OMEGA Experiments on the Shock-Ignition ICF Concept

Shock ignition\footnote{ R. Betti \textit{et al}., Phys. Rev. Lett. \textbf{98}, 155001 (2007).} is an ICF concept that assembles thermonuclear fuel to high areal densities and then ignites it by launching a strong shock wave into the compressed fuel. The low-adiabat fuel assembly implodes with a velocity that is less than that required for hot-spot ignition. An intensity spike at the end of the main drive pulse generates a strong shock that is timed to meet the return shock bouncing back from the capsule center in the hot spot. The resulting fuel assembly is non-isobaric and will ignite with less energy than a conventional isobaric implosion.$^{1}$ Experiments to study the shock-ignition concept were performed on the OMEGA Laser System using 40-\textit{$\mu $}m-thick, 0.9-mm-diam plastic shells filled with D$_{2}$ gas. The targets were driven by a relaxation adiabat-shaping laser pulse with a short picket pulse\footnote{ K. Anderson and R. Betti, Phys. Plasmas \textbf{11}, 5 (2004).} and a high-intensity spike. The implosion was optimized by measuring the fuel assembly performance as a function of the timing of the picket pulse and the spike. Neutron-averaged areal densities of $\sim $200 mg/cm$^{2}$ were measured. The shock-generated implosion showed fusion product yields enhanced by a factor of $\sim $4 compared to an implosion without the spike. The measured neutron yield for a 25-atm fill, an adiabat of 1.6, and 17 kJ of laser energy was $\sim $10{\%} of the 1-D simulation prediction. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreements DE-FC52-92SF19460 and DE-FC02-04ER54789. Contributors: R. Betti,$^{\ast }$ C. Stoeckl, K.S. Anderson,$^{\ast }$ J.A. Delettrez, V.Yu. Glebov, F.J. Marshall, D.N. Maywar, R.L. McCrory, D.D. Meyerhofer, P.B. Radha, T.C. Sangster, V.A. Smalyuk, A.A. Solodov,$^{\ast }$ B. Yaakobi, and C.D. Zhou, \textit{UR/LLE}; J.A. Frenje, C.K. Li, R.D. Petrasso, and F.H. S\'{e}guin, \textit{MIT-PSFC}; L.J. Perkins, \textit{LLNL}; D. Shvarts, \textit{NRCN (Israel)}. $^{\ast }$Also at the Fusion Science Center for Extreme States of Matter and Fast Ignition.