George R. Tynan and Farhat Beg: The way scientists think about nuclear fusion changed forever in 2022, when what some called the experiment of the century first showed that nuclear fusion could be a viable source of clean energy.
The experiment, at Lawrence Livermore National Laboratory, showed inflammation: a fusion reaction that generated more energy than was put in.
Moreover, recent years have been marked by a multi-billion dollar windfall of private investment in this area, especially in the United States.
But a host of technical challenges must be addressed before fusion can be scaled up to become a safe, affordable source of virtually unlimited clean energy. In other words, it’s engineering time.
As engineers who have been involved in fundamental science and applied engineering in nuclear fusion for decades, we have seen much of the science and physics of nuclear fusion mature over the past decade.
But to make fusion a viable source of commercial power, engineers must now tackle a host of practical challenges. Whether the United States will seize this opportunity and become a global leader in fusion energy will depend in part on the extent to which the country is willing to invest in solving these practical problems – especially through public-private partnerships.
Building a fusion reactor
Fusion occurs when two types of hydrogen atoms, deuterium and tritium, collide under extreme conditions. The two atoms literally fuse into one atom by heating up to 100 million degrees Celsius, ten times hotter than the core of the sun. To enable these responses, fusion energy infrastructure will have to withstand these extreme conditions.
There are two approaches to achieving fusion in the laboratory: inertial fusion, which uses powerful lasers, and magnetic confinement, which uses powerful magnets.
While the ‘experiment of the century’ used inertial fusion, magnetic confinement has yet to demonstrate that it can break even in terms of power generation.
Several privately funded experiments aim to achieve this feat later this decade, and a large, internationally supported experiment in France, ITER, also hopes to break even by the end of 2030. Both use magnetic confinement fusion.
Challenges ahead
Both approaches to nuclear fusion share a set of challenges that will not be cheap to overcome. For example, researchers must develop new materials that can withstand extreme temperatures and irradiation conditions.
Fusion reactor materials also become radioactive when bombarded with high-energy particles. Researchers must design new materials that can decay within a few years to levels of radioactivity that can be removed safely and more easily.
Producing sufficient fuel, and doing so sustainably, is also an important challenge. Deuterium is abundant and can be extracted from plain water.
But ramping up production of tritium, which is usually produced from lithium, will prove much more difficult. A single fusion reactor requires hundreds of grams to one kilogram of tritium per day to function.
Currently, conventional nuclear reactors produce tritium as a byproduct of fission, but these cannot supply enough to maintain a fleet of fusion reactors.
Engineers will therefore have to develop the ability to produce tritium in the fusion device itself. This may involve covering the fusion reactor with lithium-containing material, which is converted into tritium through the reaction.
To scale up inertial fusion, engineers will need to develop lasers capable of repeatedly hitting a fusion fuel target made of frozen deuterium and tritium several times per second.
But so far, no laser is powerful enough to do this at that rate. Engineers will also need to develop control systems and algorithms that aim these lasers at the target with extreme precision.
Furthermore, engineers will need to scale up target production by orders of magnitude: from a few hundred handmade targets per year with a price tag of hundreds of thousands of dollars each, to millions costing just a few dollars each.
Magnetic containment will require engineers and materials scientists to develop more effective methods to heat and control the plasma, and more heat- and radiation-resistant materials for reactor walls. The technology used to heat and confine the plasma until the atoms fuse must function reliably for years.
These are some of the big challenges. They are heavy, but not insurmountable.
Current financing landscape
Investments from private companies around the world have increased – these are likely to remain an important factor driving fusion research forward. Private companies have attracted more than $7 billion in private investment over the past five years.
Several startups are developing different technologies and reactor designs with the aim of adding fusion to the electricity grid in the coming decades. Most are located in the United States, some in Europe and Asia.
While private sector investment has grown, the U.S. government continues to play a key role in the development of fusion technology to date. We expect this to remain the case in the future.
It was the US Department of Energy that invested approximately $3 billion in the mid-2000s to build the National Ignition Facility at Lawrence Livermore National Laboratory, where the “experiment of the century” took place twelve years later.
In 2023, the Department of Energy announced a four-year, $42 million program to develop fusion hubs for the technology. While this funding is important, it will likely not be sufficient to solve the key challenges that remain for the United States to emerge as a world leader in practical fusion energy.
One way to build partnerships between the government and private companies in this area could be to create relationships similar to those between NASA and SpaceX.
As one of NASA’s commercial partners, SpaceX receives both government and private funding to develop technology that NASA can use. It was the first private company to send astronauts to space and the International Space Station.
Like many other researchers, we are cautiously optimistic. New experimental and theoretical results, new tools and private sector investments all contribute to our growing realization that developing practical fusion energy is no longer an ‘if’, but a ‘when’.
George R. Tynan, Professor of Mechanical and Aerospace Engineering, University of California, San Diego and Farhat Beg, Professor of Mechanical and Aerospace Engineering, University of California, San Diego
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