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A practical experimental method is proposed to investigate thermal transport by characterizing the motion of plasma flows through a x-ray spectroscopic technique using tracers. By simultaneously measuring multiple parameters, namely, the mass-ablation rate, the temporal evolution of plasma flow velocities and trajectories and the temperature, it is possible to observe a variety of physical processes, such as shock wave compression, heating by thermal waves, and plasma thermal expansion, and to determine their relative importance in different phases during the irradiation of CH and Au targets. From a comparison with hydrodynamic simulations, we find significant differences in the motion of the plasma flows between CH and Au, which can be attributed to different sensitivities to the thermal transport process. There are also differences in the ablation and electron temperature histories of the two materials. These results confirm that velocities and trajectories of plasma motion can provide useful evidence in the investigation of thermal conduction, and the approach presented here deserves more attention in the context of inertial confinement fusion and high-energy-density physics.

Great efforts have been made to create a bright K-shell source using the thin metal cylindrical cavities in the past few decades. Several metal materials such as titanium (Ti), iron, and so on have been tested for high x-ray conversion efficiency mainly at the OMEGA and NIF laser facilities. Recently, x-ray sources in Ti K-shell transition energy range were investigated at the Shenguang-III prototype laser facility with ∼5 kJ laser energy. The experiments were aimed to reproduce the previous ones at OMEGA, but with an extraordinarily small volume of cylindrical cavity and detailed characterizations of the x-ray source. The cavities were 800 μm inner diameter, 800 μm length, and 30 μm thick plastic tubes supporting 1 μm thick Ti. Seven laser beams were focused to 200 μm diameter. The combination of the small cavity volume and the focused laser spots is intended to improve the electron temperature with limited laser energy since the electron temperature is a key issue for high x-ray conversion efficiency. Thomson scattering was adopted to experimentally probe the electron temperatures at special time and space zones as well as the average temperature obtained from the Ti K-shell spectrum. The evolutions of the electron temperature and density are predicted by the radiation hydrodynamic simulation. A top view and two photon energy bands of x-ray source images provide a way to directly observe the plasma movement toward the cavity axis and distinguish the different emission mechanisms between the Ti K-shell and lower energy x rays. Six Higher-energy x-ray detectors located at different angles were used to record the Ti K-shell x-ray emission and demonstrate its isotropic feature. The characteristics of the x-ray radiate intensity including the time evolution, the angular distribution, and the total yields for both the photon energy regions above and below 4 keV are compared between the cavity and planar targets. Obviously, different behaviors were found between the two photon energy regions and the two types of targets. The x-ray conversion efficiency of the Ti cylinder was determined to be ∼ 4 % and ∼ 21 % in 4 π sr in the Ti K-shell (4–7 keV) and

The research on the hydrogen passivation process for silicon solar cells has been developed for a long time. Recently, researchers have investigated the use of lasers as light sources. It has been found that hydrogen passivation technology can improve the minority carrier lifetime and passivate some impurities and defects in silicon solar cells. In this paper, a hydrogenation platform for silicon solar cells based on high intensity infrared LEDs of 940 nm was built. After a number of comparative experiments, electrical characteristics, photo-luminescence images, and light beam induced current were applied before and after hydrogenation to distinguish the passivation effect. It was found that the effect of hydrogen passivation on monocrystalline boron-doped passivated emitter and rear contact (PERC) solar cells by using infrared LEDs as the light source was satisfactory under the condition of suitable light intensity and temperature. It has a remarkable effect on improving the electrical characteristics an...

It is reported that in National Ignition Facility's shock timing campaign, there is a 2 μm layer of residual air condensation on the cold laser entrance hole window, and residual gas level of ∼5×10−6 Torr ( ∼6.6×10−4 Pa) in the chamber [Robey et al., Phys. Plasmas 19, 042706 (2012)]. On Shenguang (SG) II and III laser facilities, a nominal residual gas level in the chamber is ∼10−2 Pa in experiment. In this work, the residual Carbon (C) level in the SG II chamber is investigated experimentally using a transmission grating spectrometer (TGS). The experimental result shows that there is a clear C K edge (280–300 eV), which implies that there is residual C condensation on the charge-coupled device (CCD) silicon oxide layer. The effect of the C condensation on the CCD response is studied with a condensed-C-foil model. With the modified CCD responses, the unfolded spectra by TGS are shown, and the significant C K edge decreases as the C foil thickness increases. Compared to the simulated C K edge depth, the me...

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...

We describe an experimental technique to measure the drive symmetry of M-band radiation on the capsule in hohlraum. M-band radiation from the corona of the laser-produced gold plasma, especially the laser spot regions in the cavity, was used to pump x-ray fluorescence of a thin layer of Si-tracer coated on a solid CH-ball. The fluorescence images were time resolvedly recorded by an x-ray framing camera and the drive asymmetry due to M-band radiation was deduced from these fluorescence images. Moreover, a Si-doped gold cavity was used with the initial purpose of maximizing the fluorescence signal through resonance transitions. Since the Si-plasma expands more rapidly than the gold-plasma, the evolution of drive asymmetry was accelerated in Si-doped hohlraum.

The enhancement of laser to x-ray conversion efficiencies using low density gold targets [W. L. Shang, J. M. Yang, and Y. S. Dong, Appl. Phys. Lett. 102, 094105 (2013)] is demonstrated. Laser to x-ray conversion efficiencies with 6.3% and 12% increases are achieved with target densities of 1 and 0.25 g/cm3, when compared with that of a solid gold target (19.3 g/cm3). Experimental data and numerical simulations are in good agreement. The enhancement is caused by larger x-ray emission zone lengths formed in low density targets, which is in agreement with the simulation results.

A design of secondary hohlraum radiation source with laser focal spots blocked is introduced. The hard x-ray radiation such as the gold M-band emission and hot electrons from the coronal plasma were designed to be shielded using a cylindrical shield. Three-dimensional view factor analysis was carried out to optimize the shield structure to achieve higher radiation temperature. An experiment was performed at Shenguang III prototype laser facility to verify the design. Velocity Interferometer System for Any Reflector was used to measure the shock wave speed in a three-stepped Al sample driven by this radiation source and the peak radiation temperature of the radiation source was estimated to be about 90 eV.

In the hohlraum used in laser indirect-drive inertial confinement fusion experiments, hydrodynamic processes of radiation-ablated high-Z plasma have a great effect on laser injection efficiency, radiation uniformity, and diagnosis of hohlraum radiation field from diagnostic windows (DW). To study plasma filling in the DWs, a laser-irradiated Ti disk was used to generate 2–5 keV narrow energy band X-ray as the intense backlighter source, and laser-produced X-ray in a hohlraum with low-Z foam tamper was used to heat a small hole surrounded by gold wall with 150 μm in diameter and 100 μm deep. The hydrodynamic movement of the gold plasma in the small hole was measured by an X-ray framing camera and the results are analyzed. Quantitative measurement of the plasma areal density distribution and evolution in the small hole can be used to assess the effect of plasma filling on the diagnosis from the DWs.

Accurate opacity and equation of state (EOS) data are important parameters for reliable modeling and understanding many phenomena of high energy density physics. However, they are difficult to obtain either theoretically or experimentally especially for high-Z plasmas. In this paper, we proposed a simple method to verify the opacity and EOS of high-Z plasmas in rarefactive states, which is build on the two key aspects of ablation processes, i.e., the propagation of heatwave into materials and the hydrodynamic expansion of the blow-off plasmas. Based on the integrated analysis of the Au foil burnthrough and foam-confined plasma expansion experiments performed on the Shenguang II and Shenguang III prototype laser facilities, we suggested two semi-empirical multipliers to adjust the opacity and EOS of Au plasma. These adjusted opacity and EOS may then provide a foundation for other radiation hydrodynamic simulations under similar drive conditions.

Laser-irradiated Au layer with CH foam coating is investigated numerically. It is found that when coated with under-critical density CH foam more thermal radiation is produced, while less radiation is produced when coated with over-critical density CH foam. The under-critical density CH foam coating, which is heated supersonically and volumetrically by lasers, hampers the expansion of high-Z plasma and helps increase the density and temperature of Auplasma in the radiation zone. It is a practical and simple way to increase the laser x-ray conversion efficiency of hohlraum by coated with low-Z foam of under-critical density. This idea is tested with an experiment in an analogous geometry. The line emission from laser-irradiated Ti layer coated with CH foam was measured, and the increment of x-ray when coated with under-critical density CH foam was found.

A 1D space resolving x-ray spectrum diagnostic system has been developed to study the radiation opacity of hot plasma on SG-II laser facility. The diagnostic system consists of a 2400 lines/mm flat-field holographic grating and a gated microchannel plate coupled with an optical CCD and covers the wavelength range of 5-50 Å. The holographic grating was compared with a ruled one by measuring the emission spectra from a laser-produced molybdenum plasma. The results indicate that the holographic grating possesses better sensitivity than the ruled grating having nearly similar spectral resolution. The spectrograph has been used in radiative opacity measurement of Fe plasma. Simultaneous measurements of the backlight source and the transmission spectrum in appointed time range in one shot have been accomplished successfully with the holographic grating spectrometer. The 2p-3d transition absorption of Fe plasma near 15.5 Å in has been observed clearly.

Experiments are presented, which demonstrate the properties of x-ray radiation and redistribution of radiant thermal energy in high Z cylindrical cavities filled with low Z CH foam. Time integrated spectra records were obtained by a calibrated space-resolved transmission grating spectrometer. The x-ray radiation became weaker in intensity and was changed to a softer near-Planckian radiation light after a 1500 μm long transport in the foam filling cavity. The experimental redistribution of the radiant thermal energy was plotted and compared to the numerical results of a simplified model. Good agreements have been achieved.

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...

X-ray streak cameras are extensively used to study transient x-ray processes in experiments carried out on various laser facilities at the Research Center of Laser Fusion. Precise calibration and clear description of the sweep speed of the x-ray streak camera are vital for obtaining precise temporal information to understand the fast physics phenomena. An x-ray streak camera named wide-slit x-ray streak camera has been calibrated using a small-scale laser facility with pulse duration of 8 ps. Sweep speeds on most part of the output screen (charge coupled device) are obtained. These calibration results can be used to correct the nonlinearity of sweep speed in measurement of temporal processes.