Effects of self-generated magnetic fields on the stagnation phase of cryogenic direct-drive implosions and scaling to direct-drive NIF*

In this talk, the magnitude and evolution of self-generated magnetic fields in an Omega implosion is studied using the deceleration-phase code DEC2D. DEC2D simulates the stagnation-phase of implosions using an Eulerian moving mesh solver and models the growth of the Rayleigh-Taylor instability at the shell hot-spot interface. This instability can cause temperature and density gradients to misalign, generating Biermann battery magnetic fields. In order to model these magnetic fields, MHD solvers have been added in DEC2D: this includes advection, resistive diffusion, Nernst, thermal suppression, and the Righi-Leduc effect. Maximum magnetic fields of ~200 MG are estimated, with corresponding Hall parameters of  ~1.5. In direct-drive implosions, we find that when Biermann fields are included, the Righi-Leduc effect dominates the MHD terms and causes the yield to decrease by  ~2.5%.  Additionally, preliminary results suggest scaling the implosion to a direct-drive 2 MJ implosion leads to far more significant decreases in yield, due to the alpha-heating magnifying small changes in temperature.