Double-shell targets on HYDRA: detectable compressional neutrons

Target design studies for parameters attainable on HYDRA indicate a respectable number of compressional neutrons (105 to 106) might be obtained for a double-shell target with DT radius about 0.4 mm. The basic concept consists of increasing the low implosion velocities through velocity multiplication from the (nearly) elastic collision of two shells of differing mass. A low density buffer gas between the shells enhances the elasticity and symmetrizes nonuniformities in energy deposition and outer shell thickness. However, velocity multiplication may not be the dominant mechanism; the actual velocity imparted to the inner shell is fairly insensitive to the outer-to-inner shell mass ratio. Experiments may be unable to distinguish unambiguously the effect of velocity multiplication from the effect of spherical convergence. The results suggest that an outer shell composed of a low-Z ablator over a gold pusher might be preferable to an all-gold outer shell because of reduced symmetry requirements