Laser-direct-drive fusion target design with a high-Z gradient-density pusher shell

Area of Science:

• Nuclear Fusion Energy
• Plasma Physics
• Inertial Confinement Fusion (ICF)

Background:

• Conventional inertial confinement fusion (ICF) targets often face challenges with hydrodynamic instabilities.
• Cross-beam energy transfer (CBET) can significantly reduce laser absorption and ablation pressure in ICF implosions.
• Achieving high energy gain in ICF requires robust target designs that mitigate instability growth and energy losses.

Purpose of the Study:

• To investigate novel laser-direct-drive fusion target designs incorporating a high-Z gradient-density pusher shell (GDPS).
• To evaluate the performance of GDPS targets compared to conventional targets under various simulation conditions, including CBET.
• To identify the key physical mechanisms enabling robust ignition and energy gain in GDPS implosions.

Main Methods:

• One-dimensional (1D) and two-dimensional (2D) radiation-hydrodynamic simulations using the lilac and draco codes, respectively.
• Modeling of targets with solid deuterium-tritium (DT) fuel, a high-Z GDPS, and a gold (Au)-coated foam layer.
• Analysis of implosion characteristics such as adiabat, convergence ratios, implosion velocity, and neutron yield.

Main Results:

• GDPS targets demonstrated instability-resistant implosions with high adiabat (α≥8) and low convergence ratios (CRhs≈22, CRPS≈17).
• 1D simulations predicted neutron yields exceeding 50 MJ with 1.9–2.5 MJ of laser energy, despite CBET effects.
• 2D simulations showed GDPS targets achieving 4–10 MJ neutron yields with CBET, while conventional targets failed; yields >20 MJ are expected with mitigated CBET.

Conclusions:

• GDPS targets offer significant advantages over conventional designs, enabling robust ignition and moderate energy gain.
• Key factors include maintaining a high adiabat fuel state, reduced hot-spot heat conduction due to the high-Z layer, and potential radiation trapping.
• These findings suggest GDPS targets are a promising pathway for efficient inertial confinement fusion energy production.