New results in direct drive inertial confinement fusion
Abstract
Laboratory-based thermonuclear ignition may be realized within the decade by imploding spherical cryogenic capsules of frozen deuterium and tritium using the 192-beam, 1.8 MJ laser at the National Ignition Facility (NIF) currently under construction at Lawrence Livermore National Laboratory. Directly illuminating such a capsule with the laser beams provides the optimal coupling of laser energy into hydrodynamic motion and is referred to as direct drive inertial confinement fusion. Validating the concept of direct drive ignition at the NIF is the primary mission of the 60-beam, 30-kJ OMEGA laser at the University of Rochester Laboratory for Laser Energetics. The goal of experiments using both cryogenic fuel layers and warm, gas-filled surrogate plastic capsules is to demonstrate a uniform, high neutron-averaged fuel areal density using laser pulse shapes and capsules appropriately scaled from the ignition designs for the NIF. These experiments are designed to measure the sensitivity of the direct drive implosion performance to parameters such as the surface roughness of the frozen fuel layer, the adiabat of the fuel during the implosion, the temperature of the hot spot formed at the center of the capsule, and the laser uniformity and power balance. New results are reported from implosions of thin (<3 μm) polymer shells containing 80-100 μm D2 ice layers with a fully characterized surface roughness of 3 to 8 μm rms. These capsules (including gas-filled plastic surrogates) have been imploded with laser pulses that put the imploding fuel shell on a variety of adiabats including pulses designed to tailor the fuel adiabat to minimize the imprint of laser perturbations and the resulting growth of these perturbations due to the Rayleigh-Taylor instability. A comparison of the experimental performance (e.g., neutron yield, fuel temperature and areal density) of these capsules and pulse shapes with 2D hydrodynamic simulations will be shown. Such comparisons provide the ignition performance scaling for direct drive on the NIF. Comparisons with the recent data suggests that new target designs coupled with laser pulses that shape the adiabat of the fuel during the implosion may significantly improve the ignition margin for direct drive on the NIF. This work was supported by the U. S. DOE under Cooperative Agreement No. DE-FC03-92SF19460.
- Publication:
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APS April Meeting Abstracts
- Pub Date:
- April 2003
- Bibcode:
- 2003APS..APR.H6001S