Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Experimental Studies And Modeling Of Divertor Plasma Detachment In H Mode Discharges In The Asdex Upgrade Tokamak
Download Experimental Studies And Modeling Of Divertor Plasma Detachment In H Mode Discharges In The Asdex Upgrade Tokamak full books in PDF, epub, and Kindle. Read online Experimental Studies And Modeling Of Divertor Plasma Detachment In H Mode Discharges In The Asdex Upgrade Tokamak ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Experimental Studies and Modeling of Divertor Plasma Detachment in H-Mode Discharges in the ASDEX Upgrade Tokamak by : Felix Reimold
Download or read book Experimental Studies and Modeling of Divertor Plasma Detachment in H-Mode Discharges in the ASDEX Upgrade Tokamak written by Felix Reimold and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Modeling of Boundary Transport and Divertor Target Heat Flux - Implications for Advanced Divertor Concepts by : Sean Bozkurt Ballinger
Download or read book Modeling of Boundary Transport and Divertor Target Heat Flux - Implications for Advanced Divertor Concepts written by Sean Bozkurt Ballinger and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tokamaks are currently being designed and built to achieve net positive unharnessed fusion energy, an important milestone on the path to electricity production. Experimental trends predict an additional challenge in these upcoming devices: a decrease in the area of the metal wall on which the plasma deposits significant heat flux, increasing the likelihood of melting damage. The heat deposition area is proportional to a parameter called the heat flux width, which decreases with increasing poloidal magnetic field and average plasma pressure. In devices designed to achieve physics breakeven such as ITER and SPARC, the heat flux width is predicted by some estimates to be less than 1 millimeter. It is therefore crucial to develop methods to more accurately predict the heat flux width and to mitigate large heat fluxes. Data from the Alcator C-Mod tokamak are particularly relevant in the effort to predict conditions in SPARC, as both are designed to use a higher magnetic field than other major tokamak experiments. Before this work, the relationship between the heat flux width and edge profiles of plasma density and temperature in C-Mod was unknown. Studies with plasma edge simulation codes were limited to a small number of discharges at a time, with many model settings being ad-hoc and difficult to evaluate for general applicability. Simulations of C-Mod had a much shorter outer divertor leg compared to SPARC, making it difficult to use detachment studies in C-Mod to speculate on detachment in SPARC. Finally, there was only a rough idea of edge plasma conditions in SPARC, and it was not known whether detachment would even be feasible. This thesis uses data from Alcator C-Mod and simulations with the UEDGE code to investigate heat flux width scalings, detachment, and advanced divertor concepts to inform the design of next-generation tokamaks that can pro duce significant fusion energy while remaining safe against heat flux damage. This thesis begins by augmenting a C-Mod heat flux width database (containing ~300 discharges) with midplane density and temperature profile data. Detailed analysis finds that the outer target heat flux width depends on the edge plasma pressure, but fails to find a clear dependence on edge gradients. The scaling of the heat flux width with the edge pressure varies by confinement mode and is used to confirm predictions of the heat flux width of 0.2-0.4 mm in SPARC and 0.4-0.6 mm in ITER H-mode scenarios. The UEDGE code is then used to simulate the edge of Alcator C-Mod plasmas. 75 discharges from the heat flux width database are successfully modeled in UEDGE using a fully automated process that matches experimental midplane density and temperature profiles. The resulting heat flux width in UEDGE is then compared to experimental measurements, and it is found that the UEDGE and experimental values are correlated but that UEDGE overestimates the heat flux width by an average factor of 1.8. The UEDGE-modeled discharges are modified to include single-particle drift effects and (separately) to remove flux limits. These changes do not significantly improve the UEDGE heat flux width match to experiment but demonstrate the capability of this framework to evaluate which settings in the UEDGE model improve agreement with experiment over the large range of edge plasma conditions included in the C-Mod database. One particular C-Mod attached H-mode discharge is then simulated in UEDGE, and a good match is achieved to experimental data at the midplane and outer target simultaneously with full drift effects included in the model. This discharge is also simulated with a ~2x longer outer divertor leg, an important component of advanced divertor concepts that could enable better high heat flux handling. Detachment is found to occur when a nitrogen impurity is introduced at a fixed fraction of 3.5% of the main ion density in the real C-Mod geometry, while with the longer leg, detachment occurs at a significantly lower fraction of 2.4% nitrogen. This bodes well for the SPARC design, which features a long outer leg. Finally, a full-power SPARC H-mode scenario is directly simulated with UEDGE. It is found that detachment is possible at the high heat fluxes and small heat flux width predicted for SPARC and that the heat flux at the targets can remain significantly reduced with a carbon impurity fraction around 1%. This value is not a prediction of the detachment threshold in SPARC due to the use of bifurcated attached and detached solutions obtained at low power, but is encouraging when compared to the detachment thresholds in C-Mod UEDGE simulations. This study confirms that detachment is a promising solution to mitigate high heat fluxes in the SPARC full-power scenario.
Book Synopsis Current Understanding of Divertor Detachment by :
Download or read book Current Understanding of Divertor Detachment written by and published by . This book was released on 2008 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Euro Abstracts written by and published by . This book was released on 1995 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis H-mode Discharges with Feedback-controlled Radiative Boundary in the ASDEX Upgrade Tokamak by : Arne Kallenbach
Download or read book H-mode Discharges with Feedback-controlled Radiative Boundary in the ASDEX Upgrade Tokamak written by Arne Kallenbach and published by . This book was released on 1995 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Observation And Modeling Of Inner Divertor Re-attachment In Discharges With Lithium Coatings in NSTX. by :
Download or read book Observation And Modeling Of Inner Divertor Re-attachment In Discharges With Lithium Coatings in NSTX. written by and published by . This book was released on 2011 with total page 832 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the National Spherical Torus Experiment (NSTX), modifications to the inner divertor plasma regimes are observed in high triangularity, H-mode, NBI heated discharges due to lithium coatings evaporated on the plasma facing components. In particular, the drop in the recombination rate, the reduced neutral pressure and the reduced electron density (inferred from Stark broadening measurements of high-n deuterium Balmer lines) suggested that the inner divertor, which is usually detached in discharges without lithium, re-attached. Experimental results are compared to simulations obtained with a 1D partially ionized plasma transport model integrated in the non-local thermodynamic equilibrium radiation transport code CRETIN to understand how the reduced recycling affects the divertor parameters in NSTX discharges with lithium coatings.
Book Synopsis Divertor Plasma Conditions and Their Effect on Carbon Migration in the ASDEX Upgrade Tokamak by : Leena Aho-Mantila
Download or read book Divertor Plasma Conditions and Their Effect on Carbon Migration in the ASDEX Upgrade Tokamak written by Leena Aho-Mantila and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Divertors play a critical role in power and particle exhaust and plasma-material interaction in tokamaks. Of particular concern is the release of impurities from the material components, which reduces the lifetime of the vessel wall and affects the fusion performance. Furthermore, impurities with low charge number can migrate and re-deposit forming potentially tritium-rich layers in the tokamak. Sophisticated numerical simulations are required to understand how the various complex and often nonlinear processes in the plasma boundary affect the divertor performance. This thesis investigates the plasma conditions and the migration of impurities in the divertor region, using numerical code packages with the most complete available description of the relevant physical processes. It is known from earlier studies that the codes have both weaknesses and uncertainties in their models, which limits our current predictive capabilities. In this thesis work, carbon injection experiments at the ASDEX Upgrade tokamak are modelled. The work assesses the present-day boundary plasma models and elucidates impurity migration processes by comparing the simulations with experimental data. The results show that both the local migration and the net erosion of carbon are sensitive to the divertor plasma conditions. Good agreement between the modelled and measured divertor plasma parameters is obtained for a limited operational regime at low density. In this regime, the measured carbon migration is also reproduced in the simulations, and it is shown to be significantly affected by the electric field and the collisionality of the plasma in the divertor region. A significant improvement in code-experiment agreement is obtained after drifts arising from electric and magnetic fields are included in both plasma and impurity simulations. At higher plasma densities, collisionless hot electrons are a potential explanation for the deficiencies observed when benchmarking the plasma models against experiments.
Book Synopsis Third Carolus Magnus Summer School on Plasma Physics by :
Download or read book Third Carolus Magnus Summer School on Plasma Physics written by and published by . This book was released on 1998 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Valojuova written by and published by . This book was released on 1945 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Plasma Surface Interactions in Controlled Fusion Devices by :
Download or read book Plasma Surface Interactions in Controlled Fusion Devices written by and published by . This book was released on 1978 with total page 658 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Predictive Models for the Edge of Tokamak H-mode Plasmas by : Thawatchai Onjun
Download or read book Predictive Models for the Edge of Tokamak H-mode Plasmas written by Thawatchai Onjun and published by . This book was released on 2004 with total page 330 pages. Available in PDF, EPUB and Kindle. Book excerpt: High confinement (H-mode) discharges in tokamak experiments are characterized by a narrow region of steep pressure gradient called the "pedestal" that forms at the edge of the plasma, and often by an instability called an "Edge Localized Mode (ELM)" that periodically removes energy and particles from the edge of the plasma. The parameters at the top of the pedestal and the characteristics of ELMs have a strong influence on the performance of H-mode discharges. In this study, models for the pedestal are developed initially without including the effects of ELMs. The predictions from these pedestal models yield reasonable agreement with experimental data. These pedestal models are then used to provide boundary conditions in an integrated modeling code in order to simulate plasma profiles, such as temperature and density profiles, in existing H-mode experiments. The simulated profiles obtained using predictive boundary conditions and those obtained using experimental boundary conditions have similar agreement with experimental profiles. A more advanced pedestal model with a dynamic model for ELM crashes is developed using a concept of turbulence suppression at the edge of plasma. These pedestal and ELM models are coupled with a core transport model in an integrated modeling code. An advantage of this approach is that it allows for the evolution of plasma pressure and current profiles in the pedestal region, which can lead to an instability that triggers ELM crashes that limit the growth of the pedestal. Pressure-driven ballooning and current-driven peeling instabilities are considered as the possible instabilities that trigger ELM crashes. The combined core and pedestal models, with the effect of ELMs included, are used to study the dependence of triangularity and heating power on the pedestal. An MHD stability analysis is also performed to confirm the validity of these simulations. It is found that plasma edge stability improves as triangularity increases, as a result of access to the second stability region of ballooning modes. Finally, simulations yield a pedestal height with a dependence on heating power similar to that observed experimentally when the ELM crash model is extended to include ELMS triggered by current-driven peeling instabilities.
Book Synopsis H-mode Discharges with Feedback-controlled Radiative Boundaryin the ASDEX Upgrade Tokamak by : A. (and others). Kallenbach
Download or read book H-mode Discharges with Feedback-controlled Radiative Boundaryin the ASDEX Upgrade Tokamak written by A. (and others). Kallenbach and published by . This book was released on 1995 with total page 27 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scrape-off Layer Plasma Modeling for the DIII-D Tokamak by :
Download or read book Scrape-off Layer Plasma Modeling for the DIII-D Tokamak written by and published by . This book was released on 1994 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: The behavior of the scrape-off layer (SOL) region in tokamaks is believed to play an important role determining the overall device performance. In addition, control of the exhaust power has become one of the most important issues in the design of future devices such as ITER and TPX. This paper presents the results of application of 2-D fluid models to the DII-D tokamak, and research into the importance of processes which are inadequately treated in the fluid models. Comparison of measured and simulated profiles of SOL plasma parameters suggest the physics model contained in the UEDGE code is sufficient to simulate plasmas which are attached to the divertor plates. Experimental evidence suggests the presence of enhanced plasma recombination and momentum removal leading to the existence of detached plasma states. UEDGE simulation of these plasmas obtains a bifurcation to a low temperature plasma at the divertor, but the plasma remains attached. Understanding the physics of this detachment is important for the design of future devices. Analytic studies of the behavior of SOL plasmas enhance our understanding beyond that achieved with fluid modeling. Analysis of the effect of drifts on sheath structure suggest these drifts may play a role in the detachment process. Analysis of the turbulent-transport equations indicate a bifurcation which is qualitatively similar to the experimentally different behavior of the L- and H-mode SOL. Electrostatic simulations of conducting wall modes suggest possible control of the SOL width by biasing.
Download or read book Fusion Science and Technology written by and published by . This book was released on 2006 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Driven Rotation, Self-Generated Flow, and Momentum Transport in Tokamak Plasmas by : John Rice
Download or read book Driven Rotation, Self-Generated Flow, and Momentum Transport in Tokamak Plasmas written by John Rice and published by Springer Nature. This book was released on 2022-01-13 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive look at the state of the art of externally driven and self-generated rotation as well as momentum transport in tokamak plasmas. In addition to recent developments, the book includes a review of rotation measurement techniques, measurements of directly and indirectly driven rotation, momentum sinks, self-generated flow, and momentum transport. These results are presented alongside summaries of prevailing theory and are compared to predictions, bringing together both experimental and theoretical perspectives for a broad look at the field. Both researchers and graduate students in the field of plasma physics will find this book to be a useful reference. Although there is an emphasis on tokamaks, a number of the concepts are also relevant to other configurations.
Book Synopsis Helium Transport and Exhaust Studies of H-mode Discharges in the DIII-D Tokamak by :
Download or read book Helium Transport and Exhaust Studies of H-mode Discharges in the DIII-D Tokamak written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A collaborative program has been initiated to measure helium (He) transport and exhaust on DIII-D in L-mode, ELM-free H-mode, and ELMing H-mode. These diverted plasmas operating in enhanced confinement regimes should provide valuable information for the International Thermonuclear Experimental Reactor (ITER). To simulate the presence of He ash in DIII-D, a 50 ms He puff is injected into a DIII-D plasma, resulting in a He concentration of [approximately] 15%. The time dependence of the He density profiles in the plasma core is measured with charge-exchange recombination spectroscopy and the He spatial distribution on the diverter floor is studied with an impurity monitor array. The dependence of core transport diffusivities as a function of ELM frequency have been studied and the first demonstration made of He exhaust from an H-mode plasma in a diverted tokamak. The exhaust rate of He from these ELMing H-mode plasmas appears to be within the acceptable range for a fusion reactor, like ITER, based on a measured value of [tau]*[sub He]/[tau]E [approx]14.
Book Synopsis Divertor Plasma Studies on DIII-D by :
Download or read book Divertor Plasma Studies on DIII-D written by and published by . This book was released on 1996 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma provides separation between the first wall and the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be required in the next generation of tokamaks, for without it, the divertor engineering requirements are very demanding. To successfully demonstrate a radiative divertor, a highly radiative condition with significant volume recombination must be achieved in the divertor, while maintaining a low impurity content in the core plasma. Divertor plasma properties are determined by a complex interaction of classical parallel transport, anomalous perpendicular transport, impurity transport and radiation, and plasma wall interaction. In this paper the authors describe a set of experiments on DIII-D designed to provide detailed two dimensional documentation of the divertor and SOL plasma. Measurements have been made in operating modes where the plasma is attached to the divertor strike plate and in highly radiating cases where the plasma is detached from the divertor strike plate. They also discuss the results of experiments designed to influence the distribution of impurities in the plasma using enhanced SOL plasma flow. Extensive modeling efforts will be described which are successfully reproducing attached plasma conditions and are helping to elucidate the important plasma and atomic physics involved in the detachment process.
