Bo Qing

The M-band transmission flux of the plastic foil with a coated layer of silicon or germanium

Silicon (Si) and Germanium (Ge) can be used as the dopant in the ablator material for the purpose of reducing preheating in indirect-drive inertial confinement fusion. Their performances in reducing preheating are quite different. A method to evaluate the difference of these two kinds of dopants has been presented in this letter. In the Shenguang-II high power laser facility, the M-band (1.6–4.4 keV) transmission flux of Si-coated plastic (CH) and Ge-coated plastic (CH) has been measured by using the M-band x-ray diode. In the experiment, we find that the Si-coated CH can absorb more M-band x-rays and thus reduce the preheating of the fuel in our experiment condition. By using the radiation hydrodynamic code MULTI-1D, we got the simulation result which was well suited for the experiment. The comparison of their opacities (Te = 60–100 eV and ρ = 0.1–0.5 g/cm3) also shows that the opacity of Si is higher than that of Ge almost in the whole range of 1.6–4.4 keV.

Calibration of a gated flat field spectrometer as a function of x-ray intensity

We present an experimental determination of the response of a gated flat-field spectrometer at the Shenguang-II laser facility. X-rays were emitted from a target that was heated by laser beams and then were divided into different intensities with a step aluminum filter and collected by a spectrometer. The transmission of the filter was calibrated using the Beijing Synchrotron Radiation Facility. The response characteristics of the spectrometer were determined by comparing the counts recorded by the spectrometer with the relative intensities of the x-rays transmitted through the step aluminum filter. The response characteristics were used to correct the transmission from two shots of an opacity experiment using the same samples. The transmissions from the two shots are consistent with corrections, but discrepant without corrections.

The importance of the transmission flux in evaluating the preheat effect in x-ray driven ablation

In x-ray driven ablation, the preheat effect is caused by the high energy x-rays that pass through the ablator. Thus, the transmission flux can be used to characterize preheat effect in a certain degree. With the radiation temperature being 200 eV, the transmission flux and preheat temperature of pure polymer (CH) have been studied by using the one-dimensional multi-group radiation hydrodynamic code MULTI-1D. By studying the spectrum of the transmitted x-rays, it is found that the energy of the transmitted x-rays is in the range of 2–5 keV for pure CH ablator. This is of importance for selecting a dopant for CH ablator. We also calculated both the preheat temperature of CH near the surface of thick target (47.66 μm) and the transmission flux of a thinner target (38.66 μm). It is found that the more transmission flux leads to the higher preheat temperature. Preheat effect of graded Si-doped CH targets with different doped concentrations has also been studied. The results are consistent with this phenomenon. By analyzing the relationship between the transmission flux and the preheat temperature, we have presented a novel method to evaluate preheat effect in x-ray driven ablation.

Radiative cooling induced plasma collapse observed in laser irradiation of a CH-tamped gold micro-disk

Time-resolved x-ray self-emission imaging was used to study the dynamic evolution of a laser-produced gold plasma tamped by plastic (CH), and a significant plasma collapse was observed during the laser irradiation. The plasma collapse, a kind of transverse contraction, has been ascribed to the radial compression caused by the different radiative cooling rates and thus different pressures between the central high-Z gold plasma and the surrounding low-Z CH plasma, and this has been reproduced by numerical simulations using the two-dimensional radiation-hydrodynamics code Multi2D. The experimental results represent an observation of the radiative cooling induced plasma jet within a 1 ns laser pulse duration, much more quickly than those reported previously. In addition, our experiment design may offer a method to study the radiative cooling rates of high-Z plasmas. The measured cooling rate is a factor of 2 higher than the theoretical result [Post et al., At. Data Nucl. Data Tables 20, 397 (1977)], but is wi...

A time-gated multi-channel x-ray crystal spectrometer on the Shenguang-III laser facility

An eight-channel x-ray flat crystal spectrometer was developed for high energy density physics research at the Shenguang-III (SG-III) laser facility. The spectrometer uses trihydroxymethylaminomethane crystals (2d = 8.78 Å) to record Ti K-shell emission in the photon energy range of 4.65-5.05 keV. The spectrometer couples to an x-ray framing camera to achieve time-resolution. This has four microstrips, and each strip records two snapshots of the emission image. Based on the intersection positioning system with a dual-charge coupled device, the alignment system is easily operated and efficient. The instrument was tested and used for Au hohlraum plasma diagnosis experiments on SG-III. The He-α line and its Li-like satellites and the Ly-α line of a Ti tracer were detected, from which the spectral resolution of the instrument was analyzed. The spectral resolution E/ΔE at the Ti He-α line ranges from about 500 to 880 and mainly limited by the x-ray source size.

Opacity measurements of a molybdenum plasma with open M-shell configurations

The opacity of a molybdenum plasma in local thermodynamic equilibrium with open M-shell configurations was measured in the energy range from 200 eV to 800 eV, corresponding to the Δn = 1 M to N shell and Δn = 2 M to O shell transitions. The sample was heated by thermal x-ray radiation generated with a gold cavity. The electron temperature was diagnosed with the absorption spectrum of doped aluminum, giving a value of Te = (67 ± 4) eV. The density was 9.7 mg/cm3, which was deduced from the known initial area density and the plasma thickness by radiographic measurements of the expansion of the heated foil sample. The spectrally resolved transmission data were compared to a detailed-configuration-accounting model calculation and about 20% to 100% discrepancies were found.

Comparing the soft x-rays transport in Si and Ge-sandwich targets by measuring transmission flux

Mid-Z dopant in ablator is very important in point design targets. In this paper, we develop a method to evaluate the soft x-ray transport of doped material with one dimensional planar target. The targets are designed as sandwich, so that the mid-layer is heated by M band, shock and thermal wave. The transmission fluxes from heated targets are measured with band-pass x-ray diodes. The Si and Ge dopants are evaluated with this method. The experimental results show that 1–1.6 keV x-ray transmission flux through Si-sandwich is higher than that through Ge-sandwich all the time. Also, the comparison of opacities shows that the opacity of Si is lower than that of Ge in the range of 1–1.6 keV, which is consistent with the experimental results.

Extreme ultraviolet spectrometer for the Shenguang III laser facility.

An extreme ultraviolet spectrometer has been developed for high-energy density physics experiments at the Shenguang-III (SG-III) laser facility. Alternative use of two different varied-line-spacing gratings covers a wavelength range of 10-260 Å. A newly developed x-ray framing camera with single wide strip line is designed to record time-gated spectra with ~70 ps temporal resolution and 20 lp/mm spatial resolution. The width of the strip line is up to 20 mm, enhancing the capability of the spatial resolving measurements. All components of the x-ray framing camera are roomed in an aluminum air box. The whole spectrometer is mounted on a diagnostic instrument manipulator at the SG-III laser facility for the first time. A new alignment method for the spectrometer based on the superimposition of two laser focal spots is developed. The approaches of the alignment including offline and online two steps are described. A carbon spectrum and an aluminum spectrum have been successfully recorded by the spectrometer using 2400 l/mm and 1200 l/mm gratings, respectively. The experimental spectral lines show that the spectral resolution of the spectrometer is about 0.2 Å and 1 Å for the 2400 l/mm and 1200 l/mm gratings, respectively. A theoretical calculation was carried out to estimate the maximum resolving power of the spectrometer.