plausible solutions to many technical problems, but the panel assesses that the robustness of the physics design for the LIFE target concept is low.
• The proposed LIFE target presented to the panel has several modifications relative to the target currently used in the NIC (e.g., rugby hohlraums, shine shields, and high-density carbon ablators), and the effects of these modifications may not be trivial. For this reason, R&D and validation steps would still be needed.
• There is no evidence to indicate that the margin in the calculated target gain ensures either its ignition or sufficient gain for the LIFE target. If ignition is assumed, then the gain margin briefed to the panel, which ranged from 25 percent to almost 60 percent when based on a calculation that used hohlraum and fuel materials characteristic of the NIC rather than the LIFE target, is unlikely to compensate for the phenomena relegated to it—for example, the effects of mix—under any but the most extremely favorable eventuality. In addition, the tight coupling of LIFE to what can be tested on the NIF constrains the potential design space for laser-driven, indirect-drive IFE.
Targets for Direct-Drive Laser Inertial Fusion Energy
CONCLUSION 4-6: The prospects for ignition using laser direct drive have improved enough that it is now a plausible alternative to laser indirect drive for achieving ignition and for generating energy.
• The major concern with laser direct drive has been the difficulty of achieving the symmetry required to drive such targets. Advances in beam-smoothing and pulse-shaping appear to have lessened the risks of asymmetries. This assessment is supported by data from capsule implosions (performed at the University of Rochester’s OMEGA laser), but it is limited by the relatively low drive energy of the implosion experiments that have thus far been possible. Because of this, the panel’s assessment of laser-driven, direct-drive targets is not qualitatively equivalent to that of laser-driven, indirect-drive targets.
• Further evaluation of the potential of laser direct-drive targets for IFE will require experiments at drive energies much closer to the ignition scale.
• Capsule implosions on OMEGA have established an initial scaling point that indicates the potential of direct-drive laser targets for ignition and high yield.
• Polar direct-drive targets3 will require testing on the NIF.
3 In polar direct drive, the driver beams are clustered in one or two rings at opposing poles. To increase the uniformity of the drive, polar drive beams strike the capsule obliquely, and the driver energy is biased in favor of the more equatorial beams.