1 Signatures of Asymmetry in Neutron Spectra and Images Predicted by 3D Radiation Hydrodynamics Simulations of Indirect Drive Implosions. J.P. Chittenden a) , B.D. Appelbe, F. Manke b) , K. McGlinchey, N.P.L. Niasse. Centre for Inertial Fusion Studies, The Blackett Laboratory, Imperial College, London SW7 2AZ. a) Electronic mail: j.chittenden@imperial.ac.uk b) Presently at: Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland ABSTRACT We present the results of 3D simulations of indirect drive inertial confinement fusion capsules driven by the ‘High-Foot’ radiation pulse on the National Ignition Facility (NIF). The results are post-processed using a semi-deterministic ray tracing model to generate synthetic DT and DD neutron spectra as well as primary and down scattered neutron images. Results with low-mode asymmetries are used to estimate the magnitude of anisotropy in the neutron spectra shift, width and shape. Comparisons of primary and down scattered images highlight the lack of alignment between the neutron sources, scatter sites and detector plane, which limits the ability to infer the r of the fuel from a down scattered ratio. Further calculations use high bandwidth multi-mode perturbations to induce multiple short scale length flows in the hotspot. The results indicate that the effect of fluid velocity is to produce a DT neutron spectrum with an apparently higher temperature than that inferred from the DD spectrum and which is also higher than the temperature implied by the DT to DD yield ratio. I. INTRODUCTION Non-uniformity in the radiation intensity reaching the surface of an indirect drive, inertial confinement fusion (ICF) capsule can result in strong variations in the areal density and velocity of the dense fuel layer converging on the axis. In addition, perturbations arising from the capsule mounting structure or from surface defects are amplified through Richtmyer-Meshkov and Rayleigh-Taylor instabilities during ablation and implosion and imprint upon the dense fuel layer during the deceleration phase. Such asymmetries can mean that not all of the momentum of the dense fuel is extinguished at stagnation and thus there is a reduction in the efficiency with which the kinetic energy is thermalized and hence a reduction in the pressure of the hotspot material 1,2,3,4,5 . Inhomogeneity in the dense fuel layer means that there are weak points of low