Author: Matthias HölzlPublisher:
ISBN:
Category :
Languages : en
Pages : 149
Book Description
Diffusive Heat Transport Across Magnetic Islands and Stochastic Layers in Tokamaks
Author: Matthias Hölzlحول الشباب والحرية
Author: Magnetic Stochasticity in Magnetically Confined Fusion Plasmas
Author: Sadrilla AbdullaevPublisher: Springer Science & Business Media
ISBN: 3319018906
Category : Science
Languages : en
Pages : 422
Book Description
This is the first book to systematically consider the modern aspects of chaotic dynamics of magnetic field lines and charged particles in magnetically confined fusion plasmas. The analytical models describing the generic features of equilibrium magnetic fields and magnetic perturbations in modern fusion devices are presented. It describes mathematical and physical aspects of onset of chaos, generic properties of the structure of stochastic magnetic fields, transport of charged particles in tokamaks induced by magnetic perturbations, new aspects of particle turbulent transport, etc. The presentation is based on the classical and new unique mathematical tools of Hamiltonian dynamics, like the action--angle formalism, classical perturbation theory, canonical transformations of variables, symplectic mappings, the Poincaré-Melnikov integrals. They are extensively used for analytical studies as well as for numerical simulations of magnetic field lines, particle dynamics, their spatial structures and statistical properties. The numerous references to articles on the latest development in the area are provided. The book is intended for graduate students and researchers who interested in the modern problems of magnetic stochasticity in magnetically confined fusion plasmas. It is also useful for physicists and mathematicians interested in new methods of Hamiltonian dynamics and their applications.
Heat Transport in Partially Stochastic Tokamak Magnetic Fields
Author: M. HugonPublisher:
ISBN:
Category : Nuclear fusion
Languages : en
Pages : 9
Book Description
Energy Research Abstracts
Author: Magnetic Island Effects, Interactions in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
This paper explores a number of aspects of isolated and interacting magnetic islands, and their effects, in tokamak plasmas. The temperature fluctuations induced by an isolated magnetic island in a rotating tokamak plasma are shown to be surprisingly small -- T[sub rms] [approx-lt] 0.1w[vert-bar]dT[sub 0]/dr[vert-bar] in which w is the island width. Pressure-gradient-driven neoclassical MHD magnetic islands are posited as the cause of the isolated low m/n islands sometimes observed in high performance tokamak plasmas. They also form the basis for a recently advanced interacting-island model for the tokamak magnetic ''equilibrium'' in which mostly non-overlapping islands, across which transport is rapid, are separated by ''good'' flux surface regions. In combination these bad, good transport regions produce ''stair-step'' temperature and pressure profiles. Finally, an interacting-island transport model is developed and shown to exhibit many of the transient transport properties observed in tokamak plasmas -- nonlinear response of temperature gradient to increased heating, pulse propagation faster than equilibrium, and fairly strong ''profile resiliency.''
Fusion Energy Update
Author: Possible Effects of Drift Wave Turbulence on Magnetic Structure and Plasma Transport in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
A new mechanism is proposed by which low level, drift wave type fluctuations, such as those observed in the ATC and TFR experiments, can cause anomalous radial electron heat transport in tokamaks. The model is based on the fact that since transport processes parallel to the magnetic field are many orders of magnitude more rapid than perpendicular ones, very small helically resonant magnetic perturbations that cause field lines to move radially allow the parallel transport process to contribute to radial electron heat transport. It is hypothesized that the small magnetic perturbations accompanying drift waves at any nonzero plasma .beta. are large enough to produce significant effects in present tokamak experiments. The helical magnetic component of drift waves produces magnetic island structures whose spatial widths can easily exceed the ion gyroradius. In a drift wave oscillation period, electrons circumnavigate a magnetic island, whereas the slower moving ions see only a tilt of the magnetic field lines. Thus, electrons try to diffuse radially more rapidly than ions; however, a radialpotential builds up on a very short time scale to confine the electrons electrostatically and thereby keep the particle diffusion ambipolar. Nonetheless, this parallel electron diffusion process does cause net radial electron heat conduction through an ensemble of closely packed island structures. The heat conduction coefficient is estimated. Other effects that these magnetic flutters may have on plasma transport and runaway electron processes are also discussed.
Electron Heat Transport in Tokamak H-mode Pedestals
Author: Myriam HamedPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
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.
Author: