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Languages : en
Pages :
Book Description
Gyrokinetic Analysis of Low-n Shear Alfvén and Ion Sound Wave Spectra in a High-beta Tokamak Plasma
Author: High-n Ideal and Resistive Shear Alfven Waves in Tokamaks
Author: Publisher:
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Languages : en
Pages :
Book Description
Ideal and resistive MHD equations for the shear Alfven waves are studied in a low-.beta. toroidal model by employing the high-n ballooning formalism. The ion sound effects are neglected. For an infinite shear slab, the ideal MHD model gives rise to a continuous spectrum of real frequencies and discrete eigenmodes (Alfven-Landau modes) with complex frequencies. With toroidal coupling effects due to nonuniform toroidal magnetic field, the continuum is broken up into small continuum bands and new discrete toroidal eigenmodes can exist inside the continuum gaps. Unstable ballooning eigenmodes are also introduced by the bad curvature when .beta.> .beta./sub c/. The resistivity (n) can be considered perturbatively for the ideal modes. In addition, four branches of resistive modes are induced by the resistivity: (1) Resistive entropy modes which are stable (.delta.' 0) with frequencies approaching zero as n35, (3) Resistive periodic shear Alfven waves which approach the finite frequency end points of the continuum bands and n12, and (4) Resistive ballooning modes which are purely growing with growth rate proportional to eta13.beta.23 as eta .--. O and .beta. .-->. O.
Fusion Energy Update
Author: Nonlinear Gyrokinetic Equations for Low-frequency Electromagnetic Waves in General Plasma Equilibria
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Languages : en
Pages :
Book Description
A nonlinear gyrokinetic formalism for low-frequency (less than the cyclotron frequency) microscopic electromagnetic perturbations in general magnetic field configurations is developed. The nonlinear equations thus derived are valid in the strong-turbulence regime and contain effects due to finite Larmor radius, plasma inhomogeneities, and magentic field geometries. The specific case of axisymmetric tokamaks is then considered, and a model nonlinear equation is derived for electrostatic drift waves. Also, applying the formalism to the shear Alfven wave heating sceme, it is found that nonlinear ion Landau damping of kinetic shear-Alfven waves is modified, both qualitatively and quantitatively, by the diamagnetic drift effects. In particular, wave energy is found to cascade in wavenumber instead of frequency.
Plasma Physics Index
Author: Publisher:
ISBN:
Category : Plasma (Ionized gases)
Languages : en
Pages : 732
Book Description
Alfven Waves in Gyrokinetic Plasmas
Author: Publisher:
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Category :
Languages : en
Pages :
Book Description
A brief comparison of the properties of Alfven waves that are based on the gyrokinetic description with those derived from the MHD equations is presented. The critical differences between these two approaches are the treatment of the ion polarization effects. As such, the compressional Alfven waves in a gyrokinetic plasma can be eliminated through frequency ordering, whereas geometric simplifications are needed to decouple the shear Alfven waves from the compressional Alfven waves within the context of MHD. Theoretical and numerical procedures of using gyrokinetic particle simulation for studying microturbulence and kinetic-MHD physics including finite Larmor radius effects are also presented.
Analysis and Gyrokinetic Simulation of MHD Alfvén Wave Interactions
Author: Kevin Derek NielsonPublisher:
ISBN:
Category : Magnetohydrodynamic waves
Languages : en
Pages : 188
Book Description
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfvén waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory. In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfvén waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfvén waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvénic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfvén waves by reproducing laboratory Alfvén dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfvén eigenmodes to be initialized with user specified amplitudes and phases. We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions ...
Energy Research Abstracts
Author: Study of High-n Modes in Tokamaks Using a High Speed Nonlocal Gyrokinetic Model
Author: Publisher:
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Category :
Languages : en
Pages :
Book Description
Gyrokinetic theory has been used to derive a system of integral equations which nonlocally describe low frequency, short wavelength modes in a plasma of axisymmetrical toroidal geometry with low-â and circular nonconcentric flux surfaces with small Shafranov shift. The eigenmode equations contain the two potential approximation in [variable phi] and 'A' & par; with full finite Larmor radius and trapped electron effects in the collisionless limit. The analysis makes use of the so-called "ballooning formalism" to lowest order in 1/'n' which yields a radially local calculation for the eigenfrequencies and the eigenfunctions. This representation, in conjunction with an efficient numerical algorithm, allows the eigen frequencies to be computed with sufficient accuracy and high speed for arbitrary high-' n' modes in the drift and shear-Alfven branches. This is the main accomplishment of this work. Test cases using artificial and actual tokamak experimental discharge parameters for the collisionless-trapped-electron, ion-temperature-gradient and ballooning modes have been benchmarked with the premium, comprehensive kinetic formulation of Rewoldt exhibiting favourable results.
Theory of Fusion Plasmas
Author: Olivier SauterPublisher: American Institute of Physics
ISBN: 9780735406001
Category : Science
Languages : en
Pages : 400
Book Description
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.