Influence and measurement of mass ablation in ICF implosions

Point design ignition capsules designed for the National Ignition Facility (NIF) currently use an xray-driven Be(Cu) ablator to compress the DT fuel. Ignition specifications require that the mass of unablated Be(Cu), called residual mass, be known to within 1% of the initial ablator mass. The specifications also require that the implosion bang time, a surrogate measurement for implosion velocity, be known to 50 ps RMS. Experiments designed to measure and to tune experimentally the amount of residual mass are being developed as part of the National Ignition Campaign (NIC). Tuning adjustments of the residual mass and peak velocity can be achieved using capsule and laser parameters. We currently plan to measure the residual mass using streaked radiographic imaging of surrogate tuning capsules. This technique, together with bang time measurements, should allow us to tune ignition capsules to meet NIC specs.