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Scintillations in a magnetized plasma. Part 1. The mutual coherence function

Published online by Cambridge University Press:  13 March 2009

D. B. Melrose
D. B. Melrose
Affiliation:
Research Centre for Theoretical Astrophysics, University of Sydney, NSW 2006, Australia
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Extract

A standard theory of strong scintillations in an isotropic medium is extended to the case of polarized radiation propagating through a weakly anisotropic, randomly inhomogeneous, magnetized plasma. A hierarchy of moments of the radiationfield is defined, with an nth-order moment being an nth-rank polarization tensor, and the tensor equation for the evolution of an arbitrary moment is derived. Emphasis isplaced on the mutual coherence function (a second moment), which is rewritten in terms of the Stokes parameters. The evolution of the polarized radiation through the randomly inhomogeneous, weakly anisotropic medium is described in terms ofa matrix equation for the Stokes vector. It is shown that the theory implies that a depolarization occurs as a result ofsuch propagation. This corresponds to a decrease in the degree of linear polarization for propagation through a weakly anisotropic plasma. The rate of depolarization is estimated, and an interpretation is suggested. The polarization dependence of the angular size of the apparent image is determined. Two counter-intuitive results are found: that the image canhave a circularly polarized component even for an unpolarized source, and that the angular size of the linearly polarized source can decrease. These are interpreted in terms of random variations in the ray path with opposite signs for the two natural modes, resulting in a separation of the centroids of the images in the two circular polarizations.

Type
Articles
Information
Journal of Plasma Physics , Volume 50 , Issue 2 , October 1993 , pp. 267 - 281
Copyright
Copyright © Cambridge University Press 1993

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