arXiv:1508.00803v1 [physics.plasm-ph] 4 Aug 2015 Under consideration for publication in J. Plasma Phys. 1 Hot Electron Propagation and Imposed Magnetic Field in Inertial Fusion Hohlraums DAVID J. STROZZI 1 †, L. J. PERKINS 1 , M. M. MARINAK 1 , D. J. LARSON 1 , J. M. KONING 1 , and B. G. LOGAN 1 1 Lawrence Livermore National Laboratory, Livermore, CA 94550, USA (Received ?; revised ?; accepted ?. - To be entered by editorial office) Simulations with the radiation-hydrodynamics code HYDRA of a low-adiabat ignition design for the National Ignition Facility (NIF), with and without an imposed axial mag- netic field, are presented. We also study superthermal, or “hot,” electron dynamics with the hybrid-PIC code ZUMA using plasma conditions from HYDRA. During the early- time laser picket, when hot electrons from the window are a concern (Regan et al. 2010), we find ∼ 2 × 10 −3 of the hot electron energy in a source consistent with two-plasmon decay (80 keV temperature) in the laser entrance hole deposits in the deuterium-tritium (DT) fuel, while most of the energy deposits in the high-Z wall. A 70 Tesla field, which may improve capsule performance, magnetizes hot electrons in the hohlraum fill gas, guides them to the capsule, and increases the DT deposition 12x. Early in peak laser power, electrons with >125 keV reach the DT fuel, and those with ≈185 keV deposit the largest fraction of their energy (13%) in DT. HYDRA magnetohydrodynamics (MHD) simulations with an initial 70 T field show it is frozen in to the plasma flow. Field lines ini- tially connected to capsule material that has ablated remain in the hohlraum fill instead of connecting to the capsule, and vice versa. Hot electrons consistent with stimulated Raman scattering from the inner laser beams (30 keV temperature) are mostly confined by the field to the hohlraum fill. The fraction of their energy deposited in DT decreases from 1.2 × 10 −4 with no MHD to 3.4 × 10 −6 with MHD – a 35x reduction. The field signif- icantly reduces cross-field electron thermal conduction, and results in a hotter hohlraum fill and improved inner-beam propagation. 1. Introduction A generic aspect of intense laser-plasma interactions (LPI) is the production of en- ergetic electrons. This occurs, for instance, in any parametric process that produces a Langmuir wave. Of particular interest in inertial confinement fusion (ICF) are stimu- lated Raman scattering (SRS) and two-plasmon decay (TPD). These are the decay of a light wave to a Langmuir wave and, respectively, a scattered light wave (SRS) or another Langmuir wave (TPD). In many laser-produced plasmas, the daughter Langmuir waves are damped primarily by collisionless Landau damping, instead of Coulomb collisions. Landau damping entails the resonant interaction of the wave with electrons at its phase velocity. This is typically greater than the electron thermal speed, and therefore pro- duces a population of superthermal or “hot” electrons. Experiments show the resulting hot-electron spectrum from a single parametric process is roughly exponential with “tem- perature” T h , dN/dE ∼ e −E/T h (E is the hot electron kinetic energy), and a pre-factor like E 1/2 for a non-relativistic Maxwellian. A host of relativistic processes produce > † Email address for correspondence: strozzi2@llnl.gov