In the future, the "artificial sun" will generate electricity, and the electricity bill will not be expensive, but it will not wait until after 2050

Focus

• 1 Controlled fusion has the potential to produce limitless clean energy with near-zero carbon emissions, without the hazardous radioactive waste associated with today's nuclear fission reactors.
• 2 Scientists predict that when humans learn how to perform nuclear fusion in a controlled and sustained way, electricity will become "cheap enough not to be metered and used at will."
• 3 Scientists expect controlled fusion plants to replace the still active coal-fired power plants first, then oil and gas power plants, and finally nuclear fission power plants.
• 4 Controlled fusion now seems more likely to be a future energy source than it was 10 years ago, but it will still be difficult to achieve in the next 10 to 20 years, so we also need to rely on solar energy, wind energy, nuclear fission energy, etc.

Last December, physicists working on controlled fusion claimed a major breakthrough. A team of researchers at the National Ignition Facility Laboratory (NIF) in California announced that they extracted more energy from a controlled fusion reaction than it triggered it. This is a global first and an important step for physics, but it is still far from the goal of using nuclear fusion as a practical energy source. The high-profile statement sparked an inertial response in the field of fusion research: supporters praised it, opponents questioned.

This fierce antagonistic reaction highlights the high stakes in the field of fusion research. The world increasingly needs abundant clean energy to mitigate the climate crisis caused by burning fossil fuels. Controlled fusion has the potential to produce near-zero carbon emissions without the hazardous radioactive waste associated with today's nuclear fission reactors. Physicists have been working on controlled fusion energy since the 50s of the 20th century, but it is frustrating that converting it into a practical energy source is still far away.

Will controlled fusion become an important source of energy on our energy-scarce planet? If so, will it come in time to help save the planet?

The second question is one of the few in the field with a clear answer. Most experts agree that we are unlikely to generate large-scale energy from controlled fusion before around 2050. Given that the rise in global temperatures this century may depend largely on what we did or did not do with carbon emissions until then, controlled fusion is unlikely to be a "savior."

Omar Hurricane, project leader at Lawrence Livermore National Laboratory, said: "I do think controlled fusion looks more likely to be a future energy source now than it was 10 years ago, but it's still difficult to achieve in the next 10 to 20 years, so we need other solutions." ”

Decarbonization by mid-century will therefore require reliance on other technologies, such as renewable energy sources such as solar and wind power, nuclear fission energy, and perhaps carbon capture. Looking ahead, however, there is every reason to believe that controlled fusion energy will be a key part of the energy economy by the second half of this century, when more developing countries begin to need energy budgets like those of the West. Solving climate change is not something that can be achieved overnight. If we can get through the bottlenecks of the next few decades without radically changing the climate, the road ahead could be smoother.

01 Making stars on Earth and electricity becoming super cheap?

Almost like nuclear fission, controlled fusion is also considered a potential energy source. In late 1945, at a briefing at the Manhattan Project, Italian physicist Enrico Fermi envisioned fusion reactors for power generation. Fermi led the construction of the first fission reactor in Chicago during World War II. A few years later, scientists discovered how to unleash controlled fusion energy, but only in an uncontrolled apocalyptic hydrogen bomb explosion. Some scientists predict that once we learn how to do this in a controlled and sustained way, electricity will become "cheap enough not to require metering."

Figure 1: Nuclear fission and the basic components of controlled nuclear fusion

But the challenge of achieving the goal proved to be much greater than expected. Harriken said, "It's so hard! We're basically making stars on Earth. ”

The fusion of two hydrogen atoms to form helium is the main process that produces huge amounts of energy for the sun and other stars. When this light nucleus combines with each other, it releases a huge amount of energy. But because these nuclei are positively charged, they repel each other and require enormous pressure and temperature to overcome the electrostatic barrier and cause them to fuse. If scientists can control the fusion fuel, including a plasma mixture of deuterium and tritium, two heavy isotopes of hydrogen, the energy released in the reaction can be self-sustaining. But how do you bottle plasma at a temperature of about 100 million kelvins, which is several times higher than the temperature of the center of the sun?

Figure 2: Basic building blocks of the D-T reaction, which uses deuterium and tritium to produce fusion fuel

No known material can withstand such extreme conditions, and even extremely heat-resistant metals such as tungsten can be melted in an instant. For a long time, the favorite solution for reactor design was magnetic confinement: keeping charged plasma in a "magnetic bottle" formed by a strong magnetic field so that it never touched the walls of the fusion chamber. The most popular design is called the tokamak, proposed by Soviet scientists in the 50s of the 20th century, which uses ring-shaped containers.

Figure 3: Basic design of the tokamak reactor

This process requires fine control. The hot plasma does not stand still, it tends to produce large temperature gradients, resulting in strong convection that makes the plasma turbulent and difficult to control. This instability, similar to miniature solar flares, can cause plasma to touch walls, destroying them.

The instability of other plasmas can produce high-energy electron beams that perforate the cladding of the reaction chamber. Suppressing or controlling these fluctuations has always been one of the main challenges faced by tokamak nuclear reactor designers. Steven Cowley, director of the Princeton Plasma Physics Laboratory, said: "The great success of the last 10 years is largely due to the detailed quantitative study of this turbulence. ”

One of the biggest hurdles to magnetically confinement nuclear fusion is the need to withstand rigorously processed materials from fusion plasma. In particular, deuterium-tritium controlled nuclear fusion produces strong streams of high-energy neutrons that collide with nuclei in metal walls and cladding, creating tiny melting points. The metals then recrystallize, but weakened, and the atoms move from their initial positions. In the cladding of a typical controlled fusion reactor, each atom may shift about 100 times during the lifetime of the reactor.

Figure 4: Plasma flows within the target chamber of the National Ignition Device (NIF).

The consequences of such a strong neutron bombardment are unclear, as fusion never lasts as long as needed for a running reactor. Ian Chapman, chief executive of the UK Atomic Energy Agency (UKAEA), said: "We do not know and will not know the degradation and longevity of materials until operating nuclear power plants. ”

However, important insights into these degradation problems may be gleaned from a simple experiment. This experiment produced a strong beam of neutrons that could be used to test materials. Such a facility, based primarily on the particle accelerator project, known as the International Fusion Materials Irradiation Facility, for a demonstration guided neutron source, will begin operations in Granada, Spain, in the early 30s. The U.S. is also interested in building a similar facility, called a fusion prototype neutron source, but it has not yet been approved.

There is no guarantee that these material issues will be resolved. If they prove insurmountable, an alternative is to fabricate reactor walls from liquid metal, which will not be destroyed by melting and recrystallization. But Cowley, director of Princeton's plasma physics laboratory, said that would lead to a host of other technical problems.

Another major challenge is the creation of controlled fusion fuel. Earth is rich in deuterium, an isotope that makes up 0.016% of natural hydrogen, so the oceans are indeed full of deuterium. But tritium naturally forms in small quantities, and its half-life is only 12 years, so it keeps disappearing and must be reproduced. In principle, it can be "bred" from a controlled nuclear fusion reaction, because fusion neutrons react with lithium to form it. Most reactor designs incorporate this gestation process by wrapping a layer of lithium around the reactor chamber. Still, the technique has not been proven on a large scale, and no one really knows whether tritium production and extraction is effective, or how effective it will be.

02 Build a prototype of a controlled nuclear fusion power plant and start the "moon race"

The world's largest controlled fusion project, located in ITER (Latin for "road" in southern France, originally an acronym for "International Thermonuclear Experimental Reactor"), uses a large tokamak with a plasma radius of 6.2 meters, and the entire machine will weigh 23,000 tons. If all goes according to plan, ITER will be the first fusion reactor to demonstrate sustained power output at power plant scale (about 500 megawatts), with the support of countries such as the European Union, the United Kingdom, China, India, Japan, South Korea, Russia and the United States.

Construction of ITER began in 2007 with initial hopes of producing plasma in fusion chambers around 2020, but ITER has suffered multiple delays and the estimated cost of $5.45 billion has quadrupled. In January, the head of the project announced a new setback: the project, which is scheduled to start operations in 2035, could be delayed until around 2040. ITER does not produce commercial electricity, and as its name suggests, it is a strictly experimental machine designed to solve engineering problems and pave the way for viable power plants.

Some see it as a clunky behemoth with no chance of success, and this new hurdle has sparked another round of skepticism about controlled nuclear fusion. But Harriken says such questions are expected. "ITER has taken a lot of hits, but we need to give them a breather and let them figure things out," he said. ”

Chapman agreed. "Predictably, there will be problems both politically and technically," he said. This project is doing amazing things, including building a supply chain that didn't exist before. He acknowledged that the delay was disappointing, "but I don't think we'd think it was a mistake when we look back at ITER." We would consider it very important in the origin of controlled nuclear fusion. I believe it works. ”

Tokamak nuclear reactors used to generate electricity probably don't need to be as large as ITER, and certainly not as expensive as ITER. Recently, there has been growing interest in smaller spherical units, one of which is called Spherical Tokamak Energy Production (STEP), which the UK IAEA UKAEA plans to use as a pilot power plant to be developed in parallel with ITER.

Figure 5: Design and scale of STEP and ITER reactors

The spherical design concept has been proof-of-principle with a spherical tokamak device called the Mega Amere. The installation operated between 1999 and 2013 and was jointly supervised by UKAEA and EURATOM. These smaller machines have a higher energy density and therefore a greater risk of thermal damage, especially from the "exhaust" system. An improved version, MAST Upgrade, was launched in 2020 and is capable of extracting heat about 20 times more efficiently than the original version. Chapman said: "This really opened the way for the idea of compact power plants. ”

STEP's goal is to build a prototype power plant that produces net electricity. It's still in the conceptual design stage, but the UK government has already begun to set regulations for the project, the world's first controlled fusion project, eliminating the need for a traditional nuclear license. In October, world leaders selected a coal-fired power station in northern England, which ceased operations in March and is scheduled to be dismantled in early 2024. The base already has a cooling water supply and is connected to the national grid and railway system.

Figure 6: At the International Thermonuclear Experimental Reactor (ITER) site, a polar field coil is being tested with six ring magnets that will guide the plasma in the experiment

The EU is planning its own prototype fusion power plant, called a demonstration nuclear power plant (DEMO), managed by the European Fusion Alliance (EUROFusion), with the goal of generating between 200 megawatts and 500 megawatts of electricity. Tony Donné, project manager for controlled fusion in Europe, said construction could begin in the early 21st 40s and "I believe we can build such a device in 10 years."

Downer added that South Korea, Japan and China have similar controlled fusion power plant "stepping stone" projects, and the United States plans to build a smaller device called a fusion nuclear science facility. Chapman said: "China got involved a little late, but now it is investing heavily and rapidly expanding its research and development team. It is definitely catching up with Europe and the United States. Downer believes that a "moon race" to prototype controlled fusion power plants could be beneficial as long as countries continue to share information.

03 A large number of start-ups have emerged, and the supply chain has gradually improved

Controlled nuclear fusion is not all large national and international projects, and small spherical tokamak devices are one of the technologies that will bring controlled nuclear fusion into the hands of private companies. Dozens of controlled fusion startups have sprung up around the world, such as Federal Fusion Systems (CFS) in Massachusetts, General Fusion in Canada and Tokamak Energy in the UK.

With the support of the IAEA, General Fusion has just begun construction of a demonstration power plant and hopes to be operational by 2025. According to the company's former CEO, Christofer Mowry, this will be "the first large-scale controlled nuclear fusion demonstration associated with a power plant."

Meanwhile, CFS, in collaboration with MIT's Center for Plasma Science and Fusion (PSFC) and other institutions, is building a prototype device called SPARC, which is also scheduled for completion in 2025. SPARC will be a medium-sized tokamak device in which the plasma is tightly confined by the strong magnetic field generated by a new HTS magnet developed at MIT and launched in 2021. This magnet is hailed as an important step in magnetic confinement fusion, as the power density in the plasma increases rapidly as the magnetic field strength increases.

The SPARC team's goal is to extract net energy from the plasma (about 10 times the energy output) and generate fusion energy from 50 megawatts to 140 megawatts. Although SPARC is much smaller than ITER, PSFC director Dennis Whyte says their mission is similar: to solve the scientific and technical problems that hinder the commercialization of controlled fusion. It won't feed any electricity into the grid, but it aims to clear the way for the "affordable, robust and compact" fusion reactor concept developed at MIT and promoted by CFS (Cauley's "most influential company to date").

Cauley welcomed such projects, but cautioned against seeing them as shortcuts to turning controlled fusion into a real energy source. "We're seeing a lot of enthusiasm from these startups, and a lot of them are focused on a particular part of the problem," he says. "It's unlikely that either company will commercialize controlled fusion energy technology before the giants, and many companies may give up halfway." But Chapman believes that other companies will become suppliers of valuable expertise and specialized components such as magnets, and that "most small controlled fusion companies will eventually become part of the supply chain."

04 Different designs

Devices for magnetic confinement of nuclear fusion are not necessarily limited to tokamaks. In the 50s of the 20th century, astrophysicist Lyman Spitzer thought that plasma might be more efficiently contained in annular cavities with twisted tunnel walls. With this configuration, the device can confine the plasma using the magnetic field generated by the flow of the charged plasma itself.

Figure 7: Basic design of a stellar reactor

The more complex geometry of this design, known as the Stellarator, is tricky to engineer, but several projects are trying to perfect it. A notable example is the Wendelstein 7-X sellarator in Greifswald, Germany, which was completed in 2015 and is now operational again after three years of upgrades.

Tony Donner, European fusion project manager, said: "The stellar has many advantages, but technically it is a more complex device. In Europe, we are working on a stellarator as a backup for the tokamak. "The technology is still in its relatively early stages, so if such backups prove essential, the timeline for actual controlled fusion could be pushed back again."

The National Ignition Facility Laboratory (NIF) has a completely different approach to all these projects. Instead of using a large amount of plasma limited by a magnetic field, the NIF experiment ignited deuterium and tritium. In this case, after the experiment triggers controlled fusion by suddenly squeezing the fuel and heating it intensely, the fusing plasma can only briefly remain in place by its own inertia. This scheme is called inertial confinement nuclear fusion.

NIF creates these extreme conditions by focusing a very strong laser beam on a pellet-like target. Before the hot plasma expands, fusion energy is released in a brief burst. Therefore, this energy production will be carried out in a pulsed manner, and the fuel capsules must be continuously moved one after the other to the reaction chamber for ignition. Most researchers estimate that for this method to become a reality, the capsules would have to be changed about 10 times per second.

Figure 8: Design and size of an inertial confinement fusion target in an NIF experiment

The challenge of inertial confinement nuclear fusion is daunting, and only a handful of facilities in the world are currently working on it. In addition to the largest NIF, there are France's Megajoule Laser facility and China's Shenguang-3 laser facility, which Russia could also take, but details are hard to pinpoint. Generating electricity is not actually a major part of NIF's mission; the facility is primarily designed to trigger a nuclear response to research and maintain the U.S. stockpile of nuclear weapons. Harriken said: "The main work of the NIF is entirely funded by the US national security agency, this is not a fusion reactor, nor is it intended to demonstrate any real sense of fusion energy. ”

Much remains to be done to make inertial confinement fusion a true competitor for energy supply. Tammy Ma, director of NIF's Inertial Fusion Energy Program, said: "The focus of this work is mainly on basic science, and we haven't put as much effort into the supporting technology needed for power plants. ”

05Nuclear fusion power plants will be built in ten years?

Given the diversity of controlled fusion projects, how far away is the truly operational controlled fusion energy? Chapman put it bluntly: "There is no ongoing project at the moment to build fusion power plants capable of generating energy. ”

And a true fusion power plant (not just a prototype) could take about a decade to build. Chapman said: "The experiment is progressing, and the progress is impressive. But controlled fusion will not be available as a primary energy source for at least a few years. Downer was even more blunt: "If someone tells me that they will have a controllable fusion reactor in operation in the next 5 or 10 years, they are either completely ignorant or liar." ”

Predicting when controlled fusion energy will arrive has always been difficult, but experts now mostly agree on a rough timeline. "Let's say we build a pilot fusion power plant in the late 21st century, and while there may be some progress, such a power plant is unlikely to be a blueprint for commercialization," Cowley said. So I think it will take about 10 years from a pilot power plant to the first commercial reactor. Chapman agrees that controlled fusion power plants could supply power to the grid by around 2050, and then steadily increase their importance to the energy economy in the second half of this century, especially after 2060.

Controlled fusion power plants may be about the size of today's fossil fuel or nuclear fission plants, but will output hundreds of billions of watts of electricity. This means that they can be built in the same place to replace nuclear fission with controlled fusion, and all the necessary grid infrastructure is already in place. "You could say that fusion is easily plugged in and replaces fossil fuels or nuclear fission, and that could be a very smooth transition," Downer said. He expects controlled fusion plants to replace the still-active coal-fired power plants first, then oil and gas plants, and finally nuclear fission plants.

Figure 9: Part of a plasma distortion vessel for the Wendelstein 7-X stellarator nuclear fusion experiment

Even if controlled fusion doesn't get us out of the current climate crisis, it may be the best option to meet our energy needs in the long run without destroying the planet. Lev Artsimovich, the "father of the tokamak" and Soviet fusion dreamer, once said that nuclear fusion will occur whenever the world decides it needs it.

Chapman said: "When we realize that climate change will be an existential threat, the emergence of nuclear fusion will accelerate dramatically. He compared the situation to the rapid development of a coronavirus vaccine. Currently, there simply is simply no other long-term way to achieve net-zero carbon emissions, especially since global energy demand is expected to triple between 2050 and 2100. To meet this need, Chapman said, "nuclear fusion is essential." Renewable energy sources such as wind and solar will certainly play a role, but they may not be enough, Downer said.

Building a new type of energy infrastructure from scratch presents both opportunities and challenges. Nuclear fission planners made some serious mistakes in design and public relations, but now the nascent fusion industry has an opportunity to learn from these mistakes and do better, especially when considering issues of energy equity and justice.

Tammy Ma, director of the NIF Inertial Fusion Energy Project, asked: "When we have these power plants, where do we put them to provide clean energy to all types of communities? How do we build a diverse workforce? How do we ensure that while building this industry, we are training people for the skills of the future? This time, we must at least try to get things done. (Golden Deer)