0.25 T. These parameters have been optimized for the production of C4+ based on the experience at the 10 GHz NIRS-ECR ion source and a previous prototype compact source (Kei source). The Kei2 source has a diameter of 320 mm and a length of 295 mm. The beam intensity of C4+ was obtained to be 530 μA under an extraction voltage of 40 kV. The beam stability was better than 6% at C4+ of 280 μA during 90 h with no adjustment of the operation parameters. The details of the design and beam tests of the source are described in this paper.
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87.53.-j Effects of ionizing radiation on biological systems
87.56.-v Radiation therapy equipment
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Cluster-eliminating filter for depositing cluster-free a-Si:H films by plasma chemical vapor deposition

Kazunori Koga, Naoto Kaguchi, Kouki Bando, Masaharu Shiratani, and Yukio Watanabe

Rev. Sci. Instrum. 76, 113501 (2005); http://dx.doi.org/10.1063/1.2126572 (4 pages) | Cited 2 times

Online Publication Date: 7 November 2005

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A cluster-eliminating filter is developed to reduce a volume fraction VF of amorphous silicon nanoparticles above approximately 1 nm in size (referred to as a cluster) incorporated into a-Si:H films. The filter reduces the VF value by using the difference between a sticking probability of clusters and a surface reaction probability of SiH3 radicals, which are the predominant deposition radicals. By employing the filter together with a cluster-suppressed plasma chemical vapor deposition reactor, the VF value is reduced below 1/180 compared to that for the conventional device quality films. Such cluster-free a-Si:H films have an extremely small hydrogen concentration associated with Si-H2 bonds below 5.46×10−3 at. %.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.80.Pi High-frequency and RF discharges
81.05.Gc Amorphous semiconductors

Linear ion source with magnetron hollow cathode discharge

D. L. Tang, S. H. Pu, L. S. Wang, X. M. Qiu, and Paul K. Chu

Rev. Sci. Instrum. 76, 113502 (2005); http://dx.doi.org/10.1063/1.2130933 (4 pages) | Cited 2 times

Online Publication Date: 9 November 2005

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A linear ion source with magnetron hollow cathode discharge is described in this paper. The linear ion source is based on an anode layer thruster with closed-drift electrons that move in a closed path in the E×B fields. An open slit configuration is designed at the end of the ion source for the extraction of the linear ion beam produced by the magnetron hollow cathode discharge. The special configurations enable uninterrupted and expanded operation with oxygen as well as other reactive gases because of the absence of an electron source in the ion source. The ion current density and uniformity were experimentally evaluated. Using the ion source, surface modification was conducted on polyethylene terephthalate polymer films to improve the adhesion strength with ZnS coatings.
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52.80.Hc Glow; corona
52.50.Dg Plasma sources
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
52.25.Fi Transport properties
81.65.-b Surface treatments

Cellular nonlinear networks for strike-point localization at JET

P. Arena, L. Fortuna, M. Bruno, G. Vagliasindi, A. Murari, P. Andrew, and G. Mazzitelli

Rev. Sci. Instrum. 76, 113503 (2005); http://dx.doi.org/10.1063/1.2130936 (10 pages) | Cited 2 times

Online Publication Date: 9 November 2005

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At JET, the potential of fast image processing for real-time purposes is thoroughly investigated. Particular attention is devoted to smart sensors based on system on chip technology. The data of the infrared cameras were processed with a chip implementing a cellular nonlinear network (CNN) structure so as to support and complement the magnetic diagnostics in the real-time localization of the strike-point position in the divertor. The circuit consists of two layers of complementary metal-oxide semiconductor components, the first being the sensor and the second implementing the actual CNN. This innovative hardware has made it possible to determine the position of the maximum thermal load with a time resolution of the order of 30 ms. Good congruency has been found with the measurement from the thermocouples in the divertor, proving the potential of the infrared data in locating the region of the maximum thermal load. The results are also confirmed by JET magnetic codes, both those used for the equilibrium reconstructions and those devoted to the identification of the plasma boundary.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
28.52.Fa Materials
52.55.Fa Tokamaks, spherical tokamaks
07.05.Pj Image processing
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
52.40.Hf Plasma-material interactions; boundary layer effects

Compact antenna for two-dimensional beam scan in the JT-60U electron cyclotron heating/current drive system

S. Moriyama, K. Kajiwara, K. Takahashi, A. Kasugai, M. Seki, Y. Ikeda, and T. Fujii

Rev. Sci. Instrum. 76, 113504 (2005); http://dx.doi.org/10.1063/1.2130967 (6 pages) | Cited 1 time

Online Publication Date: 23 November 2005

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A compact antenna system was designed and fabricated to enable millimeter-wave beam scanning in the toroidal and poloidal directions of the JT-60U tokamak for electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) experiments. The antenna consists of a fast movable flat mirror mounted on the tokamak vacuum vessel and a rotary focusing mirror attached at the end of the waveguide that is supported from outside the vacuum vessel. This separate support concept enables a compact structure inside a shallow port (0.68×0.54×0.2 m) that is shared with a subport for an independent diagnostic system. During a plasma shot, the flat mirror is driven by a servomotor with a 3-m-long drive shaft to reduce the influence of the high magnetic field on the motor. The focusing mirror is rotated by a simple mechanism utilizing a push rod and an air cylinder. The antenna has been operated reliably for 3 years after a small improvement to the rotary drive mechanism. It has made significant contributions to ECH and ECCD experiments, especially the current profile control in JT-60U.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.70.Ds Electric and magnetic measurements
52.55.Fa Tokamaks, spherical tokamaks
52.55.Wq Current drive; helicity injection
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Fi Transport properties
84.40.Ba Antennas: theory, components and accessories
84.40.Az Waveguides, transmission lines, striplines

Up-to-date radon-thoron discriminative detector for a large scale survey

Shinji Tokonami, Hiroyuki Takahashi, Yosuke Kobayashi, Weihai Zhuo, and Erik Hulber

Rev. Sci. Instrum. 76, 113505 (2005); http://dx.doi.org/10.1063/1.2132270 (5 pages) | Cited 24 times

Online Publication Date: 23 November 2005

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An up-to-date radon-thoron discriminative detector has been developed for conducting a large scale survey. Comparing with our previous detector, some functional problems have been solved. The lowest and highest detection limits of the detector were estimated to be around 5 and 1000 Bq m−3 for radon, and 15 and 1000 Bq m−3 for thoron, respectively, with a 6 month exposure and several theoretical assumptions. Small indoor survey were carried out in Japan and in Hungary using the present detector. The presence of thoron was demonstrated in any indoor surveys by the two results. Since any measurements without discrimination of radon isotopes will result in different risk estimates from actual situations, a special attention should be paid to thoron and its concentration should be accordingly measured as well as the radon concentration.
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29.40.Cs Gas-filled counters: ionization chambers, proportional, and avalanche counters
89.60.Ec Environmental safety

A simple far-infrared laser interferometer for measuring electron densities in reactive low-temperature plasmas

C. Pargmann, S. V. Singh, and H. Soltwisch

Rev. Sci. Instrum. 76, 113506 (2005); http://dx.doi.org/10.1063/1.2134355 (6 pages) | Cited 6 times

Online Publication Date: 23 November 2005

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A sensitive far-infrared (fir) interferometer for electron density measurements in reactive low-temperature plasmas is described. The instrument is based on an optically pumped fir laser (wavelength range 50–600 μm depending on the working gas) and makes use of the nonlinear relation between output power and cavity loss. The fir beam, which leaves the resonator through a coupling hole in the end mirror, is reflected back into the cavity, such that the coupling hole behaves like a variable “leak” with a loss rate depending on the phase of the reentering wave relative to the standing wave within the resonator. As a result of the feedback, the output intensity undergoes strong nonlinear variations if the optical distance of the external mirror is changed by small amounts, Δz. The power variation is monitored through a small opening in the external mirror. Test experiments using a wavelength of 432.6 μm and a Schottky-diode detector have yielded a minimum detectable pathlength variation of Δz = 0.4 μm, corresponding to a change of the line-integrated electron density mathe×L of about 5×1015 m−2. A first application to argon plasmas in inductively coupled rf discharges has been made, and the results have been compared to concomitant Langmuir probe measurements.
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07.60.Ly Interferometers
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges

Synchronization of multiple spark-gap switches by a transmission line transformer

Z. Liu, K. Yan, A. J. M. Pemen, G. J. J. Winands, and E. J. M. Van Heesch

Rev. Sci. Instrum. 76, 113507 (2005); http://dx.doi.org/10.1063/1.2132269 (4 pages) | Cited 3 times

Online Publication Date: 28 November 2005

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A transmission line transformer (TLT)-based multiple-switch circuit topology was recently proposed for pulsed-power generation. By means of a TLT, multiple spark-gap switches can be synchronized in a short time (ns). It is attractive to be used to design a long-lifetime repetitive large pulsed-power source (100 kW, 1 kHz) for various kinds of applications, such as corona plasma-induced gas cleaning. To gain insight into the synchronization principle and switching behavior of the individual switch, an equivalent circuit model was developed and an experimental setup with two spark-gap switches and a two-stage TLT has been constructed. We observed that in terms of switching currents, the two switches can be synchronized within 2–3 ns. The equivalent circuit model approximately fits the experimental results.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
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Short focal length Kirkpatrick-Baez mirrors for a hard x-ray nanoprobe

Wenjun Liu, Gene E. Ice, Jonathan Z. Tischler, Ali Khounsary, Chian Liu, Lahsen Assoufid, and Albert T. Macrander

Rev. Sci. Instrum. 76, 113701 (2005); http://dx.doi.org/10.1063/1.2125730 (6 pages) | Cited 31 times

Online Publication Date: 7 November 2005

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We describe progress in the fabrication of short-focal-length total-external-reflection Kirkpatrick-Baez x-ray mirrors with ultralow figure errors. The short focal length optics produce nanoscale beams (<100 nm) on conventional ( ∼ 64 m long) beamlines at third generation synchrotron sources. The total-external reflection optics are inherently achromatic and efficiently focus a white (polychromatic) or a tunable monochromatic spectrum of x rays. The ability to focus independent of wavelength allows novel new experimental capabilities. Mirrors have been fabricated both by computer assisted profiling (differential polishing) and by profile coating (coating through a mask onto ultra-smooth surfaces). A doubly focused 85×95 nm2 hard x-ray nanobeam has been obtained on the UNICAT beamline 34-ID at the Advanced Photon Source. The performance of the mirrors, techniques for characterizing the spot size, and factors limiting focusing performance are discussed.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
41.50.+h X-ray beams and x-ray optics
07.85.Qe Synchrotron radiation instrumentation

A compact nanopositioning stage with high vibrational eigenfrequencies

S. J. Ball, C. Folsom, and A. B. McLean

Rev. Sci. Instrum. 76, 113702 (2005); http://dx.doi.org/10.1063/1.2130939 (7 pages)

Online Publication Date: 9 November 2005

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A compact nanopositioning stage is described that has high vibrational eigenfrequencies and is, therefore, insensitive to external vibrations. The high eigenfrequencies are produced by a rigid structure that is designed so that it does not degrade the motional performance of the stage. Preliminary performance evaluations are presented. We describe how a positioning stage of this type could be used as an integral part of a proximal probe.
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06.30.−k
06.60.Sx Positioning and alignment; manipulating, remote handling
07.10.−h
07.10.Fq Vibration isolation
07.79.−v
07.79.Cz Scanning tunneling microscopes
46.40.Ff Resonance, damping, and dynamic stability
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