Observation of implosion dynamics by line emissions from direct-drive fusion capsules

Line emissions from Ar-doped fusion capsules were observed to investigate influence of drive uniformity on implosion behavior. To manipulate the drive non-uniformity, in particular of the mode number 6, the laser focus position was set in two representative cases. A fusion capsule was directly irradiated with 12 beams of partially-coherent green light. Imploded core plasmas were diagnosed by observing spatial distribution and time history of the Ar line emissions. Clear differences were obtained between the two irradiation cases despite the calculated irradiation uniformities for the two cases being identical. The experimental result was compared with two-dimensional fluid simulations post-processed with an X-ray spectrum analysis code. Drive uniformity and associated perturbation growth at the pusher-fuel boundary are discussed as a plausible reason for the observed differences.