Yaonan Ding

K-shell transition absorption measurement of radiatively heated Al plasma

High temperature aluminum plasmas have been produced by irradiating the layered Au–Al foils with the smoothed high power laser at the Xingguang II laser facility. High-resolution transmission spectrum of the Al plasma has been measured by using penta-erythritol tetrakis (hydroxymethy) methane C(CH2OH)4 crystal spectrometer. Absorption lines of the aluminum ion transition 1s−np(n=3,4,5) in the region of 0.61–0.70 nm, have been observed and identified. The unresolved transition array model has been introduced to calculate the transmission spectra of aluminum plasma. The measured transmission spectrum has been compared with those calculated.

Precise measurement technology of soft-x-ray spectrum using dual transmission grating spectrometer

A novel transmission grating spectrometer, called a dual-transmission grating spectrometer, has been designed and established. This spectrometer adopts two transmission gratings to disperse x rays twice, which suppresses the overlap of the grating higher-order diffraction, cuts out the transfer of experimental errors in unfolding the measured x-ray spectrum effectively, and increases the x-ray spectrum measurement precision. It was shown by experiment that the dual-transmission grating spectrometer was applicable to precisely measure the soft-x-ray spectrum from laser-created plasmas.

X-ray ultraviolet absorption measurements of laser-driven Au/CH/Al multilayers

X-ray ultraviolet absorption measurements of aluminum plasma at high temperature and high density are reported. A sample plasma was created by direct laser irradiation of a multilayered foil consisting of Au, CH, and Al. Observations were made using the method of self-backlighting spectroscopy. Simulations were performed with one-dimensional radiation-hydrodynamics code to compute the backlight profile as well as the time history of the density and temperature in the sample. By comparing the measured absorption spectra with detailed-term-accounting calculations at Te=120eV and ρ=0.1g∕cm3, it is found that the major spectral features predicted by calculations have been observed. Even better agreement between the experiment and the simulated absorption spectra was obtained by temporally averaging the radiation-hydrodynamics result over the backlight profile. This experiment shows that it is possible to measure high density and high temperature opacity by a laser-driven multilayer experiment.

Spectroscopic absorption measurement of a low-Z plasma

Low-Z plasmas have been produced by x-ray radiative heating of a low-Z sample on the “Xingguang II” laser facility. High-resolution transmission spectra of the low-Z plasma (CHO) have been measured by using a flat field grating spectrometer. Absorption lines of oxygen and carbon ions in the region from 1.6 nm to 5.0 nm have been observed clearly and identified. The unresolved transition array model (UTA) has been introduced to calculate the transmission spectra of the CHO plasma. The measured transmission spectra have been compared with the calculated ones and the results of other works.

Experimental study of the hydrodynamic trajectory of an x-ray-heated gold plasma

Hydrodynamic processes of radiation-ablated high-Z plasmas have great influence on the x-ray radiation transport both in a high-Z tube with low-Z foam filling and in a low-Z filling indirect drive cavity. Using the intense x-ray radiation to heat a low-Z foam-tamped high-Z gold plate from a half cavity, the hydrodynamic moving process of the x-ray-ablated gold plasma has been studied by an imaging method with Ti He-α line emission as the backlighter source. The hydrodynamic trajectory of the x-ray-heated gold plasma was obtained and the average trajectory velocity of (36.5±1.2) km/s was derived. The experimental trajectory was compared with the simulations using the one-dimensional (1D) RDMG [P. Gu et al., Sci. China, Ser. G 48, 345 (2005)] and two-dimensional (2D) LARED-R [K. Lan et al., Laser Part. Beams 23, 275 (2005)] codes separately. It is shown that the 2D LARED-R code simulated the measured plasma trajectory much better than the 1D RDMG code due to the fact that the lateral x-ray radiation loss wa...

High intensity x-ray line emission from aluminum plasmas generated by a 120 TW, 30 fs laser pulse

The K-shell x-ray spectra from the aluminum plasmas generated by the interaction of the 120TW, 30fs laser with aluminum targets have been measured by defocusing the laser beam. Laser energy-normalized intensity of the He-a line increases with the laser intensity approximately as a power law e∝ILγ with the much smaller exponent of γ=0.062 compared to γ=0.2∼0.5 in the previous experiments, which is caused by the stronger radial thermal diffusivity in the target for the smaller laser spot. Laser-to-He-a line conversion efficiency of up to 1.9×10−3 and as high as about 3×1013 photons/2π Sr aluminum He-a line x-ray source have been achieved for a single shot due to the preplasma effect and relatively large laser spot and energy for the single shot. The x-ray spectra as a function of the laser intensity are also analyzed to get the electron temperature and density.

Two-tracer spectroscopy diagnostics of temperature profile in the conduction layer of a laser-ablated plastic foil

A technique that combines the diagnostics of electron temperature history and the measurements of ablation velocity with two-tracer x-ray spectroscopy has been developed for diagnosing the temperature profiles in the thermal conduction layers of laser-ablated plastic foils. The electron temperature in the plastic ablator was diagnosed using the isoelectronic line ratios of Al Lyα line to Mg Lyα line, emitted from a tracer layer of Al/Mg mixture buried under the ablator. The ablation velocity was inferred from the time delay between the onset time of x-ray line emissions from Al and Mg tracer layers buried at two depths in the ablator, respectively. From the measured electron temperatures and ablation velocity, the electron temperature profile in the conduction layer was inferred. The measured temperature profile was compared with the simulated one and reasonable agreement was found.

Progress of opacity experiment on the Shengguang II Laser Facility

In recent years, a series of opacity diagnostics have been developed at the Research Center of Laser Fusion in China. Two types of cavities (a conical cavity called a type I target, and a cylindrical cavity with foam baffles called a type II target) were designed to convert the eight-beam laser into x-ray radiation to efficiently heat the sample and to prevent the sample from irradiation of the reflected laser and plasmas on the Shengguang II laser facility. Typical opacity experiments have been carried out using the two target designs, respectively. The results show that a sample temperature of about 95 eV has been reached using the type II target which is the highest obtained on the high power laser facility.