High-energy laser beams interacting with flowing plasmas can produce a plasma response that leads to deflection of the beam, beam bending. Such beams have usually a speckle structure generated by optical smoothing techniques that reduce the spatial and temporal coherence in the laser field pattern. The cumulative plasma response from laser speckles slows down the velocity of the incoming flow by momentum conservation. For slightly super-sonic flow the cumulative plasma response to the ponderomotive force exerted by the beam speckle ensemble is the strongest, such that slowing down the flow to subsonic velocities leads eventually to the generation of a shock around the cross section of the beam. This scenario has been predicted theoretically and is confirmed here by our hydrodynamic simulations in two dimensions with speckled beams and in one dimension with a reduced model. The conditions of shock generation are given in terms of the ponderomotive pressure, speckle size and the flow velocity. The nonlinear properties of the shocks are analyzed using Rankine–Hugoniot relations. According to linear theory, temporally smoothed laser beams exhibit a higher threshold for shock generation. Numerical simulations with beams that are smoothed by spectral dispersion compare well with the linear theory results, diverging from those produced by beams with only a random phase plates in the nonlinear regime. The conditions necessary for shock generation and their effects on the laser plasma coupling in inertial confinement fusion (ICF) experiments are also discussed.
L’interaction d’un faisceau laser de puissance avec un plasma en écoulement peut produire une réponse du plasma tel que le faisceau subit une déflection. Les faisceaux des lasers de puissance ont généralement une sous-structure de « points chauds » générée par les techniques du « lissage » optique qui a le but de réduire la cohérence spatiale et temporelle du champ laser sur la cible. La réponse cumulative du plasma chaud suite aux points chauds peut décélérer la vitesse du flot entrant due à la conservation du moment. Pour un flot faiblement super-sonique cette réponse cumulative due à la force pondéromotrice exercée par les points chauds est assez forte pour que la décélération du flot à des vitesses sub-soniques provoque la formation d’une onde de choc qui se propage contre le flot entrant. Ce scénario a été prédit par des travaux théoriques. Nos simulations hydro-dynamiques en deux dimensions avec des faisceaux « lissés » et en une dimension avec un modèle réduit confirment la formation de ce type de chocs qui dépend essentiellement du potentiel pondéromoteur des faiscaux laser, de la taille des points chauds et du nombre Mach du flot entrant. Deux méthodes de lissage optique sont étudiées, le lissage spatial par lames de phases aléatoires (random phase plates :« RPP » ) et le lisssage spatio-temporel par dispersion spectrale (smoothing by spectral dispersion : « SSD » ), ce dernier provoquant des chocs plus forts que dans le cas de la RPP pour le régime non linéaire des flux laser élevés. Les conditions nécessaires pour observer la formation de ce type de chocs dans le contexte de la Fusion par confinement intertiel (FCI) par laser sont également discutées.
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Mots-clés : chocs laser, interaction laser-plasma, lissage optique
S. Hüller 1; J. D. T. Ludwig 2; H. A. Rose 3; C. Bruulsema 2; W. Farmer 2; P. Michel 2; A. L. Milder 4; G. F. Swadling 2; W. Rozmus 4
@article{CRPHYS_2024__25_G1_353_0, author = {S. H\"uller and J. D. T. Ludwig and H. A. Rose and C. Bruulsema and W. Farmer and P. Michel and A. L. Milder and G. F. Swadling and W. Rozmus}, title = {Modeling and simulations of hydrodynamic shocks in a plasma flowing across randomized {ICF} scale laser beams}, journal = {Comptes Rendus. Physique}, pages = {353--365}, publisher = {Acad\'emie des sciences, Paris}, volume = {25}, year = {2024}, doi = {10.5802/crphys.200}, language = {en}, }
TY - JOUR AU - S. Hüller AU - J. D. T. Ludwig AU - H. A. Rose AU - C. Bruulsema AU - W. Farmer AU - P. Michel AU - A. L. Milder AU - G. F. Swadling AU - W. Rozmus TI - Modeling and simulations of hydrodynamic shocks in a plasma flowing across randomized ICF scale laser beams JO - Comptes Rendus. Physique PY - 2024 SP - 353 EP - 365 VL - 25 PB - Académie des sciences, Paris DO - 10.5802/crphys.200 LA - en ID - CRPHYS_2024__25_G1_353_0 ER -
%0 Journal Article %A S. Hüller %A J. D. T. Ludwig %A H. A. Rose %A C. Bruulsema %A W. Farmer %A P. Michel %A A. L. Milder %A G. F. Swadling %A W. Rozmus %T Modeling and simulations of hydrodynamic shocks in a plasma flowing across randomized ICF scale laser beams %J Comptes Rendus. Physique %D 2024 %P 353-365 %V 25 %I Académie des sciences, Paris %R 10.5802/crphys.200 %G en %F CRPHYS_2024__25_G1_353_0
S. Hüller; J. D. T. Ludwig; H. A. Rose; C. Bruulsema; W. Farmer; P. Michel; A. L. Milder; G. F. Swadling; W. Rozmus. Modeling and simulations of hydrodynamic shocks in a plasma flowing across randomized ICF scale laser beams. Comptes Rendus. Physique, Volume 25 (2024), pp. 353-365. doi : 10.5802/crphys.200. https://comptes-rendus.academie-sciences.fr/physique/articles/10.5802/crphys.200/
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