Hua Shu

Laser-driven shock wave stability in Al through Au and determination of the TPa hugoniot point in Au

High-quality shock waves were produced using the ninth laser beam (converted to 2ω) of Shenguang-II laser facility and the beam smoothing technology of a lens array. The spatial uniformity of the shock wave was estimated by measurements of the self-emission from the target rear surface. An Al–Au four-step target with 30μm Al base and four Au steps was fabricated and used to investigate the temporal steadiness of the shock wave in the Al–Au two-layer target. The Al–Au four-step target experiment indicated that the shock wave steadily propagated in the Au material with thickness range <11μm. A modified Al–Au impedance-match target was designed, which could simultaneously measure shock-wave stability and Au Hugoniot data in one shot. The experiment results indicated that the shock wave steadily propagated in the Al target with thickness of about 30–47μm under a power density of ∼1.0×1014W∕cm2.

Plastic behavior of aluminum in high strain rate regime

The aim of this experiment was to study the plastic response of Al to dynamic loading at high strain rates. Dynamic loading was applied by direct laser ablation of the sample with pulse width of 3 ns long. The free surface velocity histories of shock loaded samples, 60-310 μm thick at room temperature, and 150 μm thick with initial temperature from 293 to 893 K, have been recorded using a line velocity interferometer for any reflections (VISAR) system. The line VISAR could measure free surface velocity profile with high temporal resolution (∼100 ps). The measured amplitudes of the elastic precursor waves have been approximated by power functions of the propagation distance with the power index of 0.581, and these data have been converted into relationships between the shear stress at Hugoniot elastic limit and the initial plastic strain rate. The peak longitudinal elastic stress and the strain rate meet a power law dependency with the power index of 0.44. Samples were recovered for post-shot metallographi...

Analysis of measurement error in the experiment of laser equation of state with impedance-match way and the Hugoniot data of Cu up to ∼2.24 TPa with high precision

This article has reported the detailed analysis about the error in the experimental measurement of laser equation of state. A kind of matrix method to calculate the uncertainty of state parameter was put forward and applied to the error estimation in the experiment with Al-Cu impedance-match target. The shock adiabatic data of Cu with the pressure up to ∼2.24 TPa and the relative uncertainty of shock velocity of ∼2% have been also presented.

Measuring preheat in laser-drive aluminum using velocity interferometer system for any reflector: Experiment

In this paper, we systematically study preheating in laser-direct-drive shocks by using a velocity interferometer system for any reflector (VISAR). Using the VISAR, we measured free surface velocity histories of Al samples over time, 10–70 μm thick, driven directly by a laser at different frequencies (2ω, 3ω). Analyzing our experimental results, we concluded that the dominant preheating source was X-ray radiation. We also discussed how preheating affected the material initial density and the measurement of Hugoniot data for high-Z materials (such as Au) using impedance matching. To reduce preheating, we proposed and tested three kinds of targets.

Shock-timing experiments in polystyrene target

Direct-drive and indirect-drive inertial confinement fusion (ICF) targets use temporally shaped drive pulses to optimize target performance. The timing of multiple shock waves is crucial to the performance of ICF ignition targets. Velocity interferometer system for any reflector (VISAR) is the principal diagnostic tool for shock-timing experiments. We present velocity measurements from the shock waves in polystyrene targets driven by two 200-ps pulses separated by 1-2 ns. These pulses drive two shock waves that coalescence in the target. Coalescence time and transit times are observed by VISAR.