title: Ion separation effects in mixed-species ablators for inertial-confinement-fusion implosions.
abstract: Recent efforts to demonstrate significant self-heating of the fuel and eventual ignition at the National Ignition Facility make use of plastic (CH) ablators [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014)]. Mainline simulation techniques for modeling CH capsule implosions treat the ablator as an average-atom fluid and neglect potential species separation phenomena. The mass-ablation process for a mixture is shown to lead to the potential for species separation, parasitic energy loss according to thermodynamic arguments, and reduced rocket efficiency. A generalized plasma barometric formula for a multispecies concentration gradient that includes collisionality and steady flows in spherical geometry is presented. A model based on plasma expansion into a vacuum is used to interpret reported experimental evidence for ablator species separation in an inertial-confinement-fusion target [J. S. Ross et al., Rev. Sci. Instrum. 83, 10E323 (2012)]. The possibility of "runaway" hydrogen ions in the thermoelectric field of the ablation front is conjectured.
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Amendt
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
authors.forename: Claudio
authors.initials: C
authors.lastname: Bellei
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
authors.forename: J Steven
authors.initials: JS
authors.lastname: Ross
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
authors.forename: Jay
authors.initials: J
authors.lastname: Salmonson