Numerical Modeling of the Sensitivity of X-Ray Driven Implosions to Low-Mode Flux Asymmetries

摘要

The sensitivity of inertial confinement fusion implosions of the typeperformed on the National Ignition Facility (NIF) to low-mode flux asymmetrieshas been investigated numerically. It is shown that large-amplitude, low-ordermode shapes (Legendre polynomial P4), resulting from associated low order fluxasymmetries, cause spatial variations in capsule and fuel momentum that preventthe DT ice layer from being decelerated uniformly by the hot spot pressure.This reduces the transfer of kinetic to internal energy of the central hotspot, thus reducing neutron yield. Furthermore, synthetic gated x-ray images ofthe hot spot self-emission indicate that P4 shapes may be unquantifiable for DTlayered capsules. Instead the positive P4 asymmetry aliases itself as an oblateP4 in the x-ray self emission images. Correction of this apparent P2 distortioncan further distort the implosion while creating a round x-ray image. Longwavelength asymmetries may be playing a significant role in the observed yieldreduction of NIF DT implosions relative to detailed post-shot 2D simulations.