If you’ve kept up with the news, you may have heard that a recent breakthrough was made in the field of fusion energy; one that has the potential to make cheap, carbon-free energy a reality in the future. To understand what all this means, let’s discuss what fusion actually is, why scientists have been pursuing it for the past half-century, and how close we really are to fusion power.
What is Fusion
I would advise you to re-read the first section of my entry on fission and radiation, as I will be using a lot of the same language and concepts from that post.
Nuclear fusion is the process of producing energy by fusing smaller atoms into larger ones. Now if you’re like me as a child, your first thought upon hearing this will be “why would fusing atoms together produce energy when ripping large atoms apart also produces energy?” Put as simply as possible, energy is produced whenever a less stable system is made more stable. A bowling ball on top of a house is less stable than a bowling ball on the ground. It took energy to move the bowling ball from the ground to the roof and you can get that energy back by “moving” the ball from the roof back to the ground, probably ruining the grass in the process. The same thing happens in chemistry; water and carbon dioxide molecules are held together more strongly than molecules of oxygen and hydrocarbons, so a chemical reaction that reconfigures hydrocarbons and oxygen into CO2 and water (more commonly known as ‘fire’) will produce energy as weaker molecules are turned into stronger ones. In nuclear physics, the most stable atoms on the periodic table are those of Iron-56, atoms with 26 protons and 30 neutrons. I’ll go into why in a second, but this means that energy is produced when atoms are created closer in size to Iron-56, either by tearing larger atoms apart or fusing smaller atoms together.
But just because a certain state might be more stable doesn’t mean everything will automatically jump to said state. A bowling ball on your roof won’t fall off unless you push it, oxygen and hydrocarbon molecules need to be torn apart with thermal energy before they can be recombined into stronger molecules (can’t start a fire without a spark), and small atoms won’t just merge into larger atoms on their own.
The reason every small atom in the universe hasn’t merged into Iron-56 yet is because atoms repel each other electromagnetically. The attractive force that holds protons and neutrons together, called the strong nuclear force, is a hundred times stronger than the electromagnetic force pushing protons apart. But the strong nuclear force has a very small range, only slightly larger than the width of a proton. This is why atoms become less stable as they get bigger than Iron-56; they outgrow the force that holds them together while the force that tries to rip them apart still works. This means that in order to make two atoms fuse, they must get very, very close to each other all the while pushing against each other until the very last second.
You probably know that the Sun uses fusion to produce heat and light, just like every other star. The Big Bang produced all the matter in the universe, most of it being huge clouds of Hydrogen-1. Gravity pulled these clouds together into enormous spheres of hydrogen. As more and more hydrogen was pulled into these spheres, their gravitational pull grew. This immense gravity created immense pressure at the star’s core which created immense heat. This heat and pressure squeezed hydrogen atoms closer together until it overwhelmed the electromagnetic forces pushing them apart. At this point they are close enough to fuse. Because two nucleons are more stable stuck together than as separate particles, their fusion created energy that made the new Hydrogen-2 atom* even hotter than surrounding atoms. This extra heat pushed nearby atoms to fuse, which pushed other nearby atoms to fuse, until the whole core was fusing. The energy given off by the fusing core turns the star into a glowing ball of plasma with the force of nuclear fusion pushing outward while gravity pushes inward. A star is just an enormous nuclear explosion that’s too heavy to actually explode.
Fusion Power
Scientists have spent the entire nuclear age trying to replicate nuclear fusion, both for weapons and for energy. For the mass of fuel, fusion reactions produce many times the energy of fission reactions and the products of fusion reactions aren’t radioactive. The problem with fusion is that it is far harder to trigger these reactions than fission reactions. To fuse atoms, the Sun’s core is roughly 15 million degrees Celsius (27 million degrees Fahrenheit) and at a pressure over 260 billion times that of Earth’s atmosphere at sea level. We have found one way to replicate these conditions; hydrogen bombs work by using the heat and force of a fission bomb to trigger a far more powerful fusion reaction. But this energy is released all at once which can damage the infrastructure meant to harness this energy while allowing most of the energy to dissipate as waste heat. Turning nuclear bombs into a source of electricity is not efficient, cheap, safe, or sane (so of course the United States tried it during the Cold War), so designs for reactors that could produce fusion energy slowly as needed have been a research topic for over fifty years. The obstacle hasn’t been creating fusion reactions; scientists have been making atoms fuse with laboratory particle accelerators since the 1930s. The problem is that creating the immense heat and pressure of the Sun’s core has historically required more energy than is created by the fusion reactions; it takes more energy to create fusion reactions than you get from those reactions.
One of the projects focused on fusion power has been the National Ignition Facility (NIF), a machine in the Lawrence Livermore National Laboratory in California. First built between 1994 and 2009, the machine consists of the planet’s most powerful laser generators. Taking up ten stories of an area equivalent to three football fields, these lasers together can produce a laser pulse lasting only a few nanoseconds but with 500 terawatts of power. Put another way: in a millionth of the time it takes for a single neuron to fire, these lasers are using one thousand times the amount of energy the rest of the United States is using in that same nanosecond. This incredible power lasts such a short time that it only delivers about 1.85 megajoules of energy to its target, or about the energy of a Snicker’s bar, but the reactions the NIF was built to study only take a few nanoseconds.
NIF Laser Bay NIF Target Chamber
https://en.wikipedia.org/wiki/National_Ignition_Facility https://commons.wikimedia.org/wiki/File:NIF_target_chamber_2.jpg
These lasers produce 192 beams that are all aimed at a single target from every direction, delivering its incredible energy all at once across the target’s surface. This target can vary depending on what experiment the facility is performing; the NIF is also used to replicate the interiors of nuclear weapons, which has applications for safe storage and handling of nuclear materials. For fusion experiments, the target is a hollow gold cylinder (called a hohlraum) about the size of a dime. Inside the hohlraum is a BB-sized bead of cryogenically frozen hydrogen (specifically the isotopes H-2 and H-3). The laser beams fire into the hohlraum which focuses their energy onto the fuel bead, compressing the bead and heating it up to ten times that of the Sun’s core. This obliterates the hohlraum as the hydrogen atoms in the fuel bead fuse into helium, giving off x-rays and neutron radiation. The target chamber which contains the hohlraum includes numerous detectors that measure how much energy was produced in the experiment. For more details, here’s a video from the NIF itself.
NIF Hohlraum Hohlraum mounted on target positioner
https://en.wikipedia.org/wiki/National_Ignition_Facility https://en.wikipedia.org/wiki/National_Ignition_Facility
The National Ignition Facility has been operating since 2009. It has performed fusion experiments for most of that time, using the data it collects to further refine and perfect subsequent experiments. These include experimenting with fuel isotopes, hohlraum materials, and laser strength and arrangement, as well as improvements in the manufacturing of the fuel bead and hohlraum (which have to be perfectly smooth and spherical to most efficiently create fusion). Finally, on the 5th of December, 2022, the NIF produced 3.15 megajoules of fusion energy using just 2.05 megajoules of laser energy. The reactor produced 50% more power than it consumed. It cannot be overstated how much of a scientific breakthrough this was, a breakthrough decades in the making with the potential to radically change our society.
Future of Energy?
Nuclear fusion has long been lauded by scientists and futurists as the next big leap in human energy production. A perfectly efficient fusion reactor could power 3 million US homes with only a kilogram of fuel per day (2.2 pounds). The fuel in question would be hydrogen†, which can be procured by running an electrical current through water. The waste products of a fusion reactor would be helium, which is non-radioactive, not particularly poisonous, and has several industrial uses. The reactors themselves would give off some neutron radiation, but that would only be dangerous to those in the reactor while it was running. Melting down would be impossible, as the difficulty of fusion lies in sustaining the reaction instead of controlling it. In the long-term, near limitless energy would mean other technologies could be developed faster and further, from indoor farming to super efficient rocket engines. Fusion could be the key to cheap, clean, plentiful electricity with minimal dependence on any particular region for fuel. So, given this new breakthrough, can we expect fusion to save us from climate change and begin powering our homes in the near future?
No.
As profound as this breakthrough was, it is just the first step in a long road to practical fusion energy. First off, NIF only technically produced more energy than it consumed. The laser generators at NIF are only 10% efficient, meaning only 10% of the electricity pumped into them actually goes into the lasers, the rest becoming waste heat and light. While the fusion reaction produced more energy than the lasers that triggered the reaction, it still took more energy to power the lasers than the fusion reaction produced. Secondly, even if we only pay attention to the laser beams, the NIF only produced 1.1 megajoules of energy, or a little bit more than it would take to boil a gallon of water. To create a proper fusion power plant, far more research needs to be done on how to scale up fusion reactors, how to do continuous fusion reactions, and how best to collect this energy to generate electricity. Many experts believe the design used by the NIF is highly unlikely to be what future fusion reactors look like, as it produces very small batches of power that would be very difficult to turn into electricity. The NIF was designed to be a science lab, not a power plant. And of course, the cost of building such reactors will remain prohibitively high for the foreseeable future given these reactors are such complex and specialized equipment.
These aren’t problems without solutions though. Currently under construction is the International Thermonuclear Experimental Reactor (ITER) in France’s Cadarache facility. Funded and run by six nations and the EU, ITER will be the world’s largest tokamak, a machine designed to heat and compress plasma using incredibly powerful magnetic fields. Along with powerful microwave generators and superheated plasma injectors, it should be able to create the heat and pressure needed to make hydrogen plasma fuse. In addition to fusion itself, the facility will be working on the techniques and equipment needed to create fusion reactors for large-scale power production. This includes using the heat of fusion to make neighboring atoms fuse, thus creating a somewhat self-sustaining reaction, and using the neutron radiation created by fusion to breed more fuel and to heat water for steam. ITER will finish construction and begin experiments in 2025.
Fusion energy will not save us from climate change. As I’ve discussed before, a proper response to climate change will necessitate both finding new energy sources for the long term and cutting carbon emissions in the short term. It could be decades before the first fusion power plants are ready for commercial use and decades more before they’re inexpensive enough to be our planet’s primary energy source. We still need other technologies and infrastructure investment to deal with the climate crisis now. That said, this very well could be the long-term future of energy production. Further investment and research will be needed to turn such a vision into reality, but securing such funding could become easier now that we’ve seen it’s possible. What happened this past month was historic, and it’s just the first chapter.
For More Details
*Hydrogen-2 would be 1 proton, 1 neutron despite it being formed from the fusing of two protons. Protons can turn into neutrons and vice versa through a force called weak interaction. They do this if they would be more stable as the other particle, such as a proton turning into a neutron because a proton and neutron stuck together is stable while two positively-charged protons stuck together are wildly unstable.
†Fusion reactors would not use the most common isotope of hydrogen (Hydrogen-1) as it would take several less energetic reactions to get it to the point it could fuse into helium. Instead, fusion reactors today experiment with the isotopes Hydrogen-2 and Hydrogen-3. H-2 can be found in regular water at a concentration of 150 ppm and is already used in some nuclear reactors, so there already exists infrastructure to extract H-2 from water. H-3 doesn’t exist in nature due to it being radioactive and very short lived, but it can be produced by irradiating elements like lithium, boron, and maybe even Hydrogen-2. Since nuclear reactors will produce some neutron radiation, some have proposed lining reactors with these materials to convert them into future fuel.
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