- 标题
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Impact of asymmetries on fuel performance in inertial confinement fusion
摘要： Low-mode asymmetries prevent effective compression, con?nement, and heating of the fuel in inertial con?nement fusion (ICF) implosions, and their control is essential to achieving ignition. Ion temperatures (Tion) in ICF experiments are inferred from the broadening of primary neutron spectra. Directional motion (?ow) of the fuel at burn also impacts broadening and will lead to arti?cially in?ated “Tion” values. Flow due to low-mode asymmetries is expected to give rise to line-of-sight variations in measured Tion. We report on intentionally asymmetrically driven experiments at the OMEGA laser facility designed to test the ability to accurately predict and measure line-of-sight differences in apparent Tion due to low-mode asymmetry-seeded ?ows. Contrasted to CHIMERA and xRAGE simulations, the measurements demonstrate how all asymmetry seeds have to be considered to fully capture the ?ow ?eld in an implosion. In particular, ?ow induced by the stalk that holds the target is found to interfere with the seeded asymmetry. A substantial stalk-seeded asymmetry in the areal density of the implosion is also observed.
关键词： CHIMERA,xRAGE simulations,OMEGA laser facility,inertial con?nement fusion,ion temperatures,low-mode asymmetries
更新于2025-09-23 15:21:21
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Effect of fast electrons on the gain of a direct-drive laser fusion target
摘要： The results of numerical and theoretical studies of the gain of a direct-drive inertial con?nement fusion target, which includes a kinetic description of energy transfer by laser-accelerated fast electrons, are presented. The range of the initial temperature of the fast electrons and the fraction of laser energy contained in these particles were chosen based on the results of recent experiments at the National Ignition Facility. The effect of ‘wandering’ of fast electrons is taken into account which is due to the remoteness of the region of fast electron generation from the ablation surface of the imploded target. As a result a signi?cant fraction of particles do not fall into the compressed part of target. The ‘wandering’ effect leads to a decrease in the negative effect of fast electron generation on the gain of the target.
关键词： implosion,energy transfer,fast electrons,direct-drive targets,inertial con?nement fusion
更新于2025-09-23 15:19:57
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Numerical study on the laser ablative Rayleigha??Taylor instability
摘要： The laser ablative Rayleigh–Taylor instability plays an important role in the ignition of inertial re?nement fusion. An accurate simulation of this process is important to control the growth of ?ow instability during the implosion. In this paper, taking the simulations of the hydrodynamics, the laser energy deposition and the electronic thermal conductivity into consideration, a massively parallel laser ablative Rayleigh–Taylor instability code based on Euler method is developed. Some open source codes are used to improve the code development ef?ciency. The accuracy of the hydrodynamics simulation is tested by an analytical theory about the weakly nonlinear Rayleigh–Taylor instability with double interfaces. The benchmark of an one dimensional heat conductivity is used to test the accuracy of the thermal conductivity simulation. The laser ablative plane target and the laser ablative Rayleigh–Taylor instability are used to test the reliability of the code on the simulation of the whole laser ablative process. It is shown that the con?dence of our numerical simulation code is high and the code framework we designed is effective. It can be a basis on studying the problems about the laser ablative instability in inertial re?nement fusion.
关键词： Rayleigh–Taylor instability,Numerical simulation,Inertial con?nement fusion,Laser ablation
更新于2025-09-23 15:19:57
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Coarse Grained Simulation and Turbulent Mixing || Laser Driven Turbulence in High Energy Density Physics and Inertial Confinement Fusion Experiments
摘要： The mixing of initially separate materials in a turbulent ?ow by the small scales of turbulent motion is a critical and often poorly understood element of many research programs, such as inertial con?nement fusion (ICF), supernova implosions and explosions, and combustion, as well as many other applications in engineering, geophysics, and astrophysics. In typical contexts of interest, we are interested in achieving detailed understanding of interpenetration, hydrodynamical instabilities, and mixing arising from perturbations at the material interfaces, that is, driven by Rayleigh–Taylor (RT), Richtmyer–Meshkov (RM), and Kelvin–Helmholtz (KH) instabilities (buoyancy, shock, and shear induced instabilities, respectively). Laboratory observations typically provide only limited integrated measures of complex nonlinear three-dimensional physical processes, leaving many details and mechanisms unresolved. Carefully controlled computational experiments based on the numerical simulations play a crucial complementary role, providing insight into the underlying dynamics. Collaborative laboratory/computational studies are used to establish predictability of the models in conjunction with the development of frameworks for analysis, metrics for veri?cation and validation, and uncertainty quanti?cation.
关键词： Richtmyer–Meshkov instability,Rayleigh–Taylor instability,inertial con?nement fusion,turbulent mixing,high energy density physics,Kelvin–Helmholtz instability
更新于2025-09-12 10:27:22
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Burst behavior due to the quasimode excited by stimulated Brillouin scattering in high-intensity laser–plasma interactions
摘要： The strong-coupling mode, called the “quasimode”, is excited by stimulated Brillouin scattering (SBS) in high-intensity laser–plasma interactions. Also SBS of the quasimode competes with SBS of the fast mode (or slow mode) in multi-ion species plasmas, thus leading to a low-frequency burst behavior of SBS re?ectivity. Competition between the quasimode and the ion-acoustic wave (IAW) is an important saturation mechanism of SBS in high-intensity laser–plasma interactions. These results give a clear explanation of the low-frequency periodic burst behavior of SBS and should be considered as a saturation mechanism of SBS in high-intensity laser–plasma interactions.
关键词： stimulated Brillouin scattering,inertial con?nement fusion,quasimode,ion-acoustic waves,Brillouin ampli?cation
更新于2025-09-12 10:27:22
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Characterization of suprathermal electrons inside a laser accelerated plasma via highly-resolved K?-emission
摘要： Suprathermal electrons are routinely generated in high-intensity laser produced plasmas via instabilities driven by non-linear laser-plasma interaction. Their accurate characterization is crucial for the performance of inertial con?nement fusion as well as for performing experiments in laboratory astrophysics and in general high-energy-density physics. Here, we present studies of non-thermal atomic states excited by suprathermal electrons in kJ-ns-laser produced plasmas. Highly spatially and spectrally resolved X-ray emission from the laser-de?ected part of the warm dense Cu foil visualized the hot electrons. A multi-scale two-dimensional hydrodynamic simulation including non-linear laser-plasma interactions and hot electron propagation has provided an input for ab initio non-thermal atomic simulations. The analysis revealed a signi?cant delay between the maximum of laser pulse and presence of suprathermal electrons. Agreement between spectroscopic signatures and simulations demonstrates that combination of advanced high-resolution X-ray spectroscopy and non-thermal atomic physics offers a promising method to characterize suprathermal electrons inside the solid density matter.
关键词： suprathermal electrons,non-thermal atomic physics,X-ray spectroscopy,inertial con?nement fusion,laser-plasma interaction
更新于2025-09-12 10:27:22
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Progress on next generation gamma-ray Cherenkov detectors for the National Ignition Facility
摘要： Fusion reaction history and ablator areal density measurements for Inertial Con?nement Fusion experiments at the National Ignition Facility are currently conducted using the Gamma Reaction History diagnostic (GRH 6m). Future Gas Cherenkov Detectors (GCDs) will ultimately provide ～100x more sensitivity, reduce the effective temporal response from ～100 to ～10 ps, and lower the energy threshold from 2.9 to 1.8 MeV, relative to GRH 6m. The ?rst phase toward next generation GCDs consisted of inserting the existing coaxial GCD-3 detector into a reentrant well which puts it within 4 m of the implosion. Reaction history and ablator gamma measurement results from this Phase I are discussed here. These results demonstrate viability for the follow-on Phases of (II) the use of a revolutionary new pulse-dilation photomultiplier tube to improve the effective measurement bandwidth by >10x relative to current PMT technology; and (III) the design of a NIF-speci?c “Super” GCD which will be informed by the assessment of the radiation background environment within the well described here.
关键词： pulse-dilation photomultiplier tube,Gas Cherenkov Detectors,Gamma-ray Cherenkov detectors,Inertial Con?nement Fusion,National Ignition Facility
更新于2025-09-10 09:29:36
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Development of an ultra-fast photomultiplier tube for gamma-ray Cherenkov detectors at the National Ignition Facility (PD-PMT)
摘要： A new ultra-fast photomultiplier tube and associated drivers have been developed for use in the next generation of gamma-ray high pressure gas Cherenkov detectors for inertial con?nement fusion experiments at the National Ignition Facility. Pulse-dilation technology has been applied to a standard micro-channel-plate-based photomultiplier tube to improve the temporal response by about 10×. The tube has been packaged suitably for deployment on the National Ignition Facility, and remote electronics have been designed to deliver the required non-linear waveforms to the pulse dilation electrode. This is achieved with an avalanche pulse generator system capable of generating fast arbitrary waveforms over the useful parameter space. The pulse is delivered via fast impedance-matching transformers and isolators, allowing the cathode to be ramped on a sub-nanosecond time scale between two high voltages in a controlled non-linear manner. This results in near linear pulse dilation over several ns. The device has a built-in ?ducial system that allows easy calibration and testing with ?ber optic laser sources. Results are presented demonstrating the greatly improved response time and other parameters of the device.
关键词： inertial con?nement fusion,gamma-ray Cherenkov detectors,National Ignition Facility,ultra-fast photomultiplier tube,pulse-dilation technology
更新于2025-09-09 09:28:46