[en] Hohlraum physics is fundamental to the indirect drive inertial fusion. The ultimate goal of laser-driven hohlraum is to create a radiation environment that ablatively implodes a capsule to ignite and burn. To obtain high fusion yield with minimum laser energy, the hohlraum radiation drive must meet both the high X-ray conversion and excellent uniformity. By optimizing the hohlraum structures and materials, the hohlraum performance could be improved in flux intensity, uniformity and spectrum. The hohlraum physics study focuses on the laser propagation through the underdense plasma, x-ray conversion by the laser interacting with the high-Z material and X-ray heating of high-Z walls. All of these issues are important for understanding the hohlraum. On the Shenguang-Ⅲ prototype laser facility, extensive experiments have been performed to characterize laser-heated hohlraum. We have demonstrated good understanding of the hohlraum energetics and radiation feature. Experimental study on vacuum hohlraum energetics obtains the scaling of the scattered light and radiation temperature with laser energy and hohlraum size. Gas-filled hohlraum impedes the motion of ablated wall plasma with the low-density, low-Z gas plasma, and exhibits a reduction of Au M-band flux that might adversely preheat the capsule. Several quantitative studies that concentrate on the specific regions inside the hohlraum have been performed. The laser spot movement with different flux limiter according to electron heat conduction has been investigated. The movement of laser heated corona plasma could be controlled by varying initial gas density. The ratio of the X-ray emission between the laser spot and the reemitting wall was measured in the same shot, which might contribute to the optimization of the hohlraum flux symmetry. (authors)

[en] The implosion experiment with double quads on SGⅢ facility was the first time laser indirect-drive implosion experiment, also the first time neutron experiment. The experiments used ϕ1400 mm × 2100 mm hohlraum with ϕ1000 mm LEH and ϕ500 mm CH target with 1 MPa DD fuel, and the laser was injected the hohlraum by 55°. The highest neutron yield was 9.7 × 10⁸, up to now, the highest indirect-drive DD neutron yield in domestic experiment. The experimental results show that the coupling efficiency of the hohlraum approximates 50%; the hohlraum is too long, and the pellet is compressed to a 'pancake'; neutron yield is positively correlated with the laser energy; the Bang Time depends on the thickness of the ablative layer. (authors)

[en] The principle, structure, performance and application of a fluorescent radiation source excited by protons are described. When the K-400 proton accelerator provides a proton beam of 1 mA at 270 kV, the source intensities at nine energy points between 183 eV and 3000 eV are about 10¹⁰ ∼ 10¹³ photons/sec. The source has been employed to develop diagnostic techniques for low energy x rays

[en] In the interaction of intense laser-plasma, hot electrons, which can preheat the core of the fuel and lower the compression efficiency, are produced by collective processes such as stimulated Raman Scattering (SRS), resonance absorption (RA), two plasma decay (TPD) and ion acoustic decay (IAD). It is very important to study hot electrons experimentally and theoretically. The spectrum and total energy of hard X-rays outside the cavity targets have been measured for many years. In order to correct theoretical model and improve accuracy of calculating the total energy of hot electrons in cavities, it is urgent to identify the traveling direction of hot electrons and the regions of hard X-rays generation. In the experiment reported, specific cavities was designed to investigate the angular distribution of hot electrons in cavity and the region of hard X-ray generation. Experiments were conduced on Shengguang high power laser facility. The cavity target was irradiated by one beam laser (λ = 1.06 μm, E_L = 450∼550 J, τ≅ 0.8 ns, I_L ≅10¹⁵ W·cm^-2). A ten channel filter fluorescence spectrometer and an array of separate GaAs photoconductor were used to measure the spectra, angular distribution, and total energy of hard X-rays, and the energy of stimulated Raman scattering light was also measured for comparison. From the specific structure of cavities and the experimental results, the following two main results were inferred: (1) Most of the hot electrons in cavity are inclined to travel along the direction of laser wave vector, not isotropically. (2) Hard X-rays were mainly produced by Bremsstrahlung effect of hot electrons' collision with gold cavity wall

[en] On Shenguang III laser facility, 32 laser beams were symmetrically injected a gas-filled hohlraum to create plasma situation which is close to the ignition condition. An X-ray framing camera on the polar station and an X-ray streak camera near the pole were utilized to obtain the temporal and spacial evolution X-ray images of the plasma from the hohlraum wall and near the laser entrance hole (LEH), which were used to analyse the LEH closure feature of the hohlraum with various LEH size. The experimental results clearly demonstrated the evolution of laser spot motion, plasma expanding near the LEH and closure of the LEH, which supplied the foundation to optimize the LEH dimension. (authors)

[en] This paper reports the laser transfer in plasma produced by CH on Shengguang Ⅱ. The laser transmission rate was decided by the plasma density. When the laser incidence was 0.5 μm CH on Shengguang Ⅱ, the plasma density would be under critical value after 200 ps, the laser would pass the plasma. When the plasma density was 1% critical density after 700 ps, the laser could pass the plasma completely. (authors)

[en] A method for measuring laser ablation depth with time-integrated crystal spectrometer is introduced. Ablation depth, mass ablation rate and ablation pressure for aluminium and C₈H₈ material driven by laser are obtained from experimental data. Finally the experimental results are analyzed and discussed

[en] In the paper, we briefly introduce the basic principle of the filter fluoresce spectrometer (FFS), the detailed process unfolding hard X-ray energy spectrum emitted by plasma from the experimental data measured by FFS was presented. In experiments, the energy channel number of FFS was limited by spatial arrangements. The real fluorescence signal has been interfered by background of nonelastic scattering and fluorescence produced by high energy X-ray. Therefore, the process to unfold hard X-ray energy spectrum is quite complex. Here, we assume that the hot electrons obey to MAXWELL distribution law, and do not considering the fine process of the slowing down of hot electrons. We used iteration with method of minimum squares in the unfolding processes. The temperature of hot electrons, the spectrum and total energy of hard X-ray have been unfolded from the experimental data measured by the ten channel FFS

[en] The passive diagnostic for radiation driven shock velocity is of critical importance in the research of radiation driven fusion and extreme high-pressure equation of state. Such diagnostic has been set up on SG-Ⅱ and the laser prototype facility. The control technique of signal-to-noise of shock breakout images has been developed based on the theoretical analysis and experimental study which shows that the stray light such as stimulated scattering light is 4 order stronger than the shock light. The precise temporal-resolved technique has also been developed based on the successful application of the faster sweep rate of the streak camera with aids of high-quality light triggering instead of traditional electronic triggering. The developed passive diagnostic has been validated successfully by an experiment whose results show the shock image is clear and the deduced shock velocity is consistent with the calculated one. (authors)

[en] Soft-X-ray spectrometers are used in diagnosis of the equivalent radiation temperature of hohlraum in indirectly driven inertial confinement fusion experiments. Uncertainties of the soft-X-ray optical elements and electronic devices of the spectrometer, and the recovery methods are determined, which influence the measurement of the radiation temperature. The uncertainty analysis method based on Monte-Carlo sampling is implemented and uncertainty of the radiation temperature including all kinds of uncertainty factors is obtained. The alignment of signals from different detection channels of the multi-channel spectrometer is analyzed separately, which proves to be a large uncertainty source. (authors)