Thermal decoupling of deuterons and tritons during the shock-convergence phase in Inertial Confinement Fusion implosions

A series of thin glass-shell shock-driven DT gas-filled capsule implosions were conducted at the OMEGA laser facility. These experiments generate plasmas with similar collisionality to the central hot-spot plasma during the shock-convergence phase of ignition-relevant ablatively-driven Inertial Confinement Fusion (ICF) implosions. Hydrodynamic simulations with DUED [1] match the measured DTn and DDn yields as well as burn duration for implosions with a high initial gas-fill density (4 mg/cm³), but greatly over predict the yield for implosions with lower initial densities down to 0.2 mg/cm³. Kinetic simulations with the implicit Fokker-Planck (iFP) code reproduce the measured nuclear yields and burn duration at both low and high initial density. The temperatures inferred from the DTn and DDn spectra are most consistent with a two-ion-temperature plasma, where the initial temperature ratio T_t/T_d is 1.5. This is the first experimental confirmation of the long-standing conjecture that plasma shocks couple energy proportional to the species mass in multi-ion plasmas. The temperature ratio dependence on equilibration time matches expected thermal equilibration described by hydrodynamic theory. This measured trend is reproduced in the kinetic iFP simulations and indicates that deuterons and tritons have different energy distributions during the shock-convergence phase in ignition-relevant ICF implosions. This work was supported in part by the US DOE, LLE, LLNL, and DOE NNSA Center of Excellence.

[1] S. Atzeni, Computer Physics Communications 43, 107 (1986).