SG-III Prototype Facility Research Articles

Extended x-ray absorption fine structure measurement of ramp compressed Ti using laser-irradiated metallic foil as x-ray source on SGIII prototype laser facility

Laser-irradiated metallic foils were considered as x-ray sources for extended x-ray absorption fine structure (EXAFS) measurements and confirmed by experiments on the SGIII prototype facility. The Au foils were irradiated by laser beams with a total energy of 2.77 kJ and full width at half maximum (FWHM) of 1 ns to create an x-ray source. The x-ray emission was spectrally smooth in the energy range of Ti EXAFS, the FWHM of Au foil x-ray radiation pulse in the energy range of 0.1–4000 eV was 0.99 ns, and the FWHM of x-ray pulse in the energy range of 5000–6000 eV was deduced to be 0.55 ns according to simulation results. A shaped laser pulse was designed to achieve the Ti sample’s laser-direct-driven ramp compression process. By creating a quasi-stable state lasting longer than 1 ns as the probing window during the compression process, the demand for temporal resolution was reduced. EXAFS spectra of compressed Ti in α and ω-phase were obtained and compared, and structural phase transition was verified by EXAFS pattern changes. The velocity of the back interface of the Ti sample was measured by the velocity interferometer system for any reflector, and the maximum of the deduced pressure in the middle of the Ti sample was 8.2 GPa, which is consistent with the α-ω phase transition.

X-ray source improvements for EXAFS measurement on SGIII prototype facility

A proper x-ray source is crucial to extended x-ray absorption fine structure (EXAFS) measurement as parameter diagnosis for compressed materials on large laser facilities. In this article, modification of the CH capsule as an x-ray source has been done through simulations and experiments for the SGIII prototype laser facility. On the one hand, simulation results show that the radiation intensity of the CH capsule increases largely while wall thickness decreases. On the other hand, chlorine atoms whose atomic number is higher than that of carbon were brought into the capsule by doping on the inner side wall to enhance x-ray radiation intensity. CH capsules were designed, and experiments were carried out on the SGIII prototype laser facility. The x-ray source spectrum, size, radiation intensity, radiation pulse, and Ti K-edge EXAFS spectrum under ambient conditions were compared and discussed. Experimental results show that, with the doping of chlorine atoms and decreasing the wall thickness from 9 µm to 6 µm, the x-ray radiation intensity increases by about 63.5 times, energy efficiency is improved a lot, and other properties are also improved. The chlorine atom doped CH capsule with 6 µm wall thickness is proved to be the best x-ray source in the experiments in this article. Its size is 57 ± 0.5 µm, pulse width is 240 ps, and radiation intensity is about 9.1 times the undoped one with the same wall thickness. The methods can be extended to other laser facilities for the EXAFS measurement of other materials.

Research on a wide-angle diagnostic method for shock wave velocity at SG-III prototype facility

A wide-angle diagnostic method for shock wave velocity is proposed in this paper. An ellipsoidal equation deduced for wide-angle diagnosis by using geometrical optical laws is presented. The combination of an ellipsoidal mirror and a traditional velocity interferometer system for any reflector (VISAR) forms a wide-angle VISAR. Several fundamental problems such as assembly, imaging, and interference in the wide-angle VISAR are discussed. The method is proven to be feasible based on the results of an eight-beam laser direct drive experiment at SG-III prototype facility. The diagnostic method is expected to be usable in a wide variety of experiments, especially those related to implosion compression, including high-pressure equation of state experiments, materials characterization experiments, shock characterization for Rayleigh–Taylor experiments, and shock timing experiments for inertial confinement fusion research.

The shaped pulses control and operation on the SG-III prototype facility

The laser driven inertial confined fusion experiments require careful temporal shape control of the laser pulse. Two approaches are introduced to improve the accuracy and efficiency of the close loop feedback system for long term operation in TIL; the first one is a statistical model to analyze the variation of the parameters obtained from previous shots, the other is a matrix algorithm proposed to relate the electrical signal and the impulse amplitudes. With the model and algorithm applied in the pulse shaping in TIL, a variety of shaped pulses were produced with a 10% precision in half an hour for almost three years under different circumstance.

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-dependent behaviour of the radiation temperatures at different viewing angles.

Investigation into the design and diffraction efficiency of shifted dual transmission grating

In inertial confined fusion (ICF) experiments, the temporal evolution of X-ray spectrum can provide important diagnostic information such as electron temperature and density on laser-plasma interaction. Accurate diagnostic requires a wide range of X-ray spectrum from several hundred eV to kilo eV to be measured with high temporal resolution. For traditional single grating spectrometer coupled with streak cameras, the limited recording length of streak cameras severely restricts measured X-ray spectral range in one laser shot. Here we design a shifted dual transmission grating (SDTG) spectrometer for laser-produced plasma X-ray diagnostics in ICF experiments which can provide wide-range X-ray spectrum measurement from 100 eV to 5 keV with high temporal and spectral resolution. This SDTG spectrometer comprises two X-ray gratings: one with high line density and the other with low line density. The high line density grating is used to measure X-ray spectrum from 1000 eV to 5000 eV and the low line density grating measures X-ray spectrum from 100 eV to 1000 eV respectively. These two kinds of X-ray gratings are arranged in a plane with their centers shifted by a certain distance. A shifted double slit component is designed according to the spatial positions of the two gratings and set in front of the photocathode in the streak camera to ensure that two sets of X-ray spectra by two shifted gratings are projected on the photocathode without overlapping. This novel SDTG-based X-ray spectrometer can take the most of recording panel space, offering a path to realize a high resolution and broad spectral ranges in diagnosing soft X-rays. In this paper, the design method and the technical data of the SDTG-based X-ray spectrometer are given. The SDTG-based X-ray spectrometer is integrated, debugged and used to measure X-ray pulse at SG-III prototype facility located in Laser Fusion Research Center of Chinese Academy of Engineering Physics. The time integral results are captured by the SDTG spectrometer in the ICF fluid RT experiments and time-resolved spectra are recorded in indirect drive implosion experiment. Experimental results show the SDTG-based X-ray spectrometer can capture X-ray spectrum ranging from 0.1 keV to 5 keV, with a spectral resolution of 0.04 nm and a temporal resolution of better than 30 ps. By fully utilizing limited recording length, the SDTG-based X-ray spectrometer can realize a wide range temporal X-ray spectrum measurement with enough spectral resolution and temporal resolution. This SDTG spectrometer is a good temporal X-ray diagnostic tool for ICF experiments and other high energy density physics experiments.

Temporal-shaping experiment of three-step pulses for eight laser beams

Based on the 3ω (0.351-μm-wavelength) energy curve, in the SG-III prototype facility in China we have obtained three-step temporal shaping pulses required for a physics experiment after three or four shots. The emphases of shaping include many feedbacks and iterative modifications from the latter to the former, which are effective and practical.

The laser uniformity of polar drive design on the SG-Ⅲ prototype facility

In this paper, the train of thought and contents of studying the polar drive for SG-Ⅲ prototype facility are teased out, and the beam approximation principle regarding the illumination uniformity on the target is proposed. Based on such a principle, the increase-by-degrees design method is developed and numerically simulated as well. The required laser parameters of target symmetrical illumination are optimally designed under various conditions. The investigation results are experimentally demonstrated on SG-Ⅲ prototype facility, showing that they are in excellent agreement with the designed illumination uniformity on the target. The obtained conclusions can give powerful guidance for the theoretical and experimental study of polar drive in the future.

Integrated all fiber optical pulse generation system for laser fusion driver

We demonstrate an integrated all fiber optical pulse generation system for laser fusion driver. CW laser signal generated from a single longitudinal fiber oscillator was modulated by phase modulator and amplitude modulator to form an optical pulse with shaped waveform and bandwidth of 0.1 nm. The pulse was amplified and split by fiber multiplexer to four pulses. Time delay of each pulse was controlled by synchronization unit and power of each pulse was adjusted by programmable variable optical attenuator. The four pulses were amplified and then transmitted through a 150 m fiber to the pre-amplify system. The fiber system can generate almost arbitrarily shaped optical pulse with duration of 0.2—20 ns, bandwidth of 0.1 nm and power of several nJ. As the front-end of the SG-Ⅲ prototype facility, it has successfully lunched about 2.6 million shots of pulses. The fiber system is compact and highly stable and reliable.

Laser beam automatic alignment in multipass amplifier

A laser beam automatic alignment system is applied in a multipass amplifier of the SG-III prototype laser. Considering the requirements of the SG-III prototype facility, by combining the general techniques of the laser beam automatic alignment system, according to the image relayed of the pinholes in the spatial filter, and utilizing the optical position and the spatial distribution of the four pinholes of the main spatial filter in the multipass amplifier of the SG-III prototype, a reasonable and optimized scheme for automatic aligning multipass beam paths is presented. It is demonstrated on the multipass amplifier experimental system. (C) 2004 Society of Photo-Optical Instrumentation Engineers.