The Numerical Study of Filament Dynamics in Tokamak Scrape-off Layer Plasmas PDF Download
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Author: William Agnelo Gracias
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Filamentary transport has been experimentally observed in a multitude of magnetically confined fusion devices, especially of the tokamak type. Filaments are carriers of large quantities of particles and heat and as such, their presence in the SOL has implications for the target surface design in future fusion reactors. To better understand their nature, this doctoral thesis studies filaments through computer simulations as isolated structures and spontaneously forming structures, using a 3D fluid model called the TOKAM3X. Parametric studies using the model for studying the effect of the plasma's parallel resistivity and magnetic shear, and also the filament's parallel extension and size/density amplitude are performed and analysed. The studies reveal the strong impact of the parallel resistivity on filament velocities and hence their lifetimes in the SOL. The doctoral work also looked at the impact of strong local magnetic shear and the separatrix on the motion and generation of filaments. The results from the simulations performed reveal that strong shear mechanisms may be key to the destruction and formation of filaments. Further, a comparison of spontaneously forming and seeded filaments shows that seeded filaments do not behave completely the same way as spontaneously forming ones. But their mean velocity characteristics are still retained to a good degree.
Author: William Agnelo Gracias
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Filamentary transport has been experimentally observed in a multitude of magnetically confined fusion devices, especially of the tokamak type. Filaments are carriers of large quantities of particles and heat and as such, their presence in the SOL has implications for the target surface design in future fusion reactors. To better understand their nature, this doctoral thesis studies filaments through computer simulations as isolated structures and spontaneously forming structures, using a 3D fluid model called the TOKAM3X. Parametric studies using the model for studying the effect of the plasma's parallel resistivity and magnetic shear, and also the filament's parallel extension and size/density amplitude are performed and analysed. The studies reveal the strong impact of the parallel resistivity on filament velocities and hence their lifetimes in the SOL. The doctoral work also looked at the impact of strong local magnetic shear and the separatrix on the motion and generation of filaments. The results from the simulations performed reveal that strong shear mechanisms may be key to the destruction and formation of filaments. Further, a comparison of spontaneously forming and seeded filaments shows that seeded filaments do not behave completely the same way as spontaneously forming ones. But their mean velocity characteristics are still retained to a good degree.
Author: C Wendell Horton, Jr
Publisher: World Scientific
ISBN: 9814678686
Category : Science
Languages : en
Pages : 248
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The promise of a vast and clean source of thermal power drove physics research for over fifty years and has finally come to collimation with the international consortium led by the European Union and Japan, with an agreement from seven countries to build a definitive test of fusion power in ITER. It happened because scientists since the Manhattan project have envisioned controlled nuclear fusion in obtaining energy with no carbon dioxide emissions and no toxic nuclear waste products.This large toroidal magnetic confinement ITER machine is described from confinement process to advanced physics of plasma-wall interactions, where pulses erupt from core plasma blistering the machine walls. Emissions from the walls reduce the core temperature which must remain ten times hotter than the 15 million degree core solar temperature to maintain ITER fusion power. The huge temperature gradient from core to wall that drives intense plasma turbulence is described in detail.Also explained are the methods designed to limit the growth of small magnetic islands, the growth of edge localized plasma plumes and the solid state physics limits of the stainless steel walls of the confinement vessel from the burning plasma. Designs of the wall coatings and the special 'exhaust pipe' for spent hot plasma are provided in two chapters. And the issues associated with high-energy neutrons — about 10 times higher than in fission reactions — and how they are managed in ITER, are detailed.
Author: Guanghui Q. Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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In recent years, coherent structures in edge plasmas are believed to be one of the major factors in cross-field transport. The present dissertation is dedicated to using theoretical and numerical methods to study the dynamics of individual coherent structure, or so-called blob, moving from bulk plasma to the chamber wall. Blob is a filament structure extended along magnetic filed lines. We focus on two different types of blob. One is ending up at target plates, the other is not, i.e. the SOL and HB blobs. Two dimensional blob models are derived. Characteristic spatial scale, time scale, and velocity for blob are obtained and calculated for different tokamaks. They are in agreement with experimental measurements. Scaling analysis shows blob dynamics sensitive to spatial scale length. Stability analysis shows that blobs with spatial scales less than may move as coherent structures to large distances. In the SOL model simulation we have found the most structurally stable blob has scale length around . Blobs smaller than evolve into mushroom-like structures. Blobs larger than are subject to the fingering instability. Blobs with spatial scales close to can coherently move to long distances. Simulation results show that high density background effectively narrows down blob size and the inertia term in vorticity equation drives blob to mushroom shape and builds up vortex dipole within the structure. We also compare results with and without the Boussinesq approximation. In the HB model simulation it is shown that blobs have wider stable range. Their steep nose and long relaxation tail can explain experimentally detected asymmetric profile. HB blob moves with a constant velocity. In the biasing potential model a critical magnitude of the potential barrier is derived. A strong deformation of the blob as coherent structure will be observed while blob pass through a barrier higher than the critical value. Simulation results confirm the theoretical prediction. In the rotational blob model simulation results show the suppression of radial velocity and the generation of poloidal velocity. Fingering and mushroom effects are inhibited, but blobs evolve into rotational instability at later stage.
Author:
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Category : Power resources
Languages : en
Pages : 1052
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Semiannual, with semiannual and annual indexes. References to all scientific and technical literature coming from DOE, its laboratories, energy centers, and contractors. Includes all works deriving from DOE, other related government-sponsored information, and foreign nonnuclear information. Arranged under 39 categories, e.g., Biomedical sciences, basic studies; Biomedical sciences, applied studies; Health and safety; and Fusion energy. Entry gives bibliographical information and abstract. Corporate, author, subject, report number indexes.
Author:
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Category : Power resources
Languages : en
Pages : 1048
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Category : Controlled fusion
Languages : en
Pages : 100
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Category : Aeronautics
Languages : en
Pages : 994
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Author:
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Category :
Languages : en
Pages : 44
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The structure of a collisionless scrape-off-layer (SOL) plasma in tokamak reactors is being studied to define the electron distribution function and the corresponding sheath potential between the divertor plate and the edge plasma. The collisionless model is shown to be valid during the thermal phase of a plasma disruption, as well as during the newly desired low-recycling normal phase of operation with low-density, high-temperature, edge plasma conditions. An analytical solution is developed by solving the Fokker-Planck equation for electron distribution and balance in the SOL. The solution is in good agreement with numerical studies using Monte-Carlo methods. The analytical solutions provide an insight to the role of different physical and geometrical processes in a collisionless SOL during disruptions and during the enhanced phase of normal operation over a wide range of parameters.
Author:
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Category :
Languages : en
Pages : 10
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A summary is given of the work carried out under the LDRD project 09-ERD-025 entitled Scrape-Off-Layer Flow Studies in Tokamaks. This project has lead to implementation of the new prototype Fourier Transform Spectrometer edge plasma flow diagnostic on the DIII-D National Fusion Facility at General Atomics, acquisition of carbon impurity concentration and flow data, and demonstration that the resulting data compare reasonably well with LLNL's edge plasma transport code UEDGE. Details of the work are contained in attached published papers, while the most recent results that are being written-up for publication are summarized in the report. Boundary plasma flows in tokamak fusion devices are key in determining the distribution of fuel and impurity ions, with tritium build-up in the walls an especially critical operational issue. The intrusion of impurity ions to the hot plasma core region can result in serious energy-loss owing to line radiation. However, flow diagnostic capability has been severely limited in fusion-relevant hot edge plasmas where Langmuir-type probes cannot withstand the high heat flux and traditional Doppler spectroscopy has limited resolution and signal strength. Thus, new edge plasma flow diagnostic capabilities need to be developed that can be used in existing and future devices such as ITER. The understanding of such flows requires simulation with 2-dimensional transport codes owing to the geometrical complexity of the edge region in contact with material surfaces and the large number of interaction physical processes including plasma flow along and across the magnetic field, and coupling between impurity and neutral species. The characteristics of edge plasma flows are substantially affected by cross-magnetic-field drifts (ExB/B2 and BxVB/B2), which are known to introduce substantial convergence difficulty for some cases. It is important that these difficulties be overcome so that drifts can be included in transport models, both for validation with existing data and for projection to future devices.
Author:
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Category : Physics
Languages : en
Pages : 1058
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