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Modifications of the laser beam coherence inertial confinement fusion plasmas; Modifications des proprietes de coherence des faisceaux laser dans les plasmas de fusion par confinement inertiel

Abstract

Inertial confinement fusion by laser requires smoothed laser beam with well-controlled coherence properties. Such beams are made of many randomly distributed intensity maxima: the so-called speckles. As the laser beam propagates through plasma its temporal and spatial coherence can be reduced. This phenomenon is called plasma induced smoothing. For high laser intensities, instabilities developing independently inside the speckles are responsible for the coherence loss. At lower intensities, only collective effects, involving many speckles, can lead to induced smoothing. This thesis is a theoretical, numerical and experimental study of these mechanisms. Accounting for the partially incoherent behavior of the laser beams requires the use of statistical description of the laser-plasma interaction. A model is developed for the multiple scattering of the laser light on the self-induced density perturbations that is responsible for a spreading of the temporal and spatial spectra of the transmitted light. It also serves as a strong seed for the instability of forward stimulated Brillouin scattering that induces both, angular spreading and red-shift of the transmitted light. A statistical model is developed for this instability. A criterion is obtained that gives a laser power (below the critical power for filamentation) above which the instability growth is important. Numerical  More>>
Authors:
Publication Date:
Jun 15, 2007
Product Type:
Thesis/Dissertation
Report Number:
FRNC-TH-7348
Resource Relation:
Other Information: TH: These noyaux, atomes, agregats et plasmas; 123 refs.; Also available from Bibliotheque Universitaire des Sciences et Techniques - S.C.D. DE Bordeaux 1, Allee Baudrimont, 33405 - Talence Cedex (France)
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAM DYNAMICS; BRILLOUIN EFFECT; COMPUTERIZED SIMULATION; LASER RADIATION; LASER-PRODUCED PLASMA; MULTIPLE SCATTERING; P CODES; PARAMETRIC INSTABILITIES; PLASMA DIAGNOSTICS; PLASMA SIMULATION
OSTI ID:
21096908
Research Organizations:
Bordeaux-1 Univ., 33 (France)
Country of Origin:
France
Language:
French
Other Identifying Numbers:
TRN: FR0800967107537
Availability:
Available from INIS in electronic form
Submitting Site:
FRN
Size:
254 pages
Announcement Date:
Dec 05, 2008

Citation Formats

Grech, M. Modifications of the laser beam coherence inertial confinement fusion plasmas; Modifications des proprietes de coherence des faisceaux laser dans les plasmas de fusion par confinement inertiel. France: N. p., 2007. Web.
Grech, M. Modifications of the laser beam coherence inertial confinement fusion plasmas; Modifications des proprietes de coherence des faisceaux laser dans les plasmas de fusion par confinement inertiel. France.
Grech, M. 2007. "Modifications of the laser beam coherence inertial confinement fusion plasmas; Modifications des proprietes de coherence des faisceaux laser dans les plasmas de fusion par confinement inertiel." France.
@misc{etde_21096908,
title = {Modifications of the laser beam coherence inertial confinement fusion plasmas; Modifications des proprietes de coherence des faisceaux laser dans les plasmas de fusion par confinement inertiel}
author = {Grech, M}
abstractNote = {Inertial confinement fusion by laser requires smoothed laser beam with well-controlled coherence properties. Such beams are made of many randomly distributed intensity maxima: the so-called speckles. As the laser beam propagates through plasma its temporal and spatial coherence can be reduced. This phenomenon is called plasma induced smoothing. For high laser intensities, instabilities developing independently inside the speckles are responsible for the coherence loss. At lower intensities, only collective effects, involving many speckles, can lead to induced smoothing. This thesis is a theoretical, numerical and experimental study of these mechanisms. Accounting for the partially incoherent behavior of the laser beams requires the use of statistical description of the laser-plasma interaction. A model is developed for the multiple scattering of the laser light on the self-induced density perturbations that is responsible for a spreading of the temporal and spatial spectra of the transmitted light. It also serves as a strong seed for the instability of forward stimulated Brillouin scattering that induces both, angular spreading and red-shift of the transmitted light. A statistical model is developed for this instability. A criterion is obtained that gives a laser power (below the critical power for filamentation) above which the instability growth is important. Numerical simulations with the interaction code PARAX and an experiment performed on the ALISE laser facility confirm the importance of these forward scattering mechanisms in the modification of the laser coherence properties. (author)}
place = {France}
year = {2007}
month = {Jun}
}