Cryogenic THD and DT layer implosions with high density carbon ablators in near-vacuum hohlraums

High Density Carbon (HDC or diamond) is a promising ablator material for use in near-vacuum hohlraums, as its high density allows for ignition designs with laser pulse durations $< 10$ ns. A series of experiments in 2013 on the National Ignition Facility culminated in a DT layered implosion driven by a 6.5 ns, 2-shock laser pulse. This talk describes these experiments and comparisons with the design code HYDRA. Backlit radiography of a THD layered capsule demonstrated an ablator implosion velocity of 385 km/s with a slightly oblate hot spot shape; however, other diagnostics suggested an asymmetric compressed fuel layer. The streak camera-based SPIDER diagnostic showed a double-peaked history of the capsule self-emission. Simulations suggest that this is a signature of a low-temperature hot spot. Changes to the laser pulse-shape and pointing for a subsequent DT implosion resulted in a higher temperature, prolate hot-spot and a thermonuclear yield of $1.8 \times 10^{15}$ neutrons.