A recently proposed octahedral spherical hohlraum with six laser entrance holes (LEHs) is an attractive concept for an upgraded laser facility aiming at a predictable and reproducible fusion gain ...with a simple target design. However, with the laser energies available at present, LEH size can be a critical issue. Owing to the uncertainties in simulation results, the LEH size should be determined on the basis of experimental evidence. However, determination of LEH size of an ignition target at a small-scale laser facility poses difficulties. In this paper, we propose to use the prepulse of an ignition pulse to determine the LEH size for ignition-scale hohlraums via LEH closure behavior, and we present convincing evidence from multiple diagnostics at the SGIII facility with ignition-scale hohlraum, laser prepulse, and laser beam size. The LEH closure observed in our experiment is in agreement with data from the National Ignition Facility. The total LEH area of the octahedral hohlraum is found to be very close to that of a cylindrical hohlraum, thus successfully demonstrating the feasibility of the octahedral hohlraum in terms of laser energy, which is crucially important for sizing an ignition-scale octahedrally configured laser system. This work provides a novel way to determine the LEH size of an ignition target at a small-scale laser facility, and it can be applied to other hohlraum configurations for the indirect drive approach.
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.
We report experimental research on laser plasma interaction (LPI) conducted in Shenguang laser facilities during the past ten years. The research generally consists of three phases: (1) developing ...platforms for LPI research in mm-scale plasma with limited drive energy, where both gasbag and gas-filled hohlraum targets are tested; (2) studying the effects of beam-smoothing techniques, such as continuous phase plate and polarization smoothing, on the suppression of LPI; and (3) exploring the factors affecting LPI in integrated implosion experiments, which include the laser intensity, gas-fill pressure, size of the laser-entrance hole, and interplay between different beam cones. Results obtained in each phase will be presented and discussed in detail.
The first laser–plasma interaction experiment using lasers of eight beams grouped into one octad has been conducted on the Shenguang Octopus facility. Although each beam intensity is below its ...individual threshold for stimulated Brillouin backscattering (SBS), collective behaviors are excited to enhance the octad SBS. In particular, when two-color/cone lasers with wavelength separation 0.3 nm are used, the backward SBS reflectivities show novel behavior in which beams of longer wavelength achieve higher SBS gain. This property of SBS can be attributed to the rotation of the wave vectors of common ion acoustic waves due to the competition of detunings between geometrical angle and wavelength separation. This mechanism is confirmed using massively parallel supercomputer simulations with the three-dimensional laser–plasma interaction code LAP3D.
The low-mode shell asymmetry and high-mode hot spot mixing appear to be the main reasons for the performance degradation of the National Ignition Facility (NIF) implosion experiments. The effects of ...the mode coupling between low-mode P2 radiation flux asymmetry and intermediate-mode L = 24 capsule roughness on the implosion performance of ignition capsule are investigated by two-dimensional radiation hydrodynamic simulations. It is shown that the amplitudes of new modes generated by the mode coupling are in good agreement with the second-order mode coupling equation during the acceleration phase. The later flow field not only shows large areal density P2 asymmetry in the main fuel, but also generates large-amplitude spikes and bubbles. In the deceleration phase, the increasing mode coupling generates more new modes, and the perturbation spectrum on the hot spot boundary is mainly from the strong mode interactions rather than the initial perturbation conditions. The combination of the low-mode and high-mode perturbations breaks up the capsule shell, resulting in a significant reduction of the hot spot temperature and implosion performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Detailed knowledge of energy exchange between electrons and ions is of fundamental importance for the description of temperature relaxation and also other nonequilibrium physics in Inertial ...Confinement Fusion (ICF). We present a theoretical model for the temperature relaxation rate and the related generalized Coulomb logarithm based on the Quantum Lenard–Balescu (QLB) kinetic equation, where no special cutoffs are needed to be introduced. To describe the collective modes characterizing the ionic acoustic waves, a single-pole approximation is introduced for the ionic dielectric response. The proposed model for the generalized Coulomb logarithm is examined over a wide range of plasma conditions for electron temperatures between 10
2
and 10
5
eV and electron densities between 10
22
and
10
26
c
m
−
3
. The values of the generalized Coulomb logarithm are demonstrated to be in excellent agreement with the ones evaluated using the original QLB kinetic approach but with much less computational cost. Comparisons with molecular dynamics simulations and other theoretical approaches are presented. For further applications of our model, we present results for the recently measured experimental Coulomb logarithm. Compared to other widely applied models such as the Landau–Spitzer Coulomb logarithm, our model provides more consistent descriptions for the results of molecular dynamics simulations and also for the experimental outcomes. Our model for the generalized Coulomb logarithm is easy to calculate and can benefit efficient and reliable simulations for the ICF implosions.
Abstract
In a laser-irradiated plasma, the Langdon effect can result in a super-Gaussian electron energy distribution function (EEDF), imposing significant influences on stimulated backward Raman ...scattering (SRS). In this work, the influence of a super-Gaussian EEDF on the nonlinear evolution of SRS is investigated by the three wave coupling model simulation and Vlasov–Maxwell simulation for plasma parameters covering a wide range of
kλ
De
from 0.19 to 0.48 at both high and low intensity laser drives. In the early stage of SRS evolution, it is found that besides the kinetic effects due to electron trapping (2018
Phys. Plasmas
25
100702), the Langdon effect can also significantly widen the parameter range for the absolute growth of SRS, and the time for the absolute SRS to reach saturation is greatly shortened by the Langdon effect within certain parameter regions. In the late stage of SRS, when secondary instabilities such as decay of the electron plasma wave to beam acoustic modes, rescattering, and Langmuir decay instability become important, the Langdon effect can influence the reflectivity of SRS by affecting secondary instabilities. The comprehension of the Langdon effect on nonlinear evolution and saturation of SRS would contribute to a better understanding and prediction of SRS in inertial confinement fusion.
Abstract
Low-mode drive asymmetries are known as significant performance degradation factors in indirect-drive inertial confinement fusion (ICF) implosions. We propose a two-dimensional (2D) dynamic ...model to explore the impact of time-dependent low-mode drive asymmetries on the shell asymmetries in acceleration phases of implosions. Since during acceleration, the shell areal density (
ρ
R
s
) asymmetries are relatively small, we can treat the shell as thin shell pieces with finite mass and infinitesimally small thicknesses, neglecting the angular flows between these pieces. The radial motion of each shell piece is dominated by Newton’s law. Through this model, the evolution of the shell radial velocity
v
s
and the shell radius
R
s
asymmetries of degree
n
can be characterized in terms of the drive temperature, time-dependent drive asymmetry of degree
n
and the average
ρ
R
s
,
v
s
,
R
s
obtained from one-dimensional (1D) simulations. The acceleration phases of typical gas-fill capsule and layered DT capsule implosions with
P
2
or
P
4
drive asymmetries are explored using this model and validated using both 2D radiation hydrodynamic simulations and available backlit shell distortion measurements. This model gives a useful tool for ICF design, with an advantage of simplicity and speed.
A one-step hydrothermal method for preparation of copper oxides with different valences using ascorbic acid as a reducing reagent was developed for environmental remediation. The results suggested ...that the notable degradation performance of CuO
0
may be attributable to the abundant active sites, such as Cu or Cu–O, and was not significantly related to the Cu valence state. In contrast to direct degradation of pollutants by traditional superoxide radicals (O
2
•−
), O
2
•−
played an important role in the reduction of high-valence Cu ions (Cu(III)). In addition, a series of radical quenching, electron paramagnetic resonance (EPR), and electrochemical experiments validated the existence of direct electron transfer between methylene blue (MB) and PMS mediated by CuO
0
and surface-bound radicals. The results suggested that the CuO
0
/PMS system may be less susceptible to diverse ions and natural organic matter other than dihydrogen phosphate anions. The mechanism of MB degradation under alkaline conditions was different from that under acidic conditions in that it was not reliant on radicals or charge transfer but direct oxidation by PMS. This study provides new insights into the heterogeneous processes involved in PMS activation by the copper oxides. Furthermore, this paper devotes to providing theoretical basis on pollutant removal via PMS activated by copper oxides and developing low-cost and high-efficiency catalysts.
Full text
Available for:
CEKLJ, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
In a laser-irradiated plasma, the Langdon effect makes the electron energy distribution function tend to a super-Gaussian distribution, which has important influence on laser plasma ...instabilities. In this work, the influence of a super-Gaussian electron energy distribution function on the convective stimulated backward Raman scattering and stimulated backward Brillouin scattering is studied systematically for a wide range of typical plasma parameters in the inertial confinement fusion. Distinct behaviors are found for stimulated Raman scattering and stimulated Brillouin scattering in the variation trend of the peak spatial growth rate and the corresponding wavelength of the scattered light. Especially, the Langdon effect on the stimulated Brillouin scattering in plasmas with different ion species and isotopes is analyzed in detail, and the parameter boundary for judging the variation trend of the peak spatial growth rate of stimulated Brillouin scattering with the super-Gaussian exponent is presented for the first time. In certain plasma parameter region, it is found that the Langdon effect could enhance stimulated Brillouin scattering in mixed plasma, which may attenuate the improvement in suppressing stimulated Brillouin scattering by mixing low-Z ions into the high-Z plasma. The comprehension of Langdon effect on stimulated Raman scattering and stimulated Brillouin scattering would contribute to a better understanding of laser plasma instabilities in experiments.
PDF
