Simulated Signatures of Ignition

Ignition on the National Ignition Facility [1] provides a novel opportunity to evaluate past data [2] to identify signatures of inertial confinement fusion capsule failure mechanisms as well as signatures of the ignition cliff, where capsule performance is highly sensitive to small perturbations. We have used new simulations of high yield implosions as well as some from past studies [3-5] in order to identify unique signatures of different failure mechanisms: jetting due to the presence of voids or defects [3], interfacial mixing due to instabilities (using a Reynolds-Averaged Navier-Stokes model for the development of material mixing) or due to plasma transport, radiative cooling due to hot spot contaminant, long-wavelength drive asymmetry, and preheat. Individually, these failure mechanisms involve very different physics, which exhibit unique performance trajectories as they traverse the ignition cliff that can be distinguished through the relationships between experimental observables such as neutron yield, down-scattered ratio, and burn width. Our simulations include both plastic and high density carbon capsule implosions spanning early low-foot [6] through modern HybridE [7] designs, and the variability across designs is much smaller than the differences due to failure mechanisms. In all cases, there is a clear distinction between three regimes that we identify as ignition failure, ignition cliff, and robust ignition. The experimental trajectories are most consistent with preheat and voids/defects, which are indistinguishable in our analysis, and least consistent with pre-mix and interfacial mixing. This suggests that compression improvements have played a primary role in enabling high yields.



References

[1] Abu-Shawareb et al, PRL 129, 075001, 2022.

[2] Landen et al, HEDP 36, 100755, 2020.

[3] Haines et al, Phys. Plasmas 29, 042704, 2022.

[4] Haines et al, Phys. Plasmas 27, 082703, 2020.

[5] Haines et al, Phys. Plasmas 24, 052701, 2017.

[6] Haan et al, Phys. Plasmas 18, 051001, 2011.

[7] Kritcher et al, PRE 106, 025201, 2022.