Study of collective speckles driven simulated Raman scattering development in laser-plasma interaction
Description
Laser-plasma instabilities which occur in millimetric hot plasma, typical in ICF experiments, are still a preoccupying topic because they lead to reflectivity levels higher than predicted. in this context, this work focuses on stimulated Raman scattering (SRS) through a multi-scale analysis: mono, bi and multi speckle scales. This picosecond experimental study highlights the difference between isolated and collective speckle behaviors in SRS development. A weak speckle, stable if isolated, may become unstable under the influence of SRS driven local plasma modifications generated by an intense nearby speckle: kinetic perturbations with suprathermal electrons and/or wave coupling with electromagnetic and electrostatic seeds. From set of experimental campaigns, featuring a highly spatially- and temporally-resolved Thomson-scattering diagnostic and backward Raman imaging, we evidenced and characterized this collective behavior. An experimental difference between these two kinds of perturbations was observed which lead to differentiate their contributions. In parallel, 2D PIC simulations using CALDER were performed to interpret bi-speckle experimental results and in particular to understand the influence from both kinds of perturbations. (author)
Abstract (French)
Les instabilites parametriques qui se developpent dans l'interaction laser-plasma a haute intensite dans les plasmas chauds de plusieurs millimetres typiques des experiences de FCi, entrainent des taux de retrodiffusion importants, ce qui en fait un sujet toujours preoccupant. Les travaux de cette these se concentrent sur l'etude d'une des instabilites parametriques, la diffusion Raman stimulee, dans les cas mono-, bi- et multi-speckles ou points chauds que l'on retrouve dans les taches focales des gros lasers de puissance. Cette etude experimentale, effectuee en regime picoseconde, a etabli la difference des comportements en regime isole ou collectif de la retrodiffusion Raman: la modification des proprietes locales du plasma induite par un point chaud intense peut rendre instable un point chaud voisin, stable vis-a-vis de l'instabilite s'il etait isole, par l'intermediaire d'un couplage cinetique et/ou d'un couplage d'ondes. Une serie d'experiences utilisant des diagnostics de diffusion Thomson a hautes resolutions spatiale et temporelle couplees avec une imagerie de la retrodiffusion Raman a permis de mettre en evidence l'existence de ce comportement collectif, de saisir sa dynamique puis de caracteriser a l'echelle picoseconde son influence dans le developpement global de l'instabilite Raman en discriminant l'aspect cinetique (electrons suprathermiques) de l'aspect ondulatoire (couplage par l'intermediaire des ondes excitees par l'instabilite). Les mesures experimentales bispeckle ont ete interpretees a l'aide de simulations particulaires 2D du code CALDER qui reproduit cette discrimination entre ces deux types de perturbations. (l'auteur)
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Additional details
Additional titles
- Original title (French)
- Etude du comportement collectif des speckles dans le developpement de la diffusion Raman stimulee lors de l'interaction laser-plasma
Publishing Information
- Imprint Pagination
- 197 p.
- Report number
- FRCEA-TH--9886
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 50054854
- Subject category
- S70: PLASMA PHYSICS AND FUSION TECHNOLOGY;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- INERTIAL CONFINEMENT; INSTABILITY; LASER-PRODUCED PLASMA; TAIL ELECTRONS; THERMONUCLEAR REACTIONS
- Descriptors DEC
- CONFINEMENT; ELECTRONS; ELEMENTARY PARTICLES; FERMIONS; LEPTONS; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; PLASMA; PLASMA CONFINEMENT; SYNTHESIS
Optional Information
- Notes
- 83 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses; Also available from Bibliotheque Centrale de l'Ecole Polytechnique, Route de Saclay, 91128 Palaiseau (France)