bluuebunny/crossref_metadata_2025 huggingface dataset:
CH4 sources estimated from atmospheric observations of CH4 and its 13C/12C isotopic ratios: 2. Inverse modeling of CH4 fluxes from geographical regions
Authors: Mikaloff Fletcher Sara E. , Tans Pieter P. , Bruhwiler Lori M. , Miller John B. , Heimann Martin
Published: October 2004

We present a time‐dependent inverse modeling approach to estimate the magnitude of CH4 emissions and the average isotopic signature of the combined source processes from geographical regions based on the observed spatiotemporal distribution of CH4 and 13C/12C isotopic ratios in CH4. The inverse estimates of the isotopic signature of the sources are used to partition the regional source estimates into three groups of source processes based on their isotopic signatures. Compared with bottom‐up estimates, the inverse estimates call for larger CH4 fluxes in the tropics (266 ± 25 Tg CH4/yr) and southern extratropics (98 ± 15 Tg CH4/yr) and reduced fluxes in the northern extratropics (252 ± 18 Tg CH4/yr). The observations of 13C/12C isotopic ratios in CH4 indicate that the large a posteriori CH4 source in the tropics and Southern Hemisphere is attributable to a combination both bacterial sources and biomass burning and support relatively low estimates of fossil CH4 emissions.
Seasonal and long‐term dynamics of the upper ocean carbon cycle at Station ALOHA near Hawaii
Authors: Keeling Charles D. , Brix Holger , Gruber Nicolas
Published: October 2004

Long‐term trends and average seasonal variability in the upper ocean carbon cycle are investigated at Station ALOHA, the site of the U.S. JGOFS Hawaii Ocean Time series program (HOT), on the basis of a 14‐year time series (1988–2002) of dissolved inorganic carbon (DIC), alkalinity, and 13C/12C ratio of DIC data. Salinity‐normalized DIC (sDIC) and computed oceanic pCO2 show distinct upward trends of 1.2 ± 0.1 μmol kg−1 yr−1 and 2.5 ± 0.1 μatm yr−1, respectively, while the 13C/12C isotopic ratio of DIC (expressed as δ13Coc) decreases at a mean rate of −0.027 ± 0.001‰ yr−1. More than half of the rates of change in sDIC and oceanic pCO2, and most of the change in 13C/12C, are attributed to the uptake of isotopically light anthropogenic CO2 from the atmosphere. The residual trends appear to be caused mainly by a regional change in the net freshwater budget, perhaps associated with a regime change of the North Pacific climate system near 1997. Computed oceanic pCO2 is below atmospheric pCO2 for nearly the entire year, leading to an annual mean surface ocean pCO2 undersaturation of about 18 μatm, and to an annual uptake of CO2 from the atmosphere, which we compute to be 1.0 ± 0.1 mol m−2 yr−1. We estimate that about 30% of this flux relates to the uptake of anthropogenic CO2, and the remainder to biologically mediated export of organic carbon. Using a modified version of the diagnostic model of Gruber et al. [1998], constrained by δ13Coc, we infer net community production of organic carbon (NCP) to be the dominant process generating the observed seasonal variability in sDIC. The annual integral of NCP, 2.3 ± 0.8 mol m−2 yr−1, is comparable to previous estimates of biological production in the subtropical North Pacific. Annually integrated fluxes of air‐sea gas exchange and NCP at Station ALOHA are each about two thirds of those computed for the upper ocean near Bermuda using similar methods of estimation [Gruber et al., 1998, 2002]. However, the seasonal amplitudes of sDIC and δ13Coc near Hawaii are only half as large as near Bermuda, because air‐sea gas exchange and NCP tend to oppose each other near Hawaii, but reinforce each other near Bermuda.
Relative concentrations of molecular and metallic ions in midlatitude intermediate and sporadic‐E layers
Authors: Roddy P. A. , Earle G. D. , Swenson C. M. , Carlson C. G. , Bullett T. W.
Published: October 2004

A NASA sounding rocket launched from Wallops Island, VA (37.84 N, 75.48 W) on 1 July 2003 at 2:50 EST made the first in situ measurement of the relative concentrations of Fe+, Mg+, O2+, and NO+ within a nighttime intermediate layer below 140 km altitude. Ion composition measurements were made from 80–220 km altitude and included observations of three separate regions having high concentrations of metallic ions: the intermediate layer at 118 km, a sporadic‐E layer at 105 km, and a third layer above 160 km altitude. These observations demonstrate that metallic ions may be a significant source of ionization in the nighttime E and F region ionosphere at midlatitudes.
Cluster survey of cusp reconnection and its IMF dependence
Authors: Twitty C. , Phan T. D. , Paschmann G. , Lavraud B. , Rème H. , Dunlop M.
Published: October 2004

We have surveyed the occurrence of tailward‐of‐the‐cusp reconnection detected by Cluster as a function of the interplanetary magnetic field (IMF) clock angle. The survey covers 3 years (2001–2003) of cusp and magnetopause (MP) crossings and is restricted to periods of relatively stable IMF. Our survey indicates that the reconnection associated plasma flows occur almost exclusively when the IMF has a northward component (or the clock angle is within ∼90° of the GSM +z direction). This finding at first seems inconsistent with the component merging model which should allow reconnection to occur for larger than 90° clock angle (or less than 90° in magnetic shear angle). However, it is possible that this is a geophysical effect. When the IMF has a southward component, reconnection equatorward of the cusp could prevent tailward‐of‐the‐cusp reconnection by (1) creating low‐shear condition behind the cusp, and (2) preventing the formation of a plasma depletion layer adjacent to dayside MP, resulting in super‐Alfvenic magnetosheath flows at high latitude. No reconnection flows can be detected sunward of the X‐line in this regime. Finally, the occurrence rate of tailward‐of‐the‐cusp reconnection flows is ∼90% when the IMF has a northward component, indicating that simultaneous reconnection in the northern and southern cusps is common during northward IMF.
The impact of Greenland's deglaciation on the Arctic circulation
Authors: Dethloff K. , Dorn W. , Rinke A. , Fraedrich K. , Junge M. , Roeckner E. , Gayler V. , Cubasch U. , Christensen J. H.
Published: October 2004

The influence of Greenland's deglaciation on the atmospheric winter and summer circulation of the Arctic have been quantified with the high‐resolution regional atmospheric model HIRHAM4. Greenland's deglaciation exerts a pronounced influence on the atmospheric winter circulation of the Arctic. The land areas over Siberia and the Canadian archipelago are warmed by up to 5°C. Parts of the Atlantic and the Arctic Ocean are cooled by up to 3°C. A north‐eastward shift of the storm tracks occurs over the North Atlantic as well as an increase of synoptic activity over Alaska. The pronounced P‐E changes connected with shifts in the synoptic storm tracks during winter would have important consequences for the atmospheric freshwater input into the Arctic Ocean and the Nordic sea with the potential to cause variability in the Arctic Ocean dynamics on centennial to millennial time scales. The significant differences between simulations with and without Greenland result in a decrease of the geopotential height and a dominant barotropic response of the Arctic atmosphere. These changes correspond to an enhanced winter polar vortex and stratospheric conditions more favorable for large Arctic ozone losses.
Continuum percolation theory and Archie's law
Authors: Hunt A. G.
Published: October 2004

Results for the unsaturated hydraulic conductivity, K, are adapted to generate the electrical conductivity, σ, as a function of moisture content, θ. The result for σ, evaluated θ = ϕ, (ϕ the porosity), yields σ ∝ ϕm, known as Archie's Law. This result is based on the fact that σ must vanish as the critical moisture content for percolation, θt, is approached, and on the apparent proportionality of θt to ϕ, at least in coarser porous media (with insignificant clay content). In three dimensions the power is expected to be 1.88, but in two dimensions, approximately 1.35. The former result is compatible with data summarized in Thompson et al., giving m = 1.86 ± 0.19, while the latter appears compatible with two‐dimensional simulations by Kuentz et al., who found m = 1.28 ± 0.07. The same analysis demonstrates that K cannot be written as a power of the porosity.
A comparative analysis of low‐latitude Pi2 pulsations observed by Ørsted and ground stations
Authors: Han De‐Sheng , Iyemori Toshihiko , Nosé Masahito , McCreadie Heather , Gao Yufen , Yang Fuxi , Yamashita Satoru , Stauning Peter
Published: October 2004

Ørsted is a low‐altitude polar orbiting satellite, which is advantageous for investigating the spatial structure of low‐frequency events like Pi2 pulsations. Using 1‐s vector magnetic field data from April 1999 to May 2002 obtained from Ørsted and Kakioka magnetic observatories, we found that the field aligned component (B∥) of Pi2 pulsations at the satellite height is highly correlated with the H component on the ground, but the other two components, i.e., eastward component (BE) and radial component (BR), do not show a clear correlation with the ground observations. The observed results for nightside events provide evidence that nightside Pi2s at low latitude are generated from cavity resonance. Two cases observed by Ørsted when it was located on the dawnside or duskside also show cavity resonance properties. However, when Ørsted was on the dayside, the oscillations observed by the satellite are out of phase with that observed on the ground, suggesting that the dayside Pi2s are more likely related to some dayside ionospheric current systems rather than that caused by a global cavity resonance mode. The amplitude variation recorded by Ørsted shows a peak in the equatorial region, which, for the first time, gives clear observational support for earlier model calculations. We also estimated the screening effect of the ionosphere on MHD waves and suggest that when the cavity resonance mode is valid for generation of Pi2 pulsations at low latitudes, the screening effect is negligible; that is, the compressional waves are seen directly as Pi2 pulsations at the ground.
Modeling ozone photochemistry and evaluation of hydrocarbon emissions in the Mexico City metropolitan area
Authors: West J. Jason , Zavala Miguel A. , Molina Luisa T. , Molina Mario J. , San Martini Federico , McRae Gregory J. , Sosa‐Iglesias Gustavo , Arriaga‐Colina Jose Luis
Published: October 2004

Emissions of volatile organic compounds (VOCs) and of CO are often underestimated, and correcting this underestimate is important for modeling ozone formation and sensitivity. The California Institute of Technology three‐dimensional photochemical model is used to test the official emissions inventory for the Mexico City metropolitan area through a direct comparison of measured and modeled total nonmethane hydrocarbons (NMHCs) and CO. The model is applied to six 2‐day periods during the IMADA measurement campaign of March 1997. When using emissions based on the official emissions inventory, the model significantly underestimates measurements of total NMHCs and of CO. A best fit to the measurements (with lowest bias) is found when increasing emissions of CO and VOCs by factors of 2 and 3, respectively. Adjusting total emissions accordingly, the model produces good estimates of ozone and NOx, with average normalized biases over 6 days of 3% and 32%, respectively, and with better agreement during daytime hours. This agreement for ozone and NOx supports the suggestion that VOC and CO emissions are underestimated. Other uncertainties are analyzed, finding that while some uncertainties are important, none is individually significant enough to account for the discrepancy. Correcting the total emissions, the overall model performance is found to be adequate, particularly on 3 days, for the model to be used for analysis of control strategies. Using the results of a chemical mass balance identification of NMHC sources highlights sources that are more likely underestimated, but confidence in the appropriate correction to emissions from different sources is low and should be investigated further.
Stand‐specific diurnal dynamics of CH4 fluxes in boreal lakes: Patterns and controls
Authors: Juutinen Sari , Alm Jukka , Larmola Tuula , Saarnio Sanna , Martikainen Pertti J. , Silvola Jouko
Published: October 2004

Diurnal variation in methane fluxes can cause systematic errors in flux estimates, particularly at places with aquatic vegetation. Closed chamber measurements were made during the ice‐free period in central Finland. Methane fluxes were quantified at an interval of a few hours for several boreal lakeshore communities consisting of Phragmites australis (Cav.) Trin. ex Steud. and of wetland sedges, grasses, and herbs. The automated measurement system was operated for 4 months in a P. australis stand and for 2 months in a site with mixed wetland vegetation. Additional manual measurements lasted for a few days. In P. australis stands the CH4 fluxes were typically highest around noon. On the average, efflux of CH4 measured during office hours (0800–1600 local time (LT)) should be corrected using a factor 0.68 to obtain a more reliable estimate of daily CH4 release. The fluctuation magnitude varied between different locations and over the study period, being the greatest in the most productive parts of the stands in August. A harmonic regression model, scaled with temperature and stand biomass, was successfully applied to reconstruct CH4 flux in P. australis stand. In the sedge, grass and herb stands the diurnal fluctuation in CH4 flux was generally small. Commonly, daily maximum in efflux occurred during evening or night and large (threefold) diurnal differences were occasionally found. Daytime measurements alone can result in a slight or moderate underestimate of the total flux for the wetland communities. These results recommend that spatial and seasonal differences in diurnal CH4 flux dynamics should be considered when planning measuring or modeling CH4 fluxes.
Tropospheric ionization and aerosol production: A model study
Authors: Kazil J. , Lovejoy E. R.
Published: October 2004

Recent observations of ultrafine aerosol production in the atmosphere support the hypothesis of ions acting as nucleation agents. We use a numerical model of ion‐induced aerosol formation based on experimental cluster ion thermodynamics to study the production of ultrafine aerosol in the troposphere and its response to variations in background ionization. An analytical model is used to explain the findings. Our results show a considerable ultrafine particle and surface area production due to ion‐induced nucleation. Both particle and surface area production readily respond to variations in ionization, such as resulting from the modulation of the galactic cosmic ray intensity by the 11 year solar cycle. However, this response may be positive or negative, depending on ambient conditions. We explain the mechanism responsible for this behavior. The large particle production seen in our simulations suggests that ion‐induced nucleation is an important atmospheric process, which may promote the solar cycle signal to the troposphere.
Model study on particle size segregation and deposition during Asian dust events in March 2002
Authors: Han Zhiwei , Ueda Hiromasa , Matsuda Kazuhide , Zhang Renjian , Arao Kimio , Kanai Yutaka , Hasome Hisashi
Published: October 2004

A size‐segregated aerosol model that includes most of the major physical processes (generation, transport, and dry and wet deposition) is developed. This model is coupled with a Regional Air Quality Model (RAQM) and is applied to simulate Asian dust storms during the 10‐day period of 15–24 March 2002. A nonhydrostatic mesoscale model (MM5) is used to provide meteorological fields. Model results are verified by available observational data including surface weather observations and size‐segregated particle concentrations. The validation demonstrates a good capability of this model system in capturing most of the key features of dust evolution and reproducing the particle mass size distribution along the transport pathway of soil dust. An apparent feature has been both observed and reproduced by the model, showing a shift of size range with peak mass concentration from coarse mode to finer mode on the pathway from source regions to distant downwind areas. The maximum dust concentration averaged over 10 days is simulated to be 3000 μg m−3 over the southern China‐Mongolia border. Total dry deposition of soil dust for 10 days is up to 30 g m−2 in the Gobi desert along the southern China‐Mongolia border. Distribution and magnitude of particle deposition are strongly dependent on both concentration and size‐segregated dry deposition velocity and scavenging rate. While dry deposition dominates the removal of dust particles in or in the vicinity of source regions, the influence of wet deposition increases along the transport pathway of soil dust, with high removal efficiency for coarser particles (>2 μm) and very low efficiency for particles in the accumulation mode. Of the total dust emission (43.2 megatons), about 71% is redeposited onto the underlying surface by the dry deposition process, 6% is removed by the wet deposition process, and the remaining 23% is suspended in the atmosphere or subject to long‐range transport.
Toward regional‐scale modeling using the two‐way nested global model TM5: Characterization of transport using SF6
Authors: Peters W. , Krol M. C. , Dlugokencky E. J. , Dentener F. J. , Bergamaschi P. , Dutton G. , Velthoven P. v. , Miller J. B. , Bruhwiler L. , Tans P. P.
Published: October 2004

We present an evaluation of transport of sulfur hexafluoride (SF6) in the two‐way nested chemistry‐transport model “Tracer Model 5” (TM5). Modeled SF6 values for January 2000 to November 2003 are compared with NOAA CMDL observations. This includes new high‐frequency SF6 observations, frequent vertical profiles, and weekly flask data from more than 60 sites around the globe. This constitutes the most extensive set of SF6 observations used in transport model evaluation to date. We find that TM5 captures temporal variability on all timescales well, including the relatively large SF6 signals on synoptic scales (2–5 days). The model overestimates the meridional gradient of SF6 by 19%, similar to previously used transport models. Vertical profiles are reproduced to within the standard error of the observations, and do not reveal large biases. An important area for future improvements is the mixing of the planetary boundary layer which is currently too slow, leading to modeled SF6 mixing ratios that are too large over the continents. Increasing the horizontal resolution over North America from 6×4°, to 3×2°, to even 1×1° (lon×lat) does not affect the simulated global scale SF6 distribution and potentially minimizes representation errors for continental sites. These results are highly relevant for future CO2 flux estimates with TM5, which will be briefly discussed.
Incarceration of the Retroverted Uterus at Term Gestation
Authors: Matsushita Hiroshi , Kurabayashi Takumi , Higashino Masahiko , Kojima Yumi , Takakuwa Koichi , Tanaka Kenichi
Published: October 2004

Incarceration of the retroverted uterus is a rare complication of pregnancy and rarely persists until term. The diagnosis is extremely difficult to make and a cesarean section should be performed in such cases. A 33-year-old Japanese woman was admitted at 40 weeks gestation for evaluation of preeclampsia. Vaginal examination revealed that the uterine cervix could hardly be visualized, although the fetal head was impacted in the pelvis. These findings suggested incarceration of the retroverted uterus. Magnetic resonance imaging (MRI) was performed and clarified the exact anatomical relationship and confirmed the diagnosis. She therefore underwent a cesarean section and a male infant weighing 3552 g was delivered with Apgar scores of 9 and 10 at 1 and 5 minutes, respectively. At surgery she was found to have an adhesion between the uterus and the pouch of Douglas. MRI is a useful tool in correctly making the diagnosis of uterine incarceration and facilitates preparation for a cesarean section.
Incorporation of fast laser beam shunting and a broadband polarizer in the MAST Thomson scattering systems
Authors: Walsh M. J. , Carolan P. G. , Darke A. C. , Dunstan M. R. , Forrest M. J. , Huxford R. B. , O’Gorman R. , Pechstedt K. , Prunty S. L. , Scannell R.
Published: October 2004

Both ruby laser (300 points) and NdYAG laser (19 points) Thomson scattering systems are used on MAST. Fast nonlinear optical switching shunts laser beams from the four 50 Hz NdYAG lasers to obtain coaxial plasma illumination. The technique allows for future expandability to many laser systems. The ruby laser system is used in parallel. A broadband thin-plate polariser, based on nanotechnology, has been incorporated in the collection optics. It has a wide field of view and it almost halves the detected laser stray light and plasma background for both laser spectral regions. This allows much of the collection optics to function effectively in both spectral regions simultaneously.
Three-dimensional plasma structure reconstruction from mutually orthogonal streaks of nonaxisymmetric laser-produced plasma plumes
Authors: Kim Yong W. , Lee Hedok
Published: October 2004

A method is developed for structure reconstruction of an arbitrary plasma from two luminosity streaks and a front-view snapshot as a weighting function (WF). Two scaling relations link the pressure and temperature to the local specific emission intensity. A trial plasma structure is proposed in terms of specific intensity, and the luminosity streaks are calculated according to the Saha equilibrium. Plasma absorption is included. Error signals between the calculated and measured luminosity are allocated according to the WF to find corrections to local specific intensities. Minimization of the errors completes the reconstruction at a given time, which in turn updates the WF for the next time step. Summing over the full plasma over time facilitates calculation of the total plasma mass, energy and beam attenuation through the plasma. When agreement with their measured counterparts is maximized, the scaling relations are calibrated.
Linear stability of static equilibrium states in the Hall-magnetohydrodynamics model
Authors: Hameiri Eliezer , Torasso R.
Published: October 2004

The magnetohydrodynamic (MHD) plasma model, as modified by the Hall effect, is given a Hamiltonian formulation and its stability properties are studied. It is found that, in most cases, a stable MHD plasma remains stable after the addition of the Hall effect. The most notable exceptions are when the pressure profile decreases with increasing density or when the entropy increases with density. The Hamiltonian structure of the equations enables the derivation of bounds that restrict the location of eigenfrequencies in the complex plane in some cases. The phenomenon of overstability, whereby the real part of a marginally stable eigenfrequency does not vanish, appears to be typical.
KB–PJX—A streaked imager based on a versatile x-ray microscope coupled to a high-current streak tube (invited)
Authors: Gotchev O. V. , Jaanimagi P. A. , Knauer J. P. , Marshall F. J. , Meyerhofer, D. D.
Published: October 2004

A re-entrant, highly adaptable, x-ray streaked imager has been developed for OMEGA to increase the sensitivity and spatial resolution in hydrodynamic-stability experiments. It is based on a four-mirror Kirkpatrick–Baez (KB) microscope, coupled to a high-current streak tube. The unique mechanical assembly of the KB optic allows a choice between single- or multi-image modes and one- or two-dimensional imaging. Currently, the optic uses an Ir coating at a grazing angle of 2.1°. The incidence angle has been optimized to maximize throughput in the chosen energy band, centered at 1.5 keV with a full width at half maximum of about 0.4 keV. A calculated resolution of better than 5 μm over the central 200 μm of the field of view was verified in inertial confinement fusion experiments. New multilayer mirror elements for high-energy or multiband imaging, take advantage of the flexible mechanical design. Some important features of the PJX streak tube are described.
Calculation of edge toroidal current density distributions from DIII-D lithium beam measurements using Ampère’s law
Authors: Thomas D. M. , Leonard A. W. , Mueller H. W.
Published: October 2004

The local edge current density j(r) is a parameter of basic importance in understanding the stability of high performance tokamaks, as well as the dynamics of edge localized mode behavior. On DIII-D, the lithium beam polarimetry diagnostic provides precise measurements of the local magnetic field projection along the field of view at 32 radial locations in the plasma edge. Using these measurements, the known spatial calibration and a minimal amount of information about the magnetic field shape from equilibrium reconstructions, Ampères law may be used to provide a straightforward parameterization for the edge toroidal current density in terms of the measured magnetic field and its radial derivative. This approach is relatively insensitive to errors in the reconstruction and is simple to apply.
Near infrared spectroscopy of the divertor region in the Alcator C-Mod tokamak
Authors: Furno I. , Wurden G. A.
Published: October 2004

A new system for near infrared spectroscopic measurements (1.2–2.6 μm) is designed for the Alcator C-Mod tokamak. These measurements will provide a new window into understanding the physics of detached and/or high radiating plasmas. The system, located on top of the Alcator C-Mod concrete igloo, will view a 30×30 cm2 region of the lower divertor by means of a re-entrant 5 m long ZnSe based periscope. A McPherson 218 spectrometer will disperse the light that will then be detected by a thermoelectrically cooled InGaAs, 256-element linear image sensor. The signals from each pixel will be digitized by a 16-bit, 333 kHz analog/digital board and then transmitted over optical link to a personal computer (PC) located in Alcator C-Mod control room. The PC will remotely control the system and store the data in the MDSplus database.
Development of the megahertz planar laser-induced fluorescence diagnostic for plasma turbulence visualization
Authors: Kuritsyn Aleksey , Levinton Fred M.
Published: October 2004

A megahertz laser-induced fluorescence-based diagnostic system for measuring ion density fluctuations in two spatial dimensions is described. Well resolved spatial and temporal two-dimensional (2D) images of turbulent structures will be useful in understanding ion turbulence in magnetically confined plasmas which is a key factor in the performance of fusion experimental devices. A sheet beam of a megahertz repetition rate tunable Alexandrite laser is used to excite ion emission from argon plasma. The fluorescence emitted from the plane of the laser beam is detected with a narrow band interference filter and intensified ultrafast charge coupled device camera providing 2D images of relative ion density fluctuations every microsecond. It is expected that the edge plasma on fusion devices will be accessible to this technique.
Laser-induced fluorescence measurements of three plasma species with a tunable diode laser
Authors: Keesee Amy M. , Scime Earl E. , Boivin Robert F.
Published: October 2004

Recently, we demonstrated that a single, tunable, low-power, diode laser can be used for laser-induced fluorescence (LIF) measurements of both argon ions and helium neutrals. We have now identified a third fluorescence scheme, for neutral argon atoms, accessible with the same tunable diode laser. Fluorescence measurements of a heated iodine cell are used to monitor the wavelength of the laser during the LIF measurement.
Z
eff
from spectroscopic bremsstrahlung measurements at ASDEX Upgrade and JET
Authors: Meister H. , Fischer R. , Horton L. D. , Maggi C. F. , Nishijima D. ,   ASDEX Upgrade Team, Giroud C. , Zastrow K.-D. ,   JET-EFDA Contributors, Zaniol B.
Published: October 2004

The effective ionic charge Zeff is a means to assess the impurity content of a fusion plasma. It can be derived from measurements of bremsstrahlung intensity. These have been extended at ASDEX Upgrade by the usage of the sight lines for the charge exchange recombination diagnostic. Together with a previously installed sight line array, it is now possible to routinely determine the bremsstrahlung intensity over the whole minor radius purely from spectroscopic measurements. In a tokamak where the plasma facing components are made up of various materials, this is necessary to check if measurements are contaminated by line radiation. The bremsstrahlung background of the respective spectra is determined using Bayesian probability theory, giving consistent and improved error statistics. Using the information for electron temperature and density profiles, the Zeff profile is determined by an integrated method. The same approach to assess the Zeff profile has been demonstrated to be successful also at the JET tokamak.
Three-dimensional laser-induced fluorescence measurements in a helicon plasma
Authors: Hardin R. , Sun X. , Scime E. E.
Published: October 2004

We describe a three-dimensional (3D) laser-induced fluorescence (LIF) diagnostic for argon ions in a helicon plasma source. With three different laser injection orientations at a single spatial location, LIF measurements are performed to determine the 3D ion temperature and the 3D ion flow vector. The measurement process is then repeated at multiple locations in a cross section of the plasma column to create a two-dimensional (2D) map of the 3D ion flow, the ion temperature, and metastable ion density. Scanning in the 2D plane is accomplished by mounting the injection and collection optics on stepping motor driven stages.
Analysis of visible light images from a fast-gated intensified charge coupled device camera during flux rope interaction and magnetic reconnection
Authors: Hemsing E. , Furno I. , Intrator T. , Wei D.
Published: October 2004

We present the experimental setup and analysis of visible light images from a fast double-gated intensified charge coupled device (CCD) camera currently being used on the reconnection scaling experiment (RSX) at the Los Alamos National Laboratory. In RSX, externally driven free-boundary flux ropes are generated for magnetic reconnection studies in collisional plasma. Time-resolved images of flux rope interaction on submicrosecond time scales are achieved through the use of a microchannel plate intensified CCD camera and are shown to be consistent with probe measurements of plasma pressure and magnetic structure. High experimental repeatability allows plasma evolution to be displayed and measured from images taken over hundreds of RSX discharges to elucidate flux rope interaction dynamics. Peak-intensity fit algorithms extrapolate rope separation and two-dimensional rope velocities from images in agreement with probe data. First glimpses of two flux ropes that twist and merge are presented.
Spatially resolved bolometric measurement and electron temperature measurement using diode arrays
Authors: Koguchi H. , Shimada T. , Asai T. , Yagi Y. , Hirano Y. , Sakakita H.
Published: October 2004

In this article, the measurement system for the total radiation and electron temperature profiles to be installed in a reversed-field pinch machine, toroidal pinch experiment, RX [TPE-RX, R/a=1.72/0.45 m, Ip<MA (designed)], is presented. We plan to measure the plasma radiation and electron temperature profiles using three sets of diode arrays. Each array can measure radiation along 20 lines of sight and the radial profile of the radiation. One set of the arrays is used for the bolometric measurement in the range from visible light to soft x-ray. Two sets of the arrays are used for the soft-x ray and electron temperature measurements employing a double-filter method. We will use this system to investigate the plasma-wall interaction, radiation loss, and confinement properties in the core plasma region. We will extend the use of this system for tomographic analysis of electron temperature, a concept of which is also presented.
Temporal resolved x-ray penumbral imaging technique using heuristic image reconstruction procedure and wide dynamic range x-ray streak camera
Authors: Fujioka Shinsuke , Shiraga Hiroyuki , Azechi Hiroshi , Nishimura Hiroaki , Izawa Yasukazu , Nozaki Shinya , Chen Yen-wei
Published: October 2004

Temporal resolved x-ray penumbral imaging has been developed using an image reconstruction procedure of the heuristic method and a wide dynamic range x-ray streak camera (XSC). Reconstruction procedure of the penumbral imaging is inherently intolerant to noise, a reconstructed image is strongly distorted by artifacts caused by noise in a penumbral image. Statistical fluctuation in the number of detected photon is the dominant source of noise in an x-ray image, however acceptable brightness of an image is limited by dynamic range of an XSC. The wide dynamic range XSC was used to obtain penumbral images bright enough to be reconstructed. Additionally, the heuristic method was introduced in the penumbral image reconstruction procedure. Distortion of reconstructed images is sufficiently suppressed by these improvements. Density profiles of laser driven brominated plastic and tin plasma were measured with this technique.
Coded penumbral imaging for improvements of signal-to-noise ratio
Authors: Chen Yen-Wei , Yamamoto Hiroki , Nozaki Shinya
Published: October 2004

Penumbral imaging is a power imaging technique for radiations with long mean-free path. Since the reconstruction is based on deconvolution, the technique is sensitive to noise contained in penumbral images. In this article, we proposed a uniformly redundant penumbral array (URPA) technique to improve the signal-to-noise (SN) ratio of penumbral images. In URPA, the penumbral apertures are arranged in m-sequence and the SN ratio of the penumbral image can be improved by a factor of [(r×s+1)/2]1/2, where r×s is the size of two-dimensional m sequence. The effectiveness of URPA has been demonstrated by computer simulations.
“Optical” soft x-ray arrays for fluctuation diagnostics in magnetic fusion energy experiments
Authors: Delgado-Aparicio L. F. , Stutman D. , Tritz K. , Finkenthal M. , Kaita R. , Roquemore L. , Johnson D. , Majeski R.
Published: October 2004

We are developing large pixel count, fast (⩾100 kHz) and continuously sampling soft x-ray (SXR) array for the diagnosis of magnetohydrodynamics (MHD) and turbulent fluctuations in magnetic fusion energy plasmas. The arrays are based on efficient scintillators, high thoughput multiclad fiber optics, and multichannel light amplification and integration. Compared to conventional x-ray diode arrays, such systems can provide vastly increased spatial coverage, and access to difficult locations with small neutron noise and damage. An eight-channel array has been built using columnar CsI:Tl as an SXR converter and a multianode photomultiplier tube as photoamplifier. The overall system efficiency is measured using laboratory SXR sources, while the time response and signal-to-noise performance have been evaluated by recording MHD activity from the spherical tori (ST) Current Drive Experiment-Upgrade and National Spherical Torus Experiment, both at Princeton Plasma Physics Laboratory.
Soft x-ray (0.2<E<2.0 keV) imager for z-pinch plasma radiation sources
Authors: Failor B. H. , Qi N. , Levine J. S. , Sze H. , Gullickson E. M.
Published: October 2004

Z -pinches can produce intense fluxes of argon K-shell (3 keV) radiation, but typically only a fraction of the load mass near the axis of the pinch radiates in this spectral range. The majority of the mass does not get hot or dense enough to radiate efficiently in the K-shell. We have designed, built, and tested an instrument to image pinch emission, specifically the radial emission profile, at energies below the K-shell in order to track the location of the cooler mass. A gold mirror provides a high-energy cut-off at 2 keV while a transmission grating disperses the incoming radiation and provides a low-energy cutoff at 0.1 keV. A vertical slit images the pinch radiation in the radial direction and the emission profile is recorded with either an extreme ultraviolet-sensitive charge-coupled device camera (time-integrated) or a linear photodiode array (∼1 ns time resolution). We present results for the mirror, grating, and system characterization obtained at the Advanced Light Source synchrotron located at Lawrence Berkeley National Laboratory (Berkeley, CA).
Static and time-resolved 10–1000 keV x-ray imaging detector options for NIF
Authors: Landen O. L. , Bell P. M. , McDonald J. W. , Park H.-S. , Weber F. , Moody J. D. , Lowry M. E. , Stewart R. E.
Published: October 2004

High energy (>10 keV) x-ray self-emission imaging and radiography will be essential components of many NIF high energy density physics experiments. In preparation for such experiments, we have evaluated the pros and cons of various static [x-ray film, bare charge-coupled device (CCD), and scintillator + CCD] and time-resolved (streaked and gated) 10–1000 keV detectors.
High resolution Thomson scattering for Joint European Torus (JET)
Authors: Pasqualotto R. , Nielsen P. , Gowers C. , Beurskens M. , Kempenaars M. , Carlstrom T. , Johnson D. ,   JET-EFDA Contributors
Published: October 2004

A Thomson scattering system is being developed for Joint European Torus with 15 mm spatial resolution and a foreseen accuracy for temperature better than 15% at a density of 1019 m−3. This resolution is required at the internal transport barrier and edge pedestal and it can not be fully achieved with the present light detection and ranging systems. The laser for this system is Nd:YAG, 5 Joule, 20 Hz. Scattering volumes from R=2.9 m to R=3.9 m are imaged onto 1 mm diameter fibers, with F/25 collection aperture. Two fibers are used per scattering volume. Using optical delay lines, three scattering volumes are combined in each of the 21 filter polychromators. The signals are recorded with transient digitizers, which allow the combined time delayed signals to be resolved. Knowledge of the time delay between signals allows the use of correlation techniques in determining signal levels. The ac output of the amplifier is used, which tolerates a higher level of background signal without affecting dynamic range. The noise resulting from plasma light is determined directly.
Comparison of multialkali and GaAs photocathode detectors for Joint European Torus edge light detection and ranging Thomson scattering profiles
Authors: Kempenaars M. , Nielsen P. , Pasqualotto R. , Gowers C. , Beurskens M. ,   JET-EFDA Contributors
Published: October 2004

The Joint European Torus (JET) tokamak has two light detection and ranging (LIDAR) Thomson scattering systems, one for the core and one dedicated to the edge Te and ne profiles. The LIDAR scheme is unique to JET and is envisaged for use on ITER. The system’s spatial resolution is defined by the convolution product of its components: laser pulse duration, detector response time, and digitizer speed. The original multialkali photocathode microchannel plate photomultipliers dictated the response time, resulting in a 12 cm spatial resolution along the line of sight. In the edge LIDAR system, this is improved by aligning the line of sight with the flux surfaces, thus improving the effective spatial resolution to 2 cm depending on the plasma configuration. To meet demands for better edge gradient resolution, an upgrade to higher quantum efficiency detectors was proposed. Four GaAs photocathode detectors have been procured, two of which surpass expectations. These detectors are shown to have a more than two times higher effective quantum efficiency and their response time is at least twice as fast as the multialkali detectors. Combined with a fast digitizer this improves the spatial resolution by a factor of two, down to one centimeter effective, depending on plasma configuration.
Design of core and edge Thomson scattering systems for Korea Superconducting Tokamak Advanced Research tokamak
Authors: Lee H. G. , Lee J. H. , Johnson D. , Ellis R. , Feder R. , Park H.
Published: October 2004

The core and edge Thomson systems on Korea Superconducting Tokamak Advanced Research employ two different sets of lens collection optics. Their collection systems are positioned in the front end of a long reentrant cassette for optimum viewing coverage and optical throughput. Both systems collect the scattered light from a single tangential beam of multiple 50-Hz Nd:YAG lasers and image the scattering volume from core to edge with 40 spatial points. In order to obtain a higher resolution of 5 mm, the edge system has more spatial channels than the core system. Pressure-free heat shield windows, which will absorb the radiation heat flux, are mounted in front of large vacuum windows to protect them from the radiation heat load during long-pulse discharges.
Quantified reduction of wall material influx during Hohlraum experiments
Authors: Batha Steven H. , Fincke James R.
Published: October 2004

Heating the gold walls of a Hohlraum with intense laser beams produces a rapidly expanding gold plasma. Eventually, the wall material will converge on the axis of the Hohlraum with a density sufficient to be opaque to any standard radiography source. The gold expansion makes radiography of the back wall through the laser entrance hole of a Hohlraum driven from one side difficult. This experiment demonstrates a reduction of Au influx when the Hohlraum walls are coated with 0.44 μm of parylene-N. The reduction is quantified, using an x-ray framing camera, in a cylindrical Hohlraum driven by 6.8 kJ of laser light.
Use of X-pinches of diagnose behavior of low density CH foams on axis of wire array Z-pinches
Authors: Bott S. C. , Palmer J. B. A. , Ampleford D. J. , Bland S. N. , Chittenden J. P. , Lebedev S. V.
Published: October 2004

X -pinch radiography was used to analyze the interaction between streams of coronal plasma and on-axis foam targets in wire array z-pinch experiments on the MAGPIE generator (1 MA,240 ns). The implosion of the x-pinch, used in place of a current return conductor to the load, provided a short (<2 s) small (∼5 μm) intense burst of soft x-rays, ideal for point projection backlighting. Timimg of the x-pinch was adjusted via the mass of its wires, allowing us to study the evolution of the foam during the experiment. Choice of the x-pinch materials, filters, and recording film determined the probing radiation, and hence the plasma/foam densities were resolved. Quantitative results will be discussed.
Correcting for gain effects in an x-ray framing camera in a cylindrical implosion experiment
Authors: Horsfield C. J. , Parker K. W. , Rothman S. D. , Fincke J. , Lanier N. E.
Published: October 2004

A program to investigate the mixing of a marker layer in a convergent cylindrical geometry has been carried out on the Omega laser facility. The principal diagnostic for these experiments was the Los Alamos National Laboratory (Los Alamos, NM) QXI framing camera. The results obtained displayed an unphysical pattern, partly attributed to nonlinear gain effects. We propose a method to compensate for these effects, which relies only on shot data and so can be used retrospectively on previously obtained data. Modifications carried out on the camera to minimize the effect are described and the results are compared with compensated data from previous runs. We also present results which evaluate the state of gain effects in the camera during each experimental shot day.
Optical and x-ray streak camera gain measurements
Authors: Ghosh S. , Boni R. , Jaanimagi P. A.
Published: October 2004

Measurements of streak camera gain as the number of CCD (charge-coupled-device) electrons recorded per single-electron events hitting the streak tube phosphor are presented. The CCD is fiber optically coupled to the streak tube output; there is no image intensifier in the system. The gain is measured from the signal-to-noise ratio (SNR) of the recorded photoelectrons. This technique allows us to verify that the photoelectron SNR follows Poisson statistics and to establish the linear dynamic range. Superpixel histograms of sparse streak records are also used to generate the pulse-height distribution (PHD) for recording single-electron events and corroborate the gain measurement. The noise factor and the number distribution of secondary electrons emitted per absorbed x ray from Au, KBr, and CsI photocathodes are derived from the PHD’s recorded with an x-ray streak camera.
Initial operation of the national spherical torus experiment fast tangential soft x-ray camera
Authors: Stratton B. C. , Feder R. , Goeler S. von , Renda G. F. , Mastrocola V. J. , Lowrance J. L.
Published: October 2004

Fast, two-dimensional, soft x-ray imaging is a powerful technique for the study of magnetohydrodynamic instabilities in tokamak plasmas. We have constructed an ultra-fast frame rate soft x-ray camera for the national spherical torus experiment (NSTX). It is based on a recently developed 64×64 pixel charge-coupled device (CCD) camera capable of capturing 300 frames at up to 500 000 frames per second. A pinhole aperture images the plasma soft x-ray emission (0.2–10 keV) onto a P47 scintillator deposited on a fiber-optic faceplate; the scintillator visible light output is detected and amplified by a demagnifying image intensifier and lens-coupled to the CCD chip. A selection of beryllium foils provides discrimination of low-energy emission. The system is installed on NSTX with a wide-angle tangential view of the plasma. Initial plasma data and an assessment of the system performance are presented.
Preliminary design of the soft x-ray array tomographic diagnostic system for Korea Superconducting Tokamak Advanced Research (KSTAR) plasmas
Authors: Kim Junghee , Choe Wonho
Published: October 2004

Analyses of x-ray (SXR) emission from tokamak plasmas provide valuable information about magnetohydrodynamics activities and transport phenomena. In this study, design and optimization of the SXR detector arrays were performed for the KSTAR (Korea superconducting tokamak advanced research) device. Geometrical arrangement of the array system was made by coverage mapping and tomographic reconstruction tests. The space-time tomography algorithm was developed for KSTAR-like plasmas using the fast maximum entropy method combined with singular value decomposition. Spatial setup of the components in each detector array was determined and optimized by geometrical calculation. A curved beryllium window and a developed cooling system will be mounted on the detector arrays. Due to the existence of the complex structures between outer vessel and passive stabilizers, each array is designed to be miniaturized. Hardware-optimization of the array system was cross-checked with the tomographic test results.
Independent component analysis based filtering for penumbral imaging
Authors: Chen Yen-Wei , Han Xian-Hua , Nozaki Shinya
Published: October 2004

We propose a filtering based on independent component analysis (ICA) for Poisson noise reduction. In the proposed filtering, the image is first transformed to ICA domain and then the noise components are removed by a soft thresholding (shrinkage). The proposed filter, which is used as a preprocessing of the reconstruction, has been successfully applied to penumbral imaging. Both simulation results and experimental results show that the reconstructed image is dramatically improved in comparison to that without the noise-removing filters.