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Blob properties in L- and H-mode from gas-puff imaging in ASDEX upgrade

PLASMA PHYSICS AND CONTROLLED FUSION 2014年第12期56卷

作者： Fuchert, G. Birkenmeier, G. Carralero, D. Lunt, T. Manz, P. Mueller, H. W. Nold, B. Ramisch, M. Rohde, V. Stroth, U. Univ Lorraine Inst Jean Lamour CNRS UMR 7198 F-54506 Vandoeuvre Les Nancy France Max Planck Inst Plasma Phys D-85748 Garching Germany Univ Stuttgart Inst Grenzflachenverfahrenstech & Plasmatechnol D-70569 Stuttgart Germany Tech Univ Munich Phys Dept E28 D-85748 Garching Germany

Blob properties are studied in the scrape-off layer of the tokamak ASDEX Upgrade with a fast camera. The gas-puff imaging technique is used to investigate the detection rate as well as the blob size and velocity scaling. The experiments were performed in L-and H-mode phases of the same discharges to study the change in blob properties after the L-H transition. In both regimes the detection rate is of the order of a few thousand blobs per second, which is compatible with the picture of blob generation by edge micro instabilities. The blob size increases in H-mode, while the radial velocity decreases slightly. The changes are, however, not indicating a drastic change in the blob dynamics in both phases. The experimentally found blob properties were compared to predictions from a novel blob model including effects due to a finite ion temperature, which should be more appropriate for the conditions in the SOL of fusion plasmas.

关键词： tokamak plasma turbulence blobs gas-puff imaging

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Low-viscosity mantle blobs are sampled preferentially at regions of surface divergence and stirred rapidly into the mantle

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PHYSICS OF THE EARTH AND PLANETARY INTERIORS 2010年第1-2期180卷 104-107页

作者： Manga, Michael Univ Calif Berkeley Dept Earth & Planetary Sci Berkeley CA 94720 USA

The persistence of mantle heterogeneity depends on its density and viscosity and as well as the characteristics of the convecting mantle, such as the vigour and possible stratification of convection. Low-viscosity regions stretch and deform more rapidly than their high-viscosity counterparts. Low-viscosity regions are also drawn into, and hence preferentially sampled at, regions of surface divergence such as mid-ocean ridges and plume-fed hotspots. Low-viscosity heterogeneities in the form of blobs are thus more rapidly stirred into a convecting mantle. Discrete blobs of primitive or enriched mantle are unlikely to persist for billions of years. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Mantle heterogeneity blobs Mixing Mantle plumes

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A dynamic, embedded Lagrangian model for ocean climate models. Part I: Theory and implementation

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OCEAN MODELLING 2012年 59-60卷 41-59页

作者： Bates, Michael L. Griffies, Stephen M. England, Matthew H. MIT Dept Earth Atmospher & Planetary Sci Cambridge MA 02139 USA Univ New S Wales Climate Change Res Ctr Sydney NSW Australia NOAA Geophys Fluid Dynam Lab Princeton NJ 08542 USA

A framework for embedding a Lagrangian model within ocean climate models that employ horizontal Eulerian grids is presented. The embedded Lagrangian model can be used to explicitly represent processes that are at the subgrid scale to the Eulerian model. The framework is applied to open ocean deep convection and gravity driven downslope flows, both of which are subgridscale in the present generation of level coordinate ocean climate models. In order to apply the embedded Lagrangian framework to these processes, it is necessary to partition the mass and momentum of the model into an Eulerian system and a Lagrangian system. This partitioning allows the Lagrangian model to transport seawater using a more appropriate set of dynamics. A number of schemes suitable for implementation in the embedded Lagrangian model are derived. Two dynamically passive schemes are derived that emulate existing parameterisations and two dynamically active schemes are also derived that evolve Lagrangian parcels of water (termed "blobs") according to a set of physical equations. Some details of the implementation into the Geophysical Fluid Dynamics Modular Ocean Model are also given. Finally, results are presented that show that the dynamically passive schemes are able to emulate their Eulerian counterparts to within roundoff error in idealised test cases. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Numerical model Overflow Density flow Convection Embedded Lagrangian model blobs

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A dynamic, embedded Lagrangian model for ocean climate models, Part II: Idealised overflow tests

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OCEAN MODELLING 2012年 59-60卷 60-76页

Dense gravity current overflows occur in several regions throughout the world and are an important process in the meridional overturning circulation. Overflows are poorly represented in coarse resolution level coordinate ocean climate models. Here, the embedded Lagrangian model formulated in the companion paper of Bates et al. (2012) is used in two idealised test cases to examine the effect on the representation of dense gravity driven plumes, as well as the effect on the circulation of the bulk ocean in the Eulerian model. The results are compared with simulations with no parameterisation for overflows, as well as simulations that use traditional hydrostatic overflow schemes. The use of Lagrangian "blobs" is shown to improve three key characteristics that are poorly represented in coarse resolution level coordinate models: (1) the depth of the plume, (2) the along slope velocity of the plume, and (3) the response of the bulk ocean to the bottom boundary layer. These improvements are associated with the more appropriate set of dynamics satisfied by the blobs, leading to a more physically sound representation. Experiments are also conducted to examine sensitivity to blob parameters. The blob parameters are examined over a large parameter space. (C) 2012 Elsevier Ltd. All rights reserved.

关键词： Numerical model Overflow Density flow Embedded Lagrangian model blobs

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3D Blob Modelling with BOUT++

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CONTRIBUTIONS TO PLASMA PHYSICS 2012年第5-6期52卷 348-352页

作者： Angus, J. R. Umansky, M. Krasheninnikov, S. I. Univ Calif San Diego La Jolla CA 92093 USA Lawrence Livermore Natl Lab Livermore CA 94550 USA

Plasma blobs found in the edge region of tokamaks are important to understand because they contribute to a large amount of the plasma particle transport in the SOL (scrape off layer). Most of the work to date is limited to 2D theory and simulations by ignoring the variation of blob parameters along the magnetic field line. 3D effects are examined in the electrostatic limit in this paper using the code BOUT++ by allowing for the variation of blob density and potential along the field line. It is demonstrated that the 3D variation of these parameters can lead to a Boltzmann potential relation that will cause the blob to spin and induce turbulent motion via unstable drift waves ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

关键词： blobs Tokamaks ELMS

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INITIAL PARAMETRIC REPRESENTATION OF blobs

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INTERNATIONAL JOURNAL OF COMPUTATIONAL GEOMETRY & APPLICATIONS 2009年第1期19卷 17-32页

作者： Faudot, Dominique Garnier, Lionel Univ Burgundy CNRS UMR 5158 LE2i F-21078 Dijon France

blobs, developed by J.F. Blinn in 1982, are the implicit surfaces obtained by composition of a real numerical function and a distance function. Since, many authors ( C. Murakami, H. Nishimura, G. Wyvill...) defined their own function of density, from these implicit surfaces are interesting from several points of view. In particular, their fusion makes it possible to easily obtain an implicit equation of resulting surface. However, these surfaces do not admit a parametric equation yet. In this article, we will establish the parametric equation of two blobs in fusion, defined by the function of density of C. Murakami, by using an algebraic method. Then, we will develop another method, based on the differential equations.

关键词： blobs fusion parametric equation implicit equation

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Characteristics of low-latitude ionospheric depletions and enhancements during solar minimum

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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 2012年第A10期117卷

作者： Haaser, R. A. Earle, G. D. Heelis, R. A. Klenzing, J. Stoneback, R. Coley, W. R. Burrell, A. G. Univ Texas Dallas WB Hanson Ctr Space Sci Richardson TX 75080 USA Virginia Polytech Inst & State Univ Ctr Space Sci & Engn Blacksburg VA 24061 USA NASA Goddard Space Flight Ctr Greenbelt MD 20771 USA

Under the waning solar minimum conditions during 2009 and 2010, the Ion Velocity Meter, part of the Coupled Ion Neutral Dynamics Investigation aboard the Communication/Navigation Outage Forecasting System satellite, is used to measure in situ nighttime ion densities and drifts at altitudes between 400 and 550 km during the hours 21:00-03:00 solar local time. A new approach to detecting and classifying well-formed ionospheric plasma depletions and enhancements (bubbles and blobs) with scale sizes between 50 and 500 km is used to develop geophysical statistics for the summer, winter, and equinox seasons during the quiet solar conditions. Some diurnal and seasonal geomagnetic distribution characteristics confirm previous work on equatorial irregularities and scintillations, while other elements reveal new behaviors that will require further investigation before they may be fully understood. Events identified in the study reveal very different and often opposite behaviors of bubbles and blobs during solar minimum. In particular, more bubbles demonstrating deeper density fluctuations and faster perturbation plasma drifts typically occur earlier near the magnetic equator, while blobs of similar magnitude occur more often far away from the geomagnetic equator closer to midnight.

关键词： blobs bubbles depletions enhancements ionosphere irregularities

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Three-Dimensional Imaging of a Radially Propagating Plasma Blob Using Conditional Sampling Techniques

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IEEE TRANSACTIONS ON PLASMA SCIENCE 2011年第11期39卷 3018-3019页

作者： Furno, Ivo Theiler, Christian Fasoli, Ambrogio Labit, Benoit Ecole Polytech Fed Lausanne Assoc Euratom Confederat Suisse Ctr Rech Phys Plasmas CH-1015 Lausanne Switzerland

We present 3-D imaging of plasma blobs, generated from ideal interchange turbulence in the TORPEX device, obtained by applying different conditional sampling techniques to electrostatic probe data. Time-evolving spatial profiles of electron density, temperature, and plasma potential can be reconstructed. Three-dimensional imaging is used to gain insight into the radial propagation of plasma blobs.

关键词： blobs conditional sampling filaments Langmuir probes plasma diagnostics plasma transport processes plasma turbulence TORPEX

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Iterative reconstruction for differential phase contrast imaging using spherically symmetric basis functions

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MEDICAL PHYSICS 2011年第8期38卷 4542-4545页

作者： Koehler, Thomas Brendel, Bernhard Roessl, Ewald Philips Technol GmbH Innovat Technol Res Labs D-22335 Hamburg Germany

Purpose: The purpose of this work is to combine two areas of active research in tomographic x-ray imaging. The first one is the use of iterative reconstruction (IR) techniques. The second one is differential phase contrast imaging (DPCI). Methods: The authors derive a maximum likelihood (ML) reconstruction algorithm with regularization for DPCI. Forward and back-projection are implemented using spherically symmetric basis functions (blobs) and differential footprints, thus completely avoiding the need for numerical differentiation throughout the reconstruction process. The method is applied to the problem of reconstruction of an object from sparsely sampled projections. Results: The results show that the proposed method can handle the sparsely sampled data efficiently. In particular no streak artifacts are visible which are present in images obtained by filtered back-projection (FBP). Conclusions: IR algorithms have a wide spectrum of proven advantages in the area of conventional computed tomography. The present work describes for the first time, how a matched forward and back-projection can be implemented for DPCI, which is furthermore free of any heuristics. The newly developed ML reconstruction algorithm for DPCI shows that for the case of sparsely sampled projection data, an improvement in image quality is obtained that is qualitatively comparable to a corresponding situation in conventional x-ray imaging. Based on the proposed operators for forward and back-projection, a large variety of IR algorithms is thus made available for DPCI. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3608906]

关键词： iterative reconstruction differential phase contrast imaging compressed sensing blobs

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Using Spherical Basis Functions on a Polar Grid for Iterative Image Reconstruction in Small Animal PET

Using Spherical Basis Functions on a Polar Grid for Iterativ...

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Conference on Medical Imaging 2011 - Physics of Medical Imaging

作者： Cabello, Jorge Oliver, Josep F. Rafecas, Magdalena Univ Valencia CSIC Inst Fis Corpuscular IFIC Valencia Spain

ISBN: (纸本)9780819485038

Statistical iterative methods have been extensively demonstrated to outperform analytical methods in terms of image quality in nuclear imaging. In the method, the mathematically unknown biodistribution is usually represented by cubic basis functions in 3D. Alternatively, spherical basis functions have demonstrated lower noise produced in the resulting reconstructed images. Additionally, the system response matrix (SRM), a key element required by iterative methods, is usually too large to be stored in random access memory of a regular computer. The SRM can be calculated prior to reconstruction and stored on-disk, and thus be directly accessed during the reconstruction process. But this approach usually makes the process too time consuming. To reduce the number of elements to be computed and stored, a common approach uses the scanner symmetries. In this work we use polar voxels, reducing the number of non-zero elements to be computed by a factor 72, allowing us to speed up the Monte-Carlo simulations in which the computation of the SRM is based. In this work we combine the use blobs, a type of spherical basis function, as basis functions and a polar representation in the SRM. The latter is especially important for blobs, given that due to the overlapping of blobs, the size of the SRM significantly increases. This work will show a quantitative comparison of reconstructed images using Cartesian voxels, polar voxels and blobs. We will show that blobs reduce image noise compared to voxels, producing a lower spatial resolution degradation, compared to polar voxels after Gaussian filtering.

关键词： PET iterative statistical reconstruction Monte Carlo system response matrix Spherical basis functions blobs polar voxels

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