J.-C. Gauthier, et al.
J. Phys. IV France 133 (2006) 153-157
Polar-direct-drive experiments on OMEGAF.J. Marshall, R.S. Craxton, M.J. Bonino, R. Epstein, V.Yu. Glebov, D. Jacobs-Perkins, J.P. Knauer, J.A.Marozas, P.W. McKenty, S.G. Noyes, P.B. Radha, W. Seka, S. Skupsky and V.A. Smalyuk
Laboratory for Laser Energetics, University of Rochester, 250 E. River Rd., Rochester, NY 14623, USA
Polar direct drive (PDD), a promising ignition path for the NIF while the beams are in the indirect-drive configuration [S. Skupsky et al., Phys. Plasmas 11, 2763 (2004)], is currently being investigated on the OMEGA laser system by using 40 beams in six rings repointed to more uniformly illuminate the target [R. S. Craxton et al., Phys. Plasmas 12, 056304 (2005).]. The OMEGA experiments are being performed with standard, "warm" targets (865-m-diam, 20-m-thick, CH shells filled with 15-atm D2) with and without the use of an equatorial "Saturn-like" toroidally shaped CH ring [R. S. Craxton and D. W. Jacobs-Perkins, Phys. Rev. Lett. 94, 095002 (2005)] (nominal dimensions: 2.2-mm diam measured to ring center, 0.3-mm thick). For the Saturn case, the plasma formed around the ring refracts light toward the target equator as the ring plasma expands. The nominal laser drive is a 1-ns flat pulse, 400 J per beam, employing 1-THz, 2-D SSD with polarization smoothing. Target implosion symmetry is diagnosed with framed x-ray backlighting using additional OMEGA beams and by time-integrated x-ray imaging of the stagnating core. The best results have been obtained with Saturn targets by varying the beam pointing and ring diameter, achieving 75% of the fusion yield from symmetrically illuminated targets with the same total energy (60 beams, 15.3 kJ).
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