Optimizing Implosions for High Fusion Energy Gain: increased payload mass and reduced residual kinetic energy

The National Ignition Facility (NIF) consistently produces plasmas dominated by α-heating and recently achieved target gain >2.^1,2 Since 2022 we’ve embarked on a campaign to optimize fusion energy output by trading off plasma heating (i.e., implosion velocity in ICF) for plasma confinement (i.e., areal density, ρR). The premise is to increase confining ρR at peak fusion burn by increasing the initial payload mass; however, constrained by a fixed input laser power this necessarily reduces implosion velocity.^3,4 In this trade space, we explore the maximum ρR obtainable while still igniting the implosion. Simplified analytic models guide this exploration.⁵ This talk presents our current understanding of 2.20 MJ-drive implosions using experiments, modeling, and theory.



Key experimental signatures include: ρR spatial asymmetries; residual kinetic energy (RKE) unconverted to thermal energy; hot spot bulk motion; observed T_ion spatial dependencies; and high-Z impurities radiatively cooling the fusing plasma. These are quantified and used to understand and improve performance.



Comprehensive modeling informs designs by providing time-resolved metrics such as RKE, hot spot and fuel shell shape asymmetries, and dynamics of “burn-off” implosions with α-heating removed. Simulations predict reducing RKE and shape asymmetries are a strong lever on performance, and experiments compare favorably with these predictions.



Recently a linearly ramped dopant profile was applied to this platform, achieving record yields using 2.05 MJ of laser drive.⁶ Future 2.20 MJ drive experiments will leverage this dopant strategy, continue optimizing symmetry with minimal RKE, and further increase ablator mass. This exploration of velocity vs payload mass trade space informs implosion designs for the next-generation of high-yield laser facilities.





¹ H. Abu-Shawareb et al., Phys. Rev. Lett. (2024)

² D.J. Schlossberg et al., Phys. Rev. Lett. (in prep. 2025)

³ A.L. Kritcher et al., Phys. Rev. E (2024)

⁴ A. Pak et al., Phys. Rev. E (2024)

⁵ O.A. Hurricane et al., Phys. Plasmas (2020)

⁶ D.S. Clark, M. Hohenberger, this APS-DPP meeting (2025)