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2D X-ray radiography of imploding capsules at the national ignition facility
J R Rygg1, O S Jones1, J E Field1
1Lawrence Livermore National Laboratory, Livermore, California 94551, USA.
Physical Review Letters
|June 1, 2014
Summary
Researchers measured the in-flight shape of inertial confinement fusion (ICF) capsules using X-ray radiography. Asymmetries were observed even with round cores, but could be reduced by increasing hohlraum length.
Area of Science:
- Nuclear Fusion
- Plasma Physics
- High-Energy-Density Physics
Background:
- Inertial confinement fusion (ICF) aims to achieve controlled fusion reactions.
- Understanding capsule implosion dynamics is crucial for ICF success.
- In-flight capsule shape directly impacts fusion performance.
Purpose of the Study:
- To perform the first in-flight measurements of imploding ICF capsule shapes at the National Ignition Facility (NIF).
- To analyze shell asymmetries and their impact on implosion dynamics.
- To investigate methods for mitigating observed asymmetries.
Main Methods:
- Utilized two-dimensional X-ray radiography with area-backlit, time-gated pinhole imaging.
- Analyzed image sequences to determine implosion velocity, shape, and density asymmetries.
- Quantified shell offset and center-of-mass velocity.
Main Results:
- Observed in-flight capsule shell asymmetries even when core self-emission appeared round.
- Quantified a Y(40) mode asymmetry of ~15 μm at ~200 μm shell radius (5x radial compression).
- Demonstrated that a ~10% increase in hohlraum length mitigated this asymmetry.
Conclusions:
- In-flight capsule shape is a critical factor in ICF performance, often exhibiting asymmetries.
- X-ray radiography provides valuable data for characterizing these asymmetries.
- Adjusting hohlraum geometry offers a potential pathway to improve implosion symmetry and fusion yield.