Plasma-Density Determination from X-Ray Radiography of Laser-Driven Spherical Implosions

Abstract

The fuel layer density of an imploding laser-driven spherical shell is inferred from framed x-ray radiographs. The density distribution is determined by using Abel inversion to compute the radial distribution of the opacity from the observed optical depth . With the additional assumption of the mass of the remaining fuel, the absolute density distribution is determined. This is demonstrated on the OMEGA laser system with two x-ray backlighters of different mean energies that lead to the same inferred density distribution independent of backlighter energy.

Time-resolved compression of a capsule with a cone to high density for fast-ignition laser fusion

“…The current experiment used thicker (42 mm compared with 24 mm) plastic shells with a cone and a lower gas pressure (B0.8 atm of air compared with 15 atm of D 2 gas) imploded by a shaped laser pulse to minimize X-ray self-emission. The previous experiments with the thinner shell and the higher gas pressure were limited by a strong X-ray self-emission from the hot core that prevented a measurement at peak compression 18 . Here a short-pulse laser-driven X-ray source with shorter emission time and a higher photon energy combined with a narrow-bandwidth (DE/E ¼ 1.2 Â 10 À 3 ) crystal imager provided the necessary tool to study the fuel assembly in unprecedented detail.…”

“…The image was corrected for spatially varying backlighter intensity, similar to that described in ref. 18, and for hard X-rays that were generated in the foil and scattered in the diagnostic. The expected 8-keV X-ray transmission through the Au cone wall is B7 Â 10 À 6 , and the area shadowed by the cone should be free of X-ray signal.…”

“…rR and r can be obtained experimentally by X-ray radiography 17 . This technique has been used on OMEGA to study the implosion dynamics of deuterium gas-filled plastic shells without a cone using an B1-ns-laser-driven, B5-keV broadband backlighter and an X-ray framing camera with an B40-ps integration time 18 . A mass-density distribution r(r) and a rR of up to B60 mg cm À 2 were measured at various times outside of peak compression 18 .…”

“…This technique has been used on OMEGA to study the implosion dynamics of deuterium gas-filled plastic shells without a cone using an B1-ns-laser-driven, B5-keV broadband backlighter and an X-ray framing camera with an B40-ps integration time 18 . A mass-density distribution r(r) and a rR of up to B60 mg cm À 2 were measured at various times outside of peak compression 18 . Previous experiments with cone-in-shell targets in indirect 19 and direct drive 20,21 investigated high-adiabat (a ¼ 6) implosions with simple square pulses, which lacked quantitative comparison to simulations.…”

Multiple-view spectrally resolved x-ray imaging observations of polar-direct-drive implosions on OMEGA

“…This direct-drive approach extends the application of NIF to investigate alternative inertial confinement fusion (ICF) schemes. Extensive numerical simulation work has been done to design targets and model PDD implosions for both OMEGA [3] and NIF [4][5][6][7][8][9][10][11][12][13][14]. However, the majority of the experimental work so far has been done at OMEGA, with few experiments at NIF [4][5][6][14][15][16][17].…”