Anomalous rise of the Hugoniot elastic limit (HEL) with increasing temperature was observed for aluminum and copper single crystals. Within the temperature range from 20°C to 650°C the HEL of aluminum single crystals increased from 0.12 to 0.96 GPa for 3 mm thick samples and to 3 GPa for ∼0.25 mm thick samples. The spall strength decreased from 2.3 GPa and 3.2 GPa at room temperature to 1.3 GPa and 2.2–3 GPa near the melting temperature for thicker and thinner samples, respectively. For copper single crystals a HEL of 2.6 GPa was recorded at 833°C; whereas the spall strength decreased from 5.4 GPa at room temperature to 4.8 GPa at 485°C.

Hugoniot elastic limit and spall strength of aluminum and copper single crystals over a wide range of strain rates and temperatures

Both direct-drive and indirect-drive inertial confinement fusion targets use temporally shaped drive pulses to optimize the target performance. The timing of multiple shock waves is crucial to the performance of inertial confinement fusion ignition targets. This paper reports an experimental study on the shock wave characteristics of laser-irradiated targets. The shock wave velocity profiles are measured using the velocity interferometer system for any reflector (VISAR). Presented are measurements of velocities from shock waves in quartz targets driven by single 120 ps pulse, two 120 ps pulses separated by 1.1 ns and a special shaped pulse. These pulses drive two shock waves that coalesce in the target, and the coalescence times and transit times are observed by VISAR.

Laser-driven shock propagation into quartz targets driven by various drive pulse configurations: experiments

Tungsten is regarded as an important candidate of plasma facing material in international thermonuclear experimental reactor (ITER), so the determination and modeling of spectra of tungsten plasma, especially the spectra at high temperature were intensely focused on recently. In this work, using the atomic structure code of Cowan, a collisional radiative model (CRM) based on the spin—orbit-split-arrays is developed. Based on this model, the charge state distribution of tungsten ions is determined and the soft X-ray spectra from high charged ions of tungsten at different temperatures are calculated. The results show that both the average ionization charge and line positions are well agreed with others calculations and measurements with discrepancies of less than 0.63% and 1.26%, respectively. The spectra at higher temperatures are also reported and the relationship between ion abundance and temperature is predicted in this work.

X-ray spectra of high temperature tungsten plasma calculated with collisional radiative model

In indirect-drive experiment, the blank effect caused by X-rays from Hohlraum will show the dark area in time scale of optical streak camera (OSC). This blank effect, which was a serious problem in indirect-drive shock wave experiments, has been explained by the semiconductor model. The X-rays cause the band to band transition and the probe laser is absorbed by the intraband transition, which leads to a dark region in time scale of the OSC image. In the experiment, the reflectivity of shock wave front was measured to be about 50% at shock wave velocity 32 km/s and was compared to the theoretical calculations with the Drude free electron model. From the experimental data, it is found that the blank effect can be avoided at radiation temperature of 170 eV if the Al layer is thicker than 60 μm.

http://iopscience.iop.org/article/10.1088/1674-1056/20/6/065202/pdf

Shock wave velocity measurement in the Al 2 O 3 under ultrahigh pressure

Measuring time-resolved spectra is crucial in inertial confinement fusion and radiation source development experiments An elliptically bent crystal spectrometer is designed to measure X-rays in the range of 25–110 keV, which was achieved using four different lattice spacings of 08512, 06687, 04246, and 02749 nm with spectral resolution E/δE of ∼500 The X-rays emitted from a source at one focus of the ellipse undergo Bragg reflection off a crystal and pass through the second focus of the ellipse to a streak camera slit with 18-mm length and 80-μm width to generate a time-resolved spectrum An alignment method for the time-resolved spectrometer was developed with the straight line connecting the centers of the two small holes on the fabricated substrate being the axis of the ellipse, thus allowing the spacing between the source and the elliptical crystal to be tuned to couple with the streak camera The time-resolved spectrometer’s performance was experimentally tested at the Shenguang II laser facility The results indicate that its performance is close to that predicted theoreticallyMeasuring time-resolved spectra is crucial in inertial confinement fusion and radiation source development experiments An elliptically bent crystal spectrometer is designed to measure X-rays in the range of 25–110 keV, which was achieved using four different lattice spacings of 08512, 06687, 04246, and 02749 nm with spectral resolution E/δE of ∼500 The X-rays emitted from a source at one focus of the ellipse undergo Bragg reflection off a crystal and pass through the second focus of the ellipse to a streak camera slit with 18-mm length and 80-μm width to generate a time-resolved spectrum An alignment method for the time-resolved spectrometer was developed with the straight line connecting the centers of the two small holes on the fabricated substrate being the axis of the ellipse, thus allowing the spacing between the source and the elliptical crystal to be tuned to couple with the streak camera The time-resolved spectrometer’s performance was experimentally tested at the Shenguang II laser faci

Elliptically bent crystal x-ray spectrometer for time-resolved laser plasma experiments.

Key Techniques of Velocity Interferometer for Any Reflector

Measurement of fine structure spectra in high-stripped states laser-produced Mo plasma

High-power laser induced shocks generated by “ShenGuang II” laser facility has been used to study spall fracture of polycrystalline aluminum at strain rates more than 106/s. The free surface velocity histories of shock-loaded samples, 150 μm thick and with initial temperature from 293 K to 873 K, have been recorded using velocity interferometer system for any reflector (VISAR). From the free surface velocity profile, spall strength and yield stress are calculated, it demonstrates that spall strength will decline and yield strength increase with initial temperature. The loaded samples are recovered to obtain samples' section and free surface metallographic pictures through Laser Scanning Confocal Microscopy. It is found that there are more micro-voids and more opportunity to appear bigger voids near the spall plane and the grain size increases with temperature slowly but smoothly except the sharply change at 893 K (near melting point). Besides, the fracture mechanisms change from mainly intergranular fracture to transgranular fracture with the increase of initial temperature.

/pdf/high-power-laser-shock-induced-dynamic-fracture-of-aluminum-e9wr11vd7l.pdf

High-power laser shock-induced dynamic fracture of aluminum and microscopic observation of samples

Band tunable X-ray flat crystal spectrometer for laser-produced plasma spectroscopy measurements

Shock compression properties of polyethylene (CH 2 ) were studied at SG-Ⅱ laser facility. The experimental results show that the self-emission is high,which emits from the shock-front in polyethylene. And the shock-front propagates through the polyethylene step almost with constant velocity. The Hugoniot equation of state (EOS) of polyethylene was measured by using the impedance-matching method with aluminum as standard material. Pressures are high up to 0.54 TPa in polyethylene, and the relative expanded uncertainties of the measured shockwave velocity are about 2% ( K =2). Moreover, the consistency of our data is good, and our data are also consistent with existing experimental data and EOS model.

Jia Guo

Papers

Key Techniques of Velocity Interferometer for Any Reflector

Measurement of fine structure spectra in high-stripped states laser-produced Mo plasma

High-power laser shock-induced dynamic fracture of aluminum and microscopic observation of samples

Band tunable X-ray flat crystal spectrometer for laser-produced plasma spectroscopy measurements

Experimental study on shock compression properties of polyethylene