Fusion, a natural phenomenon responsible for a significant portion of our planet’s energy, occurs millions of miles away in the heart of the sun. Scientists on Earth are striving to replicate the hot and dense conditions necessary for fusion. In the core of stars, gravitational forces and extreme temperatures, reaching around 200 million degrees Fahrenheit, compress atoms to the point where their nuclei fuse, releasing excess energy.
Arianna Gleason, a staff scientist at the Department of Energy’s SLAC National Accelerator Laboratory, elucidates, “The ultimate aim of fusion research is to emulate a process that occurs routinely in stars—where two light atoms merge to form a single, heavier, more stable nucleus. Consequently, the surplus mass—the resulting nucleus has less mass than the two that combined—is converted into energy and discharged.”
This surplus mass (m) transforms into energy (E) owing to Einstein’s iconic equation E=mc². While achieving fusion on Earth is relatively straightforward and has been accomplished numerous times using various devices, the challenge lies in creating a self-sustaining process where one fusion event triggers the next, leading to a continuous “burning plasma” capable of generating clean, safe, and abundant energy for powering the electric grid.
Alan Fry, project director for SLAC’s Matter in Extreme Conditions Petawatt Upgrade (MEC-U), likens this process to lighting a match: once ignited, the flame persists. However, on Earth, the right conditions—extremely high density and temperature—are necessary to initiate fusion, and one effective method involves the use of lasers.
Enter inertial fusion energy (IFE), a prospective approach to constructing a commercial fusion power plant utilizing fusion fuel and lasers. IFE has garnered increasing national support following successful demonstrations of fusion reactions with net energy gain at Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF).
Siegfried Glenzer, professor of photon science and director of SLAC’s High Energy Density science division, elaborates on the technique employed at NIF, known as inertial confinement fusion. This approach, one of the two primary concepts explored for creating a fusion energy source, entails the use of intense lasers and a small pellet containing hydrogen isotopes, typically deuterium and tritium. The pellet is encased in a light material that vaporizes outward upon laser heating, resulting in a net inward reaction, inducing implosion.
The precision application of lasers is crucial to generate a symmetrical shockwave directed toward the center of the hydrogen mixture, initiating the fusion reaction. NIF ignition events utilize 192 laser beams to orchestrate this implosion and facilitate isotope fusion.
While progress has been made, significant challenges remain. Lasers utilized for inertial fusion energy must operate at a faster rate and improve electrical efficiency. The current lasers at NIF, due to their size and complexity, can only fire approximately three times a day. Achieving an inertial fusion energy power source requires lasers capable of operating ten times per second.
Additionally, the estimated energy gain from ignition events at NIF does not encompass the energy expended to execute laser shots. To realize IFE as a viable energy solution, both the energy output from fusion reactions and the energy input into lasers must be optimized.
The recently established Department of Energy (DOE) sponsored inertial fusion energy science and technology hubs aim to address these challenges by consolidating expertise from various institutions. SLAC’s involvement in two of these hubs underscores its role in advancing high-repetition-rate laser experiments and related technologies.
Furthermore, the ultrabright X-rays produced by SLAC’s Linac Coherent Light Source (LCLS) will aid in understanding the fusion process and material behavior during implosion. This comprehensive approach encompasses not only technological advancements but also workforce development to ensure the successful realization of fusion energy facilities.
Ultimately, fusion energy holds promise as a clean, equitable, and abundant energy source, presenting exciting opportunities for scientific exploration and technological innovation.