Abstract
In order to study the laser plasma instabilities (LPIs) in the context of some novel six-side laser-driven indirect designs like the six-cylinder-port hohlraum and the three-axis cylindrical hohlraum, where the laser beams inject in hohlraum with a large angle. LPI experiments in cylindrical hohlraum with only outer beams were designed and performed based on the current laser arrangement condition of SGIII laser facility for the first time. Stimulated Brillouin backscatter (SBS) was found to be the dominant instability with high instantaneous reflectivity in experiments. A typical feature was obtained in the time-resolved spectra of SBS, which maintained similar for different laser intensities of the interaction beam. The experimental data are analyzed by the hydrodynamic simulations combined with HLIP code, which is based on the ray-tracing model. By analysis of experimental data, it is argued that the mixture of gas and Au in the region of their interface is important to SBS, which indicates the need for the mixture model between the filled gas and the high Z plasma from hohlraum wall in the hydrodynamic simulations. Nonlinear saturation of SBS as well as the smoothed beam are also discussed here. Our effective considerations of the ions pervasion effect and the smoothed beam provide utilitarian ways for improvement of the current ray-tracing method.
Highlights
Laser plasma instabilities (LPIs) are important processes in laser-driven inertial confinement fusion (ICF).1 In the two-side laser-driven indirect concepts such as the baseline indirect target design for the National Ignition Facility (NIF),2 192 laser beams are typically arranged to irradiate a cylindrical hohlraum in four cones of different angles and form the inner and outer laser rings on the hohlraum wall
Our simulations show that the temporal change and the wavelength range of Stimulated Brillouin backscatter (SBS) signals in spectra should mainly depend on the evolution of plasma parameters on the ray path, but depend on the laser intensity weakly
The hydrodynamic simulations are performed in 2D, and the plasma evolution in hohlraum is assumed to be cylindrical symmetry, which must be different from the actual situation
Summary
Laser plasma instabilities (LPIs) are important processes in laser-driven inertial confinement fusion (ICF). In the two-side laser-driven indirect concepts such as the baseline indirect target design for the National Ignition Facility (NIF), 192 laser beams are typically arranged to irradiate a cylindrical hohlraum in four cones of different angles and form the inner and outer laser rings on the hohlraum wall. Stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), and crossed beam energy transfer (CBET) in the multi beams overlapping region are thought as the most important LPIs due to their potential harms to the ignition.. SRS and SBS can scatter the energy away from pump laser, while. CBET can redistribute the energy between different incident beams, reshape the energy distribution within each beam and further affect other LPIs.. CBET can redistribute the energy between different incident beams, reshape the energy distribution within each beam and further affect other LPIs.7–9 These effects can reduce target absorption and cause the x-ray drive asymmetry.. LPIs have been widely studied in different regimes for several decades, due to scitation.org/journal/adv their sensitivity to laser and plasma parameters, it is believed that further understand of LPIs under the complex condition especially for the gas-filled hohlraum remains an important issue before the demonstration of ignition CBET can redistribute the energy between different incident beams, reshape the energy distribution within each beam and further affect other LPIs. These effects can reduce target absorption and cause the x-ray drive asymmetry. Besides, hot electrons generated by SRS or two-plasmon decay (TPD) can preheat the capsule and prevent the energy-efficient implosions. LPIs have been widely studied in different regimes for several decades, due to scitation.org/journal/adv their sensitivity to laser and plasma parameters, it is believed that further understand of LPIs under the complex condition especially for the gas-filled hohlraum remains an important issue before the demonstration of ignition
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