INDIRECTLY DRIVEN, HIGH GROWTH RAYLEIGH-TAYLOR IMPLOSIONS ON NOVA

Indirectly-driven implosions for which the predicted Rayleigh-Taylor ( RT) instability growth rates of pre-imposed capsule surface perturbati ons are substantially increased by mid-Z-doping of the ablators have b een fielded on the Nova laser. The multiple effects on implosion perfo rmance of the additional x-ray opacity provided by the ablator dopant is discussed. For best surface finish capsules, the addition of increa sing ablator dopant levels is shown to improve the neutron yield. Howe ver, as capsule surface roughness is increased, so that RT instability growth increases, this trend is reversed, leading to decreasing yield s with increased dopant content. The RT-induced mixing between shell a nd fuel is further investigated by diagnosing the x-ray emission level s and time histories from Ti and Ar dopants in capsules with predeterm ined surface roughness. The x-ray line ratios show the expected decrea se in fuel temperature with increasing surface roughness. The spectral content, intensity and duration of the Ti spectra, however, suggest 2 - or 3-D rather than just 1-D effects are important so that higher tha n 1-D models of the mix region may be needed.