Reduced mixing in inertial confinement fusion with early-time interface acceleration

Area of Science:

• Plasma Physics
• Nuclear Fusion Engineering
• Fluid Dynamics

Background:

• Inertial confinement fusion (ICF) relies on compressing fuel to initiate fusion reactions.
• Instabilities at the fuel-ablator interface, specifically Richtmyer-Meshkov (RM) and Rayleigh-Taylor (RT) instabilities, can degrade implosion performance by reducing compression and allowing ablator material to mix with the fuel.
• Understanding and mitigating these instabilities are crucial for achieving efficient fusion burnup.

Purpose of the Study:

• To investigate the role of acceleration direction on instability growth at the fuel-ablator interface in ICF implosions.
• To explore how specific instability dynamics, particularly oscillatory motion from RT instability under negative Atwood number conditions, can suppress RM instability growth.
• To inform the design of advanced ICF targets that leverage these stabilizing effects for improved compression and reduced mixing.

Main Methods:

• Theoretical analysis of fluid instabilities in ICF conditions.
• Computational simulations of ICF implosions, including RM and RT instability evolution.
• Comparison of simulation results with experimental data from the National Ignition Facility (NIF).

Main Results:

• The study confirms that under negative Atwood number conditions, the Rayleigh-Taylor (RT) instability can induce oscillatory motion.
• This oscillatory motion has a stabilizing effect on the growth of the Richtmyer-Meshkov (RM) instability at the fuel-ablator interface.
• Simulations and theoretical models suggest this stabilizing scenario occurred in early-time NIF experiments, explaining enhanced performance over 1D models.

Conclusions:

• The interplay between RT and RM instabilities is critical for ICF performance.
• Leveraging negative Atwood number acceleration regimes offers a pathway to enhance fuel compression and minimize ablator contamination.
• This understanding is being incorporated into next-generation, lower adiabat ICF designs to improve fusion energy yields.