Nuclear fusion is one of the best and most promising forms of sustainable energy. It offers enormous amounts of power and produces no greenhouse gases. It does not use radioactive materials like uranium, which nuclear fission uses. Instead it uses hydrogen, the most abundant and simple atom in the universe, so it has a potentially unlimited supply. There is no danger like there is in nuclear fission. In the worst case scenario the atoms would just revert to their stable and safe form. Over 30 countries have started to compete for this energy source and have created multi-country consortiums. These consortiums have built machines to try to create this form of energy, and eventually, with enough funding and resources, someone will succeed. Someone will harness the power that drives our stars.
Currently, our main sources of energy are fossil fuels, which are nonrenewable and harmful. Mining for these fossil fuels damages the environment and using them does too. They produce smoke and carbon dioxide, which go into the atmosphere, swell the oceans and pollute the sky. This exposes humans to harmful ultraviolet rays, and raises the level of acidity in several oceans. This source of energy generates about 85% of the world’s electricity. Clearly the world needs a new source of energy. Nuclear fusion is our best bet.
Nuclear fusion produces energy by combining atoms. When two small atoms come together in the right conditions and the right time, they will fuse, creating a larger one. In this process, the atoms lose mass, which then turns into energy. How does this happen? Einstein’s famous equation E=mc2 explains that energy is really mass multiplied by the speed of light squared. So when atoms lose that mass, they are actually releasing energy. Now the speed of light is a very big number— 299 792 458 m/s to be exact. The speed of light squared is even larger. So even though the atoms are losing just a tiny bit of mass, they are actually giving up a great amount of energy. The most tremendous amount of fusion in our solar system is our sun, where quadrillions of hydrogen atoms combine to make quadrillions of helium atoms. The total mass of four hydrogen atoms is a little more than a helium atom, so when the sun combines atoms, they release mass in the form of energy.
Scientists have been working for years on how to collide atoms and have developed some very good ways of doing so. There exist many different ways to achieve fusion, but the most successful reactors either use inertial confinement fusion or magnetic confinement fusion, both of which are discussed next.
Inertial confinement fusion uses a hohlraum, a type of cylindrical pod, to contain two simple hydrogen isotopes, deuterium and tritium. To force these atoms to join, they have to heat them to a very high temperature, 200 million kelvins to be precise. In order to heat the atoms, scientists have also developed many sophisticated ways, two of which will be described in the passages below.
In California at the National Ignition Facility, NIF, scientists heat the atoms by pointing high energy beams of laser light at the hohlraum, which then explodes, sending shock waves through the atoms and making them combine. A different kind of inertial confinement is a Z pinch. The largest machine that uses this type of fusion is the Z-machine. It passes electricity through incredibly thin strands of wire and turn them into plasma. To do this, 26 million amps have to pass through them, each one about the diameter of 1/10 of a human hair. These wires get destroyed and turned into plasma. Even though the wires are destroyed, for a fraction of a second the magnetic field created by them remains. The ions in the plasma are affected by the magnetic field and they are all propelled towards it. During this process some of the ions stop, but since they were going so fast with so much energy they produce X-rays. These X-rays shoot in all directions and some hit a hohlraum containing the isotopes deuterium and tritium. The hohlraum containing these atoms is destroyed but the X-rays keep on advancing. They quickly meet the two isotopes and force them closer and closer. The force that repels these isotopes is called the electrostatic force but when they become close enough, another force takes over. This one is called the strong nuclear force. When the atoms come within two femtometers, the strong nuclear force takes over and brings the atoms together, which releases energy in the process. These methods for inertial confinement fusion have been successful in creating energy, but still prove incapable of using it. The miniature suns created by these high heats are just like the ones in space, giving enough light to see a new and powerful world, in this case the world of fusion.
The second method, magnetic confinement fusion, uses magnetic fields to suspend the plasma in the air, and then raise the temperature. This energizes the atoms in the plasma, and they move around so much that they collide. Two types of reactors are usually used for this method of fusion, the tokamak and the stellarator. The high heats required to energize the atoms are a vital part of the fusion process. However, since no known material can withstand a heat of 100 million Celsius, building reactors for fusion on earth requires a different approach. Luckily, someone had the smart idea to use magnetism. The World Nuclear Association (WNA) says, “The most effective magnetic configuration is toroidal, shaped like a doughnut, in which the magnetic field is curved around to form a closed loop.” This is because the magnetic field has to be infinite, allowing the atoms time to bond, which requires a closed circular magnetic field. Both the tokamak and the stellarator use a closed loop to suspend the near thermonuclear plasmas. All these reactors have contributed greatly to fusion research, and will probably contribute even more in the future.
The name tokamak is Russian for “toroidal chamber with magnetic coils’.’ The toroidal chamber is enclosed by several superconducting magnets that loop around sections of the reactor. The enormous magnets have to be generated both inside and outside to allow stable operation, but even so currents of moving particles move in different directions, destabilising the plasma. These are relatively easy to build on the scale of reactors, but the disadvantages are that the magnetic field is stronger on the inside, pushing positively charged particles upward and negative ones downward, so that there is an unstable flow in the plasma. All this is happening in the heart of the tokamak, a vacuum chamber. The stellarator, however, solves this problem. It uses an asymmetric magnetic field to ensure every plasma particle feels the same force. Supercomputer simulations show that this will allow for a continuous and stable operation. These reactors overlap in certain aspects and differ in others, but in the end they are all trying to achieve fusion.
Following the discovery of nuclear fusion, different countries joined together to combine their power and form scientific research organizations. Together these consortiums built machines they could not make on their own. These reactors include ITER, DEMO, Wendelstein 7-X and more. Each will be described in detail and explained next.
ITER originally stood for International Thermonuclear Experimental Reactor, but later the project leaders decided that the words thermonuclear, experimental and reactor linked in one sentence might scare the public. Fortunately, ITER also meant “the way” in Latin. Therefore ITER is the way to nuclear fusion. ITER is a tokamak, the biggest in the world. It has a toroidal shape and inside it is a vacuum. Inside the vacuum, under the influence of extreme heat and pressure, gassy hydrogen becomes a plasma. When the atoms join, they release energy which comes out partly as heat. This heat is then absorbed into ITER’s walls and transformed into steam. This steam is used to turn a turbine and produce electricity. As shown, the complex steps to capture the energy are challenging, but all of them are necessary.
ITER is an enormous machine with several parts that allow it to function. To keep the plasma in place ITER uses superconducting magnets, but the only way these magnets will function is if they are cooled to a temperature of -269℃. Two main questions can be asked here, why do the magnets need to be kept at such a low temperature, and how do ITER’s scientists achieve this? To answer the first question is simple. At regular temperatures the magnets are normal, meaning they are not superconducting. Why does the temperature affect the magnet? All magnets are made up of atoms. At normal temperatures, the atoms move between the poles at random, and align to produce magnetism. At a lower temperature, the atoms move less randomly and much slower. This creates a more controlled alignment of the atoms that produce magnetism, and therefore a stronger magnetic field. Now that it is understood why the magnets need to be kept cold, how does ITER do it? They simply keep them in a vacuum chamber called the cryostat. The cryostat is an enormous vacuum chamber that houses the magnets. Thirty meters wide and nearly as many in height, the chamber is enormous. It is perfectly designed, with everything from bellows for thermal contraction to auxiliary heating, and is one of the marvels of the scientific world.
Even though the magnets do a very good job of controlling the plasma, high energy neutrons still escape. Fortunately, ITER uses this to its advantage. ITER captures them by surrounding the walls of the tokamak with a blanket of lithium about one meter thick. This blanket is made up of about 440 smaller pieces, each heavier than a car. The high energy neutrons that escape the fusion reaction are caught there, and collected by a water coolant. Without this ITER would not get any energy, so this is an essential piece of the tokamak.
Now for the last main part of the ITER tokamak- the divertor. ITER says that the main use of this component, located at the bottom of the cryostat, is to “[extract] heat and ash produced by the fusion reaction, [minimize] plasma contamination, and [protect] the surrounding walls from thermal and neutronic loads.” Basically the divertor pulls the bad stuff out of the plasma, meaning the things that might lower the temperature, speed or density, and it also protects the walls from harm. These are the main parts of the tokamak, and together they make ITER.
DEMO is another monster of a machine. While ITER and the Z-machine have not yet been able to create a reliable energy source, DEMO is intended to bring us one step closer to nuclear fusion as a commercially viable source of energy. It plans to walk in the footsteps of ITER, and use ITER’s discoveries for a more reliable power source. DEMO will be the first commercial fusion power plant, and will use ITER’s technology to make a demonstration power plant that can supply the world with the energy it needs. DEMO will hopefully produce 2-4 gigawatts of electricity, which is more than 7,000 times an average American uses per year. It will produce about 25 times the amount of energy put in, and have the shape of a tokamak.
Another kind of reactor is called the stellarator. These complex machines have a curving magnetic field, which allows all plasma particles to feel the same force. So far the biggest stellarator is Wendelstein 7-X, built in Germany and finished in the fall of 2015. Its curved magnetic field also allows for a stable flow in the plasma, which can then run for up to 30 minutes straight. New Scientist magazine says that when comparing the two reactors “ [You’re] balancing the physics advantages of the stellarator over the engineering advantages of the tokamak.” Stellarators have been called the “black horse” in the physics community because of the notoriously difficult process to build them. Stellarators and tokamaks are all very good when it comes down to the scientific reasons behind fusion, but the opinion of the public is a different matter.
Like every energy source, nuclear fusion has its advantages and disadvantages. As said before, the advantages of nuclear fusion are numerous. No greenhouse gases, which contribute to global warming, so no smoke or carbon dioxide in the atmosphere. It has virtually limitless fuel because deuterium can be found in every 6420 atoms of sea water, the reactor only needs a few, and tritium can be bred in the reactor by energizing the neutrons in lithium-6, which occurs naturally. Another advantage is that there is perfect safety. It is much easier to control than nuclear fission. Also it is very easy to stop. The last, and perhaps greatest advantage, is the amount of energy produced. With just 40 litres of seawater and 5 grams of lithium the same amount of energy can be produced as 40 tons of coal. On the other hand no one has yet actually produced energy with nuclear fusion and it is still a theoretical source of energy. There is also a matter of cost. The expensive machinery in a reactor costs billions of dollars, and research is also costly. Why spend all this money on an unproven energy source when the world could spend it on renewables like solar or wind instead? As shown, there are many controversial opinions, some based in fact and others not. However, if someone could achieve an energy source using nuclear fusion, the entire world would benefit.
How could nuclear fusion affect the world? The enormous idea and concept of nuclear fusion can change the world in ways both large and small. The price of energy would go down tremendously, and electricity and fuel would be commonplace. The ozone layer, damaged by fossil fuels, would stop deteriorating and the sea levels and fish inside them will once again be safe. More ambitious technological and scientific experiments will not only take place but they will succeed, and extensive space travel could be conducted. The growing population of the world will meet its energy demands, and developing countries can advance to a better place more quickly. The extensive amount of energy could be used to build more buildings and houses, transportation would produce no smoke, and electricity bills would drop tenfold. Our planet would be sufficient and clean, sustainable and plentiful, for a golden age of prosperity will have fallen over the world.
Nuclear fusion is one of the best sources of energy for the world. All on its own, nuclear fusion can save our planet from climate change, and help us live in a world where cheap and reliable energy is found everyday, everywhere. I personally believe that this energy source is the doorstep to a new world, a world so exquisite and perfect that we have only just begun to comprehend it.