Optimization of laser-driven cylindrical implosions on the OMEGA laser

• Published in: Physics of plasmas 2018-12, Vol.25 (12)
• Main Authors: Hansen, E. C., Barnak, D. H., Chang, P.-Y., Betti, R., Campbell, E. M., Davies, J. R., Knauer, J. P., Peebles, J. L., Regan, S. P., Sefkow, A. B.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Computer simulation; Emission analysis; Energy; Energy absorption; Energy transfer; Experiment design; Experiments; Hydrodynamics; ICF; Implosions; Incidence angle; Inertial fusion (reactor); Laser beams; Lasers; Numerical simulations; Optimization of Laser-driven Cylindrical Implosions on the OMEGA; Plasma physics; Simulation; Soft x-rays
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.5055776

Laser-driven cylindrical implosions were conducted on the OMEGA laser as part of the laser-driven mini-MagLIF (Magnetized Liner Inertial Fusion) Campaign. Gated x-ray images were analyzed to infer shell trajectories and study the energy coupling in these implosions. Two-dimensional and three-dimensional HYDRA simulations were performed and post-processed to produce synthetic x-ray self-emission images for comparison. An analysis technique, which could be applied to both experimental and simulated x-ray images, was developed to characterize the shape and uniformity of the implosion. The analysis leads to a measurement of the average implosion velocity and axial implosion length, which can then be used to optimize the beam pointing and energy balance for future experiments. Discrepancies between simulation results and experiments allude to important physical processes that are not accounted for in the simulations. In 2-D simulations, the laser beam's azimuthal angle of incidence is not included because the ϕ-direction is not simulated, and thus, energy absorption is over-predicted. The 3-D simulation results are more consistent with the experiments, but the simulations do not include the calculation of cross-beam energy transfer or non-local thermal transport, which affects the energy coupled to the implosion. By appropriately adjusting the simulated energy balance and flux limit, the simulations can accurately model the experiments, which have achieved uniform implosions over a 700-μm-long region at velocities of approximately 200 km/s.