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NUCLEAR FUSION: HOW CLOSE ARE WE TO CLEAN LIMITLESS ENERGY?

In a world struggling to kick its addiction to fossil fuels and feed its growing appetite for energy, there’s one technology in development that almost sounds too good to be true: nuclear fusion.

If it works, fusion power offers vast amounts of clean energy with a near limitless fuel source and virtually zero carbon emissions. That’s if it works. But there are teams of researchers around the world and billions of dollars being spent on making sure it does.

In February last year a new chapter of fusion energy research commenced with the formal opening of Wendelstein 7-X. This is an experimental €1 billion (A$1.4bn) fusion reactor built in Greifswald, Germany, to test a reactor design called a stellarator.

It is planned that by around 2021 it will be able to operate for up to 30 minutes duration, which would be a record for a fusion reactor. This is an important step en-route to demonstrating an essential feature of a future fusion power plant: continuous operation.

But the W-7X isn’t the only fusion game in town. In southern France ITER is being built, a $US20 billion (A$26.7bn) experimental fusion reactor that uses a different design called a tokamak. However, even though the W-7X and ITER employ different designs, the two projects complement each other, and innovations in one are likely to translate to an eventual working nuclear fusion power plant.

Twists and turns

Fusion energy seeks to replicate the reaction that powers our Sun, where two very light atoms, such as hydrogen or helium, are fused together. The resulting fused atom ends up slightly lighter than the original two atoms, and the difference in mass is converted to energy according to Einstein’s formula E=mc².

Here you can see the twist in the plasma within a tokamak. CCFE

The difficulty comes in encouraging the two atoms to fuse, which requires them to be heated to millions of degrees Celsius. Containing such a superheated fuel is no easy feat, so it’s turned into a hot ionised gas – a plasma – which can be contained within a magnetic field so it doesn’t actually touch the inside of the reactor.

What makes the W-7X particularly interesting is its stellarator design. It comprises a vacuum chamber embedded in a magnetic bottle created by a system of 70 superconducting magnet coils. These produce a powerful magnetic field for confining the hot plasma.

Stellarators and tokamaks are both types of toroidal (doughnut-shaped) magnetic confinement devices that are being investigated for fusion power. In these experiments a strong toroidal (or ring) magnetic field creates a magnetic bottle to confine the plasma.

However, in order for the plasma to have good confinement in the doughnut-shaped chamber, the magnetic field needs to have a twist. In a tokamak, such as in the ITER reactor, a large current flows in the plasma to generate the required twisted path. However, the large current can drive “kink” instabilities, which can cause the plasma to become disrupted.

If the plasma is disrupted, the reactor needs to be flooded with gas to quench the plasma and prevent it from damaging the experiment.

A complex array of magnets keep the plasma (illustrated in pink) contained. IPP

In a stellarator, the twist in the magnetic field is obtained by twisting the entire machine itself. This removes the large toroidal current, and makes the plasma intrinsically more stable. The cost comes in the engineering complexity of the field coils and reduced confinement, meaning the plasma is less easily contained within the magnetic bubble.

Come together

While the W7-X and ITER use different approaches, most of the underlying technology is identical. They are both toroidal superconducting machines, and both use external heating systems such as radio frequency and neutral beam injection to heat the plasma, and much of the plasma diagnostic technology is in common.

In a power plant, heavy isotopes of hydrogen (deuterium and tritium) fuse to form helium along with an energetic neutron. While the helium is contained within the plasma, the neutron is has a neutral electric charge, and shoots off into the “blanket” surrounding the plasma. This heats it up, which in turn drives a steam turbine that generates electricity.

Bringing the Wendelstein 7-X from concept to reality.

A common feature across fusion power is the need to develop materials that can withstand the high heat and fast neutrons generated by the fusion reaction. Regardless of design, the first wall of a fusion reactor has to withstand a massive bombardment from high energy particles throughout its lifetime.

At this stage, it’s too early to tell whether the tokamak design used by ITER or the stellarator used by W-7X will be better suited for a commercial fusion power plant. But the commencement of research operation of W-7X will not only help decide which technology might be best to pursue, but will contribute valuable knowledge to any future fusion experiments, and perhaps one day a true energy revolution.

Matthew Hole, Senior Research Fellow, Plasma Research Laboratory, Australian National University

This article was originally published on The Conversation. Read the original article.

For centuries, humans have dreamed of harnessing the power of the sun to energize our lives here on Earth. But we want to go beyond collecting solar energy, and one day generate our own from a mini-sun. If we’re able to solve an extremely complex set of scientific and engineering problems, fusion energy promises a green, safe, unlimited source of energy. From just one kilogram of deuterium extracted from water per day could come enough electricity to power hundreds of thousands of homes.

Since the 1950s, scientific and engineering research has generated enormous progress toward forcing hydrogen atoms to fuse together in a self-sustaining reaction – as well as a small but demonstrable amount of fusion energy. Skeptics and proponents alike note the two most important remaining challenges: maintaining the reactions over long periods of time and devising a material structure to harness the fusion power for electricity.

As fusion researchers at the Princeton Plasma Physics Lab, we know that realistically, the first commercial fusion power plant is still at least 25 years away. But the potential for its outsize benefits to arrive in the second half of this century means we must keep working. Major demonstrations of fusion’s feasibility can be accomplished earlier – and must, so that fusion power can be incorporated into planning for our energy future.

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Unlike other forms of electrical generation, such as solar, natural gas and nuclear fission, fusion cannot be developed in miniature and then be simply scaled up. The experimental steps are large and take time to build. But the problem of abundant, clean energy will be a major calling for humankind for the next century and beyond. It would be foolhardy not to exploit fully this most promising of energy sources.

Why fusion power?

image-20161128-22732-1e9j6q6.jpg

Adding heat to two isotopes of water can result in fusion. American Security Project, CC BY-ND

In fusion, two nuclei of the hydrogen atom (deuterium and tritium isotopes) fuse together. This is relatively difficult to do: Both nuclei are positively charged, and therefore repel each other. Only if they are moving extremely fast when they collide will they smash together, fuse and thereby release the energy we’re after.

This happens naturally in the sun. Here on Earth, we use powerful magnets to contain an extremely hot gas of electrically charged deuterium and tritium nuclei and electrons. This hot, charged gas is called a plasma.

The plasma is so hot – more than 100 million degrees Celsius – that the positively charged nuclei move fast enough to overcome their electrical repulsion and fuse. When the nuclei fuse, they form two energetic particles – an alpha particle (the nucleus of the helium atom) and a neutron.

Heating the plasma to such a high temperature takes a large amount of energy – which must be put into the reactor before fusion can begin. But once it gets going, fusion has the potential to generate enough energy to maintain its own heat, allowing us to draw off excess heat to turn into usable electricity.

Fuel for fusion power is abundant in nature. Deuterium is plentiful in water, and the reactor itself can make tritium from lithium. And it is available to all nations, mostly independent of local natural resources.

Fusion power is clean. It emits no greenhouse gases, and produces only helium and a neutron.

It is safe. There is no possibility for a runaway reaction, like a nuclear-fission “meltdown.” Rather, if there is any malfunction, the plasma cools, and the fusion reactions cease.

All these attributes have motivated research for decades, and have become even more attractive over time. But the positives are matched by the significant scientific challenge of fusion.

Progress to date

The progress in fusion can be measured in two ways. The first is the tremendous advance in basic understanding of high-temperature plasmas. Scientists had to develop a new field of physics – plasma physics – to conceive of methods to confine the plasma in strong magnetic fields, and then evolve the abilities to heat, stabilize, control turbulence in and measure the properties of the superhot plasma.

Related technology has also progressed enormously. We have pushed the frontiers in magnets, and electromagnetic wave sources and particle beams to contain and heat the plasma. We have also developed techniques so that materials can withstand the intense heat of the plasma in current experiments.

It is easy to convey the practical metrics that track fusion’s march to commercialization. Chief among them is the fusion power that has been generated in the laboratory: Fusion power generation escalated from milliwatts for microseconds in the 1970s to 10 megawatts of fusion power (at the Princeton Plasma Physics Laboratory) and 16 megawatts for one second (at the Joint European Torus in England) in the 1990s.

A new chapter in research

Now the international scientific community is working in unity to construct a massive fusion research facility in France. Called ITER (Latin for “the way”), this plant will generate about 500 megawatts of thermal fusion power for about eight minutes at a time. If this power were converted to electricity, it could power about 150,000 homes. As an experiment, it will allow us to test key science and engineering issues in preparation for fusion power plants that will function continuously.

ITER employs the design known as the “tokamak,” originally a Russian acronym. It involves a doughnut-shaped plasma, confined in a very strong magnetic field, which is partly created by electrical current that flows in the plasma itself.

Though it is designed as a research project, and not intended to be a net producer of electric energy, ITER will produce 10 times more fusion energy than the 50 megawatts needed to heat the plasma. This is a huge scientific step, creating the first “burning plasma,” in which most of the energy used to heat the plasma comes from the fusion reaction itself.

ITER is supported by governments representing half the world’s population: China, the European Union, India, Japan, Russia, South Korea and the U.S. It is a strong international statement about the need for, and promise of, fusion energy.

The road forward

From here, the remaining path toward fusion power has two components. First, we must continue research on the tokamak. This means advancing physics and engineering so that we can sustain the plasma in a steady state for months at a time. We will need to develop materials that can withstand an amount of heat equal to one-fifth the heat flux on the surface of the sun for long periods. And we must develop materials that will blanket the reactor core to absorb the neutrons and breed tritium.

The second component on the path to fusion is to develop ideas that enhance fusion’s attractiveness. Four such ideas are:

1) Using computers, optimize fusion reactor designs within the constraints of physics and engineering. Beyond what humans can calculate, these optimized designs produce twisted doughnut shapes that are highly stable and can operate automatically for months on end. They are called “stellarators” in the fusion business.

2) Developing new high-temperature superconducting magnets that can be stronger and smaller than today’s best. That will allow us to build smaller, and likely cheaper, fusion reactors.

3) Using liquid metal, rather than a solid, as the material surrounding the plasma. Liquid metals do not break, offering a possible solution to the immense challenge how a surrounding material might behave when it contacts the plasma.

4) Building systems that contain doughnut-shaped plasmas with no hole in the center, forming a plasma shaped almost like a sphere. Some of these approaches could also function with a weaker magnetic field. These “compact tori” and “low-field” approaches also offer the possibility of reduced size and cost.

Government-sponsored research programs around the world are at work on the elements of both components – and will result in findings that benefit all approaches to fusion energy (as well as our understanding of plasmas in the cosmos and industry). In the past 10 to 15 years, privately funded companies have also joined the effort, particularly in search of compact tori and low-field breakthroughs. Progress is coming and it will bring abundant, clean, safe energy with it.

The ConversationStewart Prager, Professor of Astrophysical Science, former director of the Princeton Plasma Physics Laboratory, Princeton University and Michael C. Zarnstorff, Deputy Director for Research, Princeton Plasma Physics Laboratory, Princeton University

This article was originally published on The Conversation. Read the original article.

STAR IN A JAR:

Inside our Sun, hydrogen is constantly being converted into helium, producing a tremendous amount of energy – enough to heat the planets, melt comets, and support life on Earth. So it’d be pretty good if we could replicate that process on our own planet, right?

That’s what scientists have been trying to do for decades now. Nuclear fusion, also known as “star in a jar” technology, has seemingly always been on the horizon but never quite within reach. A number of recent breakthroughs, however, suggest we may soon be mimicking the power of the Sun on Earth.

One of the most recent breakthroughs was made using Germany’s Wendelstein 7-X (W7-X) fusion device. In early December 2016, scientists at the Max Planck Institute in Greifswald managed to sustain a hydrogen plasma in the experimental reactor for a few milliseconds.

It may not sound like a big deal, but this was hugely significant for a number of reasons. First, to kickstart nuclear fusion, extremely high temperatures – about 100 million °C (180 million °F) – are required to make a plasma cloud. This cloud must also be confined by extremely powerful magnets so that it does not touch the cold walls of the reactor.

Second, this process had only previously been achieved with a helium plasma. Hydrogen fusion provides much more energy, so is much more desirable. Just getting to this stage at all at the W7-X has taken 19 years and cost $1.1 billion.

The W-7X is a type of fusion reactor known as a stellarator, which is shaped like a twisted donut to keep the plasma confined, by twisting the magnetic fields around it. Another type of fusion reactor, known as a tokamak, achieves this twisted magnetic field in a different way. They are more regularly shaped donuts, but use a large current to achieve the same twisting effect in the plasma. Both methods have their advantages and disadvantages.

In a bit of a coincidence, last December also saw a tokamak reach a major breakthrough. Scientists at the National Fusion Research Institute (NFRI) in South Korea managed to sustain a high-performance plasma for a mammoth 70 seconds, a new world record. It was widely reported that this was done with a hydrogen plasma.

This might beg the question, why even bother with the stellarator if the tokamak is so much more impressive? The reason is that while the stellarator is more complex, it is easier to maintain, and if it can be improved then it could rival the tokamak in sustaining a plasma.

It’s unclear who is going to win the race to make a working “star in a jar”. Another project underway is the International Thermonuclear Experimental Reactor (ITER) in France. This international project is going down the tokamak route, but has had a troubled development time; it was first initiated way back in 1988.

However, they are hopeful of generating their first plasma by 2025. If it all works, this reactor – and the others – will be a precursor of what is to come.

And, well, that could be rather fantastic. Nuclear fusion has the added benefit of generating zero waste products, and a working reactor would theoretically produce more energy than is put in. This would give us an essentially limitless and clean source of energy.

Whether the dream will be realized remains to be seen. But, for nuclear fusion at least, we’ve had a rather good year. A working “star in a jar” may not be too far away.

OVERALL

Fusion energy represents a new era in energy generation. Fusion reactors create miniature suns from which we can draw enough energy to power 150,000 homes. Both government agencies and private enterprise are working tirelessly to make this a reality.

For centuries, humans have dreamed of harnessing the power of the sun to energize our lives here on Earth. But we want to go beyond collecting solar energy, and one day generate our own from a mini-sun. If we’re able to solve an extremely complex set of scientific and engineering problems, fusion energy promises a green, safe, unlimited source of energy. From just one kilogram of deuterium extracted from water per day could come enough electricity to power hundreds of thousands of homes.

fusion-energy_home_v1
CLICK TO VIEW COMPLETE INFOGRAPHIC

 

Since the 1950s, scientific and engineering research has generated enormous progress toward forcing hydrogen atoms to fuse together in a self-sustaining reaction – as well as a small but demonstrable amount of fusion energy. Skeptics and proponents alike note the two most important remaining challenges: maintaining the reactions over long periods of time and devising a material structure to harness the fusion power for electricity.

As fusion researchers at the Princeton Plasma Physics Lab, we know that realistically, the first commercial fusion power plant is still at least 25 years away. But the potential for its outsize benefits to arrive in the second half of this century means we must keep working. Major demonstrations of fusion’s feasibility can be accomplished earlier – and must, so that fusion power can be incorporated into planning for our energy future.

Unlike other forms of electrical generation, such as solar, natural gas, and nuclear fission, fusion cannot be developed in miniature and then be simply scaled up. The experimental steps are large and take time to build. But the problem of abundant, clean energy will be a major calling for humankind for the next century and beyond. It would be foolhardy not to exploit fully this most promising of energy sources.

WHY FUSION POWER?

Adding heat to two isotopes of water can result in fusion. American Security Project, CC BY-ND
Adding heat to two isotopes of water can result in fusion. American Security Project, CC BY-ND

In fusion, two nuclei of the hydrogen atom (deuterium and tritium isotopes) fuse together. This is relatively difficult to do: Both nuclei are positively charged, and therefore repel each other. Only if they are moving extremely fast when they collide will they smash together, fuse and thereby release the energy we’re after.

This happens naturally in the sun. Here on Earth, we use powerful magnets to contain an extremely hot gas of electrically charged deuterium and tritium nuclei and electrons. This hot, charged gas is called a plasma.

The plasma is so hot – more than 100 million degrees Celsius – that the positively charged nuclei move fast enough to overcome their electrical repulsion and fuse. When the nuclei fuse, they form two energetic particles – an alpha particle (the nucleus of the helium atom) and a neutron.

Heating the plasma to such a high temperature takes a large amount of energy – which must be put into the reactor before fusion can begin. But once it gets going, fusion has the potential to generate enough energy to maintain its own heat, allowing us to draw off excess heat to turn into usable electricity.

Fuel for fusion power is abundant in nature. Deuterium is plentiful in water, and the reactor itself can make tritium from lithium. And it is available to all nations, mostly independent of local natural resources.

Fusion power is clean. It emits no greenhouse gases, and produces only helium and a neutron.

It is safe. There is no possibility for a runaway reaction, like a nuclear-fission “meltdown.” Rather, if there is any malfunction, the plasma cools, and the fusion reactions cease.

All these attributes have motivated research for decades, and have become even more attractive over time. But the positives are matched by the significant scientific challenge of fusion.

WORLD’S FIRST FUSION REACTOR

IN BRIEF
  • Tokamak Energy’s fusion reactor has achieved first plasma and is on track to produce temperatures of 100 million degrees Celsius (180 million degrees Fahrenheit) by 2018.
  • Tokamak Energy CEO says to expect fusion energy “in years, not decades.”

ACHIEVING FIRST PLASMA

After being turned on for the first time, the UK’s newest fusion reactor has achieved first plasma. This simply means that the reactor was able to successfully generate a molten mass of electrically-charged gas — plasma — inside its core.

Called the ST40, the reactor was constructed by Tokamak Energy, one of the leading private fusion energy companies in the world. The company was founded in 2009 with the express purpose of designing and developing small fusion reactors to introduce fusion power into the grid by 2030.

Fusion Energy: A Practical Guide [Infographic]
Click to View Full Infographic

Now that the ST40 is running, the company will commission and install the complete set of magnetic coils needed to reach fusion temperatures. The ST40 should be creating a plasma temperature as hot as the center of the Sun — 15 million degrees Celsius (27 million degrees Fahrenheit) — by Autumn 2017.

By 2018, the ST40 will produce plasma temperatures of 100 million degrees Celsius (180 million degrees Fahrenheit), another record-breaker for a privately owned and funded fusion reactor. That temperature threshold is important, as it is the minimum temperature for inducing the controlled fusion reaction. Assuming the ST40 succeeds, it will prove that its novel design can produce commercially viable fusion power.

Tokamak Energy CEO David Kingham commented in a press release: “Today is an important day for fusion energy development in the UK, and the world. We are unveiling the first world-class controlled fusion device to have been designed, built, and operated by a private venture. The ST40 is a machine that will show fusion temperatures – 100 million degrees – are possible in compact, cost-effective reactors. This will allow fusion power to be achieved in years, not decades.”

FUSION POWER: COMING SOONER

Nuclear fusion is a potentially revolutionary power source. It is the same process that fuels stars like our Sun, and could produce a potentially limitless supply of clean energy without producing dirty waste or any significant amount of carbon emissions. In contrast to nuclear fission, the atom splitting that today’s nuclear reactors engage in, nuclear fusion requires salt and water, and involves fusing atoms together. Its primary waste product is helium. It’s easy to see why scientists have tried to figure out how to achieve this here on Earth, but thus far it’s been elusive.

The journey toward fusion energy undertaken by Tokamak Energy is planned in the short-term and moving quickly; the company has already achieved its half-way goal for fusion power delivery. Their ultimate targets include producing the first electricity using the ST40 by 2025 and producing commercially viable fusion power by 2030.

Kingham remarked in the press release: “We will still need significant investment, many academic and industrial collaborations, dedicated and creative engineers and scientists, and an excellent supply chain. Our approach continues to be to break the journey down into a series of engineering challenges, raising additional investment on reaching each new milestone.”

PROGRESS TO DATE

The progress in fusion can be measured in two ways. The first is the tremendous advance in basic understanding of high-temperature plasmas. Scientists had to develop a new field of physics – plasma physics – to conceive of methods to confine the plasma in strong magnetic fields, and then evolve the abilities to heat, stabilize, control turbulence in and measure the properties of the superhot plasma.

Related technology has also progressed enormously. We have pushed the frontiers in magnets, and electromagnetic wave sources and particle beams to contain and heat the plasma. We have also developed techniques so that materials can withstand the intense heat of the plasma in current experiments.

It is easy to convey the practical metrics that track fusion’s march to commercialization. Chief among them is the fusion power that has been generated in the laboratory: Fusion power generation escalated from milliwatts for microseconds in the 1970s to 10 megawatts of fusion power (at the Princeton Plasma Physics Laboratory) and 16 megawatts for one second (at the Joint European Torus in England) in the 1990s.

Lockheed Martin, the American aerospace and defence conglomerate, made a extraordinary announcement last week, declaring to have made progress toward a controlled nuclear fusion. If everything goes according to plan, the company could even aim at developing small and workable reactors within 10 years. Is it really possible?
Fusion 1

It’s too early to say. For what is known so far, Lockheed has started working on this project, headed by Tom McGuire, at Lockheed’s secretive Skunk Works location in Palmdale, California four years ago. The objective is building small reactors – the size of a truck – that, thanks to the amazing energy provided by fusion, provide enough power for a small city. The main issue, here as in all previous efforts, is controlling the heat and pressure generated by the process, almost impossible at small scale.  Lockheed would do it by using a “magnetic bottle” to get it under control, even though the technicalities have not been made clear so far.

By containing this reaction, we can release [the heat] in a controlled fashion to create energy we can use. The heat energy created using this compact fusion reactor will drive turbine generators by replacing the combustion chambers with simple heat exchangers. In turn, the turbines will then generate electricity or the propulsive power for a number of applications.” (Lockheed, October 15, 2014, company statement.)

And herein lies the issue. The announcement has provoked a great deal of excitement in the press, but also a lot of caution. The main doubts are, obviously, about control. No matter that deuterium-tritium reaction is the easiest one to initiate: the optimal temperature needed is still about 100 million degrees C. Way hotter than the Sun itself. So far, the company has not clarified how it is going to do that, so it is impossible to know how close it really is.
Fusion 3

Experiments toward a controlled fusion – in reactors called tokamak – have been ongoing since at least the 1950s. The latest one, a device called ITER, is currently under construction in France, and it’s the result of a multinational effort. Many believe that, in order to succeed in making its own prototype operational, Lockheed will need the help of the international scientific community, together with external funding, and these are the reasons why the firm is going public at this stage.

Also, hypes are common in fusion energy. A famous one is about cold fusion, the (still hypothetical) type of nuclear reaction that would occur at room temperature. No matter the claims and experiments, there’s not yet an accepted theoretical model.

Fusion 5
While we might not be still there, there are high hopes we will get there eventually. Fusion energy has huge advantages: for a start, it has a lower environmental impact than other sources of energy, nuclear or not, because it doesn’t use uranium, but deuterium and tritium. So, emissions are limited and there is no radioactive waste like in the case of fission. Furthermore, deuterium (hydrogen’s isotope) and tritium are elements both cheap and abundant, and available to everybody.

There are also other, more exotic options, like the one NASA is working on – called LENR. While a close relative of the fusion explored so far, LENR (low-energy nuclear reaction) is different from either fission or traditional fusion.  It is cold (=room temperature) fusion, for a start. But, while fission or traditional fusion are underpinned by strong nuclear force, LENR aims at capturing power from weak nuclear force – which has so far been proved elusive.

Last but not least, we could try with antimatter. But if fusion is challenging, this one is (still) far in the realm of science-fiction for now.

A NEW CHAPTER IN RESEARCH

Under construction: the ITER research tokamak in France. ITER
Under construction: the ITER research tokamak in France. ITER

Now the international scientific community is working in unity to construct a massive fusion research facility in France. Called ITER (Latin for “the way”), this plant will generate about 500 megawatts of thermal fusion power for about eight minutes at a time. If this power were converted to electricity, it could power about 150,000 homes. As an experiment, it will allow us to test key science and engineering issues in preparation for fusion power plants that will function continuously.

ITER employs the design known as the “tokamak,” originally a Russian acronym. It involves a doughnut-shaped plasma, confined in a very strong magnetic field, which is partly created by electrical current that flows in the plasma itself.

Though it is designed as a research project, and not intended to be a net producer of electric energy, ITER will produce 10 times more fusion energy than the 50 megawatts needed to heat the plasma. This is a huge scientific step, creating the first “burning plasma,” in which most of the energy used to heat the plasma comes from the fusion reaction itself.

ITER is supported by governments representing half the world’s population: China, the European Union, India, Japan, Russia, South Korea and the U.S. It is a strong international statement about the need for, and promise of, fusion energy.

THE ROAD FORWARD

A look inside the ITER tokamak reactor. ITER
A look inside the ITER tokamak reactor. ITER

From here, the remaining path toward fusion power has two components. First, we must continue research on the tokamak. This means advancing physics and engineering so that we can sustain the plasma in a steady state for months at a time. We will need to develop materials that can withstand an amount of heat equal to one-fifth the heat flux on the surface of the sun for long periods. And we must develop materials that will blanket the reactor core to absorb the neutrons and breed tritium.

The second component on the path to fusion is to develop ideas that enhance fusion’s attractiveness. Four such ideas are:

1) Using computers, optimize fusion reactor designs within the constraints of physics and engineering. Beyond what humans can calculate, these optimized designs produce twisted doughnut shapes that are highly stable and can operate automatically for months on end. They are called “stellarators” in the fusion business.

2) Developing new high-temperature superconducting magnets that can be stronger and smaller than today’s best. That will allow us to build smaller, and likely cheaper, fusion reactors.

3) Using liquid metal, rather than a solid, as the material surrounding the plasma. Liquid metals do not break, offering a possible solution to the immense challenge how a surrounding material might behave when it contacts the plasma.

4) Building systems that contain doughnut-shaped plasmas with no hole in the center, forming a plasma shaped almost like a sphere. Some of these approaches could also function with a weaker magnetic field. These “compact tori” and “low-field” approaches also offer the possibility of reduced size and cost.

Government-sponsored research programs around the world are at work on the elements of both components – and will result in findings that benefit all approaches to fusion energy (as well as our understanding of plasmas in the cosmos and industry). In the past 10 to 15 years, privately funded companies have also joined the effort, particularly in search of compact tori and low-field breakthroughs. Progress is coming and it will bring abundant, clean, safe energy with it.

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