An empirical target discharging model for direct-drive implosions on OMEGA

Capsule charging of inertial confinement fusion (ICF) targets, observed previously on OMEGA, is detrimental to achieving the high areal densities ($\rho $R) required for ignition and gain. This is because the target potential traps energetic electrons that can preheat the fuel, raise the adiabat and degrade compression. The decay-time of this potential is therefore an important parameter for preheat calculations. A non-linear model of the electrical discharging of ICF capsules has been developed. The empirical model, which captures the essential dynamics of the target voltage decay, incorporates previous charged-particle spectroscopic and radiographic measurements of the fields. It is shown that return currents through the target support fiber have a profound effect on the voltage-decay time. Implications of these findings for inertial fusion energy (IFE) are considered. This work was supported in part by DOE, LLE and LLNL.