Multi-Messenger Imaging Reveals Shockwave Dynamics in Fusion Research
Researchers have for the first time simultaneously utilized ultrafast X-rays and electrons to image a shockwave in water, providing detailed insights previously unattainable. This "multi-messenger" approach revealed an unexpected layer of water vapor that contributed to the shockwave's symmetric compression, a characteristic also observed in specific targets used for inertial confinement fusion (ICF).
The experiment demonstrates the application of laser-plasma accelerators (LPAs) for exploring the microphysics of plasmas, which is pertinent to advancing fusion energy research.
Advancing Fusion Energy Understanding
Fusion energy research aims to replicate the process occurring in the sun, where atomic nuclei merge to release energy, providing a potential source of power. A key challenge involves understanding microscopic interactions during fusion reactions to enhance process control. In ICF, targets are bombarded with lasers to generate shockwaves, which heat and compress the fuel, initiating fusion. Observing these complex interactions in detail has historically been difficult.
At the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), a research team developed a method to observe a shockwave moving through water with high precision. This observation provided an analog for laser-ICF target interactions. The process was captured using both X-rays and an electron beam, marking the initial application of this multi-messenger imaging technique to study fusion physics. This method is anticipated to facilitate future small- and mid-scale experiments, improving models and aiding in the design of fusion systems.
Experimental Details and Discoveries
The research, led by the University of Michigan through DOE's LaserNetUS program, involved collaborators from Berkeley Lab's Accelerator Technology & Applied Physics (ATAP) Division and four additional institutions. The study was published on December 16, 2025, in Nature Communications.
Hai-En Tsai, a research scientist at ATAP, noted the experiment's precision, stating interactions were observed in picosecond steps with micrometer imaging resolution. These precision levels are significant for verifying simulation models used in ICF.
The experiment utilized a flowing water jet, approximately the thickness of a human hair, as the target. The setup allowed for a laser pulse rate of once per second, which is faster than traditional solid targets that require replacement after each interaction. A laser-plasma accelerator generated ultrafast X-rays and high-energy electron beams. A second, synchronized laser delivered the shockwave to the water. Adjusting the timing between pulses allowed for the creation of a high-speed sequence illustrating the shockwave's evolution.
Initial experiments, which used only X-rays, showed discrepancies with simulations. Subsequent experiments in 2020 and 2023 incorporated an electron probe alongside the X-ray view. This dual perspective revealed a thin layer of water vapor surrounding the jet. This vapor layer acted as a cushion, promoting the symmetric compression of the water. This phenomenon is comparable to the role of low-density foam layers around ICF targets, which aid in uniform compression for successful implosions. This "vapor-assisted" symmetry had not been clearly observed previously and provided a scaled-down model for studying symmetry effects in fusion-relevant conditions.
Cameron Geddes, director of ATAP, highlighted how LaserNetUS facilitates collaborations to gain insight into high-gain fusion and future energy sources. Jeroen van Tilborg, senior scientist and deputy director for experiments at the BELLA Center, emphasized that the simultaneous use of two radiation pulses provides comprehensive details, making the total information greater than its individual parts. The compact nature of laser-plasma technology means it could potentially be integrated into fusion facilities for improved imaging.
Collaborators and Funding
The experiment was conducted at the BELLA Center's 100-terawatt laser system, which is accessible to external scientists via the LaserNetUS program. It involved experts from Berkeley Lab, the University of Michigan, SLAC National Accelerator Laboratory, Lawrence Livermore National Laboratory, The University of Texas at Austin, and Imperial College London.
Funding for this research was provided by the U.S. Department of Energy's Office of Fusion Energy Sciences (FES) through the LaserNetUS program, the Office of High Energy Physics, and the National Nuclear Security Administration.