Measurement of the shell decompression in direct-drive inertial-confinement-fusion implosions

Area of Science:

• Plasma Physics
• Inertial Confinement Fusion

Background:

• Understanding shell dynamics is crucial for inertial confinement fusion (ICF) energy gain.
• The adiabat, a measure of shell entropy, significantly influences implosion performance.

Purpose of the Study:

• To investigate the impact of shell adiabat on in-flight shell thickness during direct-drive implosions.
• To identify the primary mechanisms driving shell nonuniformities.

Main Methods:

• Performed direct-drive implosions on the OMEGA laser facility.
• Measured in-flight shell thickness across a range of adiabat values.
• Utilized hydrodynamic simulations to analyze instability growth and laser imprint effects.

Main Results:

• In-flight shell thickness decreased from 75±2 to 60±2μm as the adiabat was reduced from 6 to 4.5.
• Further adiabat reduction to 1.8 resulted in increased shell thickness (75±2μm) due to Rayleigh-Taylor instability.
• Hydrodynamic simulations indicated laser imprint as the dominant initial perturbation source.

Conclusions:

• The adiabat plays a critical role in controlling in-flight shell thickness.
• Rayleigh-Taylor instability growth becomes significant at low adiabat values, counteracting initial thinning.
• Laser imprint is a critical factor to mitigate for stable ICF implosions.