Neutron Imaging System (NIS) has been used to image the burn volume and cold fuel volume of imploding fusion capsules. In this work, we present a design of neutron imaging aperture for inertial confinement fusion in Laser Fusion Research Center. Since the total neutron yield should be less than 1014, the penumbral aperture has been chosen. A geometric model has been developed to assess the performance of the neutron imaging system, including the spatial resolution, the field of view and the signal-to-noise ratio. This model reproduces the performances of neutron image systems on OMEGA. The spatial resolution of designed NIS is about 22 μm for a field of view of 250 μm. The signal-to-noise ratio can be better than 10, if the neutron yield is higher than 1013.
The physics of laser-plasma interaction is studied on the Shenguang III prototype laser facility under conditions relevant to inertial confinement fusion designs. A sub-millimeter-size underdense hot plasma is created by ionization of a low-density plastic foam by four high-energy (3.2 kJ) laser beams. An interaction beam is fired with a delay permitting evaluation of the excitation of parametric instabilities at different stages of plasma evolution. Multiple diagnostics are used for plasma characterization, scattered radiation, and accelerated electrons. The experimental results are analyzed with radiation hydrodynamic simulations that take account of foam ionization and homogenization. The measured level of stimulated Raman scattering is almost one order of magnitude larger than that measured in experiments with gasbags and hohlraums on the same installation, possibly because of a greater plasma density. Notable amplification is achieved in high-intensity speckles, indicating the importance of implementing laser temporal smoothing techniques with a large bandwidth for controlling laser propagation and absorption.
A high quality hot spot is crucial in the laser driven inertial confinement fusion. The hot spot self-emitted X-ray images in a high spatial resolution may be used to analyze the hot spot asymmetry and some fine structures induced by mix. The high spatial resolved X-ray imaging diagnostics can also serve in the hydrodynamic instability growth radiography and some other physical research in the inertial confinement fusion. The Kirkpatrick-Baez microscope can provide a higher resolution and throughput efficiency diagnostic. A new four-channels KB microscope was designed and built for the < 10 keV X-ray imaging. The Pt coated reflective mirror pairs were used to obtain a wide grazing angle bandwidth. The variation of the X-ray reflectivity was small in a large field of view. The microscope had a magnification of about 20. The spatial resolution in the central field of view was about 7 µm. The similarities between the different channel images were about 97%. The KB microscope is in operation in the directly or indirectly driven implosions by 10-100 kJ lasers on Shenguang laser facility in China. The time-integral hot spot asymmetry has been diagnosed, and the time-resolved imaging will be implemented in the following work.
K: Plasma diagnostics -interferometry, spectroscopy and imaging; Plasma diagnosticshigh speed photography 1Corresponding author.
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 measured spectrum presents that the condensed C foil thickness is 27 nm in the SG II chamber. The correction ratio for the TGS measured flux is 1.165, and there is an insignificant effect on the M band (>1800 eV) fraction measurement in SG II.
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