5
Remaining Hurdles
Several technical issues should be pursued in parallel with NIF construction. While none is sufficiently serious to constitute a ''showstopper," continued attention to all of them will help to ensure the NIF's success and its contributions to SBSS.
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Consistent physical understanding of NIF-relevant phenomena. Efforts should continue to better understand the requirements for convergence and compression with a modified NOVA configuration (HEP 5), laser-plasma interactions and the resulting "spot motion," the effects of hohlraum wall motion and the physics of plasma instabilities in gas-filled hohlraums, and the prediction, control, and diagnostics of the x-ray drive in hohlraums. Experiments to be conducted include the following:
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Complete the 10-beam smoothing and wall-motion experiments in gas-filled hohlraums on NOVA. Implementation of the full smoothing by spectral dispersion (SSD) and random phase plates (RPPs) on all 10 beams will demonstrate further understanding of the potential limiting effects of laser-plasma interactions. Demonstrated low levels of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), and the resulting acceptable radiation temperatures, are expected.
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Conduct experiments on retarding wall motion with improved azimuthal symmetry and a wider range of plasma conditions to further investigate the NIF hohlraum design.
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Vigorously pursue experiments to study the behavior of Rayleigh-Taylor and Richtmyer-Meskov hydrodynamic instabilities in converging geometries.
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Need for and challenges of three-dimensional simulations. Current three-dimensional computer codes are inadequate for integrated calculations of ignition; their improvement will contribute significantly to increasing the probability of ignition. These codes must be adapted to run on ASCI platforms. The development of new, less empirical three-dimensional models and algorithms is necessary, as is benchmarking of three-dimensional codes by ICF experiments and test data. This effort is further challenged by the different characteristics of the machines purchased under the ASCI program.
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Cryogenic capsule technology. Advances should be sought in assembly, fill, and surface smoothness. Continued development of handling and delivery systems is also important to ignition, as are methods of characterizing the fuel in optically opaque cells. Researchers should explore target-design alternatives, advance target design and fabrication technology, and pursue cryogenic target experiments on OMEGA.
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Optics damage thresholds and cost. While the current cost estimate contains funds to purchase slow-growth KDP crystals if necessary, the effect on schedules must be considered if the fast-growth crystals fail to meet damage threshold requirements.
