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Author: Publisher: ISBN: Category : Languages : en Pages : 16
Book Description
A qualitative as well as quantitative evaluation of experimentally observed plasma parameters in the detached regime proves to be difficult for several tokamaks. A series of ohmic discharges have been performed in ASDEX Upgrade and DIII-D at similar as possible plasma parameters and at different line averaged densities, {bar n}{sub e}. The experimental data represent a set of well diagnosed discharges against which numerical simulations are compared. For the numerical modeling the fluid-code B2.5 coupled to the Monte Carlo neutrals transport code EIRENE is used. Only the combined enhancement of effects, such as geometry, drift terms, neutral conductance, increased radial transport and divertor target composition, explains a significant fraction of the experimentally observed asymmetries of the ion fluxes as a function of {bar n}{sub e} to the inner and outer target plates in ASDEX Upgrade. The relative importance of the mechanisms leading to detachment are different in DIII-D and ASDEX Upgrade.
Author: Publisher: ISBN: Category : Languages : en Pages : 16
Book Description
A qualitative as well as quantitative evaluation of experimentally observed plasma parameters in the detached regime proves to be difficult for several tokamaks. A series of ohmic discharges have been performed in ASDEX Upgrade and DIII-D at similar as possible plasma parameters and at different line averaged densities, {bar n}{sub e}. The experimental data represent a set of well diagnosed discharges against which numerical simulations are compared. For the numerical modeling the fluid-code B2.5 coupled to the Monte Carlo neutrals transport code EIRENE is used. Only the combined enhancement of effects, such as geometry, drift terms, neutral conductance, increased radial transport and divertor target composition, explains a significant fraction of the experimentally observed asymmetries of the ion fluxes as a function of {bar n}{sub e} to the inner and outer target plates in ASDEX Upgrade. The relative importance of the mechanisms leading to detachment are different in DIII-D and ASDEX Upgrade.
Author: Asgeir Brekke Publisher: Wiley ISBN: 9780471960188 Category : Science Languages : en Pages : 0
Book Description
An overview of the relationship between the near space and upper atmospheres. This book discusses basic elements in the auroral process including interplanetary plasma and fields, atmospheres, geomagnetic fields and the ionosphere.
Author: P.C Stangeby Publisher: CRC Press ISBN: 9780750305594 Category : Science Languages : en Pages : 738
Book Description
The Plasma Boundary of Magnetic Fusion Devices introduces the physics of the plasma boundary region, including plasma-surface interactions, with an emphasis on those occurring in magnetically confined fusion plasmas. The book covers plasma-surface interaction, Debye sheaths, sputtering, scrape-off layers, plasma impurities, recycling and control, 1D and 2D fluid and kinetic modeling of particle transport, plasma properties at the edge, diverter and limiter physics, and control of the plasma boundary. Divided into three parts, the book begins with Part 1, an introduction to the plasma boundary. The derivations are heuristic and worked problems help crystallize physical intuition, which is emphasized throughout. Part 2 provides an introduction to methods of modeling the plasma edge region and for interpreting computer code results. Part 3 presents a collection of essays on currently active research hot topics. With an extensive bibliography and index, this book is an invaluable first port-of-call for researchers interested in plasma-surface interactions.
Author: Publisher: ISBN: Category : Languages : en Pages : 20
Book Description
MHD theory applied to tokamak plasma scrape-off layer (SOL) equilibria requires Pfirsch-Schlueter current, which, because the magnetic lines are open, normally closes through electrically conducting divertor or limiter components. During detached divertor operation the Pfirsch-Schlueter current path to the divertor target is sometimes blocked, in which case theory predicts that the plasma develops a poloidal pressure gradient around the upstream SOL and a corresponding parallel flow, in order to satisfy all the conditions of MHD equilibrium. This paper reports the only known examples of detached diverted plasma in the DIII-D tokamak with blocked Pfirsch-Schlueter current, and they show no clear SOL poloidal pressure differences. However, the predicted pressure differences are small, near the limit of detectability with the available diagnostics. In the more usual DIII-D partially detached divertor operation mode, the Pfirsch-Schlueter current appears to never be blocked, and no unusual poloidal pressure differences are observed, as expected. Finally, a local overpressure is observed just inside the magnetic separatrix near the X-point in both attached and detached Ohmically heated plasmas.
Author: Rebecca Lee Masline Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
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
Book Description
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.
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Author: Mark Lloyd Adams
Author: Asgeir Brekke
Author: P.C Stangeby
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Author: Steffen Potzel
Author: Rebecca Lee Masline
Author: Sergei Krasheninnikov
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