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 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 Advanced Tokamak Stability Theory written by Linjin Zheng and published by Morgan & Claypool Publishers. This book was released on 2014-04-01 with total page 178 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book describes the advanced stability theories for magnetically confined fusion plasmas, especially in tokamaks. As the fusion plasma sciences advance, the gap between the textbooks and cutting-edge researches gradually develops. This book fills in

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 Tokamaks written by John Wesson and published by Oxford University Press. This book was released on 2011-10-13 with total page 828 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

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 Magnetohydrodynamic Stability of Tokamaks written by Hartmut Zohm and published by John Wiley & Sons. This book was released on 2015-02-09 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book bridges the gap between general plasma physics lectures and the real world problems in MHD stability. In order to support the understanding of concepts and their implication, it refers to real world problems such as toroidal mode coupling or nonlinear evolution in a conceptual and phenomenological approach. Detailed mathematical treatment will involve classical linear stability analysis and an outline of more recent concepts such as the ballooning formalism. The book is based on lectures that the author has given to Master and PhD students in Fusion Plasma Physics. Due its strong link to experimental results in MHD instabilities, the book is also of use to senior researchers in the field, i.e. experimental physicists and engineers in fusion reactor science. The volume is organized in three parts. It starts with an introduction to the MHD equations, a section on toroidal equilibrium (tokamak and stellarator), and on linear stability analysis. Starting from there, the ideal MHD stability of the tokamak configuration will be treated in the second part which is subdivided into current driven and pressure driven MHD. This includes many examples with reference to experimental results for important MHD instabilities such as kinks and their transformation to RWMs, infernal modes, peeling modes, ballooning modes and their relation to ELMs. Finally the coverage is completed by a chapter on resistive stability explaining reconnection and island formation. Again, examples from recent tokamak MHD such as sawteeth, CTMs, NTMs and their relation to disruptions are extensively discussed.

Download or read book Self Organization of Hot Plasmas written by Yu.N. Dnestrovskij and published by Springer. This book was released on 2014-07-08 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this monograph the author presents the Canonical Profile Transport Model or CPTM as a rather general mathematical framework to simulate plasma discharges. The description of hot plasmas in a magnetic fusion device is a very challenging task and many plasma properties still lack a physical explanation. One important property is plasma self-organization. It is very well known from experiments that the radial profile of the plasma pressure and temperature remains rather unaffected by changes of the deposited power or plasma density. The attractiveness of the CPTM is that it includes the effect of self-organization in the mathematical model without having to recur to particular physical mechanisms. The CPTM model contains one dimensional transport equations for ion and electron temperatures, plasma density and toroidal rotation velocity. These equations are well established and in fact are essentially a reformulation the laws of energy, particle and momentum conservation. But the expressions for the energy and particle fluxes, including certain critical gradients, are new. These critical gradients can be determined using the concept of canonical profiles for the first time formulated in great detail in the book. This concept represents a totally new approach to the description of transport in plasmas. Mathematically, the canonical profiles are formulated as a variational problem. To describe the temporal evolution of the plasma profiles, the Euler equation defining the canonical profiles is solved together with the transport equations at each time step. The author shows that in this way it is possible to describe very different operational scenarios in tokamaks (L-Mode, H-Mode, Advanced Modes, Radiating Improved Modes etc...), using one unique principle. The author illustrates the application of this principle to the simulation of plasmas on leading tokamak devices in the world (JET, MAST, T-10, DIII-D, ASDEX-U, JT-60U). In all cases the small differences between the calculated profiles for the ion and electron temperatures and the experimental is rather confirm the validity of the CPTM. In addition, the model also describes the temperature and density pedestals in the H-mode and non steady-state regimes with current and density ramp up. The proposed model therefore provides a very useful mathematical tool for the analysis of experimental results and for the prediction of plasma parameters in future experiments.

Download or read book Experimental Observation and Study of Core Transport Barrier in DIII D Discharges with Dominant Electron Cyclotron Heating written by Ruifeng Xie and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fusion power offers the prospect of abundant, carbon-neutral and sustainable energy. A fusion reactor’s main challenge is creating a controlled, confined and burning plasma at its core. Magnetic confinement fusion (MCF) is a promising route, and the tokamak approach is the the most widely adopted design among the MCF configurations. To achieve high fusion gain in tokamaks, the high-confinement mode (H-mode) has been explored and utilized. Compared to low-confinement mode (L-mode), H-mode operation produces better confinement and thus better performance, making it more attractive as the operational scenario for future reactors. One distinguishing feature of H-mode plasma is the presence of a transport barrier, a localized region of reduced transport, in the pedestal region at the edge of the plasma. Due to the strong dependence of fusion performance on pedestal parameters, transport in the pedestal region has been extensively studied. However, many questions regarding transport mechanisms in the plasma core remain unaddressed. This dissertation investigates the changes in core transport in tokamak plasmas discharges that transition to H-mode solely with electron cyclotron heating (ECH). This type of discharges often produce strong off-axis electron temperature peaking near the ECH heating location. In this work, we experimentally study the electron heat transport properties and identify evidence for the presence of internal transport barriers (ITBs) in the core region. These results are compared with numerical solutions of the time-dependent electron thermal equation, which matches the experimental observations. We proceed to study the formation of these ITBs and linked their formation to the modification of safety factor q by ECH during L-H transition. Other potential causes of ITB formation and future work are also discusses

Download or read book Electron heat transport in current carrying and currentless thermonuclear plasmas written by Michiel Peters and published by . This book was released on 1995 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nonlinear Trapped electron Mode and Anomalous Heat Transport in Tokamaks written by and published by . This book was released on 1982 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We take the phenomenological point of view that the anomalous electron thermal conductivity produced by the nonlinear trapped electron mode should also influence the stability properties of the mode itself. Using a model equation, we show that this effect makes the mode self-stabilizing. A simple expression for the anomalous thermal conductivity is derived and its scaling properties discussed.

Download or read book Theory of Tokamak Transport written by Leslie Colin Woods and published by John Wiley & Sons. This book was released on 2006-05-12 with total page 252 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this new approach for a consistent transport theory in nuclear fusion processes Leslie Woods draws on over 40 years of fusion research to directly compare theoretical findings with experimental results, while taking into account recently discovered phenomena. This is thus the first book to find theoretical explanations to the sometimes-puzzling tokamak observations. Following a look at the quest for fusion power, the author goes on to examine tokamak magnetic fields and energy losses, as well as plasma flow and loop voltage. There is also a discussion of the technical constraints on the recently announced ITER design.

Download or read book Electron Transport in the Plasma Edge with Rotating Resonant Magnetic Perturbations at the TEXTOR Tokamak written by Henning Stoschus and published by Forschungszentrum Jülich. This book was released on 2011 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Electron Heat Transport in a Tokamak with Destroyed Magnetic Surfaces written by A. B. Rechester and published by . This book was released on 1977 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Measurements of Energy Transport in Tokamak Plasmas written by Dmitry Meyerson and published by . This book was released on 2010 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: A tokamak plasma near equilibrium can be perturbed with modulated power sources, such as modulated electron cyclotron heating, or repeated cold pulse application. Temperature response to cyclical changes in profiles parameters that are induced by modulated power deposition can be used to test theoretical transport models as well as improve experimental phenomenology used to optimize tokamak performance. The goal of this document to discuss some methods of analyzing electron temperature data in the context of energy transport. Specific experiments are considered in order to demonstrate the methods discussed, as well as to examine the electron energy transport properties of these shots. Electron cyclotron emission provides a convenient way to probe electron temperature for plasmas in thermal equilibrium. We can show that in tokamak devices, barring harmonic overlap, we can associate a particular frequency with a particular location in a tokamak, by carefully selecting the detection frequency and line of sight of the responsible antenna. ECE radiometers typically measure temperature at tens of locations at a time with a spatial resolution on the order of a few centimeters. Tracking the evolution of electron energy flux depends on careful analysis of the resulting data. The most straightforward way to analyze temperature perturbations is to simply consider various harmonics of the driving source and consider the corresponding harmonics in the temperature. We can analyze the phase and amplitude of the response to find the effective phase velocity of the perturbation which can in turn be related to parameters in the selected heat flux model. The most common example is to determine, the diffusion coefficient that appears in the linearized energy transport equation. The advantages and limitation of this method will be discussed in detail in Section 3. A more involved approach involves using the perturbed temperature data to compute modulated heat flux at any given point in the perturbation cycle, rather than using the temperature data directly. As before the heat flux can then be related to measured profile parameters and theoretical predictions. The advantages and limitations of this approach will be discussed in more detail. Both of the mentioned analysis methods are used to probe electron energy transport in a quiescent H mode (QH mode) shot conducted at DIIID. The nature of the internal transport barrier that is present in the shot is considered in light of the results.

Download or read book Electron Heat Transport in a Tokamak with Destroyed Magnetic Surfaces written by A. B. Rechester and published by . This book was released on 1977 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Magnetic Fusion Energy written by George Neilson and published by Woodhead Publishing. This book was released on 2016-06-02 with total page 634 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magnetic Fusion Energy: From Experiments to Power Plants is a timely exploration of the field, giving readers an understanding of the experiments that brought us to the threshold of the ITER era, as well as the physics and technology research needed to take us beyond ITER to commercial fusion power plants. With the start of ITER construction, the world’s magnetic fusion energy (MFE) enterprise has begun a new era. The ITER scientific and technical (S&T) basis is the result of research on many fusion plasma physics experiments over a period of decades. Besides ITER, the scope of fusion research must be broadened to create the S&T basis for practical fusion power plants, systems that will continuously convert the energy released from a burning plasma to usable electricity, operating for years with only occasional interruptions for scheduled maintenance. Provides researchers in academia and industry with an authoritative overview of the significant fusion energy experiments Considers the pathway towards future development of magnetic fusion energy power plants Contains experts contributions from editors and others who are well known in the field