Systematic Trends of Hot-Spot Flow Velocity in Laser-Direct-Drive Implosions on OMEGA*

DT cryogenic targets and DT gas-filled, spherical plastic or glass targets are imploded on the OMEGA Laser System using laser-direct-drive inertial confinement fusion. The hot-spot flow velocity is diagnosed using multiple neutron time-of-flight detectors arranged along four quasi-orthogonal diagnostic lines of sight.[1] A systematic study of the magnitude and direction of the mode-1 asymmetry observed at stagnation[2] will be presented and possible seeds of mode-1 asymmetry from inaccuracies in beam pointing, beam-to-beam energy/power imbalance, inaccuracies in target positioning, laser–plasma interactions,[3] and target asymmetries will be discussed. It is shown that beam mispointing leads to a significant mode l = 1 illumination nonuniformity being the dominate cause for the hot-spot flow. With improved beam pointing, inaccuracies in target positioning and laser-plasma interactions are the leading causes for the hot-spot flow.

 

[1] O. M. Mannion et al., Rev. Sci. Instrum. 92, 033529 (2021).

[2] O. M. Mannion et al., Phys. Plasmas 28, 042701 (2020).

[3] D. H. Edgell et al., “Nonuniform Absorption and Scattered Light in Direct-Drive Implosions Driven by Polarization Smoothing,” to be published in Physical Review Letters.