bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the human HCN1 channel and its inhibition by capsazepine
Authors: Gill Catherine H , Randall Andrew , Bates Stewart A , Hill Kerstin , Owen Davina , Larkman Phil M , Cairns William , Yusaf Shahnaz P , Murdock Paul R , Strijbos Paul J L M , Powell Andrew J , Benham Christopher D , Davies Ceri H
Published: October 2004

The human hyperpolarization‐activated cyclic nucleotide‐gated 1 (hHCN1) subunit was heterologously expressed in mammalian cell lines (CV‐1 and CHO) and its properties investigated using whole‐cell patch‐clamp recordings. Activation of this recombinant channel, by membrane hyperpolarization, generated a slowly activating, noninactivating inward current.

The pharmacological properties of hHCN1‐mediated currents resembled those of native hyperpolarization‐activated currents (Ih), that is, blockade by Cs+ (99% at 5 mM), ZD 7288 (98% at 100 μM) and zatebradine (92% at 10 μM). Inhibition of the hHCN1‐mediated current by ZD 7288 was apparently independent of prior channel activation (i.e. non‐use‐dependent), whereas that induced by zatebradine was use‐dependent.

The VR1 receptor antagonist capsazepine inhibited hHCN1‐mediated currents in a concentration‐dependent (IC50=8 μM), reversible and apparently non‐use‐dependent manner.

This inhibitory effect of capsazepine was voltage‐independent and associated with a leftward shift in the hHCN1 activation curve as well as a dramatic slowing of the kinetics of current activation.

Elevation of intracellular cAMP or extracellular K+ significantly enhanced aspects of hHCN1 currents. However, these manipulations did not significantly affect the capsazepine‐induced inhibition of hHCN1.

The development of structural analogues of capsazepine may yield compounds that could selectively inhibit HCN channels and prove useful for the treatment of neurological disorders where a role for HCN channels has been described.

British Journal of Pharmacology (2004) 143, 411–421. doi:10.1038/sj.bjp.0705945
New insights into the human 5‐HT4 receptor binding site: exploration of a hydrophobic pocket
Authors: Rivail Lucie , Giner Mireille , Gastineau Monique , Berthouze Magali , Soulier Jean‐Louis , Fischmeister Rodolphe , Lezoualc'h Frank , Maigret Bernard , Sicsic Sames , Berque‐Bestel Isabelle
Published: October 2004

A body of evidences suggests that a hydrophobic pocket of the human 5‐HT4 receptor contributes to the high affinity of some bulky 5‐HT4 ligands. A thorough study of this pocket was performed using mutagenesis and molecular modeling.

Ligand binding or competition studies with selected bulky ligands (RS39604, RS100235, [3H]GR113808 and ML11411) and small ligands (5‐HT and ML10375) were carried out on wild‐type and mutant receptors (W7.40A/F, Y7.43F, R3.28L) transiently transfected in COS‐7 cells. The functional activity of the mutated receptors was evaluated by measuring the ability of 5‐HT to stimulate adenylyl cyclase.

For W7.40F mutation, no changes in the affinity of studied ligands and in the functional activity of the mutant receptor were observed, in contrary to W7.40A mutation, which abolished both binding of ligands and 5‐HT‐induced cAMP production.

Mutation R3.28L revealed a totally silent receptor with a basal level of cAMP production similar to the mock control despite its ability to product cAMP in the presence of 5‐HT. Moreover, a one order loss of affinity of RS39604 and a 45‐fold increase of ML11411 affinity were observed.

Mutation Y7.43F modified the affinity of GR113808, which displays a 13‐fold lower affinity for the mutant than for the wild‐type receptor.

In conclusion, in the hydrophobic pocket, two polar amino acids are able to interact through hydrogen bonds with bulky ligands depending on their chemical properties. Moreover, these experimental data may validate the proposed new three‐dimensional model of the human 5‐HT4 receptor.

British Journal of Pharmacology (2004) 143, 361–370. doi:10.1038/sj.bjp.0705950
Characterization of BaTi1−xZrxO3 thin films obtained by a soft chemical spin-coating technique
Authors: Pontes F. M. , Escote M. T. , Escudeiro C. C. , Leite E. R. , Longo E. , Chiquito A. J. , Pizani P. S. , Varela J. A.
Published: October 2004

Single-phase perovskite structure BaZrxTi1−xO3 (BZT) (0.05⩽x⩽0.25) thin films were deposited on Pt–Ti–SiO2–Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1−xO3 thin films, corroborate to the structural change caused by the zirconium doping. On the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181–138, and low dielectric loss tanδ<0.03 at the frequency of 1kHz. The leakage current density of the BZT thin films was studied at elevated temperatures and the data obey the Schottky emission model. Through this analysis the Schottky barrier height values 0.68, 1.39, and 1.24eV were estimated to the BZT5, BZT15, and BZT25 thin films, respectively.
Design of a portable near infrared system for topographic imaging of the brain in babies
Authors: Vaithianathan Tharshan , Tullis Iain D. C. , Everdell Nicholas , Leung Terence , Gibson Adam , Meek Judith , Delpy David T.
Published: October 2004

A portable topographic near-infrared spectroscopic (NIRS) imaging system has been developed to provide real-time temporal and spatial information about the cortical response to stimulation in unrestrained infants. The optical sensing array is lightweight, flexible, and easy to apply to infants ranging from premature babies in intensive care to children in a normal environment. The sensor pad consists of a flexible double-sided circuit board onto which are mounted multiple sources (light-emitting diodes) and multiple detectors (p-i-n photodiodes), all electrically encapsulated in silicone rubber. The control electronics are housed in a box with a medical grade isolated power supply and linked to a PC fitted with a data acquisition card, the signal acquisition and analysis being performed using LABVIEW™. The signal output is displayed as an image of oxy- and deoxyhemoglobin concentration ([HbO2], [Hb]) changes at a frame rate of 3 Hz. Experiments have been conducted on phantoms to determine the sensitivity of the system, and the results have been compared to theoretical simulations. The system has been tested in volunteers by imaging changes in forearm muscle oxygenation, following blood pressure cuff occlusion to obtain typical [Hb] and [HbO2] plots.
Monochromatic x-ray imaging experiments on the Sandia National Laboratories Z facility (invited)
Authors: Sinars D. B. , Bennett G. R. , Wenger D. F. , Cuneo M. E. , Hanson D. L. , Porter J. L. , Adams R. G. , Rambo P. K. , Rovang D. C. , Smith I. C.
Published: October 2004

The Z facility is a 20 MA, 100 ns rise time, pulsed power driver for z-pinch plasma radiation sources. The Z facility can make >200 TW, 1–2 MJ, near-blackbody radiation sources through the compression of cylindrical wire arrays. These sources are being used as drivers to study inertial-confinement fusion capsule implosions, complex radiation–hydrodynamic jet experiments, and wire-array z-pinch physics tests. To backlight plasmas in this environment we have built diagnostics based on spherically bent crystals that provide high spatial resolution (9–10 μm), a narrow spectral bandpass (<0.5 eV), and a large field of view (4 mm×20 mm). These diagnostics use the 2 TW, multi-kJ Z-Beamlet laser to produce x-ray emission sources at 1.865 or 6.151 keV for backlighting.
Bottom axial diagnostic package on Z
Authors: Nash T. J. , Sanford T. W. L. , Leeper R. J. , Chandler G. A. , Bailey J. E. , Mehlhorn T. A. , Deeney C. D. , Seaman J. F. , McGurn J. , Torres J. A. , Jobe D. O. , Mock R. C. , Gilliland T. , Nielsen D. S. , Lucas J. , Moore T.
Published: October 2004

A bottom axial diagnostic package has recently been developed and fielded on the 100 ns, 20 MA pinch-driver Z. The bottom package was developed to measure the power radiated to the bottom of Z and compare it to the power radiated to the top of Z on dynamic hohlraum pinch loads. When an up/down power asymmetry was measured, the bottom package was expanded in an effort to determine the source of the asymmetry. The bottom package contains one port directly on axis, six ports at 3.4° to the axis, and four ports at 9° to the axis. Typical diagnostics fielded on the bottom package are a time-resolved pinhole camera, time-integrated spatially resolved convex crystal spectrometers, a time-resolved crystal spectrometer, x-ray diodes, bolometers, and photoconducting detectors. We will present some typical data from these bottom diagnostics on dynamic hohlraum shots on Z and briefly discuss their relevance to the up/down power asymmetry.
Application of the singular value decomposition method for inversion of interferometer measurements in fusion plasmas
Authors: Carey C. S. , Furno I. , Weisen H. , Behn R. , Fable E. , Angioni C.
Published: October 2004

We present applications of a recently developed method, the singular value decomposition inversion (SVD-I), for inverting line integrated multichannel interferometer measurements in fusion devices. The method expands the local electron density profiles into a limited series of orthogonal basis functions formed from the singular value decomposition of Thomson scattering measurements, which are obtained at much lower frequencies than the interferometer data. Because these basis functions are formed from a local measurement of the electron densities in the same plasmas, they are well adapted to the class of density profiles to be reconstructed. Using this expansion, the inversion of the interferometer data are reduced to solving an overdetermined set of equations. SVD-I is significantly faster than regularization methods and more accurate for reconstructing hollow profiles. This method, which combines the high bandwidth of interferometer systems with the spatial accuracy of Thomson scattering, is applied to invert data from a 14-chord interferometer on the TCV tokamak.
Calibration of National Ignition Facility neutron detectors in the energy range E<14 MeV
Authors: Schmid G. J. , Koch J. A. , Moran M. J. , Phillips T. W. , Glebov V. Yu. , Sangster T. C. , Stoeckl C. , Wender S. A. , Morse E. C.
Published: October 2004

We examine various options for calibration of the National Ignition Facility neutron detectors in the energy range E<14 MeV. These options include: downscatter of D–T fusion neutrons using plastic targets; nuclear reactions at a Tandem Van de Graaf accelerator; and “white” neutrons from a pulsed spallation source. As an example of the pulsed spallation option, we present calibration data that was recently acquired with a single crystal chemical vapor deposition diamond detector at the Weapons Neutron Research Facility at Los Alamos National Laboratory.
Development of the motional Stark effect with laser-induced fluorescence diagnostic
Authors: Foley E. L. , Levinton F. M.
Published: October 2004

The motional Stark effect diagnostic (MSE) is presently a widely accepted technique for measuring the magnetic field pitch angle in high field (>1 T) plasma devices. A hydrogen neutral beam passing through a magnetic field perceives υ×B electric field, and its Balmer-α spectral emission is split and polarized by the linear Stark effect. The technique cannot be readily used at lower magnetic fields, due to loss of polarization fraction when lines of different polarization overlap due to line broadening which is on the order of the separation. This article describes the development of a technique to extend the capability of MSE to include lower fields (0.01 T and up) and the field magnitude as well as direction. The technique employs laser-induced fluorescence on a diagnostic neutral beam. The narrow-band laser and low energy spread neutral beam allow the observed linewidths to be significantly narrower than these observed from previously employed collisionally induced fluorescence systems.
Multipulse supersonic helium beam diagnostic in the TJ-II stellarator
Authors: Hidalgo A. , Tafalla D. , Brañas B. , Tabarés F. L.
Published: October 2004

The well known He beam diagnostic, able to provide profiles of the electronic plasma edge parameters, has undergone a significant improvement by the application of supersonic expansion techniques in the last years. The use of pulsed fast piezoelectric valves was initiated in the TJ-IU and implemented in the TJ-II stellarators. In its former configuration the repetition rate of the beam was ultimately limited in the expansion chamber by the pressure buildup. In the actual upgraded version, however, a repetition rate up to 200 Hz can be achieved, and the recording of the electron temperature and density profiles with millisecond resolution is possible. In the present work, the technical development of the diagnostic required for optimized performance is described. In addition, the validation of the collisional–radiative model needed for the reconstruction of the edge profiles and the analysis of the complementary information given by the beam attenuation is also addressed.
Charge exchange imaging of space plasmas (invited)
Authors: Scime Earl , Zaniewski Anna
Published: October 2004

Detection of neutral atom emission from hot plasmas has evolved to the point where it is now possible to image hot plasmas in neutral atom emission. In this work, we review a variety of successful approaches to space-based neutral atom imaging and discuss the qualitative and quantitative information that can be obtained from neutral atom images, e.g., hot ion transport and ion temperatures. A challenging aspect of neutral atom imaging of the Earth’s magnetosphere is that the combination of small neutral fluxes and spacecraft motion necessitates the development of algorithms capable of summing neutral emission obtained from different vantage points over many months to obtain statistically significant images. The image summing algorithm and typical summed images are also presented in this work.
Feasibility study of fast ion diagnosis in ITER by collective Thomson scattering, millimeter waves to CO2 laser
Authors: Bindslev H. , Meo F. , Tsakadze E. L. , Korsholm S. B. , Woskov P.
Published: October 2004

Here we report on a study of the feasibility of measuring the fast ion phase space distribution in the International Thermonuclear Experimental Reactor (ITER) by collective Thomson scattering (CTS). The study covers the full range of potential probe frequencies from gyrotron based millimeter waves to the infrared of the CO2 laser. It is assessed whether the systems can meet the ITER measurement requirements and which technological developments may be required. The relative merits of the systems are compared. The study reveals that a CTS system based on a 60 GHz probe has the highest diagnostic potential, and is the only system expected to be able to meet all the ITER fast ion measurement requirements with existing or near term technology. With modest additions this system may also provide measurements of the fuel ion ratio.
Deterministic domain formation observed in ferroelectrics by electrostatic force microscopy
Authors: Shin S. , Baek J. , Hong J. W. , Khim Z. G.
Published: October 2004

The effect of crystalline defects on the formation of ferroelectric domains in triglycine sulfate (TGS) crystals has been investigated using a dynamic contact electrostatic force microscopy. This detection method, based on the Coulomb interaction between the charge on the tip and the surface charge on the sample, yields a good spatial resolution as well as a complete separation between the topography and the domain image. The crystal imperfections, degraded surface, and strain in the crystal affect strongly the static domain configuration. Comparison of the topography to the domain image reveals a deterministic behavior in the formation of the equilibrium domain configuration, which is determined by twin boundaries in the crystal. Surface imperfections appear different depending on the polarization direction. Positively polarized regions show circular islands, whereas negatively polarized region shows circular holes as well as islands of various shapes. When TGS samples were cooled below the Curie temperature from a paraelectric state, the relaxation rate of the domains from the nonequilibrium configuration to the equilibrium configuration is substantially decreased forthe sample that contains many defects, indicating a pinning effect by the crystal imperfections such as the degraded surface and stress in the crystal.
A new large-eddy simulation near-wall treatment
Authors: Iovieno M. , Passoni G. , Tordella D.
Published: October 2004

Two different types of instantaneous wall boundary conditions have been proposed for resolved large scale simulations that extend inside the viscous sublayer. These conditions transfer the physical no-slip and impermeability/permeability information, which can only be rigorously applied to the unfiltered variables, to the filtered variables. The first condition is universal, while the second one specifies the wall stress and relevant distribution and can be used to treat inverse flow problems. The filter scale close to the wall is a function which varies according to its position and thus the problem of the noncommutation of the filter and differentiation operators arises. Used together with the explicit noncommutation procedure by Iovieno and Tordella, these boundary conditions constitute a wall treatment which could improve the use of the large-eddy methodology in relation to aspects that are independent of the modeling of the subgrid scale motion. When applied in the test case of the plane periodic channel, intentionally using the most crude subgrid scale model (Smagorinsky, with no dynamic procedure or wall damping function) to prove its efficacy, the proposed near-wall treatment yielded resolved large-eddy simulations which compare well with both direct numerical simulations and with experimental data. The effects of the Reynolds number on the structure of the flow are retained. Distributions of the noncommutation error on the turbulent solution are also reported.
Shock-induced irreversible transition from α-quartz to CaCl2-like silica
Authors: Berterretche P. , de Rességuier T. , Hallouin M. , Petitet J. P.
Published: October 2004

Previous analyses of quartz samples recovered after being submitted to laser shocks of very short duration (nanosecond order) have shown the presence of CaCl2-like silica [T. de Rességuier, P. Berterretche, M. Hallouin, and J. P. Petitet, J. Appl. Phys. 94, 2123 (2003)]. To date, this transition has never been observed under shocks of longer duration (microsecond order) generated by explosives or plate impacts. While this phase is produced from stishovite under static compression at very high pressure (above 50GPa) and disappears on pressure release, it is observed after low pressure laser shocks (below 5GPa) and it is quenched to ambient conditions. The origins of these differences are still unclear. This paper presents complementary laser shock experiments involving setups to provide additional information on the influence of various shock parameters. The results suggest a direct transition from α-quartz to CaCl2-type silica following a diffusionless mechanism involving high shear strains. They also show the presence of vitreous silica characterized by an “organized” ringlike structure, and we propose that this amorphous phase is an intermediate structure between the quartz lattice and grains of the high-pressure phase.
Interpretation of neutral beam emission spectra as the beam-component density distribution
Authors: Rowan William L. , Sampsell M. B. , Granetz R. S.
Published: October 2004

Diagnostic neutral beams (DNBs) are used on tokamaks and stellarators for measurement of ion temperature, plasma current density, and other critical quantities. It is important to optimize the density in the energy components of the DNB for the diagnostic application. Measured component densities are also useful for interpretation of beam diagnostics and for design of new diagnostics. The spectrally resolved photon emission from the interaction of the neutral beam with a background neutral gas is commonly used for this measurement. The emission cross sections available for interpretation of the measurement are reviewed here. Simulations employ these cross sections with other data to infer the properties of the plasma sources from which the beams are extracted. The simulations are also reviewed. Empirical examples are drawn from beam emission spectra measured for beams installed at the Alcator C-Mod facility.
Laser wavefront analyzer for imploding plasma density and current profile measurements
Authors: Qi N. , Prasad R. R. , Campbell K. , Coleman P. , Krishnan M. , Weber B. V. , Stephanakis S. J. , Mosher D.
Published: October 2004

The laser wavefront analyzer (LWA) consists of a polarized laser beam pulse that traverses an imploding z-pinch, and a microlens array that focuses the laser beam into a large number (104) of very tiny spots. LWA image analysis determines the refractive bending angles (due to density gradients) and Faraday rotation angles (due to the magnetic field-density integral) throughout the plasma cross section. Electron density and current distributions are derived from LWA data in an imploding gas-puff z-pinch plasma.
Two-dimensional phase contrast interferometer for fluctuations study on LHD
Authors: Sanin A. L. , Tanaka K. , Vyacheslavov L. N. , Kawahata K. , Akiyama T.
Published: October 2004

C O 2 laser based phase contrast interferometer was used previously on LHD to study plasma density microfluctuations. New two-dimensional 6×8 elements array of CdHgTe photoconductors was employed for detection. In addition to commonly measured intensity, frequency spectrum, and two-point correlation two-dimensional detector array allows determining the direction of propagation of waves in plasma. From the angular distribution it is possible to obtain localized along the viewing line properties of fluctuations using strong magnetic shear in LHD. As a result, the radial profiles of density microfluctuations can be obtained with 1 μs temporal resolution determined by detector bandwidth. The described scheme was tested using ultrasonic wave in air. New imaging diagnostics has been installed on LHD and first experimental results are reported.
Hypervelocity dust beam injection for national spherical torus experiment
Authors: Wang Zhehui , Wurden G. A.
Published: October 2004

An internal magnetic field measurement technique using hypervelocity dust beam injection is described for eventual implementation on the National Spherical Torus experiment. The principle of the diagnostic has been described previously [Wang and Wurden, Rev. Sci. Instrum. 74, 1887 (2003)]. Approximately 200 kV of electrostatic potential will be used to accelerate multiple dust particles to velocities in the range of 1.0–10 km/s. A fast framing camera will be used to visualize and map two-dimensional internal magnetic field structure from the orientation of the visible light emissions generated by the plumes associated with the hypervelocity dust.
A high throughput spectrometer system for helium ash detection on JET
Authors: Hillis D. L. , Fehling D. T. , Bell R. E. , Johnson D. W. , Zastrow K.-D. , Meigs A. , Negus C. , Giroud C. , Stamp M. , Contributors JET-EFDA
Published: October 2004

Acquiring information about helium ash production and transport is fundamental for future burning plasma devices, such as International Thermonuclear Experimental Reactor, since the helium ash must be continuously removed from the plasma to prevent the dilution of the deuterium–tritium (DT) fuel. This diagnostic for future JET DT operation uses charge-exchange recombination spectroscopy (CXRS) in conjunction with the JET neutral heating beam to measure the helium density at 20 radial locations across the JET plasma via the 4686 Å He+ line and an array of heated 1 mm quartz fibers. The CXRS diagnostic utilizes a high throughput short focal length spectrometer with f/1.8 input optics, two entrance slits, a holographic transmission grating, and refractive optics. The detector is a thinned back-illuminated charge coupled device that has high quantum efficiency, a 10 MHz readout speed, and a time resolution of 5 ms.
Feasibility of a motional Stark effect system on the TCV tokamak
Authors: Siegrist M. R. , Hawkes N. , Weisen H.
Published: October 2004

This paper presents a feasibility study for a motional Stark effect (MSE) [F. M. Levinton et al., Phys. Rev. Lett. 63, 2060 (1989)] diagnostic on the TCV tokamak. A numerical simulation code has been used to identify the optimal port arrangement and geometrical layout. It predicts the expected measurement accuracy for a range of typical plasma scenarios. With the existing neutral beam injector (NBI) and a detection system based on current day technology, it should be possible to determine the safety factor with an accuracy of the order of 5%. A vertically injected beam through the plasma center would allow one to measure plasmas which are centered above the midplane, a common occurrence in connection with electron cyclotron resonance heating and electron cyclotron current drive experiments. In this case a new and ideally more powerful NBI would be required.
Design of a D-alpha beam-ion profile diagnostic
Authors: Luo Y. , Heidbrink W. W. , Burrell K. H.
Published: October 2004

Injected neutral beams ionize to create a population of beam ions. As they orbit around the tokamak and pass through the heating beams, some beam ions re-neutralize and emit D-alpha light. The intensity of this emission is weak compared to the signals from the injected neutrals, the warm (halo) neutrals, and the edge recombination neutrals but, for a favorable viewing geometry, the emission is Doppler shifted away from these bright interfering signals. Preliminary data from the DIII-D tokamak show that signals from re-neutralized beam ions have already been detected. A three-channel prototype instrument consisting of a spectrometer, mask, camera lenses, and frame-transfer charge coupled device is under development for measurements of the spatial profile of the beam ions.
Submicron resolution infrared microscopy by use of a near-field scanning optical microscope with an apertured cantilever
Authors: Masaki Tatsuhiro , Inouye Yasushi , Kawata Satoshi
Published: October 2004

We extend the spectral range of near-field infrared microscopy attaining submicron resolution by using tunable infrared radiation generated by difference frequency generation and an apertured cantilever. The custom-built cantilever has a hollow tip with a wide opening angle and offers two orders of magnitude higher optical throughput than that of other IR probes. In near-field observation of a line/space structured poly(methylmethacrylate) film at a 5.78 μm wavelength corresponding to absorption band of the C=O bonds, the microscope achieved a λ/7 spatial resolution, less than 1 μm. This shows the possibility of submicron resolution infrared microscopy in the fingerprint region.
Loss cone boundary measurement using diagnostic neutral beam and neutral particle analyzer in a compact helical system
Authors: Matsushita H. , Ida K. , Okamura S. , Isobe M. , Akiyama R. , Yoshimura Y. ,   the CHS Group
Published: October 2004

A horizontally scannable diagnostic neutral beam (DNB) has been installed on the compact helical system (CHS) in order to study the confinement of energetic ions with different pitch angles by varying the injection angle. The DNB has been designed to provide energetic ions as a test particle source with (1) no heating to background plasma and (2) small divergence angle. A charge-exchange neutral particle analyzer (NPA) to measure energetic ions injected by the DNB is also scannable and varies the observation angle on the equatorial plane in CHS. A combination of horizontally scannable DNB and NPA provides information on whether the energetic ions with different pitch angle are confined in the plasma or immediately lost. The experimental results are consistent with the prediction of single particle full orbit calculation in CHS.
Solid state neutral particle analyzer array on National Spherical Torus Experiment
Authors: Shinohara K. , Darrow D. S. , Roquemore A. L. , Medley S. S. , Cecil F. E.
Published: October 2004

A solid state neutral particle analyzer array has been installed on the National Spherical Torus Experiment (NSTX). The array consists of four chords viewing through a common vacuum flange. The tangency radii of the viewing chords are 60, 90, 100, and 120 cm. They view across the three co-injection neutral beam lines [deuterium, 80 keV (typically) with tangency radii 48.7, 59.2, and 69.4 cm] on NSTX and detect co-going energetic ions. A silicon photodiode was calibrated by using a monoenergetic deuteron beam source. Deuterons with energy above 40 keV can be detected with the present setup. The degradation of the performance was also investigated. Lead shot and epoxy are used for neutron shielding to reduce handling any hazardous heavy metal. This method also enables us to make an arbitrary shape to be fit into the complex flight tube.
Fluorescence spectroscopy as a diagnostic of the radiation environment in high energy density experiments (invited)
Authors: Hoarty D. J. , Smith C. C. , Clark E. L. , Foster J. M. , Gales S. G. , Magelssen G. , Workman J. , Wood W. M. , Caldwell S. , Chrien R. , Sandoval J. , Sedillo T. , Walsh P. , Carpenter B. , Compton S. , Perry T.
Published: October 2004

A fluorescence spectroscopy technique has been developed to measure conditions in high energy density (HED) experiments. The experimental technique and modeling of the spectra are described and results of fluorescence measurements are presented. Fluorescence spectra were measured from an aluminium microdot over a small hole in the wall of an experimental package or a hohlraum. The aluminium was photopumped from a broadband radiation source, without perturbing the temperature. To date, fluorescence spectroscopy has been used to diagnose the radiative heating of plasmas in the temperature range 20–80 eV. Fluorescence spectroscopy has several advantages over x-ray absorption and self-emission spectroscopy in the diagnosis of HED experiments and these are discussed in the article. Extension of the technique to higher temperature plasma is discussed.
Laser Faraday rotation measurement of current density fluctuations and electromagnetic torque (invited)
Authors: Ding W. X. , Brower D. L. , Deng B. H. , Craig D. , Prager S. C. , Svidzinski V.
Published: October 2004

Far-infrared laser polarimetry with time response up to ∼1 μs and spatial resolution ∼8 cm has been successfully implemented on the Madison Symmetric Torus reversed-field pinch. Internal magnetic field and current density fluctuations are nonperturbatively measured. This is accomplished by taking parallel polarimetry chords which measure the line-integrated magnetic field fluctuations via Faraday rotation. With suitable analysis we are able to obtain information on spatial profiles of magnetic field fluctuations and current density fluctuations. Coherent interaction between these fluctuations is also measured and observed to generate an electromagnetic fluctuation-induced torque 〈δJ×δB〉.
Operation of a multiple cell array detector in plasma experiments with a heavy ion beam diagnostic
Authors: Gonçalves B. , Malaquias A. , Nedzelskiy I. S. , Pereira L. , Silva C. , Varandas C. A. F. , Cabral J. A. C. , Khrebtov S. M. , Dreval N. B. , Krupnik L. I. , Hidalgo C. , Depablos J.
Published: October 2004

A multiple cell array detector (MCAD) has been developed to investigate the spatial structure of plasma turbulence in fusion plasmas. This system is expected to provide simultaneous measurements of edge and core density fluctuations with both temporal and spatial resolution, extending the range and number of the sample volumes simultaneously recorded by a heavy ion beam diagnostic (HIBD). Since the detector (usually located close to the vessel wall of a plasma device) operates in a strong plasma radiation environment, the effective shielding of the detector presents a special problem. This article describes and compares the MCAD operation conditions on ISTTOK tokamak and TJ-II stellarator. Experimental results of the detector performance are presented together with the first measurements of neσeff in the TJ-II plasmas.
Preliminary calculations of expected signal levels of a thin Faraday foil lost alpha particle diagnostic for International Thermonuclear Experimental Reactor
Authors: Cecil F. E. , Darrow D. S. , Budny R. V.
Published: October 2004

Thin Faraday collectors are being considered as a diagnostic of lost alpha particles on International Thermonuclear Experimental Reactor (ITER). In an effort to evaluate the viability of this diagnostic, we are undertaking a series of calculations of the signal levels (A/cm2) for such devices. Preliminary results assuming a model high yield ITER plasma have been obtained for locations near the outer wall assuming a toroidally symmetric vacuum vessel. We find signal levels to be a strong function of foil location and orientation. Specifically the signal level will be optimized at a vertical location 0.5 m above the machine midplane and with the normal to the foil directed in the lower, radially outward, toroidally counterclockwise octant. A foil thus oriented at a radial distance of 15 cm from the vessel wall at a height of 0.583 m above the machine midplane will have an efficiency of 3.5×10−8/cm2 for alpha particles which undergo classic loss during the first ten revolutions around the torus during this model plasma. For the assumed D–T fusion power of this model plasma of 410 MW, this calculated efficiency will correspond to a measured current in the Faraday foil of 1.7 μA/cm2. Future, more realistic calculations must incorporate the effects of an asymmetrical vessel and of toroidal field ripple.
Composition change of stainless steel during microjoining with short laser pulse
Authors: He X. , DebRoy T. , Fuerschbach P. W.
Published: October 2004

Weld metal composition change in 200μm deep, 304 stainless steel microjoints fabricated using millisecond long Nd-YAG laser pulses was investigated experimentally and theoretically. The variables studied were pulse duration and power density. After welding, concentrations of iron, manganese, chromium, and nickel were determined at various locations of the microjoint using the electron microprobe analysis. The temperature field was simulated as a function of time from a well-tested three-dimensional transient heat transfer and fluid flow model. Using the computed temperature fields, vaporization rates of various alloying elements resulting from both concentration and pressure driven transport of vapors and the resultant composition change of the alloy were calculated. The calculations showed that the vaporization took place mainly from a small region near the center of the beam-workpiece interaction zone, where the temperatures were very high. Furthermore, the alloying element vaporization was most pronounced toward the end of the pulse. After the laser spot welding, the concentrations of manganese and chromium in the weld pool decreased, whereas the concentrations of iron and nickel increased. The composition changes predicted by the model were in fair agreement with the corresponding experimental results for various conditions of microjoining with short duration pulses.
Surface-roughness correlations in homoepitaxial growth of GaN(0001) films by NH3 supersonic jet epitaxy
Authors: Smith Nicholas A. , Lamb H. Henry , McGinnis Arthur J. , Davis Robert F.
Published: October 2004

Homoepitaxial GaN films were grown on GaN(0001)∕6H-SiC substrates by NH3 supersonic jet epitaxy at 750°C using a constant Ga flux of 2.9×1014cm−2s−1 and varying the NH3 flux and average kinetic energy. Atomic force microscopy (AFM), scanning electron microscopy, and in situ reflection high-energy electron diffraction evidence an abrupt transition from quasi-two-dimensional basal-plane growth to three-dimensional faceted growth at approximately 1∕2 of the maximum Ga-limited growth rate, irrespective of NH3 kinetic energy. Topographical scaling analysis of the AFM images reveals that the smooth and rough GaN(0001) films have static scaling exponents (α) of 0.88±0.05 and 1.10±0.06, respectively. The dynamic scaling exponent (β) for rough films is approximately 0.25. A comparison of these scaling exponents with predictions based on continuum growth models indicates that competition between surface diffusion and stochastic roughening governs the evolution of surface morphology during GaN growth.
Perpendicular-current giant magnetoresistance of M∕Cu∕M (001) junctions (M=Fe, Co, or Ni): An ab initio study
Authors: Vlaic P. , Alouani M. , Dreyssé H. , Bengone O. , Turek I.
Published: October 2004

The electronic structure and magnetic properties of semi-infinite Cu(001)∕M∕Cu∕M∕semi-infinite Cu (001) multilayer systems with M=Fe, Co, or Ni have been studied by means of a first-principle Green’s function technique based on the tight-binding linear muffin-tin orbital method. The results show that at the M∕Cu (M=Fe or Co) interfaces there is a net charge transfer from iron and cobalt atoms to the neighboring paramagnetic copper atoms and an enhancement of the iron magnetic moment while at the Ni∕Cu interface, the nickel magnetic moment is reduced compared with its bulk value. This behavior is explained in terms of the relative positions of the Fermi levels of the magnetic material and copper. The conductance is determined in the ballistic limit, in the current-perpendicular-to-the-plane geometry by means of transmission matrix formulation of Kubo-Landauer formalism. It is shown that the oscillations of the giant magnetoresistance ratio are mainly the result of the oscillations of the minority-spin conductance.
Analysis of excess scattering in optical fibers
Authors: Mazumder Prantik , Logunov Stephan L. , Raghavan Srikanth
Published: October 2004

We have systematically analyzed the excess scattering in a relatively large index optical fiber operating in the single mode regime. A mathematical model based on the theory of scattering of plane waves from a randomly perturbed core-clad interface is presented that predicts excess scattering confined within a small angle in the forward direction. An experimental system is developed that can measure the angular distribution of the scattering over ∼0°–180°. Excellent agreement between computed and measured scattering distribution is observed over multiple wavelengths and wide angular range. The spectral and angular distribution of the excess scattering and its response to the perturbation parameters are analyzed.
Spurious oscillations affecting FIR polarimetry measurements
Authors: Elbèze D. , Gil C. , Giannella R. , De Pasqual L. ,   JET-EFDA Contributors
Published: October 2004

Polarimetry measurements of Faraday rotation on Tore Supra are systematically affected by spurious oscillations that may seriously hinder the reconstruction of plasma current profiles. The same behavior has also been regularly observed on other experiments, such as JET and as RFX. Causes of this phenomenon are interferences between the probing beam and stray radiations having the same frequency. It perturbs the intensity of the signals from the detectors installed on the two orthogonal polarization channels. Experimental tests confirm the dependence of the oscillation amplitudes on the Faraday angle as predicted by the analytical and numerical description of the phenomenon. Special care must be taken to eliminate stray beams: When the stray beam polarization is parallel to the incident one, a relative ratio of the electric field amplitudes <1% has been found to be acceptable (error <0.06°) but a much lower ratio must be achieved when polarization is perpendicular. Such oscillations can be also present on polarimeters using beams with modulating polarization. For existing and future polarimeters, special care should be taken to make sure that all the possible sources of stray beams are sufficiently minimized.
Improved common-path fast-scanning heterodyne interferometer system as potential dense-plasma diagnostics
Authors: Nam Y. U. , Cheon M. S. , Ha J. H. , Hwang Y. S.
Published: October 2004

An improved common-path fast-scanning heterodyne interferometer system has been developed. The mechanical vibration is one of the most critical error sources in typical interferometry system. These errors can be mostly eliminated in a common-path interferometry using a full common-mode rejection scheme. Taking advantage of it, the common-path interferometry is suitable for the measurements in noisy environments and can be applied even to the scanning interferometry. A prototype common-path interferometer system with He–Ne laser has been constructed with the capability of fast scanning by adding a rotating polygon mirror. A test of this system has been completed successfully by measuring the thickness profile of the scratched glass. In this study, the interferometer system is proposed and discussed as a potential density profile diagnostics for dense plasmas. By using a CO2 laser instead of a He–Ne laser, it may also be applied to get the time evolution of steep density profiles of plasma transport barriers in tokamak plasmas.
Phase error correction method for a vibration compensated interferometer
Authors: Van Zeeland M. A. , Carlstrom T. N.
Published: October 2004

In order to compensate for vibrations while simultaneously measuring plasma line-averaged density, the existing real-time interferometer on DIII-D uses both a HeNe and CO2 laser operating at 10.59 and 0.632 μm, respectively. The line density resolution is 1018 m−2 which is predominantly determined by the measurement electronics. In particular, errors resulting from detection of the CO2 phase shift and finite bit size in the processing electronics are the major limiting factors. This article describes a method for postshot error correction generally applicable to two-color interferometers that utilize analog quadrature phase detection. The error correction scheme exploits the facts that error introduced by the phase comparator is periodic and that measurements can be made while the density is zero and only the errors are recorded. Application of this method will reduce unphysical density oscillations which are purely a result of vibration induced phase shifts. Application to DIII-D data shows a 25% reduction in noise amplitude on line density measurements.
Computer simulation of photoinduced mass transport on azobenzene polymer films by particle method
Authors: Barada Daisuke , Itoh Masahide , Yatagai Toyohiko
Published: October 2004

The formation and erasure of photoinduced surface relief gratings (SRGs) on azobenzene-containing polymers are simulated using a calculation model based on the moving-particle semi-implicit method. For the convection calculation, an anisotropic diffusion model is proposed. The gradient force of the optical electric field and the influence of surface tension are considered as driving forces for photoinduced mass transport. The viscosity of polymer films changes with the light intensity in our model. Particle motions in SRG formation and erasure are calculated and the SRG pitch and polarization dependences of the SRG growing and erasing rates are investigated. These theoretical results coincide qualitatively with our experimental results.
Observations of laser cooling by resonant energy transfer in CO2-N2 mixtures
Authors: Liakhou G. , Paoloni S. , Bertolotti M.
Published: October 2004

The effects produced by absorption of an intensity modulated CO2 laser in CO2-N2 mixture are investigated here by means of the photothermal deflection technique. The deflection signal arises from CO2 molecule deactivation and energy transfer from CO2 to N2 molecules, which are responsible for heating and cooling the mixture, respectively. The dominant mechanism is determined by the pressure of the gas mixture, which, in turn, affects the CO2 molecule lifetime. A theoretical model based on rate equations for the CO2-N2 system is presented, in which the deflection signal is given as a function of the excited molecule populations. The theoretical predictions are shown to be in reasonable agreement with the experimental results.
Ferroelectric domain wall relaxation in Ba0.25Sr0.75TiO3 films displaying Curie-Weiss behavior
Authors: Boikov Yu. A. , Khamchane K. , Claeson T.
Published: October 2004

Ferroelectric films may be used in integrated circuits for high frequency and memory applications. Losses and interfaces between films and electrodes are problematic. This work concerns the temperature and electric field response of the complex dielectric permittivity and the relaxation of domain walls in a ferroelectric layer that is of sufficient quality to show a Curie-Weiss behavior. Laser ablation was used to deposit 1200 nm thick Ba0.25Sr0.75TiO3 layers between metallic oxide, (100 nm) SrRuO3 and (120 nm) La0.67Ca0.33MnO3, films in epitaxial heterostructures. The electric field response (E⩽80kV∕cm) of the real ϵ′ and imaginary ϵ″ parts of the complex permittivity of the intermediate Ba0.25Sr0.75TiO3 layer in these parallel plane film capacitors was studied at temperatures above and below the phase transition point TCurie. The latter was determined from the temperature dependence of the inverse dielectric permittivity and its value, TCurie=145K, agrees well with that of bulk single crystal. ϵ′ of the Ba0.25Sr0.75TiO3 layer could be suppressed about 80% by a field E=80kV∕cm at temperatures close to TCurieϵ′(T,E) and ϵ″(T,E) curves were used to gain insight into the relaxation dynamics of ferroelectric domain walls (DW) in the Ba0.25Sr0.75TiO3 layer. Their influence on ϵ′ was noticed up to T=230K, well above TCurie. The most probable relaxation time τ of the DW in Ba0.25Sr0.75TiO3 follows a relation τ=τ0exp[(ϕ−βE)∕kT], where τ0=1.2×10−10sϕ=75–105meV, and β=4.7×10−24Jm1∕2V−1∕2.