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Radiative shocks produced from spherical cryogenic implosions at the National Ignition Facilitya)
a)Paper KI3 1, Bull. Am. Phys. Soc. , 198 (2012).
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Image of FIG. 1.
FIG. 1.

Shot N120412 experimental setup, capsule composition, core x-ray, and neutron images. (a) Experimental setup, a 10 mm long, 5.75 mm diameter hohlraum, is irradiated using 192 laser beams with a combined energy of 1.66 MJ. The resulting hohlraum x-ray flux implodes a cryogenic capsule target, located in the center of the hohlraum. The x-ray self emission from the imploding capsule is imaged along the polar and equatorial axis using two harden hGXI diagnostics. Primary neutrons (14 MeV) created in the hot central core are down-scattered in the surrounding dense DT shell. The NI diagnostic images both the primary and down-scattered (6–10 MeV) neutrons along the equatorial axis. (b) A pie diagram representing the composition and initial dimensions, given in microns, of the spherical fusion capsule target. (c) An image of the x-ray self emission at peak compression as seen from the polar hGXI diagnostic. The red contour indicates an average radius of 21.32 m at a value of 17% of peak emission. (d) The image of the down-scattered neutrons. The average radius, taken at the 17% contour of peak emission, was found to be 41 μm, and is indicative of the radius of the dense shell of DT ice that surrounds the core of the implosion. (e) An image of the x-ray emission at peak compression as seen from the equatorial hGXI diagnostic. The red contour indicates an average radius of 21.67 m at a value of 17% of peak emission.

Image of FIG. 2.
FIG. 2.

Image from the polar hGXI diagnostic showing the spatial and temporal evolution of the x-ray emission along three strips for shot N120412. Time t = 0 denotes peak x-ray emission. Approximately 200 ps after peak x-ray emission, a limb-brightened shell of x-ray emission, created by a spherically expanding shock wave, suddenly appears at a radius of ∼100 m. This emission is observed to expand outwards until ∼500 ps after peak x-ray emission, at which time the signal drops below the detectable level. The color scale has been changed between strip 1 and strips 2 and 3 to enhance the visibility of the shocked material.

Image of FIG. 3.
FIG. 3.

The radius of x-ray emission produced by the outward going spherical shock wave vs. time. Data produced from a DT capsule implosion conducted with 1.66 MJ (squares) and 1.42 MJ (triangles) of laser energy is shown. The two dashed lines represent the results from a linear fit to the expansion data. The solid line represents the predicted radius of x-ray emission vs. time from a 1-D HYDRA simulation that used 1.6 MJ of laser energy to irradiate the hohlraum.

Image of FIG. 4.
FIG. 4.

(a) Details of the convergent ablation experimental setup and results from shot N120409. Here, a probe laser irradiates a zinc foil, creating a burst of x-rays that radiographs the capsule implosion over a duration of ∼2 ns. A slit images the capsule radiograph in one direction onto the DISC streak camera, which temporally resolves the implosion. The dimensions in microns and composition of the capsule target are also shown. Here, a symmetry capsule target is used, which replaces the DT fuel layer and gas fill by an equivalent mass of CH and a gas fill, respectively. (b) The measured 1-D radiograph vs. time of a capsule implosion. The dense shell absorbs the x-ray probe creating two dark limbs, which converge inwards with time as the shell is compressed by the hohlraum x-ray flux. The dark absorption band located approximately at the center of the capsule is created by a wire fiducial and partially obscures the bright self emission from the core. Time t = 0 denotes the time of maximum self emission from the capsule core. Emission created by the outward going radiative shock is seen to appear at . (c) Radial location of the peak of emission from the outward going shock vs. time. Data shown in blue are in good agreement with the simulated emission location calculated with HYDRA shown in red.

Image of FIG. 5.
FIG. 5.

Results from a 1-D radiation hydrodynamic simulation showing the evolution of the electron temperature (red), material density (blue), and material velocity (dashed black) profiles at , 100, and 200 ps from stagnation, in (a), (b), and (c), respectively. A strong shock is located at the interface between the dense shell of DT fuel and unablated CH plasma. After stagnation, the shock propagates outwards into the lower density surrounding CH plasma. (d) The simulated radiance of the material, including the detector filter transmission, at , 100, and 200 ps from stagnation. Simulations are in agreement with experimental observations that show the sudden appearance of a ring of x-ray emission at a radius of ∼100 m hundreds of picoseconds after peak x-ray emission.

Image of FIG. 6.
FIG. 6.

(a) Luminosity of the limb-brightened ring of x-ray emission vs. time, at x-ray energies between 5.9 and 12.4 keV. The solid squares and triangles are the observed luminosity produced from an implosion conducted with 1.66 and 1.42 MJ of laser energy, respectively. The solid lines are the predicted luminosity profiles from 1-D hydrodynamic simulations. The upper curve is from a simulation that used 1.6 MJ of laser energy and the lower curve is from a simulation that used 1.4 MJ of laser energy, to irradiate the hohlraum, respectively. (b) Results from the 1.6 MJ simulation showing the temporal evolution of the shock front (black), the peak post-shock electron temperature (red), and a simple analytic prediction given by Eq. (4) of the immediate post-shock temperature (dashed). (c) The temporal evolution of the in-flowing material velocity, U1 (solid), and upstream temperature, T1 (dashed), taken from the simulation conducted with 1.6 MJ of laser energy.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Radiative shocks produced from spherical cryogenic implosions at the National Ignition Facilitya)