Simulation of the Interaction Between Alfvén Waves and Fast Particles PDF Download

Author: Tamás Béla Fehér
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

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A plasma simulation code is used to study the resonant interactions between streaming ions and Alfven waves. The medium which supports the Alfven waves is treated as a single, one-dimensional, ideal MHD fluid, while the ions are treated as kinetic particles. The code is used to study three ion distributions: a cold beam; a monoenergetic shell; and a drifting distribution with a power-law dependence on momentum. These distributions represent: the field-aligned beams upstream of the earth's bow shock; the diffuse ions upstream of the bow shock; and the cosmic ray distribution function near a supernova remnant shock. 92 refs., 31 figs., 12 tabs.

Author: Tao Xu
Publisher:
ISBN:
Category :
Languages : en
Pages : 286

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Author: Sergei Sharapov
Publisher: CRC Press
ISBN: 1351002813
Category : Science
Languages : en
Pages : 156

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The study of energetic particles in magnetic fusion plasmas is key to the development of next-generation "burning" plasma fusion experiments, such as the International Thermonuclear Experimental Reactor (ITER) and the Demonstration Power Station (DEMO). This book provides a comprehensive introduction and analysis of the experimental data on how fast ions behave in fusion-grade plasmas, featuring the latest ground-breaking results from world-leading machines such as the Joint European Torus (JET) and the Mega Ampere Spherical Tokamak (MAST). It also details Alfvenic instabilities, driven by energetic ions, which can cause enhanced transport of energetic ions. MHD spectroscopy of plasma via observed Alfvenic waves called "Alfvén spectroscopy" is introduced and several applications are presented. This book will be of interest to graduate students, researchers, and academics studying fusion plasma physics. Features: Provides a comprehensive overview of the field in one cohesive text, with the main physics phenomena explained qualitatively first. Authored by an authority in the field, who draws on his extensive experience of working with energetic particles in tokamak plasmas. Is suitable for extrapolating energetic particle phenomena in fusion to other plasma types, such as solar and space plasmas.

Author: A. J. Dessler
Publisher: Cambridge University Press
ISBN: 9780521520065
Category : Science
Languages : en
Pages : 572

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A valuable reference work for those doing research in magnetospheric physics and related disciplines.

Author: Jörg Büchner
Publisher: Springer
ISBN: 3540365303
Category : Science
Languages : en
Pages : 363

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The aim of this book is twofold: to provide an introduction for newcomers to state of the art computer simulation techniques in space plasma physics and an overview of current developments. Computer simulation has reached a stage where it can be a highly useful tool for guiding theory and for making predictions of space plasma phenomena, ranging from microscopic to global scales. The various articles are arranged, as much as possible, according to the - derlying simulation technique, starting with the technique that makes the least number of assumptions: a fully kinetic approach which solves the coupled set of Maxwell’s equations for the electromagnetic ?eld and the equations of motion for a very large number of charged particles (electrons and ions) in this ?eld. Clearly, this is also the computationally most demanding model. Therefore, even with present day high performance computers, it is the most restrictive in terms of the space and time domain and the range of particle parameters that can be covered by the simulation experiments. It still makes sense, therefore, to also use models, which due to their simp- fying assumptions, seem less realistic, although the e?ect of these assumptions on the outcome of the simulation experiments needs to be carefully assessed.

Author: Joseph Allen Fitzpatrick
Publisher:
ISBN:
Category :
Languages : en
Pages : 306

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Author: Andrew Zachary
Publisher:
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Category : Magnetohydrodynamic waves
Languages : en
Pages : 268

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Author: Shawn Tang
Publisher:
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Category :
Languages : en
Pages : 123

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Understanding the interaction between wave excitation and damping is essential in the advancement of research on magnetized plasmas in space, laboratory, and astrophysical settings. Alfv\'en waves can be excited across all of these settings, and in fusion research plasmas such as tokamak plasmas, they are present due to energetic particles from neutral beam injection and fusion reactions. The interplay between wave-particle interaction and damping processes is at the core of understanding wave excitation. \\ In the work presented in this dissertation, an experiment was designed to investigate high frequency Alfv\'en waves excited through Doppler-shifted cyclotron resonance with energetic particles from neutral beam injection in the DIII-D tokamak. These waves, compressional (CAE) and global (GAE) Alfv\'en eigenmodes, typically have frequencies close to the ion cyclotron frequency $f_{ci}$; the frequency and amplitude of these modes was measured with the Ion Cyclotron Emission (ICE) diagnostic. The experiment utilized the unique capability of the DIII-D neutral beams to separately control the energy and injection rate. A parametric scan across many magnetic fields and beam geometries was performed to study the dependencies of these modes on various plasma parameters.\\ An energetic ion density threshold was observed during a discharge in which the voltage of an off-axis co-injecting beam was held constant while the current was ramped down by $40\%$. During this discharge, a spectrum of high frequency AEs at $f=0.58f_{ci}$ was stabilized via a controlled energetic ion density ramp for the first time in a fusion research plasma. This observation demonstrates an important property of resonant AEs: that the growth rate of these waves is set by the balance between fast-ion drive and damping processes. The controlled stabilization of this mode also validates previous simulations done on high frequency AEs in which an instability threshold was observed by varying the beam density without changing the shape of the distribution. \\ The scaling of the amplitude of this wave with the beam injection rate was found to be consistent with predictions for single mode collisional saturation near marginal stability. Analytic theory found that for the observed beam injection rate threshold, the mode was near marginal stability throughout the entire beam ramp. This is notably different from previous simulations of CAEs/GAEs that were in the collisionless regime and often far from marginal stability. \\ Modeling codes such as TRANSP and ORB\_GC were used to model and analyze the fast-ion distribution for this discharge. This analysis found that the modes were likely excited by a high energy subset of the fast-ion population with strong gradients in parallel velocity space. Resonance analysis of this subset of the fast-ion population, in conjunction with considerations from dispersion relations, shows that the mode is likely a shear-polarized GAE. This marks the first identification of a GAE excited through Doppler-shifted cyclotron resonance with sub-Alfv\'enic energetic ions, a first in fusion research plasmas.

Author: Wenjun Deng
Publisher:
ISBN: 9781267107008
Category :
Languages : en
Pages : 160

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A nonlinear gyrokinetic simulation model, which recovers the ideal magnetohydrodynamic (MHD) theory in the linear long-wavelength regime is formulated for studying kinetic MHD processes in magnetized plasmas. This comprehensive formulation enables gyrokinetic simulation of both pressure gradient-driven and current-driven instabilities including ideal and kinetic ballooning modes, kink modes, and shear Alfvén waves, as well as their nonlinear interactions in multi-scale simulations. Implemented in the gyrokinetic toroidal code (GTC), the new formulation is verified in simulations of reversed shear Alfvén eigenmode (RSAE) in fusion plasmas. The antenna excitation of RSAE provides verifications of its mode structure, frequency and damping rate from the initial perturbation simulation with kinetic thermal ions. When excited by fast ions, their non-perturbative contributions modify the mode structure relative to the ideal MHD theory. With inclusion of thermal plasma pressure, the mode frequency increases due to the elevation of the Alfvén continuum by the geodesic compressibility. The GTC simulations have been benchmarked with extended hybrid MHD-gyrokinetic simulations. The verified gyrokinetic simulation model is applied to studying the linear properties of RSAE driven by density gradient of neutral beam injected fast ions in a well-diagnosed DIII-D tokamak experiment (discharge #142111). GTC simulations find that weakly damped RSAE exists due to toroidal coupling and other geometric effects. Various damping and driving mechanisms are identified and measured in the simulations, which shows that accurate damping and growth rate calculation requires true mode structure from non-perturbative, fully self-consistent simulation. The mode structure has no up-down symmetry mainly due to the radial symmetry breaking by the radial variation of fast ion density gradient, as measured in the experiment by electron cyclotron emission imaging. The RSAE frequency up-sweeping and the mode transition from RSAE to toroidal Alfvén eigenmode are in good agreement with the experimental results when scanning the values of the minimum safety factor in simulations. Good agreements in frequencies, growth rates, and mode structures are obtained among simulations of gyrokinetic codes GTC and GYRO, and an MHD-hybrid code TAEFL, which provide further verification and validation of the gyrokinetic model for simulating the kinetic MHD processes. As a prelude to nonlinear simulations of RSAE and associated fast ion transport, properties of microturbulence in reversed shear plasmas are also studied.