Impact of beam smoothing method on direct drive target performance for the NIF
The impact of smoothing method on the performance of a direct drive target is modeled and examined in terms of its 1-mode spectrum. In particular, two classes of smoothing methods are compared, smoothing by spectral dispersion (SSD) and the induced spatial incoherence (ISI) method. It is found that SSD using sinusoidal phase modulation (FM) results in poor smoothing at low 1-modes and therefore inferior target performance at both peak velocity and ignition. This disparity is most notable if the effective imprinting integration time of the target is small. However, using SSD with more generalized phase modulation can result in smoothing at low l-modes which is identical to that obtained with ISI. For either smoothing method, the calculations indicate that at peak velocity the surface perturbations are about 100 times larger than that which leads to nonlinear hydrodynamics. Modeling of the hydrodynamic nonlinearity shows that saturation can reduce the amplified nonuniformities to the level required to achieve ignition for either smoothing method. The low l- mode behavior at ignition is found to be strongly dependent on the induced divergence of the smoothing method. For the NIF parameters the target performance asymptotes for smoothing divergence larger than {approximately}100 {mu}rad.
- 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:
- 462882
- Report Number(s):
- UCRL-JC-124509-Rev.1; CONF-9610225-16-Rev.; ON: DE97051811; TRN: 97:010139
- Resource Relation:
- Conference: 2. annual solid state lasers for applications to inertial confinement fusion (ICF), Paris (France), 22-25 Oct 1996; Other Information: PBD: Jan 1997
- Country of Publication:
- United States
- Language:
- English
Similar Records
LLE Review Quarterly Report July-September 2000
The effects of laser beam non-uniformities on x-ray conversion efficiency