LLNL simulations calculate ICF’s asymmetry limits

At LLNL’s National Ignition Facility, each inertial confinement fusion shot is carefully controlled and calibrated, ensuring targets are hit by the lasers exactly as intended. In the power plant version of this concept, where targets must be injected and imploded multiple times per second, alignment must be achieved through fast automation, and imperfections could lead to asymmetries in how the target heats up and implodes.

In a recent Physics of Plasmas paper, researchers described their process of using two-dimensional hydrodynamic simulations to study the impact of these asymmetries, showing minimal change in yield up until a point where the hot spot stops having enough time to ignite, past which performance drops severely.

“Asymmetries in the implosion tend to rob energy from the hot spot,” said LLNL physicist Timothy Johnson. “But if it's a good implosion, taking some energy away still results in a good implosion, and you're still going to ignite.”

The study also found an inherent trade-off between yield and robustness that likely will leave scientists with a range of options to consider when designing a power plant. It may be beneficial to focus initially on high robustness, even at the cost of some yield, followed by a tuning process that increases energy output and decreases the cost of electricity produced.

“As you're turning on the power plant, understanding the sources of asymmetry, over time you can tighten tolerances, solve problems, and then switch to a higher-yield but less-robust implosion,” Johnson said.