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Neutron activation diagnostics at the National Ignition Facility (invited)
D L Bleuel1, C B Yeamans, L A Bernstein
1Lawrence Livermore National Laboratory, Livermore, California 94550, USA. bleuel1@llnl.gov
The Review of Scientific Instruments
|November 7, 2012
Summary
Neutron activation diagnostics at the National Ignition Facility accurately measure fusion yields using indium, zirconium, and copper. These measurements reveal fuel velocities up to 200 km/s and significant areal density variations.
Area of Science:
- Nuclear Fusion Diagnostics
- Plasma Physics
- High-Energy Physics
Background:
- Accurate neutron yield measurements are critical for inertial confinement fusion research.
- Neutron activation diagnostics offer a method to measure primary neutrons, avoiding scattered neutron contributions.
Purpose of the Study:
- To detail the neutron activation diagnostics employed at the National Ignition Facility (NIF).
- To report on the accuracy and precision of these diagnostics for measuring fusion neutron yields and fuel properties.
- To present findings on fuel dynamics and areal density variations in NIF experiments.
Main Methods:
- Utilizing indium samples for deuterium-deuterium (2.45 MeV) neutron detection via the (115)In(n,n')(115 m)In reaction.
- Employing zirconium and copper samples for deuterium-tritium (14 MeV) neutron detection through (n,2n) reactions.
- Deploying an array of zirconium samples to map relative neutron yield anisotropies and infer fuel areal density variations.
Main Results:
- Neutron yields are measured with 7% accuracy, showing excellent agreement with other diagnostic methods.
- Relative areal density anisotropies are determined with <3% precision.
- Measurements indicate bulk fuel velocities up to 200 km/s and significant pole-to-equator areal density variations.
Conclusions:
- Neutron activation diagnostics provide reliable and precise measurements of fusion neutron yields at NIF.
- These diagnostics are effective in characterizing fuel behavior, including bulk motion and density distributions.
- The findings contribute to a deeper understanding of the physics of inertial confinement fusion.
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