3D simulations of inertial confinement fusion implosions part 2: systematic flow anomalies and impact of low modes on performances in OMEGA experiments

Abstract

We present the first 3-D radiation-hydrodynamic simulations of directly driven inertial confinement fusion implosions with an inline package for polarized crossed-beam energy transfer, which were used to assess the impact of the current Distributed Polarization Rotators (DPRs) on OMEGA as well as other known sources of asymmetry. Applied to OMEGA implosions, the simulations predict bang times with no need for ad hoc multipliers, as well as yields—if you separately account for the impacts of imprint and fuel age. Magnitude of the flow is well reproduced when the low mode sources are large, whereas the modeling of stalk is thought to be required to match the flow magnitude in the remaining cases. For the cases explored in more details, polarized CBET—the only known systematic drive asymmetry, brought the results closest to the measured flow vectors. The remaining discrepencies are shown to be stemming from the limited knowledge of the laser pointing modes. For typical current levels of beam mispointing, power imbalance, target offset, and asymmetry caused by polarized CBET, low modes degrade the yield by more than 40%. The current strategy of attempting to compensate the mode-1 asymmetry with a preimposed target offset recovers only about 1/3 of the losses caused by the low modes due to the dynamic nature of the multiple asymmetries and the presence of low modes other than l = 1. Therefore, addressing the root causes of the drive asymmetries is apt to be more beneficial. To that end, one possible solution to the specific issue of polarized CBET (10µm DPRs) is shown to work well.

Future for inertial-fusion energy in Europe: a roadmap

“…Demonstration of energy gain and reliable energy production poses new challenges. One needs reliable new laser systems able to perform many shots per day at the MJ level, a design of simple and robust targets capable of withstanding typical laser system errors [ 53 ] , which are suited for mass-manufacturing and are cost-effective. One of the possible solutions is the dynamic shell concept [ 52 , 54 ] using foam as a structural element.…”

“…One major physics question is that of LPIs, particularly during the high-intensity laser spike pulse, which may reduce the amount of laser energy absorbed in the target [ 73 ] , reduce the amplitude of the shock wave [ 53 ] and prematurely heat the fuel by hot electrons [ 74 ] . Low-entropy implosions of standard direct-drive capsules have shown a high risk of failure, indicating new sufficiently resistant and robust target designs are needed.…”

3d Simulations Capture the Persistent Low Mode Asymmetries Evident in Laser-Directdrive Implosions on Omega.

“…For these reasons, the accurate knowledge of the pointing modes is limited. Calculations of the same shots using various pointing data suggest that the resulting flow direction can change in the 10-40 • range and the velocity magnitude by ∼ 20 km/s [21]. For this reason, 20 • and 20 km/s uncertainties were added for the flow direction and magnitude on the simulation results given in Fig.…”

3D Simulations Capture the Persistent Low-Mode Asymmetries Evident in Laser-Direct-Drive Implosions on OMEGA.

“…Shot 94343 is a cryogenic implosion typical of c, d). The error bars on the simulated neutron yield estimate the effect from higher modes (l = 64 to 128) as a ∼ 30% yield drop, obtained from higher resolution simulations with the same model [21]. Experimental yields are corrected for tritium aging [8].…”

“…2: Comparison of the simulated (colored symbols) and measured (gray shaded areas) bang time (a), neutron yield (b), flow velocity magnitude and angular distance from measurement (c, d). The error bars on the simulated neutron yield estimate the effect from higher modes (l = 64 to 128) as a ∼ 30% yield drop, obtained from higher resolution simulations with the same model[21]. Experimental yields are corrected for tritium aging[8].…”