Non-diffusive Cross Field Transport in Scrape-off-layer in Tokamak PDF Download
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Author: Guanghui Q. Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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Book Description
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: Guanghui Q. Yu
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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Book Description
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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 9
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Book Description
Fast intermittent transport has been observed in the scrape-off layer (SOL) of major tokamaks including Alcator C-Mod, DIII-D, and NSTX. This kind of transport is not diffusive but rather convective. It strongly increases plasma flux to the chamber walls and enhances the recycling of neutral particles in the main chamber. We discuss anomalous cross-field convection (ACFC) model for impurity and main plasma ions and its relation to intermittent transport events, i.e. plasma density blobs and holes in the SOL. Along with plasma diffusivity coefficients, our transport model introduces time-independent anomalous cross-field convective velocity. In the discharge modelling, diffusivity coefficients and ACFC velocity profiles are adjusted to match a set of representative experimental data. We use this model in the edge plasma physics code UEDGE to simulate the multi-fluid two-dimensional transport for these three tokamaks. We present simulation results suggesting the dominance of anomalous convection in the far SOL transport. These results are consistent with the hypothesis that the chamber wall is an important source of impurities and that different impurity charge states have different directions of anomalous convective velocity.
Author: Brian LaBombard
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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Book Description
Particle transport in the edge plasma and scrape-off layer will play a key role in the performance and operation of a tokamak fusion reactor: setting the width of the scrape-off layer density profile and its impurity screening characteristics, regulating the energetic particle fluxes onto first-wall components and associated impurity generation rates, and determining the effectiveness of the divertor in receiving particle exhaust and controlling neutral pressures in the main-chamber. The processes which govern particle transport involve plasma turbulence, phenomena which can not yet be reliably computed from a first-principles numerical simulation. Thus, in order to project to a reactor-scale experiment, such as ITER, one must first develop an understanding of particle transport phenomena based on experimental measurements in existing plasma fusion devices. Over the past few years of research, a number of fundamental advances in the understanding of the cross-field particle transport physics have occurred, replacing crude, incorrect, and often misleading transport models such as the "constant diffusion coefficient" model with a more appropriate description of the phenomenon. It should be noted that this description applies to transport processes in the absence of ELM phenomenon, i.e., physics underlying the "background" plasma state. In this letter, we first review the experimental support for this understanding which is based extensively on data from L-mode discharges and from H-mode discharges at time intervals without ELMs. We then comment on its implications for ITER.
Author: John Wesson
Publisher: Oxford University Press
ISBN: 0199592233
Category : Science
Languages : en
Pages : 828
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Book Description
The tokamak is the principal tool in controlled fusion research. This book acts as an introduction to the subject and a basic reference for theory, definitions, equations, and experimental results. The fourth edition has been completely revised, describing their development of tokamaks to the point of producing significant fusion power.
Author: Marshall N. Rosenbluth
Publisher: Springer Science & Business Media
ISBN: 9781563961311
Category : Science
Languages : en
Pages : 514
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Book Description
Market: Scientists and students involved in thermonuclear fusion research. Thermonuclear fusion research using the confinement device tokamak represents one of the most prominent science projects in the second half of the 20th century. International Tokamak Community is now committing significant effort and funds to experiments with burning plasma, hot and dense enough to produce significant nuclear fusion reactions. The methods used to enhance tokamak performance have a profound and immediate effect on machine design. This book provides an up-to-date account of research in tokamak fusion and puts forward innovative ideas in confinement physics.
Author: Richard Joseph Procassini
Publisher:
ISBN:
Category : Plasma confinement
Languages : en
Pages : 584
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Author: I. H. Hutchinson
Publisher: Cambridge University Press
ISBN: 9780521675741
Category : Science
Languages : en
Pages : 460
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Book Description
This book provides a systematic introduction to the physics of plasma diagnostics measurements. It develops from first principles the concepts needed to plan, execute and interpret plasma measurements, making it a suitable book for graduate students and professionals with little plasma physics background. The book will also be a valuable reference for seasoned plasma physicists, both experimental and theoretical, as well as those with an interest in space and astrophysical applications. This second edition is thoroughly revised and updated, with new sections and chapters covering recent developments in the field.
Author: Ruth Laengner
Publisher: Forschungszentrum Jülich
ISBN: 3893369244
Category :
Languages : en
Pages : 175
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Author: Hans A. Claaßen
Publisher:
ISBN:
Category :
Languages : de
Pages : 0
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Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 704
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