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 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 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 Integrated Model for Transport and Large Scale Instabilities in Tokamak Plasmas written by Federico David Halpern and published by . This book was released on 2009 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: Improved models for neoclassical tearing modes and anomalous transport are developed and validated within integrated modeling codes to predict toroidal rotation, temperature and current density profiles in tokamak plasmas. Neoclassical tearing modes produce helical filaments of plasma, called magnetic islands, which have the effect of degrading tokamak plasma confinement or terminating the discharge. An improved code is developed in order to compute the widths of multiple simultaneous magnetic islands whose shapes are distorted by the radial variation in the magnetic perturbation [F. D. Halpern, et al., J. Plasma Physics 72 (2006) 1153]. It is found in simulations of DIII-D and JET tokamak discharges that multiple simultaneous magnetic islands produce a 10% to 20% reduction in plasma thermal confinement. If magnetic islands are allowed to grow to their full width in ITER fusion reactor simulations, fusion power production is reduced by a factor of four [F. D. Halpern, et al., Phys. Plasmas 13 (2006) 062510]. In addition to improving the prediction of neoclassical tearing modes, a new Multi-Mode transport model, MMM08, was developed to predict temperature and toroidal angular frequency profiles in simulations of tokamak discharges. The capability for predicting toroidal rotation is motivated by ITER simulation results that indicate that the effects of toroidal rotation can increase ITER fusion power production [F. D. Halpern et al., Phys. Plasmas 15 (2008), 062505]. The MMM08 model consists of an improved model for transport driven by ion drift modes [F. D. Halpern et al., Phys. Plasmas 15 (2008) 012304] together with a model for transport driven by short wavelength electron drift modes combined with models for transport driven by classical processes. The new MMM08 transport model was validated by comparing predictive simulation results with experimental data for 32 discharges in the DIII-D and JET tokamaks. It was found that the prediction of intrinsic plasma rotation is consistent with experimental measurements in discharges with zero net torque. A scaling relation was developed for the toroidal momentum confinement time (angular momentum divided by net torque) as a function of plasma current and torque per ion.
Download or read book Predictive Integrated Modeling of Low Aspect Ratio Tokamaks and Large Scale Instabilities in Tokamaks written by Canh Ngoc Nguyen and published by . This book was released on 2004 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt: Models for large scale instabilities in tokamaks are developed, and they are tested together with models for transport and other physical processes by comparing the results of BALDUR integrated predictive modeling simulations with experimental data from tokamaks. Simulations are carried out for the low aspect ratio tokamaks, Mega Ampere Spherical Tokamak and the National Spherical Torus Experiment, to test the applicability of models that were developed for conventional tokamaks. The results indicate that neoclassical transport dominates over anomalous transport in the inner third of the plasma. Sawtooth oscillations, which are the result of an instability that periodically redistributes the central part of the plasma profiles, play a significant role by radially spreading the neutral beam injection heating profiles across the broad sawtooth mixing region. Two models for sawtooth oscillations, the Porcelli and the Kadomtsev models, are combined and tested against experimental data from the Joint European Torus and the Tokamak Fusion Test Reactor. Most of the sawtooth crashes are triggered by the m = 1 resistive internal kink mode in the semi-collisional regime. The median sawtooth period increases with increasing magnetic reconnection fraction. The best overall agreement with experimental data is obtained with a magnetic reconnection fraction of approximately 55%. Finally, plasma pressure effects are included in a quasi-linear model for saturated tearing modes, which are instabilities that produce magnetic islands. The model is used in a stand-alone code, and in the BALDUR code, to calculate the widths of saturated magnetic islands in tokamak plasmas with arbitrary cross-section and plasma pressure. The widths of tearing mode islands increase with decreasing aspect ratio and with increasing elongation. Also, the island widths increase when the gradient of the current density increases at the edge of the islands or when the current density inside the islands is suppressed. The widths oscillate in time in response to periodic sawtooth crashes. Local enhancements in the transport produced by magnetic islands have a noticeable effect on global plasma confinement in simulations of low aspect ratio, high beta tokamaks, where saturated tearing mode islands can occur with widths greater than 15% of the plasma minor radius.
Download or read book Reduced MHD modeling of tearing mode interactions in Tokamaks written by J. W. Eastwood and published by . This book was released on 1986 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 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 Multiple Mode Model of Tokamak Transport written by and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Theoretical models for radical transport of energy and particles in tokamaks due to drift waves, rippling modes, and resistive ballooning modes have been combined in a predictive transport code. The resulting unified model has been used to simulate low confinement mode (L-mode) energy confinement scalings. Dependence of global energy confinement on electron density for the resulting model is also described. 26 refs., 1 fig., 2 tabs.
Download or read book Effects of Profiles on Microinstabilities in Tokamaks written by David Dickinson and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Turbulent transport of heat and particles significantly degrades the confinement in tokamaks. Whilst the confinement improves in larger devices, these are more expensive and the economic viability of future fusion power plants depends upon understanding turbulence so that operating scenarios can be optimised. Gyrokinetic models are able to describe the plasma turbulence responsible for transport. The assumption that the equilibrium varies slowly relative to the radial width of the instability is often exploited to reduce the global gyrokinetic system to a local one. The relation between the global and local systems is a key topic in this thesis. It is shown that local solutions can only capture the true global behaviour when freedoms in the system are treated correctly. A procedure to reconstruct the global solution from the local one has been developed and successfully tested. The spontaneous transition to a regime of high confinement, observed on many tokamaks, is associated with the suppression of turbulence in a narrow region near the plasma edge, known as the pedestal, and is accompanied by edge localised instabilities (ELMs) which can eject large amounts of energy in a short time, damaging the confinement vessel. Understanding the ELM and pedestal behaviour is crucial to predict the performance of future tokamaks, as well as offering insight into techniques to reduce the threat of damage due to ELMs. The application of gyrokinetics to study microinstabilities in the edge region of MAST in the time between two ELMs is presented as part of this thesis. This work finds kinetic ballooning modes to be unstable in the pedestal whilst microtearing modes are unstable in the shallow gradient region towards the core. The transition from MTMs to KBMs at the interface between the two regions has been studied and may play an important role in the pedestal evolution.
Download or read book Computational Modeling of Neoclassical and Resistive MHD Tearing Modes in Tokamaks written by and published by . This book was released on 1996 with total page 116 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 Controlled Fusion and Plasma Physics written by Kenro Miyamoto and published by Taylor & Francis. This book was released on 2006-10-23 with total page 393 pages. Available in PDF, EPUB and Kindle. Book excerpt: Resulting from ongoing, international research into fusion processes, the International Tokamak Experimental Reactor (ITER) is a major step in the quest for a new energy source.The first graduate-level text to cover the details of ITER, Controlled Fusion and Plasma Physics introduces various aspects and issues of recent fusion research activ
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 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.
