Dong Jia-Qin

Optimization of 4.7-keV X-ray titanium sources driven by 100-ps laser pulses

An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility. A prepulse induces an underdense plasma, 2-ns later a main pulse (λL = 0.35 μm, EL ≈ 120 J, τL ≈ 100 ps) is injected into the underdense plasma and produces strong line emission from the titanium K shell (i.e., Heα at 4.7 keV). Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse, and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing. High-quality plasma images are obtained with the backlighting 4.7-keV X-rays in a Rayleigh—Taylor hydrodynamic instability experiment.

Laser-produced plasma helium-like titanium Kα x-ray source and its application to Rayleigh-Taylor instability study

Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts. X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources. By using a time-integrated space-resolved keV spectroscope and pinhole camera, potential helium-like titanium K? x-ray backlighting (radiography) line source is studied as a function of laser wavelength, ratio of pre-pulse intensity to main pulse intensity, and laser intensity (from 7.25 to ~11.3 ? 1015 W/cm2). One-dimensional radiography using a grid consisting of 5 ?m Au wires on 16 ?m period and the pinhole-assisted point projection is tested. The measurements show that the size of the helium-like titanium K? source from a simple foil target is larger than 100 ?m, and relative x-ray line emission conversion efficiency ?x from the incident laser light energy to heliumlike titanium K-shell spectrum increases significantly with pre-pulse intensity increasing, increases rapidly with laser wavelength decreasing, and increases moderately with main laser intensity increasing. It is also found that a gold gird foils can reach an imaging resolution better than 5-?m featured with high contrast. It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.

Directly driven Rayleigh—Taylor instability of modulated CH targets

Directly driven ablative Rayleigh—Taylor (R—T) instability of modulated CH targets was studied using the face-on X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R—T instability perturbation. The R—T instability growth factor has been obtained by using the methods of fast Fourier transform and seeking the difference of light intensity between the peak and the valley of the targets. Through comparison with the the theoretical simulation, we found that the experimental data had a good agreement with the theoretical simulation results before 1.8 ns, and was lower than the theoretical simulation results after that.