Time-resolved Observation of Discrete and Continuous MHD Dynamo in the Reversed-field Pinch Edge

Time-resolved Observation of Discrete and Continuous MHD Dynamo in the Reversed-field Pinch Edge
Author:
Publisher:
Total Pages: 15
Release: 1994
Genre:
ISBN:

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We report the first experimental verification of the MHD dynamo in the RFP. A burst of magnetohydrodynamic (MHD) dynamo electric field is observed during the sawtooth crash, followed by an increase in the local parallel current in the MST RFP edge. By measuring each term, the parallel MHD mean-field Ohm's law is observed to hold within experimental error bars both between and during sawtooth crashes.

Energy Research Abstracts

Energy Research Abstracts
Author:
Publisher:
Total Pages: 782
Release: 1995
Genre: Power resources
ISBN:

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Magnetic Helicity in Space and Laboratory Plasmas

Magnetic Helicity in Space and Laboratory Plasmas
Author: Michael R. Brown
Publisher: American Geophysical Union
Total Pages: 324
Release: 1999-01-26
Genre: Science
ISBN:

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Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 111. Using the concept of magnetic helicity, physicists and mathematicians describe the topology of magnetic fields: twisting, writhing, and linkage. Mathematically, helicity is related to linking integrals, which Gauss introduced in the 19th century to describe the paths of asteroids in the sky. In the late 1970s the concept proved to be critical to understand laboratory plasma experiments on magnetic reconnection, dynamos, and magnetic field relaxation. In the late 1980s it proved equally important in understanding turbulence in the solar wind and the interplanetary magnetic field. During the last five years interest in magnetic helicity has grown dramatically in solar physics, and it will continue to grow as observations of vector magnetic fields become increasingly sophisticated.

Government Reports Annual Index

Government Reports Annual Index
Author:
Publisher:
Total Pages: 1144
Release: 1994
Genre: Government reports announcements & index
ISBN:

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Spectroscopic Measurement of the MHD Dynamo in the MST Reversed Field Pinch

Spectroscopic Measurement of the MHD Dynamo in the MST Reversed Field Pinch
Author:
Publisher:
Total Pages: 295
Release: 1998
Genre:
ISBN:

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The author has directly observed the coupling of ion velocity fluctuations and magnetic field fluctuations to produce an MHD dynamo electric field in the interior of the MST reversed field pinch. Chord averaged ion velocity fluctuations were measured with a fast spectroscopic diagnostic which collects line radiation from intrinsic carbon impurities simultaneously along two lines of sight. The chords employed for the measurements resolved long wavelength velocity fluctuations of several km/s at 8--20 kHz as tiny, fast Doppler shifts in the emitted line profile. During discrete dynamo events the velocity fluctuations, like the magnetic fluctuations, increase dramatically. The toroidal and poloidal chords with impact parameters of 0.3 a and 0.6 a respectively, resolved fluctuation wavenumbers with resonance surfaces near or along the lines of sight indicating a radial velocity fluctuation width for each mode which spans only a fraction of the plasma radius. The phase between the measured toroidal velocity fluctuations and the magnetic fluctuations matches the predictions of resistive MHD while the poloidal velocity fluctuations exhibit a phase consistent with the superposition of MHD effects and the advection of a mean flow gradient past the poloidal line of sight. Radial velocity fluctuations resolved by a chord through the center of the plasma were small compared to the poloidal and toroidal fluctuations and exhibited low coherence with the magnetic fluctuations. The ensembled nonlinear product of the ion velocity fluctuations and fluctuations in the magnetic field indicates a substantial dynamo electric field which peaks during the periods of spontaneous flux generation.

Magnetohydrodynamics of Plasma Relaxation

Magnetohydrodynamics of Plasma Relaxation
Author: S. Ortolani
Publisher: World Scientific
Total Pages: 208
Release: 1993
Genre: Science
ISBN: 9789810208608

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This book gives a concise description of the phenomenon of plasma relaxation from the point of view of resistive magnetohydrodynamic (MHD) theory. Magnetized plasmas relax when they seek their natural state of lowest energy subject to certain topological constraints imposed by the magnetic field. Relaxation may be fast and dynamic or slow and gradual depending on the external environment in which the magnetoplasma system evolves. Relaxation occurs throughout the universe and may describe such diverse phenomena as dynamos, solar flares, and the operation of magnetic fusion energy experiments. This book concentrates on the dynamic, rather than variational aspects of relaxation. While the processes described are general, the book focuses on the reversed-field pinch experiment as a paradigm for plasma relaxation and dynamo action. Examples from other branches of plasma physics are also discussed. The authors draw upon their extensive experience in numerical and experimental studies of relaxation.