Sanwei Li

X-ray conversion efficiency and radiation non-uniformity in the hohlraum experiments at Shenguang-III prototype laser facility

The hohlraum radiation properties are studied experimentally by the Shenguang-III prototype laser facility and numerically by the two-dimensional code LARED with the multi-group radiation transfer model. The measured radiation temperature is consistent with the prediction of the simulations in a wide laser energy range, suggesting that the x-ray conversion efficiency is around 75% at the peak radiation temperature. The delicate hohlraum experiments further show that the radiation intensity inside the hohlraum is significantly non-uniform. The measured radiation flux of the hot spot region is over twice higher than that of the re-emitted wall region. Good agreements between the experiments and simulations further demonstrate the validity of the LARED code to study the hohlraum radiation properties.

Radiation flux study of spherical hohlraums at the SGIII prototype facility

An octahedral spherical hohlraum is a promising candidate in target design for inertial confinement fusion study, because of its potential superiority in uniform radiation and efficient coupling [Lan et al., Phys. Plasmas 21, 010704 (2014)]. Before the experimental investigation for octahedral spherical hohlraum, an energetics experiment is accomplished on the Shenguang-III prototype laser facility by using spherical hohlraums with two cylindrical laser entrance holes. Time evolution of the radiation temperature is obtained with flat response X-ray diode detectors at four different viewing angles with demonstrated repeatability of the measurements. The experimental observations are successfully explained by using a phenomenological model which considers not only the radiation flux contributed from the laser ablated and radiation ablated plasma from hohlraum wall, but also that contributed from the filling plasma inside the hohlraum. This method proves to be a simple but effective way to interpret the time...

Direct measurement of x-ray flux for a pre-specified highly-resolved region in hohlraum

A space-resolving flux detector (SRFD) is developed to measure the X-ray flux emitted from a specified region in hohlraum with a high resolution up to 0.11mm for the first time. This novel detector has been used successfully to measure the distinct X-ray fluxes emitted from hot laser spot and cooler re-emitting region simultaneously, in the hohlraum experiments on SGIII prototype laser facility. According to our experiments, the ratio of laser spot flux to re-emitted flux shows a strong time-dependent behavior, and the area-weighted flux post-processed from the measured laser spot flux and re-emitting wall flux agrees with that measured from Laser Entrance Hole by using flat-response X-ray detector (F-XRD). The experimental observations is reestablished by our two-dimensional hydrodynamic simulations and is well understood with the power balance relationship.

Uranium hohlraum with an ultrathin uranium–nitride coating layer for low hard x-ray emission and high radiation temperature

An ultrathin layer of uranium nitrides (UN) has been coated on the inner surface of depleted uranium hohlraum (DUH), which has been proven by our experiment to prevent the oxidization of uranium (U) effectively. Comparative experiments between the novel depleted uranium hohlraum and pure golden (Au) hohlraum are implemented on an SGIII-prototype laser facility. Under a laser intensity of 6 × 1014 W cm−2, we observe that the hard x-ray (hν keV) fraction of the uranium hohlraum decreases by 61% and the peak intensity of the total x-ray flux (0.1 keV~5.0 keV) increases by 5%. Radiation hydrodynamic code LARED is used to interpret the above observations. Our result for the first time indicates the advantages of the UN-coated DUH in generating a uniform x-ray source with a quasi-Planckian spectrum, which should have important applications in high energy density physics.

Characterizing the hohlraum radiation via one-end driven experiments

A new experiment is designed and performed on the Shenguang III laser facility with the first eight available beams to characterizing the hohlraum radiation, in which the hohlraum with laser entrance holes on both ends is driven through one-end only. The experiment enables us to identify the x-ray radiations originated from the hohlraum reemission wall and high-Z bubble plasmas utilizing their position and spectral characters, which provides a better test on the associated hohlraum models. The total and M-band x-ray radiation fluxes are measured with the flat response x-ray detectors and the filtered M-band x-ray detectors, respectively. Numerical simulations are conducted with the two-dimensional radiation hydrodynamic code LARED-INTEGRATION using the multi-group radiation transfer and/or diffusion models. It is found that the experimentally measured temporal profiles and angular distributions of hohlraum radiation are in good agreement with the predictions of simulation using radiation transfer models, but differ significantly from the results obtained with the multi-group radiation diffusion calculations. We thus note that to accurately represent the hohlraum radiation, a true radiation transfer model is essential.

Investigation of the cylindrical vacuum hohlraum energy in the first implosion experiment at the SGIII laser facility

The cylindrical vacuum hohlraum energy at the SGIII laser facility [X. T. He and W. Y. Zhang, Eur. Phys. J. D 44, 227 (2007) and W. Zheng et al., High Power Laser Sci. Eng. 4, e21 (2016)] is investigated for the first time. The hohlraum size and the laser energy are intermediate between the Nova and NIF typical hohlraum experiments. It is found that the SGIII hohlraum exhibits an x-ray conversion efficiency of about 85%, which is more close to that of the NIF hohlraum. The LARED simulations of the SGIII hohlraum underestimate about 15% of the radiation flux measured from the laser entrance hole, while the capsule radiation drive inferred from the x-ray bangtime is roughly consistent with the experiments. The underestimation of the SGIII hohlraum radiation flux is mainly caused by the more enclosed laser entrance hole in the LARED simulation. The comparison between the SGIII and NIF hohlraum simulations by LARED indicates that the LARED generally underestimates the measured radiation flux by 15% for the hi...

Application of the space-resolving flux detector for radiation measurements from an octahedral-aperture spherical hohlraum

Space-resolving flux detection is an important technique for the diagnostic of the radiation field within the hohlraum in inertial confinement fusion, especially for the radiation field diagnostic in the novel spherical hohlraum with octahedral six laser entrance holes (LEHs), where localized measurements are necessary for the discrimination of the radiation flux from different LEHs. A novel space-resolving flux detector (SRFD) is developed at the SG-III laser facility for the radiation flux measurement in the first campaign of the octahedral spherical hohlraum energetics experiment. The principle and configuration of the SRFD system is introduced. The radiation flux from the wall of a gas-filled octahedral spherical hohlraum is measured for the first time by placing the SRFD system at the equatorial position of the SG-III laser facility, aiming at the hohlraum wall through one of the six LEHs. The absolute radiation flux from the re-emission area on the hohlraum wall is measured, and good consistency is found between the experimental data and the calculated data from a three-dimensional view factor analysis.