The Saturn target for polar direct drive on the National Ignition Facility

A new target design concept is proposed for direct-drive implosions while the National Ignition Facility is in its initial, indirect-drive configuration. It differs from earlier polar-direct-drive designs by adding a low-Z ring around the capsule equator. Refraction in the plasma formed around this ring permits time-dependent tuning of the capsule drive uniformity. An optimized simulation shows an implosion-velocity nonuniformity at the end of the laser pulse of similar to 1% rms for a cryogenic deuterium-tritium shell, enhancing the prospects for an early direct-drive ignition demonstration on the National Ignition Facility.