Author: Sabine Nasr
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The stability of collisionless tearing modes is analyzed in the presence of an inhomogeneous magnetic field in fluid and gyrokinetic theories. It is shown by means of a fluid model that small scale modes, characterized by a negative stability parameter (∆'≺0), can be driven unstable due to a combination of the magnetic field and electron temperature gradients. The destabilization mechanism is identified as of the interchange type, similar to that for toroidal ETG modes. The resonant interaction between the mode and different classes of particles is studied in gyrokinetic theory. It is found that curvature and magnetic field inhomogeneity effectively change the mode stability through trapped particles. This is verified numerically with a gyrokinetic code (GKW) where the interchange-like destabilization is confirmed. Furthermore, the impact of a population of energetic particles is investigated. Linearly, using a gyrokinetic model, the particular case of energetic particle distribution presenting anisotropy in the temperature is taken into account. Non-linearly, the impact of the time evolution of the energetic particle density on the growth of magnetic islands is examined by means of a fluid model.
Author: Zhisong Qu
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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External heating methods such as neutral beam injection (NBI) and ion cyclotron resonance heating (ICRH) generate a large amount of fast ions in tokamak plasmas. The widely implemented MHD single fluid theory with isotropic pressure is no longer sufficient to capture the physics of such plasmas. Despite the shortcoming of a fluid theory, such as the fluid closure problem and the lack of wave-particle interactions, the use of a fluid description in a tokamak with external heated fast ions is possible and has proved fruitful due to its simple and intuitive nature, as shown in this thesis. Due the presence of the fast ions, the total plasma pressure becomes anisotropic. In other words, the pressure parallel to the magnetic field differs from its perpendicular counterpart. We have upgraded the fast ion driven instability tool chain HELENA-MISHKA-HAGIS to new versions with pressure anisotropy, taking the simplification that the whole plasma (electrons, fast and thermal ions) is a bi-Maxwellian fluid. Based on this new tool chain and analytical analysis, we have identified the impact of pressure anisotropy induced by externally heated fast ions on the plasma equilibrium, waves and instabilities. It has been found that if an isotropic model is used to describe an anisotropic plasma, a range of problems will emerge depending on the inverse aspect ratio and the magnitude of anisotropy. These problems include the inconsistency of the poloidal (diamagnetic) current, the constant pressure surface shifting away from the flux surfaces, and finally a distortion of the current and q profile. Two MAST experimental discharges are analysed, while in one of them, #29221@190ms, all three problems are presented, confirming the prediction. The equilibrium reconstructions for this discharge with/without anisotropy give different q profiles. This difference in the q profile leads to different continua, different n=1 TAE mode structures, and finally, different growth rates and saturation levels. The tool chain has also been used to carry on other physics studies such as an investigation of the dependency of the continuous spectra on different fluid closures and level of anisotropy. In addition to the waves that are supported by the thermal plasma, and modified and driven unstable by the fast ions, there are a family of waves, the energetic particle modes (EPMs), whose existence and property are determined by the fast ions, such as the energetic geodesic acoustic modes (EGAMs). The EGAMs are m=n=0 bursting and chirping modes first observed in DIII-D counter beam experiments. By considering the fast ions as a fluid with a collective flow along the field lines, we have reached a dispersion relationship that gives an unstable branch at half of the thermal GAM frequency. We have also found that when the beam is cold, there is a good agreement between our fluid theory and the existing kinetic theories. However, since the fluid theory does not capture the physics of inverse Landau damping, the source of the instability must be reactive, in contrast to the previous understandings. Furthermore, a smooth transition between the reactive EGAMs and the wave-particle interaction driven EGAMs is found when the beam temperature gradually increases, resembling the transition between the two-stream instability and the bump-on-tail instability in a beam-plasma system. This local fluid model is then extended to a global one to capture the physics of EGAM radial mode structure in the regime where fast ion drift orbit width is smaller than the mode width. The dependency of the mode structure on the equilibrium q profiles and the beam injection direction is investigated. By demonstrating the above two applications of the fluid theory and the corresponding physics discoveries, we have proved the usefulness of a fluid treatment in tokamak plasmas with external heating, serving to understanding some of the basic fast ions physics and acting as a powerful and indispensable complement to its kinetic counterpart.
Author: R.B. White
Publisher: Elsevier
ISBN: 1483293262
Category : Science
Languages : en
Pages : 374
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Book Description
This is a graduate textbook on tokamak physics, designed to provide a basic introduction to plasma equilibrium, particle orbits, transport, and those ideal and resistive magnetohydrodynamic instabilities which dominate the behavior of a tokamak discharge, and to develop the mathematical methods necessary for their theoretical analysis.
Author: Richard Fitzpatrick
Publisher:
ISBN: 9780750353670
Category : SCIENCE
Languages : en
Pages : 0
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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.
Author:
Publisher:
ISBN:
Category : Controlled fusion
Languages : en
Pages : 148
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Author:
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ISBN:
Category : Power resources
Languages : en
Pages : 784
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Author: Mitsuru Kikuchi
Publisher: Springer
ISBN: 3319189050
Category : Technology & Engineering
Languages : en
Pages : 412
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This book reviews recent progress in our understanding of tokamak physics related to steady state operation, and addresses the scientific feasibility of a steady state tokamak fusion power system. It covers the physical principles behind continuous tokamak operation and details the challenges remaining and new lines of research towards the realization of such a system. Following a short introduction to tokamak physics and the fundamentals of steady state operation, later chapters cover parallel and perpendicular transport in tokamaks, MHD instabilities in advanced tokamak regimes, control issues, and SOL and divertor plasmas. A final chapter reviews key enabling technologies for steady state reactors, including negative ion source and NBI systems, Gyrotron and ECRF systems, superconductor and magnet systems, and structural materials for reactors. The tokamak has demonstrated an excellent plasma confinement capability with its symmetry, but has an intrinsic drawback with its pulsed operation with inductive operation. Efforts have been made over the last 20 years to realize steady state operation, most promisingly utilizing bootstrap current. Frontiers in Fusion Research II: Introduction to Modern Tokamak Physics will be of interest to graduate students and researchers involved in all aspects of tokamak science and technology.
Author: Yi Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 240
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Author: Meng Li
Publisher:
ISBN:
Category :
Languages : en
Pages : 206
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This work is motivated by the nonlinear wave-particle interaction problems. To build a self-consistent theory, we consider eigenmodes of the bulk plasma as well as the dynamics of the energetic particles. The modes of our particular interest are the Alfvén Cascades and the Toroidicity Alfven Eigenmodes (TAE), which we describe using Magnetohydrodynamic(MHD) analysis and the AEGIS codes. We investigate the stabilizing effect for the Alfvenic waves from continuum damping, especially near the TAE gap. For the kinetic description of the energetic particles, we propose new canonical straight field line coordinates to model the guiding center motion. We then formulate wave-particle interaction problem using the action-angle variables. In Chapter 2, we interpret Alfvén Cascades observed in Madison Symmetric Torus (MST). We do linear MHD calculations and find the mode frequency, structure, and stability boundary. We then perform MHD simulation using the AEGIS code, with the equilibrium reconstructed from experiment. The result is discussed and compared with the experimentally observed features. In Chapter 3, we analyze continuum damping for Alfvénic waves, especially in the extreme situation near the TAE gap. We find that the continuum tip absorption feature is actually related to the existing of TAEs in the gap. On the technical level, we improve the numerical scheme of AEGIS and resolve two closely-spaced singularities. As a result, the absorption features observed in the simulation show good agreement with our analytical calculation. In order to simulate the energetic particle guiding center motion in the Hamiltonian form, we propose a new set of straight magnetic field line coordinates. The new coordinates exist for general tokamak devices and facilitate both MHD calculations and energetic particles. The new coordinate system makes it very convenient to take the advantage of the Hamiltionian structure of the guiding center motion. We use a canonical transformation to action-angle variables to formulate the interaction model for particles. The action-angle variables allow us to resolve wave-particle resonances and describe the conserved quantities for resonance particles. The model can give us a complete picture for nonlinear stage of wave-particle interaction.
Author:
Publisher:
ISBN:
Category : Plasma (Ionized gases)
Languages : en
Pages : 936
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