Diagnosing ignition with DT reaction history

Area of Science:

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

Background:

• Understanding the detailed reaction history of inertial confinement fusion (ICF) capsules is crucial for diagnosing fuel conditions and implosion performance.
• The temporal evolution of neutron production provides a sensitive probe of the conditions within the burning plasma.

Purpose of the Study:

• To investigate how the full range of deuterium-tritium (DT) reaction history can be used to diagnose fuel conditions before and during burn.
• To explore the impact of laser pulse changes, asymmetries, and fuel composition on the reaction history.
• To assess the capability of specific diagnostics for capturing this detailed reaction history.

Main Methods:

• Simulating and analyzing the full range of DT reaction history (10^9 to 10^20 neutrons) for ignition capsules.
• Examining the influence of shock waves, laser pulse variations, low and high mode asymmetries, and fuel composition (e.g., tritium-rich capsules) on the reaction history.
• Proposing the use of gas Cerenkov detectors and neutron temporal diagnostics for capturing the reaction history.

Main Results:

• The reaction history provides insights into fuel adiabat and shock strength, with measurable changes correlating to yield-degrading laser pulse variations.
• Low mode asymmetries affect the reaction history late in the burn (approx. 100 ps), while high mode asymmetries or turbulence impact it near peak burn (approx. 50 ps).
• Tritium-rich capsules exhibit a reaction history similar to ignition capsules but lack the final ignition burn.

Conclusions:

• The comprehensive DT reaction history is a powerful tool for diagnosing fuel conditions and implosion dynamics in ICF.
• Neutron temporal diagnostics, potentially combined with gas Cerenkov detectors, show promise for capturing the full reaction history of both ignition and tritium-rich capsules.
• Understanding these temporal signatures allows for better interpretation of experimental results and optimization of ICF designs.