Simulations of asymmetry in laser-driven implosions for inertial confinement fusion

Asymmetries in the implosion in the central-hotspot scheme of direct-drive ICF experiments arise as a consequence of laser nonuniformities such as beam power misbalance, mistiming and laser-target offset. Using the 2D RZ radiation hydrodynamics code Odin [Bennett et al., 2021], a series of ignition-scale direct-drive simulations were conducted to quantify the impact of such nonuniformities on implosion performance for the experimental setup described by [Goncharov et al., 2010]. An applied l = 1 perturbation to the laser power was found to be increasingly detrimental to areal density, and other hotspot parameters, as its amplitude, ap, was raised up to 5%. Laser-target offset, 'y, over a range of 5-30μm, was found to have a similarly damaging impact on implosion performance and the results are in agreement with those presented in [Hu et al., 2010]. In both scenarios, this simulation setup showed some tolerance to low levels of nonuniformity, ap < 2% and 'y < 15μm. For these simulations to be possible, multiple features were added to Odin including 3D refractive ray-tracing with face-normal interpolation, wedge boundary conditions, and options to include artificial laser power perturbations and laser-target offset. Simulations were conducted to find the impact of hot-electrons, generated as a consequence of laser-plasma instabilities, on ICF target compression. In the context of a symmetric implosion, we quantified the effect of hot-electrons with differing thermal distribution between 10-60keV, within the range of temperatures found in direct-drive experiments [Rosenberg et al., 2018]. Hot-electrons above 10keV were found to preheat the cryogenic DT fuel and damage the compression of the pellet. A thermal distribution of 30keV hot-electrons was found to reduce the areal density of the hotspot of the target by ⇠27% compared to simulations without hot-electrons. Higher temperature populations were found to be more harmful to all metrics of implosion performance up to 40keV, beyond which measurements of hotspot areal density increased from 70% to 73% at 60keV, relative to the value found in a symmetric implosion in the absence of hot-electrons. Simulations of laser nonuniformities with the inclusion of 30keV hot-electrons were carried out. Hot-electrons of 30keV were found to nullify the harmful impact of l = 1 laser power perturbations. In comparison to purely laser-driven simulations, the addition of hot-electrons in laser-offset simulations also showed some resilience to implosion performance with increasing offset. These results indicate that hot electrons can smooth perturbations caused by non-uniform laser illumination