Implosion experiments using glass ablators for direct-drive inertial confinement fusion.

Area of Science:

• Physics
• Nuclear Fusion
• Materials Science

Background:

• Direct-drive inertial confinement fusion (ICF) requires efficient energy coupling and minimal preheating.
• Plastic ablators have shown limitations in managing hot electron generation and target preheat at high drive intensities.
• High-Z materials are being investigated as advanced ablator options for ICF.

Purpose of the Study:

• To evaluate the performance of high-Z glass ablators for direct-drive ICF.
• To compare the effects of glass versus plastic ablators on hot electron generation and target preheat.
• To assess the viability of glass ablators for ignition-relevant ICF designs.

Main Methods:

• Direct-drive implosions were conducted using 20-microm-thick glass shells on the Omega Laser Facility.
• Measurements included x-ray signals, hot electron temperature, energy absorption, and compression.
• Experimental data were compared against 1D hydrodynamic predictions.

Main Results:

• Glass ablators reduced the x-ray signal from two-plasmon-decay instability by over 40x compared to plastic ablators.
• Hot electron temperature was reduced by approximately 2x with glass ablators.
• Measured absorption and compression closely matched 1D predictions, with lower-than-predicted soft x-ray production.

Conclusions:

• High-Z glass ablators effectively mitigate hot electron generation and reduce target preheat in direct-drive ICF.
• The performance of glass ablators aligns well with theoretical predictions, indicating reduced shell preheat.
• A direct-drive ignition design utilizing glass ablators is proposed based on these promising results.