Improved target stability using picket pulses to increase and shape the ablator adiabat
- Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14623 (United States)
Hydrodynamic simulations have shown that a picket pulse preceding the main target drive pulse in a direct-drive inertial confinement fusion implosion can reduce both the ablation-interface Rayleigh-Taylor (RT) seed and growth rate by increasing the adiabat (ratio of the plasma pressure to the Fermi-degenerate pressure) while maintaining the low adiabat in the inner-fuel layer for optimal target compression and a minimal drive energy for ignition. Experiments with planar and spherical targets have been carried out on the OMEGA [T. R. Boehly, D. L. Brown, R. S. Craxton, R. L. Keck, J. P. Knauer, J. H. Kelly, T. J. Kessler, S. A. Kumpan, S. J. Loucks, S. A. Letzring, F. J. Marshall, R. L. McCrory, S. F. B. Morse, W. Seka, J. M. Soures, and C. P. Verdon, Opt. Commun. 133, 495 (1997)] laser system, showing that the RT growth of nonuniformities was reduced by picket-pulse laser illumination. Adiabat shaping in spherical targets has been investigated with two types of picket pulses - a 'decaying shock wave' and a 'relaxation' picket. Planar growth measurements using a wide, intense picket to raise the adiabat of a CH foil showed that the growth of short-wavelength perturbations was reduced, and even stabilized, by adjusting the intensity of the picket. Planar imprint experiments showed the expected reduction of imprinting when a picket pulse is used. The data show that the imprint level was reduced when a picket was added and for short wavelengths was as effective as one-dimensional (1D), 1.5 A smoothing by spectral dispersion. A series of implosion experiments with a 130 ps wide picket pulse showed a clear improvement in the performance of direct-drive implosions when the picket pulse was added to the drive pulse. Results from relaxation-picket implosions show larger yields from fusion reactions when the picket drive was used. These adiabat-shaping concepts make the likelihood of achieving ignition with direct-drive implosions on the National Ignition Facility [W. S. Hogan et al., Nucl. Fusion 41, 567 (2001)] significantly more probable.
- OSTI ID:
- 20736598
- Journal Information:
- Physics of Plasmas, Vol. 12, Issue 5; Other Information: DOI: 10.1063/1.1882332; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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