bluuebunny/crossref_metadata_2025 huggingface dataset:
Diagnostic systems for the National Ignition Facility (NIF) (invited)
Authors: Kilkenny J. D. , Cable M. D. , Clower C. A. , Hammel B. A. , Karpenko V. P. , Kauffman R. L. , Kornblum H. N. , MacGowan B. J. , Olson W. , Orzechowski T. J. , Phillion D. W. , Tietbohl G. L. , Trebes J. E. , Chrien B. , Failor B. , Hauer A. , Hockaday R. , Oertel J. , Watt R. , Ruiz C. , Cooper G. , Hebron D. , Leeper R. , Porter J. , Knauer J.
Published: July 2002

A tentative schedule of experiments for the ignition campaign on the National Ignition Facility (NIF) has been developed. These experiments will be used to validate beam pointing and balance, to tune time history and symmetry of drive of NIF hohlraums, and to implode subignition and igniting targets. The initial target diagnostics are designed to validate beam pointing and to demonstrate the properties of the hohlraums.
First results with amplitude modulation reflectometry on the PBX-M tokamak
Authors: de la Luna E. , Sanchez J. , Zhuravlev V. , García-Cortés I. , Hanson G. R. , Wilgen J. B. , Harris J. H. , Dunlap J. , Kaita R. , Leblanc B. ,   the PBX-M Team, Tynan G. R. , Schmitz L. , Blush L.
Published: July 2002

Electron density profile measurements have been obtained on PBX-M by amplitude modulation reflectometry. With this technique, the measurement of the time delay is obtained from the phase delay of the modulating envelope (200 MHz in PBX-M). The system operates with the extraordinary mode, in the range 32–50 GHz. Under these conditions the density profile of PBX-M can be probed from the scrape-off layer up to typically r/a=0.7. With a final bandwidth of 40 kHz, the reflectometer is able to obtain the edge profile in 1 ms. The profiles obtained are relatively noise free and in good agreement with Thomson scattering measurements. Perturbations due to the strong-edge turbulence are kept to a minimum, and no software filtering or other signal processing was necessary to extract the time delay information from the raw data. Profiles have been measured for ohmic and Neutron Beam Injection heated discharges.
Negative ion beam development at Cadarache (invited)
Authors: Simonin A. , Bucalossi J. , Desgranges C. , Fumelli M. , Jacquot C. , Massmann P. , Pamela J. , Riz D. , Trainham R. , Belchenko Y.
Published: July 2002

Neutral beam injection (NBI) is one of the candidates for plasma heating and current drive in the new generation of large magnetic fusion devices (ITER). In order to produce the required deuterium atom beams with energies of 1 MeV and powers of tens of MW, negative D− ion beams are required. For this purpose, multiampere D− beam production and 1 MeV electrostatic acceleration is being studied at Cadarache. The SINGAP experiment, a 1 MeV 0.1 A D− multisecond beam accelerator facility, has recently started operation. It is equipped with a Pagoda ion source, a multiaperture 60 keV preaccelerator and a 1 MV 120 mA power supply. The particular feature of SINGAP is that the postaccelerator merges the 60 keV beamlets, aiming at accelerating the whole beam to 1 MeV in a single gap. The 1 MV level was obtained in less than 2 weeks, the accumulated voltage on-time of being ∼22 min. A second test bed MANTIS, is devoted to the development of multiampere D− sources. It is capable of driving discharges with current up to 2500 A at arc voltages up to 150 V. A large multicusp source has been tested in pure volume and cesiated operation. With cesium seeding, an accelerated D− beam current density of up to 5.2 mA/cm2 (2 A of D−) was obtained. A modification of the extractor is underway in order to improve this performance. A 3D Monte Carlo code has been developed to simulate the negative ion transport in magnetized plasma sources and optimize magnetic field configuration of the large area D− sources.
Porous silicon fabrication technique for large area devices
Authors: Grigoras K. , Pačebutas V.
Published: July 2002

An improved technique applied for fabrication of porous silicon layers on silicon wafers is proposed. The main principle is the vacuum pulling and holding of the sample instead of mechanical pressing or using of special acid-proof wax. Large silicon wafers can be etched in this electrochemical cell. Porous silicon coating was ‘‘deposited’’ on as-prepared solar cells. This procedure improved the cell’s performance very significantly: we have obtained ∼30% increase in efficiency on cells with no antireflection coating.
Novel bistatic polarization nephelometer for probing scattering through a planar interface
Authors: Miller D. , Quinby-Hunt M. S. , Hunt A. J.
Published: July 2002

We have developed a novel bistatic polarization-modulated nephelometer that probes a medium enabling in situ measurement of angle- and polarization-dependent light scattering through a planar interface. This is particularly important for media with a planar interface such as sea ice but also for media in which measurements at great distance or depth, e.g., the atmosphere, are desirable. The instrument sits directly and noninvasively on the planar surface of the scattering medium. Light from a laser beam is directed into the medium and the scattered light is detected by analyzer optics. The angle of both the laser and detector beams in the medium can be varied continuously. Alternating current polarimetry is used to obtain phase function and polarization information of the scattered light. Measurements from this instrument of scattering from monodisperse polystyrene (latex) spheres in the laboratory are in good qualitative agreement with the results of Mie calculations and measurements made with a conventional monostatic nephelometer. This instrument has also been used to make preliminary investigations of scattering in sea ice in Pt. Barrow, Alaska.
Direct current superconducting quantum interference device spectrometer for pulsed nuclear magnetic resonance and nuclear quadrupole resonance at frequencies up to 5 MHz
Authors: TonThat Dinh M. , Clarke John
Published: July 2002

A spectrometer based on a dc superconducting quantum interference device (SQUID) has been developed for the direct detection of nuclear magnetic resonance (NMR) or nuclear quadrupole resonance (NQR) at frequencies up to 5 MHz. The sample is coupled to the input coil of the niobium-based SQUID via a nonresonant superconducting circuit. The flux locked loop involves the direct offset integration technique with additional positive feedback in which the output of the SQUID is coupled directly to a low-noise preamplifier. Precession of the nuclear quadrupole spins is induced by a magnetic field pulse with the feedback circuit disabled; subsequently, flux locked operation is restored and the SQUID amplifies the signal produced by the nuclear free induction signal. The spectrometer has been used to detect 27Al NQR signals in ruby (Al2O3[Cr3+]) at 359 and 714 kHz.
Simple four-domain twisted nematic liquid crystal display
Authors: Chen J. , Bos P. J. , Bryant D. R. , Johnson D. L. , Jamal S. H. , Kelly J. R.
Published: July 2002

A particularly simple four-domain (4-D) twisted nematic (TN) liquid crystal display (LCD) device is proposed, which is composed of two left-handed TN and two right-handed TN subpixels. One of each pair of same handedness subpixels is rotated 180° with respect to the other, resulting in four domains that spatially average one another optically to provide a wide angle of viewing with no gray scale inversion. The detailed fabrication process is presented for a two step SiOx oblique evaporation technique used to realize this 4-D TN LCD. A reverse rubbed polyamide fabrication process has also been successfully used and will be presented in the full length article. Here we present the complete viewing angle and contrast ratio data for a simple and successful 4-D TN LCD cell.
A simple and accurate contactless frequency and amplitude meter
Authors: László Tolnai , László Marczy
Published: July 2002

This study describes a measuring instrument based on the Michelson interferometer. It is able to measure the amplitude-time function or the resonance curve in a wide frequency range simultaneously depending on the amplitude of the vibration without any kind of mechanical contacts. Compared with other instruments based on similar principles, it has the advantage of not being a heterodyne interferometer, that is of using only the phenomenon of classic interference instead of the frequency of Doppler shift of the reflected light. The reflective surface of the oscillating object or the mirror glued thereon may turn, which is often the case. The software performs a correction to the errors arising from the turning of the mirror. In the realized instrument the allowed maximum angle of rotation of the mirror is ±5°, measuring range of the amplitude is 5 micron to 1 mm, measuring range of the frequency is 1 Hz to 5×104 Hz depending on the amplitude.
Simple, compact implementation of a beetle-type scanning tunneling microscope for low temperature ultrahigh vacuum applications
Authors: Silva L. A.
Published: July 2002

A simple, compact, low temperature scanning tunneling microscope system is described which can easily be incorporated into pre-existing ultrahigh vacuum chambers designed around a centrally located sample. Cooling is achieved by the transfer of a cryogenic fluid from an external commercial Dewar to the bottom of a cold finger, where the sample and a beetle-type microscope are mounted. Details of the microscope operation with liquid nitrogen are given.
Neutron diagnostics for ITER
Authors: Johnson L. C. , Barnes Cris W. , Krasilnikov A. , Marcus F. B. , Nishitani T. ,   ITER Joint Central Team and Home Teams
Published: July 2002

Neutron diagnostics will play a prominent role in the control and evaluation of thermonuclear plasmas in ignition device to test engineering concepts (ITER). As in present D-T experiments, measurements of neutron yield and of fusion power and power density are essential. In addition, the spectral width of the 14.1-MeV t(d,n)α neutron emission should be a reliable indicator of ion temperature in an ignited plasma. More detailed measurements of the neutron spectrum may allow determination of the densities of tritium, deuterium, and confined alpha particles. Although the central fusion power density in ITER will be comparable to the maximum values obtainable in TFTR and JET, neutron flux on the first wall will be ten times higher, and the neutron yield per discharge will be about five orders of magnitude greater than previously experienced. The thermal and radiation shielding necessary to protect the ITER superconducting coils from the intense flux at the first wall will restrict diagnostic access for neutron cameras and spectrometers, complicate the design of material activation systems, and limit the applicability of conventional calibration techniques for neutron source strength monitors. These considerations, together with unprecedented reliability requirements and the need for full remote handling of many components, pose demanding challenges for the design of the ITER neutron diagnostic systems.
A time detector design for MeV particles using secondary electron emission and microchannel plates
Authors: Fang Z. , O’Connor D. J.
Published: July 2002

In this article we present some basic considerations in the design of a time detector for high energy (0.2–1.0 MeV) particle detection. Based on these considerations, a novel time detector design is proposed in order to overcome some of the problems in existing designs. Improvement in the timing resolution (<50 ps) and efficiency (>70% for 4.0 MeV α particles) is expected and a compact detector structure with ultrahigh vacuum compatibility is achieved. The new design employs a novel form of crossed electric and magnetic fields to deflect the electrons emitted from a thin foil to form a timing signal. In this design electrons are transported in a grid-free region and the energetic particle needs to pass through the grid once only. The electric field was produced by three metal plates forming a triangular prism. The magnetic field was generated by a coil pair which creates a uniform field in the electron transport region. Computer simulation and numerical analysis were performed to calculate the electric and magnetic field as well as the electron trajectory and flight time. The detector timing resolution is analyzed and the spread in electron initial energy contributes a significant portion. To avoid the complicated numerical details in field and trajectory calculations, we use an empirical approach in this article to illustrate the design principle. Some experimental results are presented to compare with the calculations.
True constant fraction trigger circuit for picosecond photon-timing with ultrafast microchannel plate photomultipliers
Authors: Ghioni M. , Cova S. , Samori C. , Zappa F.
Published: July 2002

In time correlated photon counting, the picosecond resolution offered by the reduced transit time spread of ultrafast microchannel plate (MCP) photomultipliers is fully exploited only if all other timing jitter contributions are minimized. With the ultrashort signals of MCP detectors, the commercially available circuit modules do not provide true constant fraction triggering (CFT) operation. The residual amplitude dependent time walk therefore sets the actual limit to the obtained time resolution. A new CFT scheme has been devised for obtaining true constant fraction triggering. A circuit has been accordingly developed and tested. The time walk is reduced to less than 8 ps for a 1:14 dynamic of the input signal (pulse amplitudes from 100 mV to 1.4 V) and to less than 25 ps for a 1:20 dynamic (from 70 mV to 1.4 V). It is shown that such a performance makes it possible to exploit in actual experiments the 20 ps intrinsic resolution of the fastest available MCP detectors.
Statistics and dead time correction of two-particle time-of-flight coincidence experiments
Authors: Luhmann Till
Published: July 2002

The statistics of a specific class of two-particle coincidence experiments are discussed. Detection of the first particle provides for the start of a time-of-flight measurement in which the second particle is analyzed. Dead time of the electronics used for flight time measurements and registration of coincidence signals (time-to-amplitude converter or time-to-digital converter) may cause strong distortion of coincidence spectra. The problem is complicated by the different statistics of true and false coincidences. Without a convenient correction procedure, this effect limits the source strength to a value for which the distortion is small but the measurement duration is long. A calculation method is developed from which the measured coincidence spectra can be corrected for distortion at any source strength thereby separating true and false coincidences. This technique has been successfully applied in an electron-ion coincidence experiment where free atoms were photoionized by synchrotron radiation.
ITER physics program and implications for plasma measurements
Authors: Mukhovatov V. , Costley A. E. , Bartiromo R. , Boucher D. , Fujisawa N. , Gribov Yu. , Janeschitz G. , Johnson L. , Kasai S. , de Kock L. , Marmar E. , Muraoka K. , Nagashima A. , Orlinski D. , Ortolani S. , Perkins F. , Petrov M. , Post D. , Putvinski S. , Rosenbluth M. , Sauter O. , Stott P. E. , Strelkov V. , Vayakis G. , Walker C. , Wesley J. C. , Yamamoto S. , Young K. M. ,   the ITER Physics Expert Groups,   ITER Joint Central Team and Home Teams
Published: July 2002

Key objectives of the first ten years of ITER operation are the investigation of the physics of burning plasmas and the demonstration of long-pulse ignited plasma technologies. These include studies of plasma confinement and stability, divertor operation, disruption mitigation and control, noninductive current drive, and steady state operation under conditions when the plasma is heated predominantly by alpha particles. The ITER operational plan envisages two and a half years for commissioning and initial operation with hydrogen plasmas at up to 100 MW of auxiliary heating power when initial tests of divertor operation and evaluation of disruption effects will be made. In order to meet the operational and programmatic goals, it will be necessary to make a wide range of plasma measurements. In this article the preliminary operational plan and physics program are presented and the implications for plasma measurements are outlined.
Time-resolved stopped-flow x-ray absorption fine structure system using synchrotron radiation for fast reactions in solution
Authors: Inada Yasuhiro , Hayashi Hiroo , Funahashi Shigenobu , Nomura Masaharu
Published: July 2002

A time-resolved stopped-flow x-ray absorption fine structure (XAFS) system was developed using synchrotron radiation as an x-ray source. The shortest sampling time for time-resolved measurements was on the order of 1 ms with the dead time of ∼5 ms, which was limited by the mixing procedure in the stopped-flow unit and by the drift velocity of the ions generated in the ionization chamber as a detector. The time-resolution ability and the quality of the obtained XAFS spectra were greatly improved in comparison with the laboratory stopped-flow XAFS apparatus previously constructed. The time-resolved XAFS measurements were performed for the reduction reaction of [Fe(CN)6]3− with L-ascorbic acid in an acidic aqueous solution. The rate constants obtained from the XAFS experiments were reasonable judging from the kinetic parameters previously reported.
A novel instrument for material surface treatment by pulsed high power density plasma beam
Authors: Jiang Yingbing , Zhang Hongxia , Liu Chizi , Wu Cheng , Yang Size
Published: July 2002

While great interest has been focused on low temperature plasma for material processing, the concept of using pulsed high speed and high temperature plasma beam for material surface treatment was put forward. Thus a novel instrument based on Thetatron-Pinch was built up and the plasma beam with a temperature of several hundred eVs and a density up to 1016 cm−3 was created uniformly over a large cross section. The plasma beam was then accelerated by a sample bias of 0–2.0 kV under a high vacuum circumstance. The energy density exerted on the sample surface is 1–20 J/cm2 with a duration time of less than 10 μs, which is comparable to that of laser treatment. Preliminary experiments indicate that this method has the combining feature of laser treatment and ion implantation techniques when it is used for surface modification; moreover, a transient high temperature and high pressure environment exists on the treated surface in this technique and the plasma contains a high concentration of radical particles. Both facts are advantageous to chemical vapor deposition applications.
Spatial resolution of fuel distribution in an engine using infrared absorption
Authors: Golombok M. , Cooney P. J. , Kitching J. S. , Nattrass S. R.
Published: July 2002

We describe a novel method of obtaining the fuel concentration at various points along the longitudinal axis of a spark ignition engine. This allows us to measure the effect of various engine and fuel parameters on charge stratification in the combustion chamber. The technique is based on sampling the infrared (IR) absorption spectrum through the transparent sapphire engine cylinder. The absorbance is measured at four points down the chamber axis using four IR launching fibers, each of which is matched to a collection fiber. The spectra are simultaneously dispersed and stacked on a diode array detector. We subtract the background from the absorption peak to obtain the absorbance which is shown to be directly proportional to fuel concentration. We find that the axial charge stratification and its evolution during the induction and compression strokes is a sensitive function of injection timing and swirl valve setting. The technique is also applicable to gas phase reactors and any system where spatially homogeneous mixing of reactants is required.
Parametric optimization of discharge pumped XeCl lasers
Authors: Makarov Maxime
Published: July 2002

The data gained on discharge pumped XeCl laser systems over the last 15 years were analyzed to identify common inherent regularities. It is obvious that there are three major classes of phenomena involved, namely: the electrical processes in the pumping circuit, the plasma-chemical kinetics, and the discharge contraction. It has been demonstrated that under certain conditions they can be considered separately. Such an approach allows one to estimate a priori the optimal pumping conditions and the electrical circuit parameters to obtain the required laser energy. The results presented could be used in the engineering calculations of high-performance excimer laser systems to significantly reduce the cost of the design and the optimization stages.
An intense atomic hydrogen source with a movable nozzle output
Authors: Paolini B. P. , Khakoo M. A.
Published: July 2002

The fabrication and operation of a stable and intense source of atomic hydrogen from an easily movable nozzle is described in detail. The source uses a well-known air-cooled, extended cavity microwave source using molecular hydrogen, but conducts the dissociated atoms to the experimental interaction region via inert Teflon “spaghetti” tubing. A resulting collimated beam with a dissociation fraction exceeding 0.8 and with an average number density of atomic hydrogen of 6×1012 cm−3 at a distance of 2 mm from the exit of the source is obtained. This source of H is attractive, because it is movable and easily interfaced into beam–beam type experiments.
Polarization lifetime near an induced depolarizing resonance
Authors: von Przewoski B. , Doskow J. , Dzemidzic M. , Meyer H. O. , Pollock R. E. , Rinckel T. , Sperisen F. , Thörngren Engblom P. , Daehnick W. W. , Flammang R. W. , Saha Swapan K. , Lorentz B. , Quin P. , Schwartz B. , Wise T. , Pancella P. V. , Ugorowski P.
Published: July 2002

The time dependence of the polarization of a stored proton beam was measured near an induced depolarizing resonance. The resonance was created by a magnetic field which oscillated along the beam axis. The distance to the resonance was varied by changing the frequency of the oscillating field. The resonance was approached from either side and the time dependence of the polarization was found to be symmetric with respect to the resonance, and in agreement with an earlier measurement that involved an intrinsic depolarizing resonance.
Diagnostic method for radial electric fields in Tokamaks by the observation of ripple-trapped ions
Authors: Herrmann Winfried ,   ASDEX Upgrade Team
Published: July 2002

Weakly collisional ions trapped in the toroidal field ripples at the outer plasma edge of a Tokamak can be prevented from escaping the plasma due to grad B drift by a counteracting radial electric field. This leads to an increase in the density of ripple-trapped ions, which can be monitored by the analysis of charge exchange neutrals. The minimum radial electric field Er necessary to confine ions with energy E and charge q (q=−1: charge of the electron) is Er=−E/(q×R), where R is the major radius at the measuring point. Slowing-down ions from neutral injection are usually in the right energy range to be sufficiently collisionless in the plasma edge and show confinement by radial electric fields in the range of tens of kV/m. The density of banana ions is almost unaffected by the radial electric field indicating that the change in the fluxes of ripple-trapped ions is, indeed, caused by the radial electric field and not by direct changes in plasma parameters. Single particle calculations for real ASDEX Upgrade geometry and magnetic fields but with an assumed electric field profile give a rule of thumb estimate of the electric field strength. They also make plausible the reason why the charge exchange flux may react in less than 100 μs to an abrupt onset of a radial electric field with a halfwidth of at least the Larmor diameter of the particles in question and thus make this measurement an interesting tool for the investigation of the edge radial electric field.
Versatile millimeter-wave interferometer with two frequencies in the divertor region of JT-60U
Authors: Takenaga H. , Fukuda T. , Sakurai S. , Hosogane N. , Kodama K. , Masaki K.
Published: July 2002

A millimeter-wave interferometer having a capability of concomitant electron temperature measurement, based on the electron cyclotron absorption (ECA) technique, has been developed for divertor diagnostics in JT-60U. Three lines of sight, which pass through the X point horizontally, the inboard divertor and the outboard divertor, are chosen. Two transmitter/receiver units with frequencies of 217 and 183 GHz are employed in order to eliminate the spurious vibration effect using a two color scheme. The two independent units are also arranged to enable two sight line measurements without the vibration compensation. Furthermore, these units allow us to apply the simultaneous ECA diagnostic. Due to the complexity of the transmission line inside the tokamak, the insertion loss is as large as 65 dB. However, the interferometer system can be operated with the signal-to-noise (S/N) ratio of about 20 dB due to the low equivalent input noise of −90 dB m. The measurements performed for several types of the JT-60U discharges indicate the feasibility of the system and the rapid reduction of the electron density near the X point at the high confinement mode transition is first demonstrated.
A correlation function for thermal properties estimation applied to a large thickness sample with a single surface sensor
Authors: Lima e Silva S. M. M. , Duarte M. A. V. , Guimarães G.
Published: July 2002

This article describes an experimental technique to measure simultaneously the thermal diffusivity and thermal conductivity of nonmetallic materials. The method is applied to a large thickness sample and uses a single temperature sensor located at the heating surface of a perspex sample. In addition the golden section optimization technique is used with parameter estimation for minimizing two different objective functions. Each of the thermal properties is estimated in a different way. The diffusivity estimation uses a correlation function estimator between heat flux and temperature while a square function error of experimental and estimated temperatures is the objective function used for determining the conductivity. A comparison with the guarded hot plate method indicates a deviation of 2.1% of the thermal conductivity. An error analysis for both properties is also presented.
Improving the luminance and luminous efficacy of miniature fluorescent lamps for liquid crystal display backlighting by using a double frequency drive
Authors: Shiga T. , Mikoshiba S. , Curzon F. L. , Shinada S.
Published: July 2002

A new method of driving miniature fluorescent tubes for liquid crystal display backlighting, with diameters as small as 2 mm, has been devised with the objective of improving the luminance and luminous efficacies of such lamps. The driver voltage wave form consists of high frequency oscillations at the leading and trailing edges of conventional square-wave form voltage pulses of relatively low frequency. The wave form is produced simply by inserting coils between low frequency square-wave pulse generators and the lamp electrodes. A lamp driven in this way operates in a different discharge mode from the conventional glow discharge obtained in the absence of the coils. The twofold intensity increase of visible emission from the positive column region indicates that the vacuum ultraviolet emission increases, enhancing the excitation of the phosphor in the lamp. There is evidence that the luminous efficacy is also increased by a factor of 2 as a result of more efficient use of the input energy. The minimum voltage needed to maintain a discharge is reduced.
Simple device and reproducible approach for producing high efficiency optical fiber tips for a scanning near-field optical microscope
Authors: Liu X. , Wang J. , Li D.
Published: July 2002

A heating–pulling device is established for producing the optical fiber probe used in scanning near-field optical microscopy. A CO2 laser, the power of which can be adjusted continuously between 0 and 10 W, is used as the heating source. Pulling is done by two identical motors. On the basis of the device, a novel approach different from the conventional heating–pulling method is developed, which eliminates the need for a computer, reflective mirror, and varied force during tip formation. Thus it is simple and easy to use. The cost is reduced greatly. Tips with parabolic taper, short taper region, and a diameter of 65 nm, which are optimal conditions for high transmission efficiency, are obtained.
A simplified method for accuracy estimation of nuclear magnetic resonant imaging
Authors: Arola D. F. , Powell R. L. , Barrall G. A. , McCarthy M. J.
Published: July 2002

Multi-dimensional tomographic-based data sets are now being used to calculate physical properties and transport coefficients. This article presents a method, based upon the propagation of uncertainties, for determining the valid range of values for the property calculated. The example used to demonstrate the method is the application of nuclear magnetic resonance imaging (NMRI) to measure fluid velocity profiles for the calculation of fluid viscosities. The resolution of the velocity data is shown to be the most important factor for implementation of the NMRI-based viscometry technique. Uncertainties in the velocity measurement are propagated through the shear viscosity calculation to estimate the standard deviation of the shear viscosities. Two data sets, experimental velocity resolutions of 0.6 and 1.5 mm/s, demonstrate that when the shear viscosity standard deviation exceeds 30% of the predicted shear viscosity value we observe a discrepancy between the data and viscosities obtained using conventional rheometrical instruments. Removal of those data points with a standard deviation exceeding 30% of the shear viscosity value provided data that agreed to within 6% of conventional rheometry data. The estimation methodology for property uncertainty can be applied prior to experimental measurements to design for accuracy over a specific range of the property to be determined. These findings are not restricted to NMRI and should hold for other tomography-based viscometers
Faraday rotation measurements on compact helical system by using a phase sensitive heterodyne polarimeter
Authors: Tanaka K. , Kawahata K. , Ejiri A. ,   CHS Group, Howard J. , Okajima S.
Published: July 2002

A phase sensitive heterodyne polarimeter was installed on compact helical system (CHS). An HCN laser (337 μm) and Schottky barrier diodes are used for the radiation source and for detection, respectively. By using a phase sensitive heterodyne scheme, the Faraday rotation angle can be measured from the phase variations caused by the phase difference between the right- and left-handed waves in the magnetized plasma. The purpose of the polarimeter on CHS is for a stable density monitor which is free from fringe jump and for the measurements of the internal magnetic field induced by the plasma current. The present resolution of the Faraday rotation angle is 0.1° with 10 ms time resolution and 1° with 1 ms. These are mainly determined by the laser instability.
Structures in Te profiles: High resolution Thomson scattering in the Rijnhuizen tokamak project
Authors: Beurskens M. N. A. , Barth C. J. , Lopes Cardozo N. J. , van der Meiden H. J. ,   RTP-team
Published: July 2002

In the Rijnhuizen tokamak project, the double pulse multiposition Thomson scattering diagnostic is in full operation. Its high spatial resolution enables the measurement of small scale structures in Te, ne, and pe. Thomson scattering profiles during an ordinary sawtooth crash show the displacement of the hot core in great detail. Measurements on off-axis sawtoothing plasmas show that a small central part remains unaffected. Filaments are observed in plasmas which show a transient central temperature rise in response to fast edge cooling.
Application of wavelet spectral analysis to plasma fluctuation measurements using beam emission spectroscopy
Authors: Jakubowski M. , Fonck R. , Kim J. S. , McKee G.
Published: July 2002

Beam emission spectroscopy (BES) measures localized density fluctuations in fusion plasma turbulence. A wavelet transform method of spectral analysis is applied to BES data to extract fluctuations without the long time-averaging characteristic of Fourier transform spectral analysis methods. This technique is used to observe an abrupt (∼100 μs) L–H transition on DIII–D. Wavelet-based cross correlation analysis can be used to obtain fluctuations of poloidal rotation velocity, and suggests opportunity for measurement of electrostatic potential fluctuation measurements.
High time resolution ion temperature and rotation velocity measurements by charge exchange spectroscopy using three interference filters
Authors: Koog J. S. , Sakasai A. , Koide Y. , Shirai H. , Kamada Y. , Fukuda T. , Yoshino R. ,   the JT-60 Team
Published: July 2002

The ion temperature and toroidal rotation velocity with high time resolution (τ∼1 ms) using charge exchange spectroscopy in JT-60U tokamak plasma have been measured. The method uses three interference filters that have slightly different peak wavelengths. These filters are selected according to the ion temperature and rotation velocity expected at the measured position. The system with a time resolution of 1 ms was applied to the analysis of fast plasma phenomena. As an example, the time evolution of the C VI ion temperature and toroidal rotation velocity across the L–H transition has been measured. The toroidal rotation at a normalized minor radius (r/a=0.3) increases gradually after the L–H transition, while that at the edge changes from a speed of 5 km/s before the transition to −40 km/s after the transition within a time of 5–10 ms.
High resolution photothermal imaging of high frequency phenomena using a visible charge coupled device camera associated with a multichannel lock-in scheme
Authors: Grauby S. , Forget B. C. , Holé S. , Fournier D.
Published: July 2002

We have developed a technique using a photothermal microscope from which we can make a thermal image of an electronic component working at a “high frequency” using a charge coupled device (CCD) camera and a multichannel lock-in scheme. To do this, we have created an electronic “stroboscope”: the frequency F of the thermal signal induced by a high frequency electrical excitation and the frequency of the light F+f that illuminates the device are next to each other; the signal reflected at the surface of the device whose amplitude is proportional to the variation of reflectivity and hence to the variation of temperature and whose frequency is the blinking one f is analyzed by a visible CCD camera. Amplitude and phase images of the high frequency thermal phenomenon can then be made. Moreover, this technique presents a great advantage: the spatial resolution is better than 1 μm. The amplitude and phase images presented show, with a very good spatial resolution, Joule and Peltier heating of a polycrystalline silicon 2.5 kΩ resistor across which a sinusoidal current is forced.
Dynamic force distance control suited to various probes for scanning near-field optical microscopy
Authors: Naber A. , Maas H.-J. , Razavi K. , Fischer U. C.
Published: July 2002

A dynamic force distance control for scanning near-field optical microscopy (SNOM) based on a quartz tuning fork as piezoelectric force sensor is introduced. In contrast to a similar design for shear-force feedback, the tuning fork is aligned in such a way that forces perpendicular to the surface are detected. Various near-field probes can be attached to the end of the tuning fork and serve as force sensing tip. The high force sensitivity is demonstrated for two different near-field probes by imaging the topography of organic samples. The tetrahedral tip, an apertureless high-resolution near-field probe used up to now mainly with tunnel current distance control, is for the first time successfully combined with a force distance control for SNOM. A similar distance control was used in conjunction with an only few millimeters short aluminum-coated tapered fiber tip as near-field probe. The suitability of this design for near-field optical fluorescence imaging is demonstrated. Furthermore, the dynamic force distance control with a fiber tip was applied to a soft biological sample under water. The force sensitivity turned out to be sufficiently high to reveal corrugations in the order of 1 nm.
Simultaneous measurement method of both shock state and stress profile in polymers in 1 GPa stress
Authors: Mori Yasuhito , Hidaka Kota , Nagayama Kunihito
Published: July 2002

A new procedure of recording both Hugoniot parameters and stress profile is proposed to study shock characteristics of polymers in 1 GPa stress region. The assembly consists of an in-material polyvinylidene fluoride (PVDF) stress gauge element and an optical prism pin. The PVDF gauge records the shock wave stress profile, while the prism pin records the arrival of shock front at the free surface of the target. Argon laser beam is focused onto the bottom face of the prism pin placed on the free surface so as to satisfy the condition of total internal reflection. Shock velocity can be estimated from the time difference of two signals, the PVDF gauge and the prism pin. The Hugoniot state can be calculated by the shock velocity and the projectile velocity regardless of the stress profile obtained by the PVDF gauge. A typical result for polytetrafluoroethylene (PTFE) specimen is shown with the impact velocity of PTFE flyer of 295 m/s. The obtained Hugoniot point coincides very well with the published data. Precision of the method was examined in detail, and estimated to be better than 2%.
Vibration isolation support system for a truncated icosahedral gravitational wave antenna
Authors: Velloso W. F. , Melo J. L. , Aguiar O. D.
Published: July 2002

We designed a mechanical isolation system for an icosahedral resonant gravitational wave detector we plan to construct in Brazil. We have used the NASTRAN finite element software to perform the numerical analysis. Our results show that the designed system could allow a damping factor better than −200 dB in the spectral range of interest, which is adequate to the sensibility level we want for the antenna.
High-energy neutral particle measurement system in the large helical device
Authors: Ozaki Tetsuo , Zanza Vincenzo , Bracco Giovanni , Moleti Arturo , Tilia Benedetto , Sibio Alessandro , Sudo Shigeru , Nakanishi Hideya , Kojima Mamoru , Shoji Mamoru ,   G1/G2 Experimental Group
Published: July 2002

The development of a high-energy neutral particle measurement system for ion temperature measurements and high-energy particle confinement analysis during neutral beam injection and ion cyclotron resonance frequency heating experiments in the large helical device (LHD) is described here. We have been improving the time-of-flight neutral particle analyzer for the LHD which had been developed in ENEA Frascati. The control and data acquisition systems were designed to be suitable for long discharges in the LHD. The horizontal and vertical movable stage is prepared to investigate pitch-angle distribution and loss cone. We have resolved many difficulties at installation, for example, the strong leakage magnetic field from the LHD and the limitations of magnetized materials near the LHD, the quench of the superconducting magnetic field, the narrow viewing port, and the fully remote control system. The preliminary results in plasma experiments are also described here.
Spontaneous coupling to planar and index-confined quasimodes of Fabry–Pérot microcavities
Authors: Huffaker D. L. , Deppe D. G.
Published: July 2002

Data are presented characterizing the spontaneous coupling to both planar and index-confined quasimodes of Fabry–Pérot microcavities. Index confinement is achieved using selective conversion of AlAs–AlxOy through ‘‘wet’’ oxidation to fabricate lateral cavity sizes as small as 2 μm diam. Spectral tuning and angular radiation patterns show the increased spontaneous coupling that results from three-dimensional confinement.
Green upconversion fluorescence in Er3+-doped Ta2O5 heated gel
Authors: Kojima Kazuo , Yoshida Shiro , Shiraishi Haruki , Maegawa Akira
Published: July 2002

Er3+-doped Ta2O5 bulk gels were prepared via the sol-gel process and characterized. In this heated gel, green upconversion fluorescence was observed around 545 nm under 805 nm excitation (4I15/2→4I9/2). Electron spin resonance (ESR) spectra for Er3+ in the gels were also determined at 4.2 K. Remarkable features observed in upconversion fluorescence and in ESR were discussed on the basis of dispersion of Er3+ ions in the Ta2O5 gel.
Growth of GaN on sapphire (0001) using a supersonic jet of plasma-generated atomic nitrogen
Authors: Sellidj A. , Ferguson B. A. , Mattord T. J. , Streetman B. G. , Mullins C. B.
Published: July 2002

We describe a new GaN film growth method employing a supersonic jet of nitrogen atoms and a gallium effusion cell. The nitrogen atoms were generated by exciting a 1% nitrogen in helium mixture with a radio frequency discharge. X-ray diffraction and in situ reflection high-energy electron diffraction indicate that GaN films grown on sapphire (0001) were single crystalline and epitaxial with a rough surface morphology. A GaN growth rate of approximately 0.65 μm/h was measured, independent of substrate temperature over the range of 600–750 °C. However, the crystalline quality of the film increases markedly with increasing wafer temperature.
Hydrogenation of undoped and nitrogen-doped CdTe grown by molecular beam epitaxy
Authors: Yu Zhonghai , Buczkowski S. L. , Petcu M. C. , Giles N. C. , Myers T. H.
Published: July 2002

The effect of atomic hydrogen during the growth of undoped and nitrogen-doped CdTe by photon-assisted molecular beam epitaxy was investigated. Hydrogen incorporation is enhanced by the presence of nitrogen. Infrared absorption measurements strongly suggest the formation of N–H complexes. Hall measurements indicate that the complexes are donorlike in nature. Hydrogenation radically changes the low temperature photoluminescence in both undoped and nitrogen-doped layers. Exciton-related luminescence is quenched at low temperature. Nitrogen-related donor-acceptor pair luminescence is also absent from N-doped hydrogenated layers, consistent with complex formation. Copper donor–acceptor pair luminescence appears to be enhanced by hydrogen.
Geometrical anisotropy dependence of thermal diffusivity in lyotropic nematics: Mode mismatched thermal lens measurements
Authors: Bento A. C. , Palangana A. J. , Evangelista L. R. , Baesso M. L. , Pereira J. R. D. , da Silva E. C. , Mansanares A. M.
Published: July 2002

In this work the quantitative theoretical treatment for two beam mode mismatched thermal lens spectrometry is applied to investigate the thermal diffusivity anisotropy of two lyotropic mixtures: (1) potassium laurate, decanol and water and (2) potassium laurate, potassium chloride and water in the nematic calamitic phase. The ratio between the thermal diffusivities parallel and perpendicular to the director has been shown to be smaller than those reported for thermotropic liquid crystal. This observation is explained by using a simple model where this ratio is correlated to the micellar shape anisotropy.
Electron paramagnetic resonance of erbium doped silicon
Authors: Carey J. D. , Donegan J. F. , Barklie R. C. , Priolo F. , Franzò G. , Coffa S.
Published: July 2002

Electron paramagnetic resonance measurements have been made on samples of float zone silicon, implanted with 1015 Er/cm2. One sample was coimplanted with oxygen to give an impurity concentration of 1020 O/cm3 and 1019 Er/cm3. In this coimplanted sample, sharp lines are observed which are identified as arising from a single spin 1/2 Er3+ center having a g tensor exhibiting monoclinic C1h symmetry. The principal g values and tilt angle are g1=0.80, g2=5.45, g3=12.60, and τ=2.6°. In the absence of O, the sharp lines are not observed. No Er3+ cubic centers were detected in either sample. Possible structures for the center are discussed.
High-resolution axial and lateral position sensing using two-photon excitation of fluorophores by a continuous-wave Nd:YAG laser
Authors: Florin Ernst-Ludwig , Hörber J. K. Heinrich , Stelzer Ernst H. K.
Published: July 2002

The change in position of fluorescent beads captured inside the focal volume of optical tweezers is monitored using fluorescence emission induced by two-photon absorption of a continuous-wave Nd:YAG laser (λ=1064 nm). The displacement of a bead due to interactions with its environment leads to a fluorescence intensity variation that is used to design a novel spatial sensor. We determine changes in the axial position of a CY3-labeled latex bead with a diameter of 1.03 μm to a precision better than 10 nm. At an intensity of 600 mW/ μm2 the two-photon bleaching rate is lower than 50% per 2000 s.
Application of a picosecond soft x-ray source to time-resolved plasma dynamics
Authors: Workman J. , Nantel M. , Maksimchuk A. , Umstadter D.
Published: July 2002

We demonstrate the application of an ultrashort x-ray source as an external probe to measure plasma dynamics. The plasma is generated by a 100-fs Ti:sapphire laser focused onto thin metallic films. Time-resolved spectroscopy of the gold x-ray probe transmission through a perturbed 1000 Å aluminum film reveals redshifts of the L-shell photoabsorption edge. We show that the dynamic behavior of this shift is consistent with the relaxation of the aluminum following the compression generated by a shock wave traveling through the film. An analytic plasma model, with comparison to a numerical hydrodynamics model, indicates compression up to 1.4 times solid density.
Phase separation in InGaN thick films and formation of InGaN/GaN double heterostructures in the entire alloy composition
Authors: Singh R. , Doppalapudi D. , Moustakas T. D. , Romano L. T.
Published: July 2002

We report the growth of InGaN thick films and InGaN/GaN double heterostructures by molecular beam epitaxy at the substrate temperatures 700–800 °C, which is optimal for the growth of GaN. X-ray diffraction and optical absorption studies show phase separation of InN for InxGal−xN thick films with x>0.3. On the other hand, InxGal−xN/GaN double heterostructures show no evidence of phase separation within the detection capabilities of our methods. These observations were accounted for using Stringfellow’s model on phase separation, which gives a critical temperature for miscibility of the GaN–InN system equal to 2457 K.
Advances in picosecond scanning tunneling microscopy via junction mixing
Authors: Steeves G. M. , Elezzabi A. Y. , Freeman M. R.
Published: July 2002

Ten picosecond resolution in stroboscopic scanning tunneling microscopy of repetitive phenomena has been demonstrated using tunnel junction mixing. This represents an order-of-magnitude improvement over earlier work. Through relative timing of the tunneling current signal as a function of tip position along a transmission line, additional confirmation of time-resolved signal generation at the tunnel junction has also been established.
Interface structure of fcc Mn on GaAs(001)
Authors: Jin X. , Chen Yong , Lin X. W. , Dong D. S. , Chen Yan , Xu M. , Zhu W. R. , Wang Xun , Shen X. L. , Li L.
Published: July 2002

Temperature dependent growth of Mn on GaAs(001) and their interface structure have been studied. At 400 K, fcc Mn grows epitaxially on GaAs and a “Mn2As-type” Mn–Ga–As mixed layer sandwiched between the fcc Mn and GaAs(001) is observed. It is this transition layer that plays a critical role in the stabilization of the metastable fcc-Mn-phase on GaAs(001).
Quantum dot vertical-cavity surface-emitting laser with a dielectric aperture
Authors: Huffaker D. L. , Baklenov O. , Graham L. A. , Streetman B. G. , Deppe D. G.
Published: July 2002

Data are presented on an oxide-confined vertical-cavity surface-emitting laser that uses a quantum dot active region. The laser is grown by molecular beam epitaxy, with the quantum dot active region formed from a five monolayer deposition of In0.50Ga0.35Al0.15As. Lasing occurs at wavelengths corresponding to quantum dot transitions, with a room temperature pulsed threshold as low as 560 μA for a 7 μm diameter oxide aperture.