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Feb 2005

Volume 76, Issue 2, Articles (02xxxx)

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A densely distributed high-sensitivity seismograph network in Japan:Hi-net by National Research Institute for Earth Science and DisasterPrevention

Kazushige Obara, Keiji Kasahara, Sadaki Hori, and Yoshimitsu Okada

Rev. Sci. Instrum. 76, 021301 (2005); http://dx.doi.org/10.1063/1.1854197 (12 pages) | Cited 13 times

Online Publication Date: 25 January 2005

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Seismic observations to retrieve various information from the Earth are the basis of seismology. A seismic observation system requires various technologies for vibration sensors, analog-and-digital measurement, data transmission, and computing for mass data analysis, for example. New developments in technology are adopted whenever possible in the construction of seismic observation systems. In Japan, after the disastrous Kobe Earthquake in 1995, a high-density and high-sensitivity seismograph network was constructed. The seismic network, called the National Research Institute for Earth Science and Disaster Prevention (NIED) Hi-net, uniformly covers the Japanese Islands with a spacing of 20–30 km. As a result, the detection capability for microearthquakes has been greatly improved, and various research using Hi-net data has indicated that this seismic network has a great potential to resolve the underground structure and various geophysical phenomena as a radar-array oriented toward the Earth. Equipped with modern standard techniques, the Hi-net system is designed to be able to be smoothly upgradeable in the future.
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93.85.-q Instruments and techniques for geophysical research: Exploration geophysics
91.30.Px Earthquakes
91.30.Bi Seismic sources (mechanisms, magnitude, moment frequency spectrum)
89.60.Gg Impact of natural and man-made disasters
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Stability of vacuum-ultraviolet radiometric transfer standards: Electron cyclotron resonance versus hollow cathode source

Alexander Gottwald, Mathias Richter, Gerhard Ulm, and Udo Schühle

Rev. Sci. Instrum. 76, 023101 (2005); http://dx.doi.org/10.1063/1.1835051 (6 pages) | Cited 1 time

Online Publication Date: 5 January 2005

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Established transfer standards such as Penning and hollow cathode discharge sources suffer from limited spectral range and, in particular, a limited lifetime and stability due to electrode erosion. The development of a vacuum-ultraviolet radiation source based on an electron cyclotron resonance (ECR)-created plasma might overcome these limitations. To test such a source with regard to its usefulness as radiometric transfer standard, the emission intensity of a Ne plasma was monitored over an operation period of 180 days, with regard to stability and reproducibility in the 50–75 nm wavelength range. For comparison and calibration, a hollow cathode was used as transfer standard traceable to the electron storage ring BESSY II as primary standard. It was found that the ECR source exceeded the lifetime of the hollow cathode source by far, offering a more balanced spectral emission line variety with similar stability.
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06.20.F- Units and standards
07.60.Dq Photometers, radiometers, and colorimeters

Photon detection by a cryogenic InSb detector

Ikuo Kanno, Shigeomi Hishiki, Osamu Sugiura, Ruifei Xiang, Tatsuya Nakamura, and Masaki Katagiri

Rev. Sci. Instrum. 76, 023102 (2005); http://dx.doi.org/10.1063/1.1835632 (3 pages) | Cited 1 time

Online Publication Date: 5 January 2005

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Gamma rays of math were measured by a Schottky type undoped InSb detector at 4.2 K. Although a photopeak was not observed, the signals of gamma rays were clearly separated from noises.
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07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
29.40.Wk Solid-state detectors

Free electron laser-Fourier transform ion cyclotron resonance mass spectrometry facility for obtaining infrared multiphoton dissociation spectra of gaseous ions

Jose J. Valle, John R. Eyler, Jos Oomens, David T. Moore, A. F. G. van der Meer, Gert von Helden, Gerard Meijer, Christopher L. Hendrickson, Alan G. Marshall, and Gregory T. Blakney

Rev. Sci. Instrum. 76, 023103 (2005); http://dx.doi.org/10.1063/1.1841953 (7 pages) | Cited 116 times

Online Publication Date: 5 January 2005

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A Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been installed at a free electron laser (FEL) facility to obtain infrared absorption spectra of gas phase ions by infrared multiple photon dissociation (IRMPD). The FEL provides continuously tunable infrared radiation over a broad range of the infrared spectrum, and the FT-ICR mass spectrometer, utilizing a 4.7 Tesla superconducting magnet, permits facile formation, isolation, trapping, and high-mass resolution detection of a wide range of ion classes. A description of the instrumentation and experimental parameters for these experiments is presented along with preliminary IRMPD spectra of the singly-charged chromium-bound dimer of diethyl ether (Cr(C4H10O)2+) and the fluorene molecular ion (C13H10+). Also presented is a brief comparison of the fluorene cation spectrum obtained by the FT-ICR-FEL with an earlier spectrum recorded using a quadrupole ion trap (QIT).
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07.75.+h Mass spectrometers
41.60.Cr Free-electron lasers
82.50.Bc Processes caused by infrared radiation

Performance of a reflection-type polarizer by use of muscovite mica crystal in the soft x-ray region of 1 keV

Takashi Imazono, Masahiko Ishino, Masato Koike, Hiroaki Kimura, Toko Hirono, and Kazuo Sano

Rev. Sci. Instrum. 76, 023104 (2005); http://dx.doi.org/10.1063/1.1844671 (4 pages) | Cited 9 times

Online Publication Date: 5 January 2005

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To develop the polarizer functioning in the soft x-ray region of 1 keV, the polarization performance of muscovite mica has been investigated theoretically with a simulation code based on dynamical theory. As the result of calculation, muscovite mica is found to be a promising candidate as a reflection-type polarizer with the reflectivity for s polarization of 0.03 at approximately 0.9 keV at the angle of incidence of 45°. In order to verify the polarization performance of muscovite mica experimentally, a symmetric Bragg reflection measurement of muscovite mica(002) was carried out using a linearly polarized undulator radiation. As a result, the maximum reflectivity for s polarization and the extinction ratio of muscovite mica were approximately 0.018 and 200 at 878 eV, respectively. This result indicates that muscovite mica works as a practical polarizer in the soft x-ray region.
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61.05.cp X-ray diffraction
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

High resolution kinetic energy by long time-delayed core-sampling photofragment translational spectroscopy

Guosheng Li, Hyun Jin Hwang, and Hyun Chai Jung

Rev. Sci. Instrum. 76, 023105 (2005); http://dx.doi.org/10.1063/1.1844412 (7 pages) | Cited 15 times

Online Publication Date: 6 January 2005

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A pulsed core-sampling photofragment translational spectroscopy (PTS) method with a long time-delay, which allows an extremely high kinetic energy resolution, is presented in this article. More commonly applying a short time delay between laser and pulsed acceleration electric field leads to a low kinetic energy resolution for the pulsed core-sampling method. This low kinetic energy resolution problem was overcome by applying a longer time delay. An absolute recoil velocity resolution of Δv = 8 m/s and a relative kinetic energy resolution of ΔE/E = 3.6% were obtained in this experiment, by applying a time-delay of 8 μs between the laser and the acceleration electric field. The vibrational distributions of the CH3 radical for the I* and I channel of CH3I photodissociation at 266 nm were directly resolved for first time to presented an improvement of the kinetic energy resolution.
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07.75.+h Mass spectrometers
82.80.Rt Time of flight mass spectrometry
82.50.Nd Control of photochemical reactions

Collimated, single-pass atom source from a pulsed alkali metal dispenser for laser-cooling experiments

Kevin L. Moore, Thomas P. Purdy, Kater W. Murch, Sabrina Leslie, Subhadeep Gupta, and Dan M. Stamper-Kurn

Rev. Sci. Instrum. 76, 023106 (2005); http://dx.doi.org/10.1063/1.1841852 (4 pages) | Cited 5 times

Online Publication Date: 10 January 2005

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We have developed an improved scheme for loading atoms into a magneto-optical trap (MOT) from a directed rubidium alkali metal dispenser in <10−10 Torr ultrahigh vacuum conditions. A current-driven dispenser was surrounded with a cold absorbing “shroud” held at ⩽ 0 °C, pumping rubidium atoms not directed into the MOT. This nearly eliminates background atoms and reduces the detrimental rise in pressure normally associated with these devices. The system can be well-described as a current-controlled, rapidly switched, two-temperature thermal beam, and was used to load a MOT with 3×108 atoms.
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07.77.Gx Atomic and molecular beam sources and detectors
07.30.Cy Vacuum pumps
07.30.Kf Vacuum chambers, auxiliary apparatus, and materials

Incoherent broad-band cavity-enhanced absorption spectroscopy of liquids

Sven E. Fiedler, Achim Hese, and Albert A. Ruth

Rev. Sci. Instrum. 76, 023107 (2005); http://dx.doi.org/10.1063/1.1841872 (7 pages) | Cited 21 times

Online Publication Date: 10 January 2005

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A new application of incoherent broad-band cavity enhanced absorption spectroscopy (IBBCEAS) to weak transitions in solution through a very straightforward modification of commercially available double-beam UV/VIS absorption spectrometers is reported. The improved sensitivity of the new approach is demonstrated on basis of the weak Franck–Condon inhibited absorption of the fifth C–H stretch overtone in liquid benzene. The theoretical limits of the enhancement of the signal-to-noise ratio of IBBCEAS in comparison with single pass absorption experiments are discussed for a set of given experimental cavity parameters. The optical loss properties of a typical transparent cuvette window in the cavity are also discussed.
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07.60.Rd Visible and ultraviolet spectrometers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Averaging peak-to-peak voltage detector for absolute mass determination of single particles with quadrupole ion traps

Wen-Ping Peng, Yuan T. Lee, Joseph W. Ting, and Huan-Cheng Chang

Rev. Sci. Instrum. 76, 023108 (2005); http://dx.doi.org/10.1063/1.1841791 (5 pages) | Cited 4 times

Online Publication Date: 11 January 2005

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A sine wave that controls a quadrupole ion trap is generated from a low voltage source, boosted to high voltage through a transformer. Since not even the best transformers can keep a flat amplitude response with respect to frequency, knowing the accurate peak-to-peak value of the sine wave is paramount when the frequency is varied. We have developed an averaging peak-to-peak voltage detector for such measurements and demonstrated that the device is an essential tool to make possible high-precision mass determination of single charged microparticles with masses greater than 1×1011 u. Tests of the detector with sine waves from a FLUKE 5720A standard source in the neighborhood of 1400 Vpp and frequencies ranging from 100 to 700 Hz showed a measurement accuracy better than 10 ppm. The detector settled within 5 s after each reset to 5 digits of DVM rock-steady reading, and the calibration against the same source after 3 weeks of continuous use of the circuit produced a mere overall 1 ppm difference.
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06.30.Dr Mass and density
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors

Laser Doppler velocimetry based on the photoacoustic effect in a CO2 laser

Jong-woon Choi, Moon-jong Yu, Mirek Kopica, Sam-yong Woo, and Yong-Seok Choi

Rev. Sci. Instrum. 76, 023109 (2005); http://dx.doi.org/10.1063/1.1850634 (3 pages)

Online Publication Date: 14 January 2005

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We report a simple laser Doppler velocimeter in which the photoacoustic effect was used to measure the rotation wheel speed. A Doppler signal, caused by mixing a returning wave with an originally existing wave inside the CO2 laser cavity, was detected using a microphone in the laser tube. Frequency of the microphone output was in proportion to the rotation speed of a wheel and is dependent on the cosine of the angle between the direction of the laser beam and tangent of wheel velocity. A Doppler-shifted frequency as high as 34 kHz was detected using this method. A frequency response of a few megahertz is expected from the laser Doppler velocimeter based on the photoacoustic effect in a CO2 laser by using a wider bandwidth microphone.
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42.79.Qx Range finders, remote sensing devices; laser Doppler velocimeters, SAR, and LIDAR
06.30.Gv Velocity, acceleration, and rotation
42.55.Lt Gas lasers including excimer and metal-vapor lasers

Plane-grating flat-field soft x-ray spectrometer

C. F. Hague, J. H. Underwood, A. Avila, R. Delaunay, H. Ringuenet, M. Marsi, and M. Sacchi

Rev. Sci. Instrum. 76, 023110 (2005); http://dx.doi.org/10.1063/1.1852313 (8 pages) | Cited 9 times

Online Publication Date: 14 January 2005

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We describe a soft x-ray spectrometer covering the 120–800 eV range. It is intended for resonant inelastic x-ray scattering experiments performed at third generation synchrotron radiation (SR) facilities and has been developed with SOLEIL, the future French national SR source in mind. The Hettrick–Underwood principle is at the heart of the design using a combination of varied line-spacing plane grating and spherical-mirror to provide a flat-field image. It is slitless for optimum acceptance. This means the source size determines the resolving power. A spot size of ⩽ 5 μm is planned at SOLEIL which, according to simulations, should ensure a resolving power ≥ 1000 over the whole energy range. A 1024×1024 pixel charge-coupled device (CCD) with a 13 μm×13 μm pixel size is used. This is an improvement on the use of microchannel-plate detectors, both as concerns efficiency and spatial resolution. Additionally spectral line curvature is avoided by the use of a horizontal focusing mirror concentrating the beam in the nondispersing direction. It allows for readout using a binning mode to reduce the intrinsically large CCD readout noise. Preliminary results taken at beamlines at Elettra (Trieste) and at BESSY (Berlin) are presented.
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07.85.Nc X-ray and γ-ray spectrometers
07.85.Qe Synchrotron radiation instrumentation
42.79.Dj Gratings
42.79.Bh Lenses, prisms and mirrors

Total internal reflection second-harmonic generation spectrometer system optimized for the liquid/liquid interface

Kazuhiko Fujiwara, Hideaki Monjushiro, and Hitoshi Watarai

Rev. Sci. Instrum. 76, 023111 (2005); http://dx.doi.org/10.1063/1.1854214 (5 pages) | Cited 2 times

Online Publication Date: 20 January 2005

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An apparatus for optical second-harmonic generation (SHG) spectroscopy at the liquid/liquid interface has been constructed. The fundamental laser beam of 780–920 nm was irradiated to the interface under the total internal reflection condition, and the interfacial second-harmonic spectrum was obtained during 390–460 nm. An automatically wavelength-tuned Ti:Sapphire laser was employed in this study, and it was simultaneously controlled with other peripheral instruments, such as monochromator. The acquisition time per spectrum with 2 nm interval was less than 30 min. The measurement of SHG spectrum of water-soluble porphyrin adsorbed at the heptane/water interface was demonstrated. The solvatochromic shift of the SHG maximum of the adsorbed porphyrin was ascribed to the less polar environment around the porphyrin molecule at the interface in comparison with the aqueous phase.
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07.60.Rd Visible and ultraviolet spectrometers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
68.05.Cf Liquid-liquid interface structure: measurements and simulations
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds

Automated high-resolution frequency-stabilized cavity ring-down absorption spectrometer

Joseph T. Hodges and Roman Ciuryło

Rev. Sci. Instrum. 76, 023112 (2005); http://dx.doi.org/10.1063/1.1850633 (7 pages) | Cited 23 times

Online Publication Date: 20 January 2005

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We describe a frequency-stabilized cavity ring-down absorption spectrometer with automated scanning capabilities. The system utilizes the comb of ring-down cavity resonances as frequency markers for spectral scans. The comb is actively stabilized with respect to a frequency-stabilized reference laser, and the continuous wave, single-mode probe laser frequency is in turn actively stabilized with respect to resonances of the ring-down cavity frequency comb. Ring-down spectra are obtained by locking the external-cavity diode laser probe to sequential cavity resonances (separated by the ring-down cavity free spectral range), and the ring-down cavity frequency comb is translated by controlled amounts using acousto-optic frequency shifting methods for fine frequency steps less than the free-spectral range. A computer-controlled method for automating frequency tuning and probe laser locking to the cavity resonances is described, and high-resolution near-infrared (vicinity of 10 712 cm−1) absorption spectra of water vapor are presented. A frequency resolution of ≈ 1 MHz and minimum measurable line intensity of 10−27 cm2 cm−1 molecule−1 are demonstrated.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
42.60.Fc Modulation, tuning, and mode locking

Thermoelastic effects as a way of creating transient renewable reflective optics

D. D. Ryutov

Rev. Sci. Instrum. 76, 023113 (2005); http://dx.doi.org/10.1063/1.1850671 (13 pages) | Cited 2 times

Online Publication Date: 20 January 2005

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A technique for creating renewable reflective optics suitable for focusing of pulsed laser beams is proposed. It is based on the heating of the surface of a planar reflecting slab by an auxiliary heating source that causes thermal expansion of the slab material and creates a desired surface relief, e.g., a focusing mirror. The presence of this relief is a transient phenomenon, but, for a short-enough main pulse, this does not cause any problems. If the surface is damaged by the main pulse, the shifting of the slab and repeating the whole cycle allows recreating the transient mirror. Favorable features of this approach include controlling the optics “at a distance,” without any direct mechanical contact. A detailed discussion of the possibilities provided by this technique for the focusing of x-ray beams at the planned Linac Coherent Light Source facility at Stanford is presented. It is concluded that a 20-fold increase of intensity of an 8 keV beam and 100-fold increase of intensity of a 0.8 keV beam is possible. A set of design equations and constraints is formulated. The analysis presented can be used as a template for analyses of similar transient optical systems for the UV and optical range.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Bh Lenses, prisms and mirrors
41.50.+h X-ray beams and x-ray optics
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets

Susumu Takahashi and Stephen Hill

Rev. Sci. Instrum. 76, 023114 (2005); http://dx.doi.org/10.1063/1.1852859 (10 pages) | Cited 34 times

Online Publication Date: 20 January 2005

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The cavity perturbation technique is an extremely powerful method for measuring the electrodynamic response of a material in the millimeter- and submillimeter spectral range (10 GHz–1 THz), particularly in the case of high-field/frequency magnetic resonance spectroscopy. However, the application of such techniques within the limited space of a high-field magnet presents significant technical challenges. We describe a 7.62 mm×7.62 mm (diameter×length) rotating cylindrical cavity which overcomes these problems. The cylinder is mounted transverse to the bore of the magnet, coupling is achieved through the sidewalls of the cavity, and the end plate is then rotated (by means of an external drive) instead of the body of the cavity itself. Therefore, rotation does not affect the cylindrical geometry, or the mechanical connections to the incoming waveguides. The TE011 mode frequency of the cavity is 51.863 GHz, with the possibility to work on higher-order modes to frequencies of order 350 GHz. Neither the quality factor ( ∼ 22 000 for the fundamental mode) or the coupling to the cavity are significantly affected for full 360° of rotation. The rotation mechanism provides excellent angle resolution (<0.1°), and is compact enough to enable measurements in the high-field (up to 45 T) magnets at the National High Magnetic Field Laboratory. Two-axis rotation capabilities are also possible in conjunction with split-pair magnet configurations. We present examples of angle-dependent measurements which illustrate the unique capabilities of this rotating cavity, including: high-field angle-dependent measurements of an unusual form of cyclotron resonance in anisotropic organic conductors; and angle-dependent high-frequency single-crystal electron paramagnetic resonance measurements in single-molecule magnets.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
84.40.Az Waveguides, transmission lines, striplines
78.70.Gq Microwave and radio-frequency interactions
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Electron-beam diagnostic for space-charge measurement of an ion beam

Prabir K. Roy, Simon S. Yu, Enrique Henestroza, Shmuel Eylon, Derek B. Shuman, Jozsef Ludvig, Frank M. Bieniosek, William L. Waldron, Wayne G. Greenway, David L. Vanecek, Ryan Hannink, and Monserrat Amezcua

Rev. Sci. Instrum. 76, 023301 (2005); http://dx.doi.org/10.1063/1.1847392 (8 pages) | Cited 1 time

Online Publication Date: 5 January 2005

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A nonperturbing electron-beam diagnostic system for measuring the charge distribution of an ion beam is developed for heavy ion fusion beam physics studies. Conventional diagnostics require temporary insertion of sensors into the beam, but such diagnostics stop the beam, or significantly alter its properties. In this diagnostic a low energy, low current electron beam is swept transversely across the ion beam; the measured electron-beam deflection is used to infer the charge density profile of the ion beam. The initial application of this diagnostic is to the neutralized transport experiment (NTX), which is exploring the physics of space-charge-dominated beam focusing onto a small spot using a neutralizing plasma. Design and development of this diagnostic and performance with the NTX ion beamline is presented.
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07.77.Ka Charged-particle beam sources and detectors
84.47.+w Vacuum tubes

Correction and alignment strategies for the beam separator of the photoemission electron microscope 3 (PEEM3)

Peter Schmid, Jun Feng, Howard Padmore, David Robin, Harald Rose, Ross Schlueter, Weishi Wan, Étienne Forest, and Ying Wu

Rev. Sci. Instrum. 76, 023302 (2005); http://dx.doi.org/10.1063/1.1841871 (14 pages) | Cited 6 times

Online Publication Date: 11 January 2005

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A high-resolution aberration-corrected photoemission electron microscope (PEEM3) will be installed on an undulator beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The aim of this instrument is to provide a substantial flux and resolution improvement by employing an electron mirror for correcting both the third-order spherical aberration and the primary chromatic aberration. In order to utilize this concept of correction, a beam separator is a prerequisite. Crucial to achieving a resolution of 5 nm for the high-resolution mode, and a 16-fold increase in throughput at the same resolution as its predecessor, PEEM2, specified as 20 nm at 2% transmission, for the high flux mode is the double-symmetric design of the beam separator, which eliminates all the second-order geometric aberrations. Nonetheless, substantial tuning capabilities must be incorporated into the PEEM3 design to compensate for both systematic and random errors. In this article, we investigate how to correct for nonsystematic imperfections and for systematic uncertainties in the accuracy of the magnetic fields and focus on how degradation of the resolution and the field of view can be minimized. Finally, we outline a tentative correction strategy for PEEM3.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.85.Qe Synchrotron radiation instrumentation

Transport efficiency of vacuum arc plasma in a curved magnetic filter

Yawei Hu, Liuhe Li, Ming Xu, Youming Liu, Xun Cai, Ian G. Brown, and Paul K. Chu

Rev. Sci. Instrum. 76, 023303 (2005); http://dx.doi.org/10.1063/1.1848492 (4 pages) | Cited 2 times

Online Publication Date: 14 January 2005

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We describe two methods for increasing the transmission efficiency of vacuum arc plasma through curved magnetic filters. In the first method the substrate is connected to the anode or biased to a negative voltage. In the second method a metal grid is placed between the substrate and the exit of the magnetic filter, and biased to a positive voltage whereas the substrate is biased negatively. The ion saturation current and electron saturation current of the plasma between the filter exit and the substrate were measured using a current collector plate and a Langmuir probe, respectively, and the ion density estimated. For the experimental conditions of the work described here, the measured ion flux (ion saturation current) near the duct exit was increased by up to about 80% (from 140 to 250 mA), and the measured ion density was increased by up to about 40% (from 3.7×1011 to 5.2×1011 cm−3). These results can be explained by the ambipolar influence of enhanced electron flow on the accompanying plasma ion component, leading also to enhanced ion flow.
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52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.50.Dg Plasma sources
52.30.-q Plasma dynamics and flow
52.55.-s Magnetic confinement and equilibrium
52.58.-c Other confinement methods
52.25.-b Plasma properties

Fast ion beam chopping system for neutron generators

S. K. Hahto, S. T. Hahto, K. N. Leung, J. Reijonen, T. G. Miller, and P. K. Van Staagen

Rev. Sci. Instrum. 76, 023304 (2005); http://dx.doi.org/10.1063/1.1852871 (5 pages) | Cited 5 times

Online Publication Date: 25 January 2005

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Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15 ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120 keV D+ ion beams hitting a titanium target at the center of the source.
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29.25.Dz Neutron sources
07.77.Ka Charged-particle beam sources and detectors
41.75.Ak Positive-ion beams
41.85.Ar Particle beam extraction, beam injection
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Sightline optimization of the multichannel laser interferometer for W7-X

M. I. Airila, O. Dumbrajs, M. Hirsch, J. Geiger, U. Neuner, and H.-J. Hartfuss

Rev. Sci. Instrum. 76, 023501 (2005); http://dx.doi.org/10.1063/1.1835031 (9 pages) | Cited 1 time

Online Publication Date: 5 January 2005

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A multichannel CO2 laser interferometer is planned for electron density profile measurements in the Wendelstein 7-X stellarator under construction. This article describes the mathematical methods used to find the optimum orientation of the various sightlines. The problem of reconstructing local densities from line integrated density measurements can be formulated as a matrix inversion. The quality of the reconstruction is largely determined by the condition number of the matrix describing the problem, which has to be minimized, i.e., the sightlines have to be chosen such that the information content of different channels is maximally distinct. For the W7-X interferometer four- and eight-sightline arrangements are investigated and their orientations are optimized for standard conditions of magnetic configuration and density profile. The optimized arrangements are tested by simulating the inversion of hypothetical reference density profiles in a number of different magnetic configurations. In the ideal case the error of a reconstruction using four sightlines is typically a few times larger than that with eight sightlines. The robustness of the optimization is demonstrated by a variation of the position of the whole interferometer, and the influence of noisy phase data on the reconstructed profiles is investigated. These factors significantly narrow the difference between the four- and eight-beam setups. Finally, the use of regularization methods for the analysis of experimental data is briefly discussed.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.60.Ly Interferometers
52.55.Jd Magnetic mirrors, gas dynamic traps
52.25.-b Plasma properties

Relationship among frequency, temperature of the cooling water and beam current in submillimeter wave gyrotron FU-IV

Toshihiro Hori, Toshitaka Idehara, Hiroyuki Sasagawa, Atsushi Kimura, Isamu Ogawa, and Seitaro Mitsudo

Rev. Sci. Instrum. 76, 023502 (2005); http://dx.doi.org/10.1063/1.1836351 (6 pages) | Cited 3 times

Online Publication Date: 5 January 2005

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The frequency characteristics of the gyrotron FU-IV in free running mode are examined precisely using heterodyne mixing technique. First, the frequency characteristics are measured and the short-term spectral bandwidths and the drifts of the center frequency are found to be less than 10 kHz full width at half maximum and about 10 MHz during 20 min, respectively. Next, an effective water-cooling system reduced the drifts of the center frequency within a range of several MHz. Then, the frequency, the cooling-water temperature, the beam current and the output power are monitored simultaneously to examine the relationship among these parameters. The results indicate that the beam current drift correlate with the frequency drift due to frequency pulling effect as well as the thermal expansion and contraction of the resonant cavity.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
06.30.Ft Time and frequency

Measurement of absolute electron density with a plasma impedance probe

David D. Blackwell, David N. Walker, and William E. Amatucci

Rev. Sci. Instrum. 76, 023503 (2005); http://dx.doi.org/10.1063/1.1847608 (6 pages) | Cited 17 times

Online Publication Date: 6 January 2005

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A small spherical probe is used in conjunction with a network analyzer to determine the impedance of the probe-plasma system over a wide frequency range. Impedance curves are in good agreement with accepted circuit models with plasma-sheath and electron plasma frequency resonances easily identifiable. Clear transitions between capacitive and inductive modes as predicted by the model are identified. Sheath thickness and absolute electron density are determined from the location of these transitions. The absolute electron density indicated by the location of the impedance resonance is compared to measurements using the plasma oscillation method.
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52.70.Ds Electric and magnetic measurements
07.68.+m Photography, photographic instruments; xerography
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Real time polarization monitor developed for high power electron cyclotron resonance heating and current drive experiments in large helical device

T. Notake, H. Idei, S. Kubo, T. Shimozuma, Y. Yoshimura, S. Kobayashi, Y. Mizuno, S. Ito, Y. Takita, K. Ohkubo, W. Kasparek, T. Watari, and R. Kumazawa

Rev. Sci. Instrum. 76, 023504 (2005); http://dx.doi.org/10.1063/1.1848657 (9 pages) | Cited 4 times

Online Publication Date: 20 January 2005

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The polarization state of a wave is an important factor in electron cyclotron resonance heating (ECRH) and current drive (ECCD), for it strongly affects the propagation and absorption of the wave in the plasma. A real-time monitor of the polarization of the EC beam has been developed for use in ECRH/ECCD experiments in large helical device (LHD). Two orthogonal components of the wave field are measured in one of the miter-bends by use of a specially designed coupler and a waveguide circuit with a 0°–90° phase switch to deduce the polarization parameters: the polarization angle α and the ellipticity β. Since fast-response pin diodes are used for the switches, the polarization is determined every 3 ms, facilitating real time acquisition of the polarization. This article reports on the design and the principle of this monitor as well as on the algorithm used to calculate α and β. This article also reports on the method of calibration, for the accuracy of this measurement depends on it. Finally, a comparison is made between polarization parameters measured by a monitor actually installed on one of the ECRH transmission lines on LHD and the value set by the polarizer in ECRH experiments.
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52.75.-d Plasma devices
52.70.Ds Electric and magnetic measurements
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.58.Qv Electrostatic and high-frequency confinement
52.25.Fi Transport properties

Spectroscopic imaging diagnostics for burning plasma experiments

D. Stutman, M. Finkenthal, G. Suliman, K. Tritz, L. Delgado-Aparicio, R. Kaita, D. Johnson, V. Soukhanovskii, and M. J. May

Rev. Sci. Instrum. 76, 023505 (2005); http://dx.doi.org/10.1063/1.1852317 (9 pages) | Cited 4 times

Online Publication Date: 20 January 2005

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Spectroscopic imaging of plasma emission profiles from a few electron volts to tens of kilo-electron volts enables basic diagnostics in present day tokamaks. For the more difficult burning plasma conditions, light extraction and detection techniques, as well as instrument designs need to be investigated. As an alternative to light extraction with reflective optics, we discuss normal incidence, transmissive-diffractive optics (e.g., transmission gratings), which might withstand plasma exposure with less degradation of optical properties. Metallic multilayer reflectors are also of interest for light extraction. Although a shift of the diffraction peak might occur, instrument designs that accommodate such shifts are possible. As imaging detectors we consider “optical” arrays based on conversion of the short-wavelength light into visible light followed by transport of the visible signal with hollow lightguides. The proposed approaches to light extraction and detection could enable radiation resistant diagnostics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
28.52.Lf Components and instrumentation
52.55.Fa Tokamaks, spherical tokamaks
42.79.Pw Imaging detectors and sensors
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

PROTEX: A proton-recoil detector for inertial confinement fusion neutrons

Michael J. Moran, Vladimir Yu. Glebov, Christian Stoeckl, Ryan Rygg, and Brook-Eden Schwartz

Rev. Sci. Instrum. 76, 023506 (2005); http://dx.doi.org/10.1063/1.1854213 (5 pages) | Cited 7 times

Online Publication Date: 25 January 2005

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Fusion neutron diagnostics are important to inertial confinement fusion (ICF) because they characterize fusion performance and help to provide the understanding that is needed to develop higher-yield sources. Present yields in excess of 1012 deuterium–tritium (DT) neutrons now can be measured with a proton-recoil detector. This technique, which has not been practical with lower yields, is desirable because it provides prompt, accurate, and unambiguous results. The PROTEX is a proton-recoil detector which features a compact coaxial cylindrical geometry for maximum sensitivity, in situ simultaneous measurement of background signals, and an ab initio calculated absolute sensitivity. The calculated sensitivity has an estimated absolute accuracy of 6%. With simple adjustments, PROTEX can provide absolute measurement of yield for the National Ignition Facility, the Laser Megajoule Facility, or for any ICF source having a yield greater than 1012 DT neutrons.
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07.77.Ka Charged-particle beam sources and detectors
28.52.Lf Components and instrumentation
29.40.Wk Solid-state detectors
52.70.Ds Electric and magnetic measurements
52.58.Qv Electrostatic and high-frequency confinement
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