We construct an unconventional divergence preserving discretization of updated Lagrangian ideal magnetohydrodynamics(MHD)over simplicial grids.The cell-centered finite-volume(FV)method employed to discretize the conse...We construct an unconventional divergence preserving discretization of updated Lagrangian ideal magnetohydrodynamics(MHD)over simplicial grids.The cell-centered finite-volume(FV)method employed to discretize the conservation laws of volume,momentum,and total energy is rigorously the same as the one developed to simulate hyperelasticity equations.By construction this moving mesh method ensures the compatibility between the mesh displacement and the approximation of the volume flux by means of the nodal velocity and the attached unit corner normal vector which is nothing but the partial derivative of the cell volume with respect to the node coordinate under consideration.This is precisely the definition of the compatibility with the Geometrical Conservation Law which is the cornerstone of any proper multi-dimensional moving mesh FV discretization.The momentum and the total energy fluxes are approximated utilizing the partition of cell faces into sub-faces and the concept of sub-face force which is the traction force attached to each sub-face impinging at a node.We observe that the time evolution of the magnetic field might be simply expressed in terms of the deformation gradient which characterizes the Lagrange-to-Euler mapping.In this framework,the divergence of the magnetic field is conserved with respect to time thanks to the Piola formula.Therefore,we solve the fully compatible updated Lagrangian discretization of the deformation gradient tensor for updating in a simple manner the cell-centered value of the magnetic field.Finally,the sub-face traction force is expressed in terms of the nodal velocity to ensure a semi-discrete entropy inequality within each cell.The conservation of momentum and total energy is recovered prescribing the balance of all the sub-face forces attached to the sub-faces impinging at a given node.This balance corresponds to a vectorial system satisfied by the nodal velocity.It always admits a unique solution which provides the nodal velocity.The robustness and the accuracy of this unconventional FV scheme have been demonstrated by employing various representative test cases.Finally,it is worth emphasizing that once you have an updated Lagrangian code for solving hyperelasticity you also get an almost free updated Lagrangian code for solving ideal MHD ensuring exactly the compatibility with the involution constraint for the magnetic field at the discrete level.展开更多
An analytical model of current propagation in a helical coil with varying geometry is developed.It can be used for post-acceleration and post-focusing of ions produced via laser-driven target normal sheath acceleratio...An analytical model of current propagation in a helical coil with varying geometry is developed.It can be used for post-acceleration and post-focusing of ions produced via laser-driven target normal sheath acceleration and generation of electromagnetic pulses.We calculate the current that propagates in a helical coil and suggest a method for improving its dispersion properties using a screening tube and with pitch and radius variation.The electromagnetic fields calculated with the analytical model are in agreement with particle-in-cell simulations.The model provides insights into the physics of current propagation in helical coils with varying geometries and enables a numerical implementation for rapid proton spectrum computations,which facilitate the design of such coils for future experiments.展开更多
Emerging multi-PW-class lasers and their envisioned laser-plasma interaction applications in unprecedented intensity regimes set a very demanding frame for the precise understanding of the finest properties of these s...Emerging multi-PW-class lasers and their envisioned laser-plasma interaction applications in unprecedented intensity regimes set a very demanding frame for the precise understanding of the finest properties of these systems.In this work we present a synthesis of simulation studies on a series of less known or even completely disregarded spatiotemporal effects that could potentially impact greatly the performances of high-intensity lasers.展开更多
The aim of the present work is to develop a general formalism to derive staggered discretizations for Lagrangian hydrodynamics on two-dimensional unstructured grids.To this end,we make use of the compatible discretiza...The aim of the present work is to develop a general formalism to derive staggered discretizations for Lagrangian hydrodynamics on two-dimensional unstructured grids.To this end,we make use of the compatible discretization that has been initially introduced by E.J.Caramana et al.,in J.Comput.Phys.,146(1998).Namely,momentum equation is discretized by means of subcell forces and specific internal energy equation is obtained using total energy conservation.The main contribution of this work lies in the fact that the subcell force is derived invoking Galilean invariance and thermodynamic consistency.That is,we deduce a general form of the sub-cell force so that a cell entropy inequality is satisfied.The subcell force writes as a pressure contribution plus a tensorial viscous contribution which is proportional to the difference between the nodal velocity and the cell-centered velocity.This cell-centered velocity is a supplementary degree of freedom that is solved by means of a cell-centered approximate Riemann solver.To satisfy the second law of thermodynamics,the local subcell tensor involved in the viscous part of the subcell force must be symmetric positive definite.This subcell tensor is the cornerstone of the scheme.One particular expression of this tensor is given.A high-order extension of this discretization is provided.Numerical tests are presented in order to assess the efficiency of this approach.The results obtained for various representative configurations of one and two-dimensional compressible fluid flows show the robustness and the accuracy of this scheme.展开更多
Understanding the solid target dynamics resulting from the interaction with an ultrashort laser pulse is a challenging fundamental multi-physics problem involving atomic and solid-state physics,plasma physics,and lase...Understanding the solid target dynamics resulting from the interaction with an ultrashort laser pulse is a challenging fundamental multi-physics problem involving atomic and solid-state physics,plasma physics,and laser physics.Knowledge of the initial interplay of the underlying processes is essential to many applications ranging from lowpower laser regimes like laser-induced ablation to high-power laser regimes like laser-driven ion acceleration.Accessing the properties of the so-called pre-plasma formed as the laser pulse’s rising edge ionizes the target is complicated from the theoretical and experimental point of view,and many aspects of this laser-induced transition from solid to overdense plasma over picosecond timescales are still open questions.On the one hand,laser-driven ion acceleration requires precise control of the pre-plasma because the efficiency of the acceleration process crucially depends on the target properties at the arrival of the relativistic intensity peak of the pulse.On the other hand,efficient laser ablation requires,for example,preventing the so-called“plasma shielding”.By capturing the dynamics of the initial stage of the interaction,we report on a detailed visualization of the pre-plasma formation and evolution.Nanometer-thin diamond-like carbon foils are shown to transition from solid to plasma during the laser rising edge with intensities<10^(16)W/cm^(2).Single-shot near-infrared probe transmission measurements evidence sub-picosecond dynamics of an expanding plasma with densities above 10^(23)cm^(−3)(about 100 times the critical plasma density).The complementarity of a solid-state interaction model and kinetic plasma description provides deep insight into the interplay of initial ionization,collisions,and expansion.展开更多
This paper introduces a caching technique based on a volumetric representation that captures low-frequency indirect illumination.This structure is intended for efficient storage and manipulation of illumination.It is ...This paper introduces a caching technique based on a volumetric representation that captures low-frequency indirect illumination.This structure is intended for efficient storage and manipulation of illumination.It is based on a 3D grid that stores a fixed set of irradiance vectors.During preprocessing,this representation can be built using almost any existing global illumination software.During rendering,the indirect illumination within a voxel is interpolated from its associated irradiance vectors,and is used as additional local light sources.Compared with other techniques,the 3D vector-based representation of our technique offers increased robustness against local geometric variations of a scene.We thus demonstrate that it may be employed as an efficient and high-quality caching data structure for bidirectional rendering techniques such as particle tracing or photon mapping.展开更多
Diagnosing the evolution of laser-generated high energy density(HED)systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions.Talbot–Lau interferometry constitutes a...Diagnosing the evolution of laser-generated high energy density(HED)systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions.Talbot–Lau interferometry constitutes a promising tool,since it permits simultaneous single-shot X-ray radiography and phase-contrast imaging of dense plasmas.We present the results of an experiment at OMEGA EP that aims to probe the ablation front of a laser-irradiated foil using a Talbot–Lau X-ray interferometer.A polystyrene(CH)foil was irradiated by a laser of 133 J,1 ns and probed with 8 keV laser-produced backlighter radiation from Cu foils driven by a short-pulse laser(153 J,11 ps).The ablation front interferograms were processed in combination with a set of reference images obtained ex situ using phase-stepping.We managed to obtain attenuation and phase-shift images of a laser-irradiated foil for electron densities above 1022 cm−3.These results showcase the capabilities of Talbot–Lau X-ray diagnostic methods to diagnose HED laser-generated plasmas through high-resolution imaging.展开更多
基金support by Fondazione Cariplo and Fondazione CDP(Italy)under the project No.2022-1895.
文摘We construct an unconventional divergence preserving discretization of updated Lagrangian ideal magnetohydrodynamics(MHD)over simplicial grids.The cell-centered finite-volume(FV)method employed to discretize the conservation laws of volume,momentum,and total energy is rigorously the same as the one developed to simulate hyperelasticity equations.By construction this moving mesh method ensures the compatibility between the mesh displacement and the approximation of the volume flux by means of the nodal velocity and the attached unit corner normal vector which is nothing but the partial derivative of the cell volume with respect to the node coordinate under consideration.This is precisely the definition of the compatibility with the Geometrical Conservation Law which is the cornerstone of any proper multi-dimensional moving mesh FV discretization.The momentum and the total energy fluxes are approximated utilizing the partition of cell faces into sub-faces and the concept of sub-face force which is the traction force attached to each sub-face impinging at a node.We observe that the time evolution of the magnetic field might be simply expressed in terms of the deformation gradient which characterizes the Lagrange-to-Euler mapping.In this framework,the divergence of the magnetic field is conserved with respect to time thanks to the Piola formula.Therefore,we solve the fully compatible updated Lagrangian discretization of the deformation gradient tensor for updating in a simple manner the cell-centered value of the magnetic field.Finally,the sub-face traction force is expressed in terms of the nodal velocity to ensure a semi-discrete entropy inequality within each cell.The conservation of momentum and total energy is recovered prescribing the balance of all the sub-face forces attached to the sub-faces impinging at a given node.This balance corresponds to a vectorial system satisfied by the nodal velocity.It always admits a unique solution which provides the nodal velocity.The robustness and the accuracy of this unconventional FV scheme have been demonstrated by employing various representative test cases.Finally,it is worth emphasizing that once you have an updated Lagrangian code for solving hyperelasticity you also get an almost free updated Lagrangian code for solving ideal MHD ensuring exactly the compatibility with the involution constraint for the magnetic field at the discrete level.
基金supported by the CEA/DAM Laser Plasma Experiments Validation Projectthe CEA/DAM Basic Technical and Scientific Studies Project+4 种基金supported by the National Sciences and Engineering Research Council of Canada(NSERC)(Grant Nos.RGPIN-2023-05459 and ALLRP 556340-20)Compute Canada(Job pve-323-ac)the Canada Foundation for Innovation(CFI)financial support by the IdEx University of Bordeaux/Grand Research Program“GPR LIGHT”the Graduate Program on Light Sciences and Technologies of the University of Bordeaux。
文摘An analytical model of current propagation in a helical coil with varying geometry is developed.It can be used for post-acceleration and post-focusing of ions produced via laser-driven target normal sheath acceleration and generation of electromagnetic pulses.We calculate the current that propagates in a helical coil and suggest a method for improving its dispersion properties using a screening tube and with pitch and radius variation.The electromagnetic fields calculated with the analytical model are in agreement with particle-in-cell simulations.The model provides insights into the physics of current propagation in helical coils with varying geometries and enables a numerical implementation for rapid proton spectrum computations,which facilitate the design of such coils for future experiments.
文摘Emerging multi-PW-class lasers and their envisioned laser-plasma interaction applications in unprecedented intensity regimes set a very demanding frame for the precise understanding of the finest properties of these systems.In this work we present a synthesis of simulation studies on a series of less known or even completely disregarded spatiotemporal effects that could potentially impact greatly the performances of high-intensity lasers.
基金supported by the Czech Ministry of Education grants MSM 6840770022,MSM 6840770010,LC528the Czech Science Foundation grant P205/10/0814.
文摘The aim of the present work is to develop a general formalism to derive staggered discretizations for Lagrangian hydrodynamics on two-dimensional unstructured grids.To this end,we make use of the compatible discretization that has been initially introduced by E.J.Caramana et al.,in J.Comput.Phys.,146(1998).Namely,momentum equation is discretized by means of subcell forces and specific internal energy equation is obtained using total energy conservation.The main contribution of this work lies in the fact that the subcell force is derived invoking Galilean invariance and thermodynamic consistency.That is,we deduce a general form of the sub-cell force so that a cell entropy inequality is satisfied.The subcell force writes as a pressure contribution plus a tensorial viscous contribution which is proportional to the difference between the nodal velocity and the cell-centered velocity.This cell-centered velocity is a supplementary degree of freedom that is solved by means of a cell-centered approximate Riemann solver.To satisfy the second law of thermodynamics,the local subcell tensor involved in the viscous part of the subcell force must be symmetric positive definite.This subcell tensor is the cornerstone of the scheme.One particular expression of this tensor is given.A high-order extension of this discretization is provided.Numerical tests are presented in order to assess the efficiency of this approach.The results obtained for various representative configurations of one and two-dimensional compressible fluid flows show the robustness and the accuracy of this scheme.
基金LASERLABEUROPE(Grant agreement nos.871124,European Union’s Horizon 2020 research and innovation program)and from the Bundesministerium für Bildung und Forschung(BMBF,Grant Agreements No.03VNE2068D,No.03Z1H531,No.05K19SJB,No.05K19SJC,No.05K22SJA,and No.05K22SJB).
文摘Understanding the solid target dynamics resulting from the interaction with an ultrashort laser pulse is a challenging fundamental multi-physics problem involving atomic and solid-state physics,plasma physics,and laser physics.Knowledge of the initial interplay of the underlying processes is essential to many applications ranging from lowpower laser regimes like laser-induced ablation to high-power laser regimes like laser-driven ion acceleration.Accessing the properties of the so-called pre-plasma formed as the laser pulse’s rising edge ionizes the target is complicated from the theoretical and experimental point of view,and many aspects of this laser-induced transition from solid to overdense plasma over picosecond timescales are still open questions.On the one hand,laser-driven ion acceleration requires precise control of the pre-plasma because the efficiency of the acceleration process crucially depends on the target properties at the arrival of the relativistic intensity peak of the pulse.On the other hand,efficient laser ablation requires,for example,preventing the so-called“plasma shielding”.By capturing the dynamics of the initial stage of the interaction,we report on a detailed visualization of the pre-plasma formation and evolution.Nanometer-thin diamond-like carbon foils are shown to transition from solid to plasma during the laser rising edge with intensities<10^(16)W/cm^(2).Single-shot near-infrared probe transmission measurements evidence sub-picosecond dynamics of an expanding plasma with densities above 10^(23)cm^(−3)(about 100 times the critical plasma density).The complementarity of a solid-state interaction model and kinetic plasma description provides deep insight into the interplay of initial ionization,collisions,and expansion.
基金supported by the Lavoisier Grant from French Ministry of Foreign Affairs.Xavier Granier is supported by the Open Project Program of the State Key Lab of CAD&CG,Zhejiang University under Grant No.A1007.
文摘This paper introduces a caching technique based on a volumetric representation that captures low-frequency indirect illumination.This structure is intended for efficient storage and manipulation of illumination.It is based on a 3D grid that stores a fixed set of irradiance vectors.During preprocessing,this representation can be built using almost any existing global illumination software.During rendering,the indirect illumination within a voxel is interpolated from its associated irradiance vectors,and is used as additional local light sources.Compared with other techniques,the 3D vector-based representation of our technique offers increased robustness against local geometric variations of a scene.We thus demonstrate that it may be employed as an efficient and high-quality caching data structure for bidirectional rendering techniques such as particle tracing or photon mapping.
基金supported by the National Nuclear Security Administration (DENA0003882)funding from the Conseil Règional Aquitaine (INTALAX)+1 种基金the Agence Nationale de la Recherche (ANR-10-IDEX-03-02, ANR-15CE30-0011)supported by Research Grant No. PID2019-108764RB-I00 from the Spanish Ministry of Science and Innovation
文摘Diagnosing the evolution of laser-generated high energy density(HED)systems is fundamental to develop a correct understanding of the behavior of matter under extreme conditions.Talbot–Lau interferometry constitutes a promising tool,since it permits simultaneous single-shot X-ray radiography and phase-contrast imaging of dense plasmas.We present the results of an experiment at OMEGA EP that aims to probe the ablation front of a laser-irradiated foil using a Talbot–Lau X-ray interferometer.A polystyrene(CH)foil was irradiated by a laser of 133 J,1 ns and probed with 8 keV laser-produced backlighter radiation from Cu foils driven by a short-pulse laser(153 J,11 ps).The ablation front interferograms were processed in combination with a set of reference images obtained ex situ using phase-stepping.We managed to obtain attenuation and phase-shift images of a laser-irradiated foil for electron densities above 1022 cm−3.These results showcase the capabilities of Talbot–Lau X-ray diagnostic methods to diagnose HED laser-generated plasmas through high-resolution imaging.
