Shock-tuned cryogenic-deuterium-tritium implosion performance on Omega

Cryogenic-deuterium-tritium (DT) target compression experiments with low-adiabat (α), multiple-shock drive pulses have been performed on the Omega Laser Facility [T. R. Boehly, D. L. Brown, R. S. Craxton, Opt. Commun. 133, 495 (1997)] to demonstrate hydrodynamic-equivalent ignition performance. The multiple-shock drive pulse facilitates experimental shock tuning using an established cone-in-shell target platform [T. R. Boehly, R. Betti, T. R. Boehly, Phys. Plasmas 16, 056301 (2009)]. These shock-tuned drive pulses have been used to implode cryogenic-DT targets with peak implosion velocities of 3× 10⁷cm/s at peak drive intensities of 8× 1014 W/ cm². During a recent series of α∼2 implosions, one of the two necessary conditions for initiating a thermonuclear burn wave in a DT plasma was achieved: an areal density of approximately 300 mg/ cm² was inferred using the magnetic recoil spectrometer [J. A. Frenje, C. K. Li, F. H. Śguin, Phys. Plasmas 16, 042704 (2009)]. The other condition-a burn-averaged ion temperature 〈 T_i 〉 _n of 8-10 keV-cannot be achieved on Omega because of the limited laser energy; the kinetic energy of the imploding shell is insufficient to heat the plasma to these temperatures. A 〈 T _i 〉 _n of approximately 3.4 keV would be required to demonstrate ignition hydrodynamic equivalence [Betti, Phys. Plasmas17, 058102 (2010)]. The 〈 T_i 〉 _n reached during the recent series of α∼2 implosions was approximately 2 keV, limited primarily by laser-drive and target nonuniformities. Work is underway to improve drive and target symmetry for future experiments.