Implosion symmetry of heavy-ion-driven inertial confinement fusion targets

Abstract

Mechanisms that induce implosion asymmetries in ion-driven inertial confinement fusion (ICF) targets are identified and investigated by studying the two-dimensional hydrodynamic response of the heavy-ion-driven HIBALL target [Boch, in Heavy Ion Inertial Fusion, AIP Conf. Proc. No. 152, Washington, DC (American Institute of Physics, New York, 1986), p. 23] in planar geometry. The implosion of the multilayered, single-shell target is subjected to two symmetry-reducing mechanisms: (1) spatial beam intensity nonuniformities and (2) target material interface perturbations. In self-consistent numerical calculations, the target implosion symmetry is found to be sensitive to spatial variations in beam energy deposition resulting from interface perturbations in the path of the beam and coherent intensity variations in the beam itself. The asymmetries in beam energy absorption perturb the flow in the target absorption layer. If the resulting fluid perturbations are seeded at the hydrodynamically unstable pusher–fuel interface, they can grow with rates comparable to the Rayleigh–Taylor instability when lateral wavelengths are comparable to the payload shell thickness. Coherent variations in beam intensity as small as 5%–10% at low intensity (1 TW/cm2) and 1% at high intensity (1000 TW/cm2) limit the usable target implosion energy.