Lower Temperature Ignition Hohlraums for the National Ignition Facility

The National Ignition Facility will start conducting indirect drive ignition tuning experiments in 2009 followed by ignition implosion experiments in 2010. The current ignition point design is a Be-ablator capsule inside a 300 eV hohlraum. Since laser intensity and power requirements decrease with radiation temperature, while hohlraum coupling efficiency increases, the optimum temperature for ignition may be less than 300eV. This optimum could be determined by a number of trade-offs, including estimated capsule margin, estimated levels of laser plasma interactions, implosion symmetry and required laser performance. We describe a detailed design study for a 270 eV ignition hohlraum, and examine the tradeoffs at this lower temperature.