In December, scientists at Lawrence Livermore National Laboratory achieved a major fusion milestone by igniting a fusion reaction that produced more energy than was used to trigger it for a brief moment. The achievement is a watershed moment for fusion research, which has produced thermonuclear weapons for more than 70 years but still has no reactor that can generate electrical power.
Controlled fusion poses formidable scientific and engineering challenges. But what does the experiment at LLNL’s National Ignition Facility, or NIF, mean for science and the dream of a new energy source that will power our homes and cars while emitting no CO2? In short, it’s a big deal worth celebrating, but it doesn’t portend a green energy revolution. It will still be years, if not a decade before fusion power progress bears fruit, and it is still unclear whether fusion will ever be cheap enough to radically transform our power grid. Continuing current solar and wind investments is critical to combating climate change. Here’s a look at what’s happened so far and what’s to come.
What is fusion?
Fusion happens when two lighter elements, such as hydrogen or helium, combine to form a single, heavier element. This nuclear reaction generates a large amount of energy, as demonstrated by the sun, the world’s largest fusion furnace. However, fusion is more difficult to achieve on Earth because atomic nuclei are positively charged and thus repel each other.
The enormous mass of the sun generates tremendous pressure, which overcomes the repulsion, but on Earth, other forces are required. There are two broad approaches to fusion: inertial confinement and magnetic confinement. Inertial confinement typically employs high-powered lasers to zap a pellet, resulting in an explosion that compresses the fusion fuel.
That is the method employed by NIF. The other method employs magnetic fields. It is more common among companies attempting to commercialize fusion energy.
What did the NIF experiment achieve?
It passed a critical fusion threshold when the energy generated by the fusion reaction — 3.15 million joules — exceeded the 2.05 megajoules pumped out by the lasers to start the reaction. The ratio of output energy to input energy is denoted by the letter Q by fusion researchers, and this is the first time a fusion reaction has exceeded Q = 1. Before energy generation is feasible, fusion reactors must achieve a Q = 10 threshold. That is what everyone is aiming for, including another massive government-funded project in France called ITER.
Furthermore, fusion reactors will have to achieve Q = 10 much more frequently than NIF. In some ways, it represents an academic milestone, one that fusion experiments have been working toward for decades. However, given fusion’s reputation for never arriving, it’s an important demonstration of what’s possible. Think twice before repeating the oft-quoted snide remark that fusion is and always will be the energy source of the future.
What does the NIF experiment mean for renewable energy?
For a variety of reasons, it is not a large sum. For starters, most commercial fusion energy projects use magnetic confinement rather than NIF’s laser-based approach, so the engineering challenges are different. For another, NIF is a massive $3.5 billion national lab project funded to research nuclear weapons, not to produce reliable energy for the grid at the lowest possible cost.
“Don’t expect future fusion plants to resemble NIF,” Princeton researcher Wilson Ricks tweeted. Because of massive inefficiencies in NIF’s lasers and the conversion of fusion heat to electrical power, its design is inherently impractical.” Magnetic confinement fusion holds some real promise,” he tweeted in comparison. Lowering the cost of fusion is critical to its success because it will have to compete with zero-carbon alternatives such as today’s fission-based nuclear reactors, which can generate a steady supply of power, and renewables such as wind and solar, which are less expensive but intermittent.”Fusion’s first competitor is fission,” researchers at the Princeton Plasma Physics Laboratory concluded in an unpublished October research paper assessing fusion’s prospects on the electrical grid. They believe that if the high costs of fusion can be reduced sufficiently, it will be able to replace the need for future fission plants and, if further reduced, will be able to compete with the combination of solar and energy storage. NIF is a large and complex website. Production costs should fall if fusion power plants can be built in cheaper, smaller units that look more like something off a factory line. This is due to a phenomenon known as Wright’s Law, also known as the experience curve or the learning curve, which has steadily reduced the cost of solar and wind energy. The larger and more customized a fusion plant, the lower the costs and the less competitive fusion.
Are there any indirect benefits from NIF’s findings?
Yes.
Scientists could benefit from the NIF experiment by updating fusion physics models to account for the fact that it generates its own heat rather than relying on external sources, according to Andrew Holland, CEO of the Fusion Industry Association, an industry advocacy group. And the attention could also help, given the long-standing skepticism about fusion energy.TAE Technologies CEO Michl Binderbauer called NIF’s results “a huge stepping stone into the dawn of the fusion age,” and said they demonstrate that fusion energy is a real possibility. Investors have taken notice as well. Downloads of the Fusion Industry Association’s annual report, which details the $4.8 billion in venture capital investments in fusion energy startups, have more than tenfold increase since the NIF achievement was announced, according to Holland. He added that many of those requesting it are from investment firms.
At NIF, how does fusion work?
The NIF uses 192 powerful infrared lasers with a combined energy level of 4 megajoules — roughly the same as a two-ton truck traveling at 100mph. This is converted into 2 megajoules of ultraviolet light, which is then converted into X-rays, which strike a peppercorn-sized pellet of fusion fuel. The intense X-rays cause the pellet’s outer layer to explode, compressing the pellet interior and triggering fusion. The heat produced by the fusion keeps the reaction going until it runs out of fuel or becomes lopsided and falters.
Nuclei? Hydrogen? Please refresh my knowledge of atomic physics.
Everything on Earth is made up of tiny atoms that each have a central nucleus and a cloud of negatively charged electrons. Neutrons and positively charged protons make up the nucleus. The heavier the element, the more protons there are in the nucleus.
Hydrogen typically consists of one proton and one electron. A neutron is also present in an unusual variety known as deuterium and using nuclear or fusion reactors, a third variety known as tritium with two neutrons can be created. When positive and electrical charges cause atoms to interact, chemical reactions such as iron rusting or wood burning occur. Nuclear reactions, on the other hand, occur when the nuclei of atoms split apart or join together. On Earth, it is more difficult to gather the necessary forces to cause nuclear reactions, which is why it is easier to build a steam engine than a nuclear bomb. When atoms are sufficiently heated, they become so energetic that the electrons are liberated. The resulting cloud of negatively charged electrons and positively charged nuclei is known as plasma, a more exotic state of matter than the solids, liquids, and gases we’re used to seeing at room temperature. Plasma makes up the sun, and fusion reactors require it to get those hydrogen nuclei to bounce around energetically enough. The ability of plasmas’ electrically charged particles to be manipulated with magnetic fields is a useful property. This is critical in the design of many fusion reactors.
What kind of fusion fuel do you use?
NIF and most other fusion projects use DT fuel, which is made up of two heavy forms of hydrogen, deuterium, and tritium. However, there are other options, such as hydrogen-boron and deuterium-helium-3, a type of helium with one neutron rather than the more common two. To fuse deuterium and tritium, a plasma must be heated to a whopping temperature of about 100 million degrees Celsius (180 million degrees Fahrenheit). Other reactions have even higher temperatures, such as hydrogen-boron fusion, which can reach billions of degrees. Deuterium can be extracted from ordinary water, but tritium, which decays radioactively over a few years, is more difficult to obtain. It can be produced in nuclear reactors and, in theory, future fusion reactors. However, managing tritium is complicated because it is used to boost nuclear weapon explosions and thus must be carefully controlled.
How do you convert that fusion reaction into energy?
Deuterium-tritium fusion generates fast-moving single neutrons. The kinetic energy of the neutrons can be captured in a “blanket” of liquid that surrounds the fusion reactor chamber and heats up as they collide. This heat is then transferred to water, which boils and powers standard steam turbines. Although that technology is well understood, it has yet to be linked to a fusion reactor. Indeed, today’s first generation of fusion power reactors are designed to exceed Q=1, but not to capture power. That will have to wait until the pilot plants arrive in the next wave of development.
What distinguishes fusion from fission?
The opposite of fusion is fission, which powers today’s nuclear reactors. Heavy elements, such as uranium, split apart into lighter elements during fission, releasing energy in the process.
For decades, humans have been able to achieve fusion using thermonuclear weapons. These designs slam uranium or plutonium together to cause a fission explosion, which provides the enormous energy required to start the secondary and more powerful fusion reaction. The process happens in a fraction of a second in bombs, but for energy production, fusion must be controlled and sustained.
Is there radioactive waste produced by fusion reactors?
Yes, in general, but not nearly as much as with fission reactors. For starters, the majority of radioactive emissions are short-lived alpha particles — helium nuclei with two protons and two neutrons — that are easily blocked. The fast-moving neutrons can collide with other materials, resulting in the formation of new radioactive materials. The neutron output of fusion reactors generally degrades components, necessitating periodic replacement that may necessitate downtime lasting a few months every few years. It is, however, far more manageable than the high-level nuclear waste generated by fission power plants. Hydrogen-boron fusion is more difficult to achieve than deuterium-tritium fusion, but it has the advantage of not producing neutrons or other radioactive materials.TAE Technologies is the most visible company taking this approach.
What are the dangers of fusion power?
Fusion power plants do not face the meltdown risks that have plagued fission reactors such as those at Fukushima and Chornobyl. When a fusion reaction fails, it simply fizzles out. However, there are still significant operational issues at major industrial sites, such as a lot of electrical power and high-pressure steam. In other words, the major issues are more akin to those encountered at an industrial site than at today’s fission nuclear power plants. So there are real benefits to fusion.NIF contributes to demonstrating that fusion energy has a future. However, there is still a long way to go.