Simulations of laser imprint for Nova experiments and for ignition capsules Page: 6 of 31
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1013 - 1014 W/cm2 driven with 0.35 pm or 0.53 pm light. Experiments done at Nova or at
the Vulcan laser at Rutherford Laboratory using XUV laser probes are more complicated
to understand. Although the XUV probe gives high spatial resolution and superior sensi-
tivity, the opacity of the sample to the probe wavelength depends upon the sample density.
Furthermore, the targets for these experiments were Si or Al in order to get adequate signal
though the foils at the probe wavelength. These materials emit x-rays from the corona which
cause preheat of the foils. It is more difficult to model all of these effects accurately.
We have applied the same simulation methods to assess effects of imprint upon direct
drive capsule designs intended to achieve ignition at the National Ignition Facility (NIF).
We find that the modulation due to imprint should be comparable to an achievable surface
finish of -10 nm in spherical harmonic modes l > 10. We shall discuss Rayleigh-Taylor (RT)
growth of these ablation front modulations during the implosion. We find that although RT
linear growth factors reach several thousand, when saturation is considered the capsule shell
is predicted to remain intact and the capsule to ignite.
We shall discuss our methods in Section II. In Section III we will discuss simulations
of Nova experiment using CH2 foils, and Section IV we shall discuss Nova and Vulcan
experiments using XUV laser probes. In section V, analysis of the NIF capsule design will
be presented. Section VI gives conclusions.
II. NUMERICAL METHOD
Our modeling has been done using the computer code LASNEX.15 Simulations are two-
dimensional with reflecting boundary conditions in the transverse direction, and include
multigroup radiation diffusion, electron conduction by flux-limited diffusion with a flux lim-
iter of fe = 0.1, and ray trace laser deposition. The laser ray trace does not give interference,
so the speckle intensity modulation is introduced by adjusting the powers of the rays accord-
ing to their aiming point at the surface of the target. Rays were directed at the target at
a range of angles of incidence corresponding to the focal ratio of the illumination. The ray
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Weber, S.V.; Glendinning, S.G.; Kalantar, D.H.; Key, M.H.; Remington, B.A.; Rothenberg, J.E. et al. Simulations of laser imprint for Nova experiments and for ignition capsules, article, November 8, 1996; California. (https://digital.library.unt.edu/ark:/67531/metadc692918/m1/6/: accessed May 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.