- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Absolute stimulated Raman side scatter in direct-drive laser-produced plasmas
摘要： Production of suprathermal electrons by stimulated Raman scattering (SRS) is a principal concern for contemporary direct-drive inertial confinement fusion experiments at the National Ignition Facility and similar systems since such electrons penetrate and preheat the target core, preventing efficient implosion. The higher temperatures and longer scale lengths in these experiments favor SRS over two-plasmon decay, which predominated in earlier experiments. In particular, current experiments are expected to exceed the threshold for absolute Raman side scatter, which would then dominate the interaction since it grows temporally until saturated by nonlinear mechanisms such as hot-electron production. Until recently, analyses of SRS side scatter have treated the case of a single laser beam incident on a plasma, but the direct-drive approach to laser fusion employs a multitude of beams to drive the implosion. Here, we present an analysis that can be applied to an arbitrary number of beams with varied angles of incidence and polarizations. In the case of a single beam, it allows a physically motivated derivation and verification of an analytic threshold formula. In the general case of multiple beams and arbitrary orientation and polarizations, the threshold is found by numerical integration of a set of first-order linear partial differential equations.
关键词： direct-drive,stimulated Raman scattering,inertial confinement fusion,laser-produced plasmas,suprathermal electrons
更新于2025-09-23 15:21:01
-
The interaction of parametric instabilities from 3?? laser and 2?? laser in large-scale inhomogeneous plasmas
摘要： The interaction of parametric instabilities from 3ω laser and 2ω laser in large-scale inhomogeneous plasmas. The mechanism of energy transfer from 3ω pump light to stimulated Brillouin scattering (SBS) generated by 2ω pump light is proposed. The backscattering light of stimulated Raman scattering (SRS) generated by 3ω pump light can work as a seed of the SBS of 2ω pump light, which results in the increase of the later. Adding 2ω pump light into 3ω pump light will decrease the reflectivity of SBS generated from 3ω pump light. The total reflectivity will firstly decrease and then increase with increase of the ratio of 2ω light intensity to the intensity of 2ω and 3ω lights f = I2ω0/(I2ω0 + I3ω0), and will be controlled in a lower level when this ratio f is about 10% ? 20%. These results give a method to control the total reflectivity of SBS and SRS in inertial confinement fusion (ICF) by adding 2ω light into 3ω light.
关键词： inertial confinement fusion,2ω laser,3ω laser,parametric instabilities,stimulated Raman scattering,stimulated Brillouin scattering,large-scale inhomogeneous plasmas
更新于2025-09-23 15:19:57
-
Effective electromagnetic shielding with multi-layer structure material on Shenguang laser facility
摘要： Electromagnetic pulses (EMPs) with high intensity and frequency bandwidth can be generated during the intensive laser irradiating solid targets in inertial confinement fusion (ICF). To shield the EMPs radiation and hence protect various diagnostics in and outside the target chamber, we designed a multi-layer structure material to shield the EMPs and demonstrate experimentally and numerically shielding performance of the material structure. The thickness of the multi-layer structure material has a great influence on the EMPs shielding. It is shown that, with the increase of the material thickness, the better shielding performance is obtained, and the material structure with polytetrafluoroethylene (PTFE) of 0.5 mm, copper of 0.4 mm and lead of 2.4 mm reduces 448 times compared the maximum value of EMPs voltage to that without shielded. The design of multi-layer structure material for EMPs shielding provides a promising way to reduce EMPs radiation, which is extremely useful for the diagnostics protection and signal processing in ICF.
关键词： inertial confinement fusion,Shenguang laser facility,electromagnetic pulse,shielding
更新于2025-09-12 10:27:22
-
Combined implementation of smoothing technologies for improving illumination uniformity of laser quad in multi-directions
摘要： Azimuthal smoothing (AS) that enables the focal spot of a laser quad to rotate in a period of a few picoseconds can improve the illumination uniformity. However, the smoothing performance of azimuthal smoothing is worse than that of smoothing by spectral dispersion (SSD) due to the low rotation speed in the center area of the focal spot. A combined implementation of the schemes including smoothing by spectral dispersion, radial smoothing (RS) and azimuthal smoothing is discussed to achieve better and faster illumination uniformity. The theoretical models of the combined smoothing scheme have been built up to analyse the smoothing performance. The key parameters affecting the smoothing performance of the combined smoothing scheme are analysed and optimized, including the topological charge and the wavelength difference. The simulation results show that the illumination uniformity of the laser quad can be significantly improved in multi-directions by the combined smoothing scheme.
关键词： Inertial confinement fusion,azimuthal smoothing scheme,vortex beam,radial smoothing,uniformity,smoothing by spectral dispersion
更新于2025-09-12 10:27:22
-
Improvement of irradiation uniformity by dynamic interference structures of laser array in inertial-confinement-fusion facilities
摘要： In order to improve the irradiation uniformity in inertial confinement fusion facilities, a novel scheme, smoothing by interference structures of laser array, is firstly proposed for improving the irradiation characteristics. In this approach, a pair of identical phase plates with either tilted, cylindrical, elliptical or spiral phase modulates two beamlets, and another pair of phase plates that are conjugate with the former reshapes another two beamlets. Between the beamlets with conjugate wavefront distributions, their central wavelengths are shifted but their polarization states are the same. Arising from the combined effect of the conjugate wavefront distributions and the wavelength differences among the beamlets, the dynamic interference structures are generated in the focal region and thus improve the irradiation uniformity of these beams. Simulation shows that, the superposed focal spot of the beamlets in the focal region is smoothed in transverse, radial or azimuthal direction due to the phase types of the plates, and the required time to achieve the best uniformity is much shorter than the smoothing by spectral dispersion scheme. Moreover, the phase plates can be integrated with the continuous phase plates or be placed in the beamline as pure phase plates in the high-power laser facilities.
关键词： Irradiance uniformity,Beam control,Inertial confinement fusion
更新于2025-09-12 10:27:22
-
Note: Radiochemical measurement of fuel and ablator areal densities in cryogenic implosions at the National Ignition Facility
摘要： A new radiochemical method for determining deuterium-tritium (DT) fuel and plastic ablator (CH) areal densities (ρR) in high-convergence, cryogenic inertial confinement fusion implosions at the National Ignition Facility is described. It is based on measuring the 198Au/196Au activation ratio using the collected post-shot debris of the Au hohlraum. The Au ratio combined with the independently measured neutron down scatter ratio uniquely determines the areal densities ρR(DT) and ρR(CH) during burn in the context of a simple 1-dimensional capsule model. The results show larger than expected ρR(CH) values, hinting at the presence of cold fuel-ablator mix.
关键词： cryogenic inertial confinement fusion,neutron down scatter ratio,National Ignition Facility,areal densities,fuel-ablator mix,plastic ablator,deuterium-tritium fuel,radiochemical method,Au hohlraum
更新于2025-09-04 15:30:14