Persistent Hot-Spot Mix in Cryogenic Direct-Drive Fusion Experiments

Area of Science:

• Plasma Physics
• Nuclear Fusion
• Astrophysics

Background:

• Mass injection during the acceleration phase in experimental fusion can impact hot-spot convergence and neutron production.
• Previous research identified an x-ray emission signature associated with this phenomenon.

Purpose of the Study:

• To investigate the correlation between an x-ray emission signature and experimental outcomes in fusion.
• To understand how target parameters influence this x-ray signature.

Main Methods:

• Analysis of x-ray emission signatures during the acceleration phase.
• Correlation of signature strength with hot-spot convergence and neutron yield.
• Experimental parameter variation (target mass, adiabats, debris).

Main Results:

• The x-ray emission signature correlates with poor hot-spot convergence and reduced neutron production.
• Increased target mass and higher-design adiabats reduce the signature.
• Increased debris on the target enhances the signature.
• The vapor region may contain up to twice the assumed hydrogen mass at deceleration.

Conclusions:

• The identified x-ray emission signature serves as an indicator of suboptimal fusion performance.
• Controlling target mass, adiabats, and debris is crucial for mitigating this signature and improving fusion yields.
• Accurate estimation of hydrogen mass in the vapor region is necessary for precise modeling.