Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Plasma Physics
Volume 54, Number 15
Monday–Friday, November 2–6, 2009; Atlanta, Georgia
Session QI3: ICF and Ignition |
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Chair: Debra Callahan, Lawrence Livermore National Laboratory Room: Centennial II |
Wednesday, November 4, 2009 3:00PM - 3:30PM |
QI3.00001: National Ignition Campaign Hohlraum Energetics Invited Speaker: The first series of experiments on the National Ignition Facility (NIF), as part of the National Ignition Campaign, will determine the hohlraum path forward for indirect drive ignition. These first experiments will test ignition hohlraum ``energetics,'' a term described by four broad goals: \begin{itemize} \item Measurement of laser absorption by the hohlraum \item Measurement of the x-ray radiation flux ($T_{RAD}^4$) on the surrogate ignition capsule \item Quantitative understanding of the laser absorption and resultant x-ray flux \item Determining whether initial hohlraum performance is consistent with point design requirements for ignition using either a beryllium or plastic capsule ablator. \end{itemize} In this talk, we summarize the status of NIF hohlraum energetics experiments. We describe the hohlraum target and experimental design, including an overview of the theoretical and computational tools that have been used to design the hohlraums. We explain the validation of these tools on predecessor facilities and describe their performance on the first NIF experiments. We then discuss our current understanding of NIF hohlraum performance and the resulting near-term and long-term plans for NIF ignition hohlraum experiments. [Preview Abstract] |
Wednesday, November 4, 2009 3:30PM - 4:00PM |
QI3.00002: Experimental basis for laser-plasma interaction predictions on the National Ignition Facility ignition designs Invited Speaker: Recent laser plasma interaction experiments at OMEGA (LLE, Rochester) using gas-filled hohlraums shed light on the behavior of stimulated Raman scattering (SRS) in the hot, high-density plasma that laser beams will encounter near the capsule in NIF ignition hohlraums. We will present detailed results on the SRS thresholds for densities (10-15{\%} critical) at ignition relevant intensities (10$^{14}$ - 10$^{15}$ W-cm$^{-2})$. These results follow the expected Landau damping scaling with density and quantitatively agree with full three-dimensional laser propagation simulations (pF3d) that rely on detailed hydrodynamic simulations (HYDRA), providing an experimental basis for forthcoming experiments on NIF. In addition to controlling plasma parameters, the National Ignition Campaign relies on optical beam smoothing techniques to mitigate backscatter. We will show that polarization smoothing, which was previously demonstrated to increase the stimulated Brillouin scattering threshold, is also effective at controlling SRS. Finally, we have performed a scaling of the interaction beam numerical aperture and measured its impact on backscatter, which relates directly to the evolution of a laser beam aperture as it propagates inside an ignition hohlraum. These results will also be compared with 3D simulations. Prepared by LLNL under Contract DE-AC52-07NA27344. [Preview Abstract] |
Wednesday, November 4, 2009 4:00PM - 4:30PM |
QI3.00003: Multi-laser beams scattering processes in ignition targets Invited Speaker: Inertial Confinement Fusion experiments in the indirect drive approach rely on efficient deposition of the energy from many laser beams on the interior walls of a cylindrical cavity (the hohlraum). On the National Ignition Facility, 96 laser beams will overlap at each of the two laser entrance holes (LEH) of the hohlraum. As they propagate further into the hohlraum, they can potentially trigger laser plasma instabilities (LPI) such as stimulated Raman or Brillouin scattering (SRS/SBS) where plasma conditions are favorable for LPI. In this talk, we show that the SRS or SBS light exiting the hohlraum can get collectively amplified by multiple overlapping laser beams as it goes through the LEH. Typically, a SRS or SBS seed will be very weakly amplified by each of the overlapping laser beams; however, the total contribution from all 96 beams can lead to a strong amplification. This was analyzed with a steady-state kinetic model accounting for the collective coupling to all the laser beams. The effects of possible plasma turbulence due to superimposition of multiple plasma waves, as well as nonlinear saturation mechanisms, will also be discussed. The LPI amplification process in a NIF hohlraum is thus similar to a two-stage Raman or Brillouin amplifier, with a first pre-amplifier stage inside the hohlraum followed by a post-amplifier at the LEH. We will show that the process can be controlled by separating the range of frequencies at which the seeds are generated inside the hohlraum, from those that are efficiently amplified at the LEH - i.e. by detuning the pre- and post-amplification stages of the hohlraum. This is achieved by modifying the plasma conditions inside the hohlraum and at the LEH, by appropriately changing the targets designs and compositions. Several targets will be tested on the National Ignition Facility to validate the LPI amplification process as well as its mitigation in the summer of 2009. We will present the experimental data, compare it to our prediction and discuss the results. [Preview Abstract] |
Wednesday, November 4, 2009 4:30PM - 5:00PM |
QI3.00004: Hohlraum Performance at $>$ 100 TW on the National Ignition Facility Invited Speaker: |
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