This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers at Lawrence Livermore National Laboratory (LLNL) have found that implosions designed for inertial fusion energy (IFE) can tolerate significant imperfections before performance abruptly declines, a finding that could inform the design of fuel targets for future fusion power plants. The findings were detailed in a paper titled "Robustness of inertial fusion energy relevant implosions to low-mode asymmetries," recently published in Physics of Plasmas and selected for the journal's cover.
The study was led by LLNL physicist Timothy Johnson, who directed the research and analysis, along with coauthors Daniel Casey, Chris Weber, Omar Hurricane, Ryan Nora and Seth Davidovits. The work supports research into how degradation mechanisms, including asymmetries and fuel mixing, affect IFE-relevant implosions. The motivation is as much economic as scientific, Johnson said.
If a future fusion power plant loses yield to imperfect implosions, the cost of producing electricity rises accordingly. A fusion power plant would need to produce a steady, predictable amount of energy from shot to shot. Unlike the single, carefully controlled experiments conducted at the National Ignition Facility (NIF), a power plant would need to fire multiple fuel capsules every second, with each target injected into position in rapid succession.
Small errors in how lasers strike a fast-moving target are expected in that environment, Johnson said, making it important to understand how much asymmetry an implosion can tolerate before performance is affected. Using 2D radiation hydrodynamics simulations, the researchers scaled up the design behind NIF's first ignition shot into a capsule capable of producing about 30 megajoules of energy. They then progressively introduced controlled asymmetries, or unevenness in how the driving radiation struck the capsule, to study how the implosion's performance responded.
Rather than a gradual decline, the team found that yield held essentially steady as asymmetry increased, up to a critical threshold. Beyond that point, performance dropped sharply and the capsule failed to ignite. Johnson described the underlying physics in terms of the implosion's central hot spot, the small region of superheated fuel where fusion reactions begin.
"Asymmetries in the implosion tend to rob energy from the hot spot," Johnson said. "But if it's a good implosion, taking some energy away still results in a good implosion, and you're still going to ignite." That trajectory amounts to a race against time, Johnson said. Asymmetry drains energy from the hot spot and causes the capsule to expand sooner, leaving less time to reach ignition.
Extract — continue reading at the source.
