34 Pages

Hydrodynamic Instabilities in Inertial Confinement Fusion

WithNelson M Hoffman

This chapter discusses the evolution of a single Rayleigh-Taylor-unstable mode, from its linear phase to its late-stage constant-velocity bubble growth, with a brief consideration of the saturation of linear growth. Hydrodynamic phenomena arise which are for all practical purposes equivalent to the Rayleigh-Taylor instability, appropriately generalised. The amplitude of a sinusoidal perturbation increases exponentially with time in the early stage of Rayleigh-Taylor instability. Several methods have been used to calculate the growth of hydrodynamic instabilities in inertial-confinement-fusion implosions. To represent reality as accurately as possible, the methods must account for time-varying accelerations, continuous gradients in density and velocity, and energy transport. Historically, linearised perturbation codes were used first, but recently nonlinear radiation-hydrodynamic simulation codes have been used quite widely and routinely. An approach that is more widely used than linearised perturbation calculations is that of linear instability calculations in nonlinear codes.