First high-convergence cryogenic implosion in a near-vacuum hohlraum.

Area of Science:

• Nuclear Fusion Science
• Plasma Physics
• High-Energy-Density Physics

Background:

• Cryogenic deuterium-tritium (DT) layered capsule implosions are crucial for inertial confinement fusion research.
• Traditional gas-filled hohlraums present challenges in achieving high convergence and efficiency.
• The National Ignition Facility (NIF) aims to achieve controlled fusion ignition.

Purpose of the Study:

• To evaluate the viability of near-vacuum hohlraums for high-convergence cryogenic DT implosions.
• To assess the performance improvements offered by near-vacuum hohlraums compared to conventional designs.
• To investigate the impact of high-density carbon ablators on implosion dynamics and symmetry.

Main Methods:

• Experiments conducted at the National Ignition Facility (NIF).
• Utilized a near-vacuum hohlraum with a low-pressure gas fill.
• Employed a dense ablator, specifically high-density carbon (HDC), for the cryogenic DT capsule.
• Delivered a 6.8 ns, 1.2 MJ laser pulse to drive the implosion.

Main Results:

• Achieved a 40% higher hohlraum efficiency compared to typical gas-filled hohlraums.
• Observed improved symmetry control beyond standard hydrodynamic simulation predictions.
• Generated a primary neutron yield of 1.8×10^15 neutrons.
• Reached a convergence of approximately 27× with 20% calculated alpha heating.

Conclusions:

• Near-vacuum hohlraums are a viable and efficient option for high-convergence cryogenic DT implosions.
• The use of HDC ablators facilitates shorter drive durations and enhances implosion performance.
• These experiments represent a significant advancement in NIF's fusion energy research, demonstrating high performance relative to laser energy input.