Identifying a key culprit behind inertial confinement fusion’s ‘drive deficit’ problem

In indirect-drive inertial confinement fusion (ICF) experiments, laser energy is used to irradiate the interior surface of a small hollow cylinder, called a hohlraum, which produces X-rays that implode a capsule within, triggering nuclear fusion. This multi-step process has already succeeded in generating more energy from fusion than the energy input by the driving lasers, and subsequent research has been devoted to improving efficiency and understanding.

For years, a so-called “drive deficit” problem has plagued researchers in indirect-drive ICF, where less X-ray energy is present in the experiment than predicted by simulations. This has historically been compensated for in simulations by artificially reducing the laser power to match observations.

Using upgraded diagnostics at the National Ignition Facility, Chen et al. described the origin of the drive deficit problem and provided experimental data to improve future simulations.

This work became possible with recent improvements to the Dante-1 diagnostic, which measures X-ray intensity during the experiments. These improvements reduced the absolute error rate to less than 5%, allowing the team to produce an accurate profile of the X-ray radiant intensity.

With this data, the researchers identified discrepancies between observed and simulated emission data from gold hohlraums. At high energies (above ∼2 keV), the X-ray emission from the simulations had been overestimated by as much as 50%.

“Our results pointed to the inaccuracies of the atomic line emission data of gold as the primary culprit responsible for the over-prediction of X-ray drive in the design code,” said author Hui Chen.

The authors have provided models which provide better agreement with the experimental data, and they are planning more experiments to identify additional data discrepancies.

Source: “Key advancements towards eliminating the ‘drive deficit’ in ICF hohlraum simulations,” by Hui Chen, Douglas Tod Woods, William Anthony Farmer, Nicholas Aybar, Duane Allen Liedahl, Stephan A. MacLaren, Marilyn B. Schneider, Howard A. Scott, Judith Alice Harte, Denise Hinkel, Otto L. Landen, John Douglas Moody, Mordecai D. Rosen, James S. Ross, Sonja Rogers, Nicholas T. Roskopf, George Forester Swadling, Scott Vonhof, and George Zimmerman, Physics of Plasmas (2025). The article can be accessed at https://doi.org/10.1063/5.0256856 .