Simulations of laser imprint for Nova experiments and for ignition capsules
- Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
- Rutherford Appleton Laboratory, Chilton, Didcot (United Kingdom)
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)
In direct drive inertial confinement fusion (ICF), nonuniformities in laser illumination seed ripples at the ablation front in a process called {open_quotes}imprint.{close_quotes} These nonuniformities grow during the capsule implosion and, if initially large enough, can penetrate the capsule shell, impede ignition, or degrade burn. Imprint has been simulated for recent experiments performed on the Nova laser [Campbell {ital et al.}, Rev. Sci. Instrum. {bold 57}, 2101 (1986)] examining a variety of beam smoothing conditions. Most used laser intensities similar to the early part of an ignition capsule pulse shape, I{congruent}10{sup 13} W/cm{sup 2}. The simulations matched most of the measurements of imprint modulation. The effect of imprint upon National Ignition Facility (NIF) direct drive ignition capsules has also been simulated. Imprint is predicted to give modulation comparable to an intrinsic surface finish of {approximately}10 nm rms. Modulation growth was examined using the Haan [Phys. Rev. A {bold 39}, 5812 (1989)] model, with linear growth factors as a function of spherical harmonic mode number obtained from an analytic dispersion relation. Ablation front amplitudes are predicted to become substantially nonlinear, so that saturation corrections are large. Direct numerical simulations of two-dimensional multimode growth were also performed. The capsule shell is predicted to remain intact, which gives a basis for believing that ignition can be achieved. {copyright} {ital 1997 American Institute of Physics.}
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 560660
- Report Number(s):
- CONF-961102-; ISSN 1070-664X; TRN: 98:000743
- Journal Information:
- Physics of Plasmas, Vol. 4, Issue 5; Conference: Meeting of the Division of Plasma Physics of the American Physical Society, Denver, CO (United States), 11-15 Nov 1996; Other Information: PBD: May 1997
- Country of Publication:
- United States
- Language:
- English
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