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It is important to improve the hohlraum radiation temperature for the research of high energy density physics, especially for study of inertial confinement fusion. Increasing the wall reemission ratio is an effective way to improve the temperature. It is found in theory that low density foam could reduce hohlraum wall energy loss, and then increase hohlraum temperature. In previous studies, experiments have shown that laser-to-X-ray conversion is enhanced by Au foam. However, improving reemission ratio is more important to increase hohlraum radiation temperature, because most of energy is lost in the wall.In this paper, we report our experiments carried out on SGⅢ prototype to compare the X-ray flux reemitted by Au foam and that by Au. For the experimental design, Au solid and Au foam are irradiated symmetrically along the axis by hohlraum radiation source Tr(t), which is assessed by broadband X-ray spectrometer flat-response X-ray diodes. The measured peak temperature is about 190 eV. Reemission flux from sample is measured by transmission grating spectrometer (TGS). The space-resolved image for pure Au sample shows that the hohlraum radiation is asymmetrical along the axis in the experimental conditions, temperature of top is higher than that at the bottom, which is consistent with simulation results obtained by using IRAD3D code. In order to compare the reemission flux from Au solid sample and that from Au foam sample in same conditions, we need to correct the symmetry of hohlraum radiation. By multiplying the ratio of top flux to bottom flux in pure Au target by the bottom flux in Au-Au foam target, where Au foam is on, we make sure that they are ablated by the same radiation source. The calculated results show that X-ray flux is increased by 20% by Au foam of 0.4 g/cc density when the hohlraum temperature is 190 eV. The typical observed time-integrated X-ray reemission spectra for Au solid and Au foam by TGS are also shown. We see that N-band and O-band reemission are clearly enhanced by Au foam, and the O-band reemission is almost the same as M-band reemission. The increased flux concentrates below 1 keV of the soft X-ray emission.The self-similar solution results and MULTI 1D simulation results show that the wall loss energy fraction is saved by Au foam, whose relation to reemission flux can be described by a simple expression. The theoretical solution shows that the emission flux increases about 10%, and the MULTI simulation indicates that the emission flux increases about 6.8%. They are in qualitative agreement with the experiments results. These results show an alluring prospect for Au foam to be used as hohlraum wall.

In order to achieve the high density compression in laser indirect-drive inertial confinement fusion, the implosion symmetry and hohlraum radiation uniformity are strictly required. To study the variations of implosion asymmetry with hohlraum length and time, three kinds of hohlraum lengths are adopted in experiment. X-ray emission from capsule fuel is measured by an X-ray framing camera. Based on measured capsule compression process and ellipticity variation, it is preliminarily judged that the medium hohlraum of 1700 μm long is the closest to implosion symmetry demand of Shenguang Ⅲ prototype laser facility. Time-resolved implosion asymmetry is derived from a simplified analytic model, in which used is the time-resolved hohlraum radiation nonuniformity derived from a view-factor code. The derived results of the time-resolved implosion asymmetry are basically in agreement with experimental results. The physical mechanism for how hohlraum radiation nonuniformity evolution induces the variations of implosion asymmetry with hohlraum length and time is analyzed.

High flux, Multi-keV X-rays, can be efficiently produced from nano-second laser interaction with metal target. Multi-keV backlight X-ray source is very important in inertial confinement fusion and high-energy density physics research. The one-dimensional numerical simulation results propose a laser plasmas radiation model, and the model is compared well with Shenguang II experimental results. The pinhole-assisted point-projection (PAPP) backlight is improved by the model; the rear-on PAPP backlight for low-Z metal target and the side-on PAPP backlight for middle-Z metal target are developed. The experiment is performed on Shenguang II 9th laser facility. The static stream line obtained with novel PAPP backlight provides high-quality capsule image, and the spatial resolution is better than 10 μm. Results show that novel PAPP backlight has advantages of traditional PAPP in source brightness, spatial resolution and image contrast.

With the development of the research on inertial confinement fusion (ICF), there is needed a diagnostic technique for low Z materials.The phase contrast imaging, which relies on gradients in the refractive index and wave interference, is proposed to characterize the typical ICF (inertial confinement fusion) capsule shell. In our work it is indicated that the phase contrast imaging obtained with a micro-focus X-ray source provides complementary information about the capsule shell with high resolution 2 upm, and has advantages of absorb imaging. Such a capsule shell diagnostic technique is very useful for ICF diagnoses. Besides, we propose an approach to obtaining of the optimum contrast and spatial resolution in phase contrast imaging. It is a guidance in obtaining an excellent result in phase contrast imaging experiment, and can be widely used in biomedicine, materials science.

The variation of multi-layer shell capsule in implosion process is the most important part of inertial confinement fusion. Phase contrast imaging which relies on gradients of the refractive index and wave interference is proposed to characterize the typical implosion capsule. The experiments are performed on the Shenguang Ⅱ laser facility. The point-like X-ray source at 4.75 keV can be efficiently produced from laser interactions with Ti target and observed by pinhole- point backlight technique. The phase contrast images obtained with point-like X-ray source provide complementary information about the multi-layer shell capsule, and the spatial resolution is better than 10 μm. The X-ray phase contrast imaging shows more detailed features than absorb imaging, and good agreement with one-dimensional numerical simulations.