Download or read book Microtearing Modes in the Tokamak Pedestal written by Joseph Leland Larakers and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: An economical thermonuclear reactor has the potential to serve as an on-demand, clean, and abundant energy source. The main difficulty is confining the fusion fuel to the large pressures required for the fuel to react. The energy produced from fusion reactions must be collected and confined such that it activates further reactions. Magnetic confinement is a promising strategy. Magnetic confinement devices, such as tokamaks, have steadily improved by identifying and suppressing different mechanisms of heat transport and instability. This dissertation focuses on a single mechanism known as the microtearing mode (MTM). The microtearing mode is an electromagnetic excitation that is localized about rational magnetic surfaces and is driven unstable by electron temperature gradients. The mode tears magnetic surfaces and modifies their structure. The resulting topology relaxes the radial temperature gradient via fast parallel motion. The MTM has recently gained attention as a potentially important instability in the pedestal region of H-mode tokamaks. It is theorized to be responsible for the anomalous electron heat transport and discrete bands of magnetic fluctuations observed experimentally. Here, we revisit the conventional microtearing theory and extend it to study features pertinent to the pedestal region. In doing so, we identify a new crucial parameter for MTM linear stability. This extended theory matches with the experimental observations of magnetic fluctuations and provides an explanation of their discrete nature. With an understanding of the linear dispersion characteristics, we proceed to study the nonlinear evolution of the mode. The dispersion suggests a strong mode-mode resonance between MTM harmonics. A weak turbulence model has been developed to study the nonlinear consequences of these resonances

Download or read book Simulations and Reduced Models for Microtearing Modes in the Tokamak Pedestals written by Max Tian Curie and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Renewable energy can not only help to clean the environment but also create a more peaceful world. Fusion has the potential to provide clean energy with abundant resources. The high energy density (per-footprint) nature of fusion makes it appealing in highly urbanized areas, such as Singapore, which complements wind and solar power. Magnetic confinement fusion (MCF) is one of the most promising routes to thermonuclear fusion energy. Among the prospective MCF configurations, the Tokamak is the most widely implemented scheme. A host of instabilities are suppressed in H-mode (high-confinement mode) plasmas in Tokamaks due to high flow shear and/or steep density gradients in the pedestal (the edge of the plasma). This produces higher confinement and thus better performance than L-mode (low-confinement mode) operation. Transport and instabilities in the pedestal of the plasma are studied more intensively using gyrokinetic simulations thanks to the improvement of computational and experimental capabilities. Recent studies show that the magnetic fluctuations from microtearing modes (MTM) can be commonly observed in magnetic spectrograms [1– 12]. and contribute significant electron heat transport [13–15]. This thesis further investigates MTMs in the pedestal through 3 projects: • Direct comparison between nonlinear gyrokinetic simulations (GENE) and a newly installed magnetic diagnostic Faradayeffect Radial Interferometer-Polarimeter (RIP) [2, 16, 17]. Such a comparison provides strong evidence of the MTM’s importance in the Tokamak pedestal. • A package based on a global reduced model for MTM stability [18, 19] called the slab-like MTM (SLiM) package [20]. This model provides a tool for rapid MTM stability assessment. Applications of its usage will be described in the thesis: determining the stability of MTM, poloidal mode numbers, and equilibrium reconstruction. • Equilibrium reconstruction based on the SLiM model. Neural networks were trained for faster MTM stability assessment. This allows for extensive variations of nominal equilibrium quantities in order to better match the experimentally-observed magnetic frequencies in discharges and hopefully produce more accurate equilibrium reconstructions.

Download or read book Electron Heat Transport in Tokamak H mode Pedestals written by Myriam Hamed and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In H-mode plasmas, the modeling of the pedestal dynamics is an important issue to predict temperature and density profiles in the tokamak edge and therefore in the core. The EPED model, based on the stability of large scales MagnetoHydroDynamic (MHD) modes, is most commonly used to characterize the pedestal region. The EPED model has been successful until now. However, EPED model does not take into account small scales instabilities linked the the sharp pressure gradient and the pedestal characteristics prediction in terms of width and height is still open. Moreover, some recent analysis of JET plasmas suggest that another class of instabilities, called microtearing modes, may be responsible for electron heat transport in the pedestal, and thereby play some role in determining the pedestal characteristics. Microtearing modes belong to a class of instabilities where a modification of the magnetic field line topology is induced at the ion Larmor radius scale. This leads to the formation of magnetic islands, which can enhance the electron heat transport. The stability of MTMs has been theoretically studied in the past showing that a slab current sheet is stable in the absence of collisions. In contrast, recent gyrokinetic simulations in toroidal geometry found unstable MTMs, even at low collisionality. The purpose of our work is to improve the MTM stability understanding by comparing new analytical theory to linear gyrokinetic simulations. More precisely, physical mechanisms (magnetic drift, electric potential) are progressively included in the analytical description to recover the numerical simulations results and to "reconcile" numerical MTM investigations with theory.

Download or read book Electron Temperature Gradient Mode Streamers and the End of the Tokamak Pedestal written by Austin Lee Blackmon and published by . This book was released on 2019 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fusion experiments still show discrepancies in heat flux from expected results calculated from theory and computation; calculations come up short. As needed, work continues in solving the source of these discrepancies. This thesis seeks to provide part of the answer via electron-temperature-gradient (ETG) fluctuations in the pedestal region of tokamaks, investigated with the Gyrokinetic Electromagnetic Numerical Experiment (GENE). While ETG turbulence is sometimes ignored, as it is very small scale, there may be mechanisms that make it a viable explanation of these discrepancies. In this work, we find a non-negligible heat transport from ETG turbulence in the presence of streamers. Additionally, we find a relation between flux, streamers, and velocity shear. Further analysis is required to confirm these findings, but as it stands, this thesis lays the groundwork

Download or read book The Macro and Micro instabilities in the Pedestal Region of the Tokamak written by Jingfei Ma and published by . This book was released on 2015 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper, we present the theoretical and numerical studies of the linear characteristics and nonlinear transport features of the instabilities driven by the steep profile gradient and edge current in the pedestal region of the tokamak. Two important instabilities, the peeling-ballooning (P-B) modes (macro-instability) and the drift-Alfven modes (micro-instability), are studied using the fluid analysis and the BOUT++ codes. In particular, the edge-localized modes (ELMs), which appear to be the energy burst in the nonlinear stage of the peeling-ballooning mode, are numerically studied and the results are compared with the experimental measurement. In addition, the features of the impurity transport in the edge region of the tokamak are theoretically analyzed. Firstly, we explore the fundamental characteristics of the P-B modes and the ELM bursts numerically using the three-field reduced MHD model under the BOUT++ framework, in the shifted-circular geometry, i.e. the limiter tokamak geometry. In the linear simulations, the growth rate and real frequency and the mode structure versus the toroidal mode number (n) are shown. The features of the ELM bursts are shown in the nonlinear simulations, including the time evolution of the relative energy loss (ELM size) and the pedestal profile. Secondly, two original research projects related to the P-B modes and the ELM burst are described. One is the study of the scaling law between the relative energy loss of ELMs and the edge collisionality. We generate a sequence of shifted-circular equilibria with different edge collisionality varying over four orders of magnitude using EFIT. The simulation results are in good agreement with the multi-tokamak experimental data. Another is the study of the differences of the linear behaviors of the P-B modes between the standard and snowflake divertor configurations. Using DIII-D H-mode ElMing equilibria, we found that the differences are due to the local magnetic shear change at the outboard midplane, which is the result of the realization of the snowflake configuration. Finally, the micro-instability, the drift-Alfven instability in the pedestal region of the DIII-D tokamak is studied. A modified six-field Landau fluid model under BOUT++ framework is used to study the linear characteristics and transport features of the drift-Alfven modes. Based on the DIII-D H-mode discharge, a sequence of divertor tokamak equilibria with different pedestal height is generated by the 'VARYPED' tool for our studies. Qualitative agreement is obtained between theoretical analysis and the simulation results in the linear regime. Moreover, the heat transport induced by the drift-Alfven turbulence is explored and the convection level is estimated for both ions and electrons.

Download or read book Comprehensive Dynamic Analysis of the H Mode Pedestal in DIII D written by Andrew Oakleigh Nelson and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The H-mode pedestal, characterized by steep gradients and reduced transport, is an essential feature of tokamak plasmas that couples the cold Scrape-Off-Layer (SOL) to the hot, fusion-relevant core. Though existing magnetohydrodynamic models yield some insight into the pedestal, they are (due to the complexity of interaction between the pedestal and the rest of the plasma) unable to fully predict pedestal behavior from generalized plasma conditions. To progress towards a more comprehensive understanding of pedestal dynamics, a larger context must be considered. Using state-of-the-art modeling and perturbative experimental techniques on DIII-D, this thesis develops a broader empirical understanding of dynamic pedestal behavior that will inform future modeling efforts.The pedestal obeys the physics of the continuity equation, which is set by the sourcing of particles, inter-ELM transport, and boundary conditions. In this light, three phenomena are selected for in-depth study: fueling, transport, and SOL interactions. First, the effect of particle sources on the pedestal structure is examined through a series of dedicated experiments on DIII-D. Gas and pellet fueling techniques are applied to change the neutral ionization profile at similar plasma conditions, showing that the structure of the pedestal can vary significantly with changes to the neutral source profile. Second, a novel experimental technique is used to probe the nature of inter-ELM turbulence, which is linked to the evolution and recovery of the pedestal structure. Additional current is induced in the pedestal region of several DIII-D plasmas, providing a first-of-its-kind experimental demonstration of microtearing modes (MTMs) in the tokamak edge. MTMs may contribute strongly to intense heat fluxes through the pedestal region, potentially providing the groundwork for an entirely physics-based predictive model of pedestal behavior. Finally, to develop a physics understanding of how the SOL boundary condition couples with the pedestal over the course of an entire plasma discharge, detailed modeling work is performed with the UEDGE code as a function of pedestal and ELM conditions. In this section, we establish a dynamic connection between the pedestal structure and divertor behavior, highlighting the need for a comprehensive approach to pedestal physics.

Download or read book Zonal Jets written by Boris Galperin and published by Cambridge University Press. This book was released on 2019-02-28 with total page 527 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presents a comprehensive, multidisciplinary volume on the physics of zonal jets, from the leading experts, for graduate students and researchers.

Download or read book Microtearing Instabilities and Electron Transport in the NSTX Spherical Tokamak written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We report a successful quantitative account of the experimentally determined electron thermal conductivity [chi]e in a beam-heated H mode plasma by the magnetic fluctuations from microtearing instabilities. The calculated [chi]e based on existing nonlinear theory agrees with the result from transport analysis of the experimental data. Without using any adjustable parameter, the good agreement spans the entire region where there is a steep electron temperature gradient to drive the instability.

Download or read book Final Report of the Committee on a Strategic Plan for U S Burning Plasma Research written by National Academies of Sciences, Engineering, and Medicine and published by National Academies Press. This book was released on 2019-05-31 with total page 341 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fusion offers the prospect of virtually unlimited energy. The United States and many nations around the world have made enormous progress toward achieving fusion energy. With ITER scheduled to go online within a decade and demonstrate controlled fusion ten years later, now is the right time for the United States to develop plans to benefit from its investment in burning plasma research and take steps to develop fusion electricity for the nation's future energy needs. At the request of the Department of Energy, the National Academies of Sciences, Engineering, and Medicine organized a committee to develop a strategic plan for U.S. fusion research. The final report's two main recommendations are: (1) The United States should remain an ITER partner as the most cost-effective way to gain experience with a burning plasma at the scale of a power plant. (2) The United States should start a national program of accompanying research and technology leading to the construction of a compact pilot plant that produces electricity from fusion at the lowest possible capital cost.

Download or read book Characterization and Modification of Edge Driven Instabilities in the DIII D Tokamak written by and published by . This book was released on 1999 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: The character of edge localized modes (ELMs) and the height of the edge pressure pedestal in DIII-D tokamak H-mode discharges have been modified by varying the discharge shape (triangularity and squareness) and the safety factor, increasing the edge radiation, and injecting deuterium pellets. Changes in the ELM frequency and amplitude, and the magnitude of the edge pressure gradient, and changes in the calculated extent of the region of access to the ballooning mode second stability regime are observed.

Download or read book Nuclear Fusion written by and published by . This book was released on 2006-12 with total page 632 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theory of Fusion Plasmas written by Olivier Sauter and published by American Institute of Physics. This book was released on 2008-12-02 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Joint Varenna-Lausanne International Workshop on Theory of Fusion Plasmas takes place every other year in a place particularly favorable for informal and in depth discussions. Invited and contributed papers present state-of-the art researches in theoretical plasma physics, covering all domains relevant to fusion plasmas. This workshop always allows a fruitful mix of experienced researchers and students, to allow for a better understanding of the key theoretical physics models and applications, such as: Theoretical issues related to burning plasmas; Anomalous Transport (Turbulence, Coherent Structures, Microinstabilities) RF Heating and Current Drive; Macroinstabilities; Plasma-Edge Physics and Divertors; Fast particles instabilities.

Download or read book Collisional Transport in Magnetized Plasmas written by Per Helander and published by Cambridge University Press. This book was released on 2005-10-06 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: A graduate level text treating transport theory, an essential element of theoretical plasma physics.

Download or read book Turbulent Transport In Magnetized Plasmas Second Edition written by C Wendell Horton, Jr and published by #N/A. This book was released on 2017-07-21 with total page 522 pages. Available in PDF, EPUB and Kindle. Book excerpt: For a few seconds with large machines, scientists and engineers have now created the fusion power of the stars in the laboratory and at the same time find the rich range of complex turbulent electromagnetic waves that transport the plasma confinement systems. The turbulent transport mechanisms created in the laboratory are explained in detail in the second edition of 'Turbulent Transport in Magnetized Plasmas' by Professor Horton.The principles and properties of the major plasma confinement machines are explored with basic physics to the extent currently understood. For the observational laws that are not understood — the empirical confinement laws — offering challenges to the next generation of plasma students and researchers — are explained in detail. An example, is the confinement regime — called the 'I-mode' — currently a hot topic — is explored.Numerous important problems and puzzles for the next generation of plasma scientists are explained. There is growing demand for new simulation codes utilizing the massively parallel computers with MPI and GPU methods. When the 20 billion dollar ITER machine is tested in the 2020ies, new theories and faster/smarter computer simulations running in near real-time control systems will be used to control the burning hydrogen plasmas.

Download or read book The Fairy Tale of Nuclear Fusion written by L. J. Reinders and published by Springer Nature. This book was released on 2021-05-20 with total page 628 pages. Available in PDF, EPUB and Kindle. Book excerpt: This carefully researched book presents facts and arguments showing, beyond a doubt, that nuclear fusion power will not be technically feasible in time to satisfy the world's urgent need for climate-neutral energy. The author describes the 70-year history of nuclear fusion; the vain attempts to construct an energy-generating nuclear fusion power reactor, and shows that even in the most optimistic scenario nuclear fusion, in spite of the claims of its proponents, will not be able to make a sizable contribution to the energy mix in this century, whatever the outcome of ITER. This implies that fusion power will not be a factor in combating climate change, and that the race to save the climate with carbon-free energy will have been won or lost long before the first nuclear fusion power station comes on line. Aimed at the general public as well as those whose decisions directly affect energy policy, this book will be a valuable resource for informing future debates.

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.

Download or read book Electromagnetic Metamaterials written by Christophe Caloz and published by John Wiley & Sons. This book was released on 2005-11-22 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electromagnetic metamaterials-from fundamental physics to advanced engineering applications This book presents an original generalized transmission line approach associated with non-resonant structures that exhibit larger bandwidths, lower loss, and higher design flexibility. It is based on the novel concept of composite right/left-handed (CRLH) transmission line metamaterials (MMs), which has led to the development of novel guided-wave, radiated-wave, and refracted-wave devices and structures. The authors introduced this powerful new concept and are therefore able to offer readers deep insight into the fundamental physics needed to fully grasp the technology. Moreover, they provide a host of practical engineering applications. The book begins with an introductory chapter that places resonant type and transmission line metamaterials in historical perspective. The next six chapters give readers a solid foundation in the fundamentals and practical applications: Fundamentals of LH MMs describes the fundamental physics and exotic properties of left-handed metamaterials TL Theory of MMs establishes the foundations of CRLH structures in three progressive steps: ideal transmission line, LC network, and real distributed structure Two-Dimensional MMs develops both a transmission matrix method and a transmission line method to address the problem of finite-size 2D metamaterials excited by arbitrary sources Guided-Wave Applications and Radiated-Wave Applications present a number of groundbreaking applications developed by the authors The Future of MMs sets forth an expert view on future challenges and prospects This engineering approach to metamaterials paves the way for a new generation of microwave and photonic devices and structures. It is recommended for electrical engineers, as well as physicists and optical engineers, with an interest in practical negative refractive index structures and materials.