Review of drive symmetry measurement and control experiments on the Nova laser system (invited)

Good radiation drive symmetry is crucial for achieving ignition in laboratory inertial fusion experiments. X‐ray drive symmetry in hohlraums has been the subject of investigation for more than four years and a great deal of progress has been made. Over the last two to three years, a concerted series of (indirect) drive symmetry experiments has been performed on the Nova laser system and is the subject of the present paper. The goals of this work have been to develop measurement techniques and to apply them to symmetry variation and control experiments. The principal diagnostic has utilized the symmetry signature impressed on the dense core of a target imploded by the hohlraum x‐ray environment. The core is distorted by drive asymmetries and x‐ray imaging of this core provides a mapping that can be compared with theoretical modeling and thus related to specific amounts of drive asymmetry. We will describe the instruments and measurement techniques used in these experiments and present representative data a...