Fusion is a natural phenomenon that provides our planet with most of the energy produced millions of miles from the center of the Sun. Here on Earth, scientists are trying to recreate the hot, intense conditions that lead to fusion. At the center of the star, gravitational pressure and high temperatures (about 200 million degrees Fahrenheit) energize and compress atoms close enough together to fuse their nuclei and produce excess energy.

“The ultimate goal of fusion research is to recreate the process that occurs in stars all the time,” says Arianna Gleason, a research scientist at the Department of Energy’s SLAC National Accelerator Laboratory. “Two light atoms combine to form a heavier, more stable nucleus. As a result, excess mass (one nucleus has less mass than the two nuclei that form it) is converted into energy and transported.”

The rest of the mass (m) is converted into energy (E) thanks to Einstein’s famous E=mc equation. ² . It’s surprisingly easy to do fusion on Earth, and it’s been done many times over the last few decades using a wide variety of devices. The hard part is making the process self-sustaining; so one fusion event triggers the next, creating a continuous “burning plasma” that can eventually produce clean, safe, and abundant energy to power the electrical grid.

“You can think of it like lighting a match,” explains Alan Fry. Director of SLAC’s Matter Petawatt Amplification in Extreme Conditions (MEC-U) project. “The flames continue to burn after the outbreak. We need to create the right conditions (very high density and temperature) for this process to occur on Earth, and one way to do this is with lasers.”

Enter inertial fusion energy, or IFE, a potential approach to building a commercial fusion power plant using fusion fuel and lasers. IFE has received increasing national support as scientists at Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) have repeatedly demonstrated fusion reactions that result in net energy gain for the first time in the world.

“We managed to fire with intense laser beams, which means that we obtained more energy from the fusion target than the laser energy delivered to it,” explained Siegfried Glenzer, professor of photon science and director of SLAC’s Department of High Energy Density Science.

Inertial confinement fusion: how does it work?

The technique used in NIF, known as thermonuclear fusion, is one of two main ideas being explored to create a fusion energy source. Another, known as magnetically confined fusion, uses magnetic fields to keep the fusion fuel in plasma form.

In inertial confinement fusion, a plasma is created using intense lasers and a small pellet filled with hydrogen (typically deuterium and tritium, which are isotopes with one and two neutrons in their nuclei, respectively). The pellet is surrounded by a lightweight material that evaporates outward when heated by lasers. And when this happens, there is a clear inward reaction that results in an explosion.

“It’s basically a spherical missile,” Fry explains. “It moves the rocket in the opposite direction by expelling the exhaust gases. In this case, the evaporated material on the outside of the pellet pushes the hydrogen isotopes towards the center.”

Lasers must be applied precisely to produce a symmetrical shock wave that travels towards the center of the hydrogen mixture and create the temperature and intensity necessary to initiate the fusion reaction. NIF ignition events use 192 laser beams to create this explosion and cause isotope fusion.

“Laser technology and our understanding of fusion have advanced so rapidly that we can now use laser confinement to create a burning plasma from any fusion,” Gleason said.

Faster and more efficient lasers

But there’s still a long way to go. Experts say the lasers used to power inertial fusion should be able to run faster and be more electrically efficient.

The lasers at NIF are so large and complex that they can only fire three times a day. According to Glenzer, to achieve an inertial fusion energy source, “we need lasers that can fire 10 times per second. “Therefore, we need to combine the results of NIF fusion with efficient laser and fuel target technologies.”

Fry uses the analogy of a piston in a car cylinder to explain how individual fusion reactions collectively produce constant power. “Every time you inject fuel and ignite it, the fuel expands and pushes the piston of your engine,” he said. “To move your car, you have to do this over and over again, at thousands of revolutions per minute, or tens of times per second, and that’s exactly what we need to do to convert inert fusion energy into a viable continuous source of energy.”

“To achieve the energy gain required for a fusion pilot plant, we need to go from the current gain from NIF experiments, which is about twice the energy output as input, to an energy gain of 10 to 20 times the laser energy inside,” said Glenzer. “This is unreasonable.” “We have simulations that show there is no goal, but we have to work hard to achieve it.”

Moreover, current estimates of the energy output from firing do not include all of the energy or electricity required to fire that laser shot. To make IFE an energy solution, Fry says, you need to increase the efficiency of the entire system or wall outlet, which will require progress in both directions: more energy from the fusion reaction and less energy to the laser.

The recently announced Department of Energy-sponsored Inertial Fusion Science and Technology Centers bring together the expertise of multiple institutions to address these challenges. SLAC is a partner in two of the three centers, bringing the laboratory’s expertise and capabilities in high-frequency laser experiments, laser systems, and all related technologies.

“An exciting development is the new laser facilities planned at Colorado State University and SLAC,” says Glenzer, associate director of the CSU-led RISE center. The MEC-U project at the High Power Laser Facility at CSU and SLAC’s Linac Coherent Light Source will be based on the latest laser architecture and deliver laser pulses at a rate of 10 shots per second.

“LCLS has been working with lasers at more than 100 pulses per second for the last decade, which means we have a lot of technological expertise in doing high repetition rate experiments,” Glenzer said. “We have developed new targets, diagnostics, and detectors that can leverage high repeat rates, are quite unique to the field, and align well with what we want to achieve with IFE.”

But there’s still a lot to learn about target debris and fusion power lasers, or how to accurately hit a target in the middle of the room 10 times per second without affecting or damaging the target attachment.

Fry says that as a partner of the LLNL-led STARFIRE Center, SLAC will contribute to the creation of detailed technical requirements for IFE laser systems that are closely related to those that will be created for the MEC-U project at SLAC.

“The advanced lasers at MEC-U will use a more efficient way to transfer energy to the laser and an advanced cooling scheme to operate at a higher repetition rate. The technologies we have developed and the scientific questions we can answer with them are of interest to IFE.”

Additionally, ultra-bright X-rays from LCLS could help scientists understand what happens to hydrogen fuel during fusion, or what happens to material blown out of a pellet to cause an explosion.

Bringing materials and people to work

In fact, Gleason says, materials played an important role in the development of IFE. “It is very difficult to use lasers for a uniform and spherical explosion of a target, because materials always have defects: on a mesoscale there is a dislocation, defect, chemical heterogeneity, surface roughness, porosity. In short, there are always differences and defects in materials.”

He says one of the things he is very interested in is better understanding the materials involved in IFEs at the atomic level in order to test and develop physical models for specific IFE designs.

“At SLAC we have extraordinary tools for in-depth study of materials. By understanding the physics of defects, we can turn their “imperfections” into features that can be incorporated into their designs; we can have many knobs we can turn as we adjust the compression in the synthesis process”.

Another big challenge that all three researchers want to solve is creating the workforce needed to research and operate the fusion power plants of the future.

Glenzer said the centers include funding to attract students. “We will train the next generation of scientists and technicians to take advantage of these new opportunities.”

Fry and Gleason are also committed to bringing people into the field so that fusion energy can become an inclusive enterprise as it develops.

“We’re going to need engineers, technicians, operators, people in human resources and purchasing, etc.,” Gleason said. “I think a lot of young people can get behind fusion and feel empowered to do something to reverse the climate crisis; they want to see change in their lives.”

Glenzer believes this will happen. “People assumed it would take 30 years to build a fusion power plant, but the recent breakthrough in the ignition system has brought that possibility closer to reality. We have already increased the growth of fusion by 1,000 people during our last 10 years of work at NIF,” he said.

“The potential for clean, equitable and abundant energy sources and the science and technology that comes with the development of fusion power are very exciting.”

LCLS is the user organization of the Ministry of Education and Science. Thermonuclear energy centers were created within the framework of the Inertial Thermonuclear Energy for Scientific and Technological Research (IFE-STAR) program of the Ministry of Energy.