Simulations of laser imprint for Nova experiments and for ignition capsules. Revision 1
- Lawrence Livermore National Lab., CA (United States)
- Rutherford Appleton Lab., Chilton (United Kingdom)
- Rochester Univ., NY (United States). Lab. for Laser Energetics
In direct drive ICF, nonuniformities in laser illumination seed ripples at the ablation front in a process called ``imprint``. 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 at LLNL examining a variety of beam smoothing conditions. Most used laser intensities similar to the early part of an ignition capsule pulse shape, 1 {approx_equal} 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. 27 refs., 10 figs.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 463531
- Report Number(s):
- UCRL-JC-124547-Rev.1; CONF-961102-8; ON: DE97051636; TRN: 97:010085
- Resource Relation:
- Conference: Meeting of the Division of Plasma Physics of the American Physical Society, Denver, CO (United States), 11-15 Nov 1996; Other Information: PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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