Download or read book Stabilization of Neoclassical Tearing Modes in Tokamak Fusion Plasmas Via Extremum Seeking written by William P. Wehner and published by . This book was released on 2009 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: The neoclassical tearing mode (NTM) instability produces magnetic islands in tokamak plasmas that can degrade confinement and lead to plasma disruptions. NTMs are driven by a lack of bootstrap current inside the magnetic island where the pressure profile is flattened. Suppression of these islands is necessary for sustained energy confinement and efficient operation in tokamak magnetic-fusion reactors. Compensating for the lack of bootstrap current by an Electron Cyclotron Current Drive (ECCD) has been proved experimentally as an effective method to stabilize NTMs. The effectiveness of this method is limited in practice by the uncertainties in the width of the island, the relative position between the island and the EC beam, and the EC power threshold for NTM stabilization. Heuristic Search and Suppress algorithms have been proposed and shown effective to improve the alignment of the EC beam with the island by just using an estimate of the island width. Making use of this estimate, a real-time, non-model-based, extremum-seeking optimization algorithm is proposed for EC beam steering and modulation in order to minimize the island-beam misalignment and the time (control energy) required for NTM stabilization. The efficiency of the proposed method is compared with traditional search and suppress algorithms. It is shown that the Extremum Seeking method has the potential of reducing NTM suppression times. In addition, it is shown that the Extremum Seeking method has the ability of modulating simultaneously other parameters beyond island-beam alignment that improve the effectiveness of the ECCD such as modulation duty-cycle and the phase mismatch between the ECCD and island O-point.

Download or read book Tearing Mode Dynamics in Tokamak Plasmas written by Richard Fitzpatrick and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The development of humankind's ultimate energy source, nuclear fusion, has proceeded slowly but surely over the course of the last 60 years. This comprehensive book aims to outline a realistic, comprehensive, self-consistent, analytic theory of tearing mode dynamics in tokamak plasmas. It discusses a fluid theory of a highly magnetized plasma that treats the electrons and ions as independent fluids, and then proceeds to develop the theory of tearing modes, first approximating the geometry of a tokamak plasma as a periodic cylinder, but eventually considering the toroidal structure of real tokamak plasmas. This book also describes the stability of tearing modes, the saturation of such modes, and the evolution of their phase velocity due to interaction with other tearing modes, as well as the resistive vacuum vessel, and imperfections in the tokamak's magnetic field. This text will appeal to scientists and graduate students engaged in nuclear fusion research, and would make a useful reference for graduate plasma physics courses. Part of IOP Series in Plasma Physics.

Download or read book Stochastic Averaging and Stochastic Extremum Seeking written by Shu-Jun Liu and published by Springer Science & Business Media. This book was released on 2012-06-16 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: Stochastic Averaging and Extremum Seeking treats methods inspired by attempts to understand the seemingly non-mathematical question of bacterial chemotaxis and their application in other environments. The text presents significant generalizations on existing stochastic averaging theory developed from scratch and necessitated by the need to avoid violation of previous theoretical assumptions by algorithms which are otherwise effective in treating these systems. Coverage is given to four main topics. Stochastic averaging theorems are developed for the analysis of continuous-time nonlinear systems with random forcing, removing prior restrictions on nonlinearity growth and on the finiteness of the time interval. The new stochastic averaging theorems are usable not only as approximation tools but also for providing stability guarantees. Stochastic extremum-seeking algorithms are introduced for optimization of systems without available models. Both gradient- and Newton-based algorithms are presented, offering the user the choice between the simplicity of implementation (gradient) and the ability to achieve a known, arbitrary convergence rate (Newton). The design of algorithms for non-cooperative/adversarial games is described. The analysis of their convergence to Nash equilibria is provided. The algorithms are illustrated on models of economic competition and on problems of the deployment of teams of robotic vehicles. Bacterial locomotion, such as chemotaxis in E. coli, is explored with the aim of identifying two simple feedback laws for climbing nutrient gradients. Stochastic extremum seeking is shown to be a biologically-plausible interpretation for chemotaxis. For the same chemotaxis-inspired stochastic feedback laws, the book also provides a detailed analysis of convergence for models of nonholonomic robotic vehicles operating in GPS-denied environments. The book contains block diagrams and several simulation examples, including examples arising from bacterial locomotion, multi-agent robotic systems, and economic market models. Stochastic Averaging and Extremum Seeking will be informative for control engineers from backgrounds in electrical, mechanical, chemical and aerospace engineering and to applied mathematicians. Economics researchers, biologists, biophysicists and roboticists will find the applications examples instructive.

Download or read book Turbulent Stabilization of the Tearing Mode in Tokamak Plasmas written by E. Esarey and published by . This book was released on 1985 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modelling Neoclassical Tearing Modes in Tokamak Plasmas written by Aleksandra Dudkovskaia and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Modeling of Neoclassical Tearing Mode Stability for Generalized Toroidal Geometry written by Adam Lewis Rosenberg and published by . This book was released on 2002 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A Study of Tearing Modes Via Electron Cyclotron Emission from Tokamak Plasmas written by Chuang Ren and published by . This book was released on 1998 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Neoclassical Tearing Modes in Tokamak Fusion Test Reactor Experiments Part I Measurements of Magnetic Islands and Delta Prime written by and published by . This book was released on 1997 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tearing type modes are observed in most high-confinement operation regimes in TFTR. Three different methods are used to measure the magnetic island widths: external magnetic coils, internal temperature fluctuation from electron cyclotron emission (ECE) diagnostic and an experiment where the plasma major radius is rapidly shifted ('Jog' experiments). A good agreement between the three methods is observed. Numerical and analytic calculations of delta prime (the tearing instability index) are compared with an experimental measurement of delta prime using the tearing mode eigenfunction mapped from the Jog data. The obtained negative delta prime indicates that the observed tearing modes cannot be explained by the classical current-gradient-driven tearing theory.

Download or read book Neoclassical Tearing Modes in Tokamak Fusion Test Reactor Experiments Part I Measurements of Magnetic Islands and Delta written by Zuoyang Chang and published by . This book was released on 1997 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Towards Integrated Control of Tokamak Plasmas Physics based Control of Neoclassical Tearing Modes in the TCV Tokamak written by Mengdi Kong and published by . This book was released on 2020 with total page 214 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mots-clés de l'auteur: neoclassical tearing modes (NTMs) ; modified Rutherford equation (MRE) ; triggerless NTMs ; NTM stabilization ; NTM prevention ; integrated control ; ITER ; DEMO.

Download or read book Neoclassical Tearing Modes in Tokamak Fusion Test Reactor Experiments Part 1 Measurements of Magnetic Islands and Delta Prime written by and published by . This book was released on 1997 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Tearing-type modes are observed in most high-confinement operation regimes in TFTR. Three different methods are used to measure the magnetic island widths: external magnetic coils, internal temperature fluctuation from the electron cyclotron emission (ECE) diagnostic, and an experiment where the plasma major radius is rapidly shifted ("Jog" experiments). A good agreement between the three methods is observed. Numerical and analytic calculations of delta prime (the tearing instability index) are compared with an experimental measurement of delta prime using the tearing-mode eigenfunction mapped from the jog data. The obtained negative delta prime indicates that the observed tearing modes cannot be explained by the classical current-gradient-driven tearing theory.

Download or read book Stability of Tearing Modes in Tokamak Plasmas written by C.C. Hegna and published by . This book was released on 1994 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Stabilization of the Tearing Mode in Low Density Tokamak Plasmas by Turbulent Electron Diffusion written by E. Esarey and published by . This book was released on 1982 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Stabilization of Tearing Modes to Suppress Major Disruptions in Tokamaks written by Oak Ridge National Laboratory. Fusion Energy Division and published by . This book was released on 1979 with total page 39 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Neoclassical Tearing Modes in a Tokamak written by T. S. Hahm and published by . This book was released on 1988 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Stability of Tearing Modes in Tokamak Plasmas written by and published by . This book was released on 1994 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Neoclassical Tearing Modes in a Tokamak written by and published by . This book was released on 1988 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Linear tearing instability is studied in the banana collisionality regime in tokamak geometry. Neoclassical effects produce significant modifications of Ohm's law and the vorticity equation so that the growth rate of tearing modes driven by .delta.' is dramatically reduced compared to the usual resistive MHD value. Consequences of this result, regarding the presence of pressure-gradient-driven neoclassical resistive interchange instabilities and the evolution of magnetic islands in the Rutherford regime, are discussed. 10 refs.