The image shows a 3D implosion made up of six pistons working on a hot spot. Credit: Lawrence Livermore National Laboratory.
The expansion of a classical mechanics model has been useful for understanding asymmetries in implosions from a two-piston to a six-piston model.
The work is in a book. The co-authors of the book were Ryan Nora, Paul Springer, and Alex Zylstra.
The paper shows that the key asymmetry that degrades performance in an implosion is the shell areal density at stagnation, and that the key mathematical quantity that captures the important physics is the weighted harmonic.
The paper shows that the implosion's peak velocity has a very strong impact on fusion performance and it has a direct connection to the concept of "coast time."
Hurricane said that we should strive to minimize shell asymmetry at stagnation and minimize the radius of peak velocity in order to maximize fusion performance.
Hurricane explained that the RKE or residual kinetic energy is the waste of energy in an implosion. The fusion performance is affected by the amount of energy available to the implosion. The X-ray radiation field in the hohlraum is one of the reasons why minimizing asymmetry in our implosions has been difficult.
An explanation of the work is that of mechanical pistons, such as an internal combustion engine, doing work on a gas.
The thickness of the pistons should be the same for the engine to work. Hurricane said the engine wouldn't compress the fuel-air mixture very well if one of the opposed pistons was thick.
Researchers looked at 3D implosions that are made up of six pistons doing work on a common hot-spot and converted that into a set of equations that could be solved. The solution gives a testable prediction which can be compared to simulations and data. The value of this theory is that it eliminates all the complicated details that don't matter.
A simple but powerful set of relationships between asymmetries and the damage they do to implosion performance is one of the most valuable results. In other words, we now know how much asymmetry mattered, thanks to these tools.
Hurricane said that the value of work like this is to focus our attention on what aspects of implosions are key. It gives us a way to measure how badly asymmetry is hurting our implosions by pointing out what we need to fix.
Hurricane said that while the researchers only intended to study asymmetry in this work, the important connection of peak velocity to the vague concept of coast time was found unexpectedly by following up on some of the implications of the mathematical expressions of the work. This gave researchers a better understanding of why coast time seems to matter so much in the laboratory's experiments, as has been shown in a recent experiment that achieved 1.3MJ total yield.
There are extensions of a classical mechanics "piston-model" for understanding the impact of asymmetric implosions. There is a DOI: 10.1063/5.0067699.
The journal contains information about physics of particles.
Investigating a model to understand the impacts of asymmetry on implosions.
The document is copyrighted. Any fair dealing for the purpose of private study or research cannot be reproduced without written permission. The information provided is for educational purposes.
All Rights Reserved © 2024
