Role of Edge Turbulence in Detached Divertor Plasmas PDF Download

Author: Fongyan Gang
Publisher:
ISBN:
Category :
Languages : en
Pages : 16

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Author: Prof. Sergi Krasheninnikov
Publisher:
ISBN:
Category :
Languages : en
Pages :

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In the last few years, it was clearly shown that cross-field transport in the far SOL could be significantly faster than previously thought and that this transport exhibited convective rather then diffusive features. As a result, in high density cases the plasma coming into the SOL from the core recycled at the wall of the tokamak main chamber, rather than flowing into the divertor and recycling there, as the conventional picture of edge plasma flows would suggest. It was also shown that coherent structures, often called ''blobs'', played very important roles in the particle and energy transport inside the SOL region for both L and H confinement modes. The blobs seen in the SOL are extended along the magnetic field lines and have a plasma density two to three times higher than the ambient SOL plasma density and poloidal and radial scales of about 1 cm. In experimental measurements, the blobs propagated in radial direction towards the chamber wall with a velocity {approx} 10{sup 5} cm/s, and the contribution of non-diffusive flux associated with transport of blobs to the total particle flux in the far SOL attained 70-90%. In addition, recent assessment of experimental data and theoretical models shows that plasma propagation into the SOL during ELM is somewhat similar to that of blobs.

Author: Per Helander
Publisher: Cambridge University Press
ISBN: 9780521020985
Category : Science
Languages : en
Pages : 316

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A graduate level text treating transport theory, an essential element of theoretical plasma physics.

Author: B. Lipschultz
Publisher:
ISBN:
Category :
Languages : en
Pages : 9

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Author: Dmitry Meyerson
Publisher:
ISBN:
Category :
Languages : en
Pages : 194

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Controlling the scrape-off layer (SOL) properties in order to limit divertor erosion and extend component lifetime will be crucial to successful operation of ITER and devices that follow, where intermittent thermal loads on the order of GW/m2 are expected. Steady state transport in the edge region is generally turbulent with large, order unity, fluctuations and is convection dominated. Owing to the success of the past fifty years of progress in magnetically confining hot plasmas, in this work we examine convective transport phenomena in the SOL that occur in the relatively "slow", drift-ordered fluid limit, most applicable to plasmas near MHD equilibrium. Diamagnetic charge separation in an inhomogeneous magnetic field is the principal energy transfer mechanism powering turbulence and convective transport examined in this work. Two possibilities are explored for controlling SOL conditions. In chapter 2 we review basic physics underlying the equations used to model interchange turbulence in the SOL and use a subset of equations that includes electron temperature and externally applied potential bias to examine the possibility of suppressing interchange driven turbulence in the Texas Helimak. Simulated scans in E0×B0 flow shear, driven by changes in the potential bias on the endplates appears to alter turbulence levels as measured by the mean amplitude of fluctuations. In broad agreement with experiment negative biasing generally decreases the fluctuation amplitude. Interaction between flow shear and interchange instability appears to be important, with the interchange rate forming a natural pivot point for observed shear rates. In chapter 3 we examine the possibility of resonant magnetic perturbations (RMPs) or more generally magnetic field-line chaos to decrease the maximum particle flux incident on the divertor. Naturally occurring error fields as well as RMPs applied for stability control are known to cause magnetic field-line chaos in the SOL region of tokamaks. In chapter 3 2D simulations are used to investigate the effect of the field-line chaos on the SOL and in particular on its width and peak particle flux. The chaos enters the SOL dynamics through the connection length, which is evaluated using a Poincaré map. The variation of experimentally relevant quantities, such as the SOL gradient length scale and the intermittency of the particle flux in the SOL, is described as a function of the strength of the magnetic perturbation. It is found that the effect of the chaos is to broaden the profile of the sheath-loss coefficient, which is proportional to the inverse connection length. That is, the SOL transport in a chaotic field is equivalent to that in a model where the sheathloss coefficient is replaced by its average over the unperturbed flux surfaces. Both fully chaotic and the flux-surface averaged approximation of RMP application significantly lower maximum parallel particle flux incident on the divertor.

Author: Rebecca Lee Masline
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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In this dissertation, we investigate two proposed features aimed at improving the performance of the divertor exhaust system in tokamak nuclear fusion devices. Specifically, we assess the influence of the "inverse" plasma sheath and long-leg divertor configurations on the divertor plasma using numerical simulations. First, we investigate the "inverse" plasma sheath, which has been suggested to prevent the flow of ions to the wall and promote divertor detachment. We use the UEDGE code to simulate the physics of both the inverse and standard (Bohm) sheath regime at the divertor targets. Our results show little difference in the overall plasma state, but an increase in electron heat flux to the divertor targets. Additionally, we observe a bifurcation behavior related to plasma recombination effects, and present an analytical model of this behavior. Second, we evaluate the long outer divertor leg, which is designed to increase volumetric dissipation, enhance turbulence spreading, and extend the distance between the material surface and the fragile core plasma. Using the SOLPS4.3 code, we assess the transition to the detached divertor regime, with scans on plasma density, transport coefficients, and multiple impurity species. Our results show a significant contribution to the energy balance from cross-field transport to the side walls and considerable recycling of impurities along the long leg, enabling delocalization of the radiated heat flux. Overall, this dissertation provides important insights into the physics associated with these proposed divertor features. The results suggest that the inverse plasma sheath may not have a significant impact on divertor plasma detachment, while the long-leg divertor configuration has potential to improve divertor performance by reducing impurity radiation localization and enhancing energy dissipation through cross-field transport. These findings contribute to the ongoing efforts to develop more efficient and effective divertor exhaust systems for tokamak fusion devices.

Author: Sergei Krasheninnikov
Publisher: Springer Nature
ISBN: 3030495949
Category : Science
Languages : en
Pages : 269

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This book reviews the current state of understanding concerning edge plasma, which bridges hot fusion plasma, with a temperature of roughly one million degrees Kelvin with plasma-facing materials, which have melting points of only a few thousand degrees Kelvin. In a fact, edge plasma is one of the keys to solution for harnessing fusion energy in magnetic fusion devices. The physics governing the processes at work in the edge plasma involves classical and anomalous transport of multispecies plasma, neutral gas dynamics, atomic physics effects, radiation transport, plasma-material interactions, and even the transport of plasma species within the plasma-facing materials. The book starts with simple physical models, then moves on to rigorous theoretical considerations and state-of-the-art simulation tools that are capable of capturing the most important features of the edge plasma phenomena. The authors compare the conclusions arising from the theoretical and computational analysis with the available experimental data. They also discuss the remaining gaps in their models and make projections for phenomena related to edge plasma in magnetic fusion reactors.

Author: Michael Shats
Publisher: World Scientific
ISBN: 9812566988
Category : Science
Languages : en
Pages : 397

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This book is based on the lectures delivered at the 19th Canberra International Physics Summer School held at the Australian National University in Canberra (Australia) in January 2006.The problem of turbulence and coherent structures is of key importance in many fields of science and engineering. It is an area which is vigorously researched across a diverse range of disciplines such as theoretical physics, oceanography, atmospheric science, magnetically confined plasma, nonlinear optics, etc. Modern studies in turbulence and coherent structures are based on a variety of theoretical concepts, numerical simulation techniques and experimental methods, which cannot be reviewed effectively by a single expert.The main goal of these lecture notes is to introduce state-of-the-art turbulence research in a variety of approaches (theoretical, numerical simulations and experiments) and applications (fluids, plasmas, geophysics, nonlinear optical media) by several experts. A smooth introduction is presented to readers who are not familiar with the field, while reviewing the most recent advances in the area. This collection of lectures will provide a useful review for both postgraduate students and researchers new to the advancements in this field, as well as specialists seeking to expand their knowledge across different areas of turbulence research.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 8

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A comprehensive set of experiments has been carried out on the DIII-D tokamak to measure the 2-D (R, Z) structure of the divertor plasma in a systematic way using new diagnostics. Measurements cover the divertor radially from inside the X-point to the outer target plate and vertically from the target plate to above the X-point. Identical, repeatable shots were made, each having radial sweeps of the X-point and divertor strike points, to allow complete plasma and radiation profile measurements. Data have been obtained in ohmic, L-mode, ELMing H-mode, and reversed B{sub T} operation ((nabla)B drift away from the X-point). In addition, complete measurements were made of radiative divertor plasmas with a Partially Detached Divertor (PDD) induced by D2 injection and with a Radiating Mantle induced by Impurity injection (RMI) using neon and nitrogen. The data set includes first observations of the radial and poloidal profiles of the X-point, inner and outer leg plasmas in PDD and RMI radiative divertor operation. Preliminary data analysis shows that intrinsic impurities play a critical role in determining the SOL and divertor conditions.

Author: Fulvio Militello
Publisher: Springer Nature
ISBN: 3031173392
Category : Science
Languages : en
Pages : 534

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Book Description
This book serves as an introduction to boundary plasma physics, providing an accessible entry point to the topic of plasma exhaust in magnetic confinement devices. While it delivers a concise, rigorous, and comprehensive account of all the major scientific topics relevant to those working on the subject, it also remains accessible and easy to consult due to its modular and compact structure. Beginning with the basic kinetic and fluid descriptions of plasma, and advancing through plasma-surface interactions, filamentary transport and plasma detachment, to conclude with a discussion of divertor configurations, this book represents a necessary and timely addition to the literature on the fast-growing field of boundary plasma physics. It will appeal to experienced theoreticians or experimentalists looking to enter the field as well as graduate students wishing to learn about it.