Laser-Driven Nuclear Fusion

It wasn't just 3.15 megajoules (MJ) of fusion energy: what happened in the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) at the start of December was also redemption. Since the 1960s, the LLNL has pursued the hypothesis that the fusion of two light nuclei into one heavy nucleus can be triggered by laser. After more than 60 years, the experiment on December 5, 2022, confirmed that the continuous development of the lasers, optics, computer models, simulations, and the fusion “fuel” was not a waste of time. For the first time ever, the U.S. team were able to generate more energy from fusion reactions than they used to start the process. The researchers used lasers to direct 2.05 MJ of energy onto a pellet filled with the hydrogen isotopes deuterium and tritium, which then released 3.15 MJ of fusion energy.

By its own account, the LLNL in Livermore, California, operates the largest and most powerful laser system in the world in the NIF. It is housed in a hall the size of a sports arena. The excited pellet was subject to temperatures and pressures that would otherwise be found only in the cores of stars. During the fusion, the temperatures rose to more than 120 million degrees Celsius. To trigger the process, the LLNL team uses giant pulsed lasers to direct UV light into a “cavity” with gold-coated inner walls where X-rays form and are evenly distributed. The pellet, filled with deuterium and tritium, heats up rapidly in this “X-ray furnace”. Its shell cannot withstand the temperatures and it bursts. The resulting implosion pressure compresses the hydrogen fuel enormously, which, in combination with the high temperatures, triggers the fusion of hydrogen to helium—and the release of energy. A chain reaction is not possible because the pressure and high temperatures in the reactor shift important parameters so that the remaining fuel no longer fuses.

More and more players—a long way to market readiness

Despite the recent breakthrough, there is still a long way to go before power can be generated commercially using nuclear fusion. The NIF is a USD 3.5 billion large-scale research facility in which the U.S. government is investing another USD 624 million to spur development there. The facility contains thousands of special optics that direct the energy of the laser systems onto the target in the cavity. In addition to the fact that the setup is too complex for commercial purposes, the frequency of the ignitions to date also speaks against market readiness in the near future. According to Professor Constantin Häfner, who was head of the Advanced Photon Technologies Program at the NIF until 2019, before becoming head of the Fraunhofer Institute for Laser Technology ILT in Aachen, Germany, the NIF is ignited once per day within the framework of the research. For commercial power generation, this frequency would have to be more in the range of a dozen ignitions per second. This would require highly reliable and fully automated processes to supply the reaction with the fuel pellets and to continuously dispose of any reaction residues, more compact laser systems and optics, and an efficient infrastructure to generate electricity with the released energy.

There are now dozens of companies, startups, as well as several large-scale scientific facilities in Europe and Asia dedicated to fusion research. The increasing number of players could accelerate the upcoming development—and make zero-emission nuclear fusion an important tool in the battle against climate change. Häfner believes that photonics will take on the enabler role. “Assuming that in 2050 we put several fusion power plants into operation each year so that inertial confinement fusion can contribute to the power supply—we would have to produce many hundreds of powerful lasers the size of overseas containers,” he explains. “We need to completely rethink laser and optics production and build automated production lines like in the automotive industry; but with the precision of just a few optical wavelengths.”

Impetus for innovations in photonics

The expert outlines requirements for amplifier media, optics, coatings, crystals at low costs suitable for the mass market, and for highly automated process chains. There are many complex challenges on the way to generating energy by nuclear fusion, which now need to be addressed. He assumes that an innovation spiral can be set in motion here. Innovations for fusion research would result in new solutions for other markets—and thus pay for themselves quickly. His advice to companies: “Fusion energy is an undertaking with a lot at stake. As such, it is a good strategy to get started and pursue the most promising approaches. The race is on.”