The Tokamak! Is it possible to be the future of energy?
Diving deep into the specifics of a tokamak
Let’s get into what fusion is before we get into the deep stuff.
Atoms have a nucleus at the centre composed of protons and neutrons which are surrounded by electrons that are in orbit. The nuclei are held together by strong nuclear forces.
Protons are positively charged, they repel each other due to the electromagnetic force. For fusion to happen, the nuclei must come close enough to overcome this electromagnetic repulsion and allow the strong nuclear force to take effect. However, getting the atom’s nuclei close enough for fusion is challenging due to the “Coulomb barrier” (the electrostatic repulsion). This is what is needed for fusion to take place. The combining of the atoms.
To solve the Coulomb barrier problem, fusion requires extremely high temperatures and energy. At high temperatures the nuclei move with high kinetic energy, increasing the chances of them getting close enough for the strong nuclear force to bind them. The more energy the nuclei have the faster they buzz around, which makes it easier for fusion to take place.
In fusion experiments with reactors, the fuel which is normally deuterium and tritium is heated to extremely high temperatures, around millions of degrees Celsius. At these temperatures, the gas becomes a plasma, where electrons are stripped away from the nuclei, creating a mixture of ions and electrons.
In the hot plasma, nuclei have enough thermal energy to overcome the Coulomb barrier and collide with each other. During these collisions, if the nuclei come close enough, the strong nuclear force binds them together, resulting in the formation of a heavier nucleus.
The most common fusion reactions involve deuterium which is a heavy isotope of hydrogen with one proton and one neutron, and tritium which is another isotope of hydrogen with two neutrons and one proton. When deuterium and tritium nuclei collide they can undergo a fusion reaction forming a helium nucleus which is two protons and two neutrons and releasing a large amount of energy in the form of kinetic energy of the particles.
The famous equation E=mc²
The energy released in a fusion reaction comes from the conversion of a small amount of mass into energy, as described by Einstein’s equation E=mc². The mass of the products helium nucleus and neutron is slightly less than the mass of the initial deuterium and tritium nuclei, and this mass difference is converted into energy following the famous equation.
Lets Get into the Juicy Stuff
The Tokamak is closely related to the Sun. The sun also creates heat and light using the process of combining 2 atoms, Fusion. Here on Earth, we can’t make this energy the same way the sun does as we don’t have strong enough gravity. The sun’s gravity is 28 X more powerful than ours. We do use magnets but we don’t just use magnets as magnets still can’t create as much force as the sun.
3 Principles that we use to create fusion Energy.
There are 3 ways to help create and confine hot plasma. This is Magnetic, Inertial and Gravitational. I have already briefly spoken about magnetic, and we will go a lot more detail into it. As said above we are not able to use Gravity like the sun as we don’t have a gravity force as strong as the suns, if we did we would look like the sun, we would not be able to live on planet earth. In the simplest way to explain inertial energy is when the use of powerful lasers or high energy particle beams to compress the dense fusion fuel which courses fusion to take place.
The priciple that we’re going to look at the most is magnetic confinement as this is the most promising, there are already reactors being made to create energy for the grid, after doing the scientific research it is believed that the bigger the reactor the easier it will be to keep the reactions going and get it over the breaking point and control it over there. Many of the other ways of fusion energy are still in the development stages.
Fuel
Deuterium and Tritium are isotopes of hydrogen. These isotopes are used as the fuel for the nuclear reaction because it reaches the best outcomes at the lowest temperatures and release more energy than other elements. It is also easier to join the atom as positively charged protons in the nuclei repel each other due to electrostatic forces, creating a “Coulomb barrier” that needs to be overcome for fusion to occur. Deuterium and tritium have one proton each, making them positively charged. Their relatively low mass (compared to other isotopes) means they experience weaker repulsion forces, making it easier for them to approach each other and overcome the Coulomb barrier during a fusion reaction.
Deuterium and Tritium are brought to very high temperatures, temperatures ranging from 100–200 million °C. This is because we need lots of energy to fuse these fuels and the energy is gained by the high temperature. Deuterium and Tritium fuse at the lowest temperature compared to other elements because they don’t need as much energy to get past the Coulomb barrier. Imagine trying to fuse other elements and how much heat we would need to apply, as other elements have a stronger repulsion (Coulomb barrier) when trying to fuse.
As explained above the sun does this process well but it does not heat the atoms it uses gravity, we can’t use gravity it is way too weak so we use magnets and heat instead.
When we heat the atoms to these extreme temperatures the magnets move so quickly they join together. This is where the name Fusion comes from.
Deuterium-tritium which is a mixture of both will be added to the vacuumed chamber and is ionized and heated to thermonuclear temperatures. Then these fuel particles collide with new fuel particles which gives us a sustaining fusion reaction.
Fusion energy is the process of joining atomic nuclei to release a significant amount of energy. It’s the same process that powers the sun and other stars. In fusion, two light atomic nuclei come together to form a heavier nucleus, releasing energy in the process. The most common fusion reactions involve isotopes of hydrogen, particularly deuterium and tritium.
Plasma
In a solid, the atoms are not moving at all. In a liquid, the atoms are more spread out which means they can move more freely and then they are even more spread out for a gas. At high temperature’s to create plasma the gas is ionised.
The fusion reaction in this hot plasma is known as a thermonuclear reaction. The nuclei in the plasma must have sufficiently high densities and temperatures for a significant number of fusion reactions to take place. This is defined by LAWSON CRITERION. Having plasma at a significant density, that is heated up to high temperatures and confined (kept together) for longer, will help achieve a fusion reaction.
Heating up the Plasma
We spoke about the plasma but in order for the gas to become the plasma we need to heat it to very high temperatures there are many ways. One way is Neutral Beams Injection (NBI). This is when high-energy atoms are put into magnetically confined areas to keep the plasma as dense as possible. When this is done the atoms become ionised as they pass through the plasma and get trapped in the magnetic field. The irons which are high in energy then transfer part of their energy to plasma particles in repeated collisions, increasing the overall temperature. Other ways of heating involve the use of Radio Frequency waves, high frequency electromagnetic waves with write frequency and polarisation can transfer their energy to charged particles, which in turn collide with other plasma resulting in an increase in the temperature of plasma.
Magnetic confinement:
Magnetic confinement is what the Tokamak uses to confine the hot plasma and keep the fusion reactor running. The fuel has a magnetic charge even if it is just the smallest, it can be used to keep the plasma under control. The reason why magnets are used is because it is 100,000 times stronger than the earth’s magnetic field which is gravity and at the moment it is the most researched and developed.
The simplest form of magnetic confinement systems can be a long solenoid which will prevent particle movement in the direction perpendicular to the magnetic fields. By making the particles move around the axle fields the particles can still leak out from the end limiting the confinement time. A simple way of preventing the axial leakage can be converting the long solenoid into a torus shape making it endless. The Torus shape looks a lot like a doughnut.
As explained above the magnets make the plasma move within the torus and keep the plasma confined to the centre of the torus. If the plasma was to touch the side it would cool down which will prevent fusion from happening. These coils are often made of Nb₃Sn (Niobium alloy) based CiCC. We would also need to keep the extremely hot plasma in the centre of the torus, not only does the plasma need to stay hot but the reactor needs to stay as cool as possible. The metal reactor is a conductor of heat so it will take and disperse that heat very quickly and easily which we do not want to happen. A limitation of this device is that plasma is very difficult to control and the material of the Tokamak weakens quickly. The materials used are something that we need to develop to hold the plasma at higher temperatures and for longer.
Magnets what are they made out of? We can’t just use any magnets nor resistive magnetic coils because these magnets will be exposed to super high heat which therefore will cause a big problem as this will stop the magnet from magnetising to its full potential. So there is another magnet called the superconducting coils which then are also called cryogens.
The first time that this superconductor was used was in Russa and they used Nb₃ Sn in large-scale toroidal magnets, producing a field of 3.5T at the plasma centre and storing an energy of 416 MJ in a volume of 50m³
The Tokamak
The Design of the Tokamak
The design of the tokamak is very specific, but there are still many things stopping this device from working at its maximum potential. There are many impurities present in the plasma that lead to radiation loss. There can also be impurities on the inside of the tokamak which causes similar problems. At high concentrations, impurities prevent plasma from being heated up to its required temperature for fusion to occur. This is a problem when starting up as impurities radiate at a strong rate and result in low temperatures, they can also cause problems due to edge cooling and consequently to profile modifications. It is also very difficult to clear these impurities as there is radiation material inside the reactor.
This is why the design of the Tokamak looks like this ↓ to try and prevent the impurities and the cooling of the plasma as far as possible.
The most important wall is the first wall, which is called the limiter as it is the first boundary for the hot plasma. The basic requirement of a limiter is to withstand the intense heat and particle fluxes falling on it without severe damage by evaporating melting or cracking. The limiter must also protect the vessel wall and other systems inside the chamber from damage. The Limiter material must also not generate significant impurities by thermal or particle-induced desorption or sputtering and must have good thermal conductivity for heat transfer. These requirements are a severe restraint on the choice of limiter material. Only Carbon and Beryllium are suitable for high heat loads. Others such as tungsten and molybdenum have great thermal properties and low sputtering yields and are potential candidates for the plasma-facing components.
The Blanket is the second layer in the Tokamak which has 3 lays within itself; the first layer is a region for neutron multiplication. The second layer is where the fast-flowing neutrons get slowed down and the third layer within the blanket is where the tritium is produced.
Next is the earlier conversion layer which is where the heat is captured, to boil water which then turns turbines and creates electricity.
Lastly, there is the shield that stops the final bit of plasma if anything does escape and then after that, the vacuum vessel follows.
Tokamaks can vary depending on the specific design, purpose, and the institution building it. Tokamaks are still being experimented on to confine hot plasma at extremely high temperatures and pressures in order to achieve controlled nuclear fusion reactions, similar to those that power the sun. There are a number of Tokamaks around the world which are being experimented on and so there is no one design yet.
The Tokamaks shape and how it works
The Tokamak is shaped in a way that allows the path in which the plasma moves in never runs out. The only shape that is like that is a doughnut, this is also known as a torus shape. As I said the plasma needs a path in which it can move without running out as this is the best way to keep the plasma in a magnetic field, to stop the plasma from touching any surface of the torus shape. This shape also allows plasma-surface interactions to be moved away from the LCFS. Further, the elongation allows for a larger plasma current, which leads to a strong magnetic field on the outboard side of the plasma and helps in plasma equilibrium. The larger poloidal field further allows for a higher kinetic pressure.
The shape is also specifically designed to make sure the tube is the correct size and that the magnets are able to curl all the way around it as the magnets are the ones that control the plasma. We need a big enough gap so that the big powerful magnets fit through the middle.
The current and movement of the plasma are key to getting it up to the temperatures required but at the same time also keeping it stable. In Tokamaks, we need to drive toroidal current to create a poloidal field and this also adds to the list of why we need this rotational transform. The basic methods deployed in Tokamaks for the current drive are Ohmic Current Drive through the use of a inductive current drives. You get the Radiofrequency current drive and the Neutral beam drive although there is also a limit to how quickly the plasma is driven as they are very limited which can cause high stress on the Tokamak as well as the inductive current drive.
Tokamaks are very complex devices, and they require a variety of materials for their construction and operation. We need to be very specific about the materials we use because of their weight and strength. Let’s dive deeper into the specific components. We like to think about the tokamak but we forget about all the other things which we will be able to see as we go on.
The vacuum vessel is the main chamber that holds the plasma. It is typically made of high-strength materials such as stainless steel or other advanced alloys to withstand the high temperatures and pressures of the plasma. The vacuum vessel can be quite massive due to its size and the need for structural strength.
The magnetic coils are made of conductive materials like superconducting wires or other materials that can handle high currents and generate strong magnetic fields.
The Divertor and first wall components are used to manage the plasma-wall interactions and to withstand the heat and particle flux from the plasma. They are often constructed from materials with good thermal and mechanical properties, but they can contribute to the overall weight of the tokamak due to their size and complexity.
Many tokamak components, especially those exposed to high temperatures, need cooling systems to dissipate heat. These systems can include pipes, pumps, heat exchangers, and coolants, which contribute to the weight of the Tokamak.
Some Tokamaks use superconducting magnets that require cryogenic systems to maintain the necessary low temperatures. These systems can include cryostats, insulation, and cooling equipment.
Tokamaks require power supplies to generate the necessary magnetic fields and provide energy to the plasma heating systems. These power supplies and associated equipment will also contribute to the weight of the tokamak.
The combined weight of these components can vary widely depending on the specific design, size, and purpose of the tokamak. Larger tokamaks like ITER can weigh thousands of tons due to their massive components and complex infrastructure. Smaller research tokamaks might weigh less, but they still involve substantial amounts of material and engineering.
Measuring the energy in the Tokamak
How can you measure what is happening in this metal contraption when you can’t even see it? The large energy contents make it not possible to just insert probs into the device. In order to test for what is happening to the plasma, energy, temperature, and various wave frequencies are used. There can be other devices on the edge region of the tokamak to test for other things like heat, the fuel being used, and the reactions taking place. Rogowskii loops (which is a toroid of wire) are used to measure the plasma current. Diamagnetic loops and internal magnetic pickup coils are used to record the shape and position of the plasma. Radiometers measure emissions at different frequencies, while interferometers are used for plasma density measurements. Soft X-rays emitted by plasma yield measurements of plasma temperature, while hard X-rays give information on energetic electron tails and runaway electrons. There are inferred cameras which are used to monitor the limiter surface temperatures. These are only just a few examples of the ways we measure what is happening in the tokamak. This is such a big complex device there are many more devices that are used to measure certain things, but there are replicates of devices for backups that also get readings from certain sides of the device.
The goal for the amount of energy that a Tokamak aims to produce depends on its specific design, purpose, and stage of development. The ultimate goal for many tokamak projects is to achieve “ignition,” where the energy output from the fusion reactions is significantly greater than the energy input required to sustain the plasma and maintain the necessary conditions for fusion.
We need to start looking at the goals as we need to know where we want to go if we would like to achieve something, so the goals for energy output:
In terms of specific energy output, the most commonly discussed figure is the “Q value,” which represents the ratio of the fusion power output to the input power. A Q value greater than 1 indicates that more energy is being produced by fusion than is being input to sustain the plasma.
ITER’s (International Thermonuclear Experimental Reactor) primary goal is to demonstrate the scientific and technical feasibility of sustained nuclear fusion for energy production. ITER aims to achieve a Q value of around 10, meaning it would produce 10 times more fusion energy than the energy required to maintain the plasma.
ITER has also designed a Tokamak to produce 500MW of fusion energy (Fusion power > 10). It is also a long pulse operation which is >300s and ultimately a steady state. It is still being designed and still yet to be turned on.
For future commercial fusion power plants, the target Q value is much higher, typically in the range of 20 to 30. Achieving a Q value in this range is crucial to making fusion a practical and economical energy source.
Smaller tokamaks used for research and experimental purposes might not have the goal of achieving break-even conditions. These tokamaks are often used to explore plasma behaviour, confinement, and other aspects of fusion science.
Waste Produced
Waste is a big problem, it is the reason we have global warming. Does the tokamak create waste and if so what type of waste?
Fusion reactions in a tokamak involve hydrogen isotopes which are not as radioactive as the isotopes used in nuclear fission. However, some activation of materials can occur due to interactions with high-energy neutrons produced during the fusion process. These activated materials can become radioactive and might need to be handled and managed as radioactive waste.
The interaction of the high-temperature plasma with the tokamak’s walls and components can lead to erosion and material sputtering. This can create fine dust and particles that need to be managed and potentially treated as waste.
Tokamaks often use cooling systems to manage the heat generated during operation. The cooling water or coolants used might pick up some impurities or become slightly radioactive due to neutron activation. Managing and disposing of this cooling water or coolant can require attention to prevent environmental contamination.
As with any complex machinery, tokamaks require maintenance, and over time, certain components might need to be replaced. Components removed during maintenance or replacement might become waste that needs to be managed.
Diagnostic systems that come into contact with the plasma or the tokamak’s environment might need proper handling and disposal if they become contaminated or worn out.
Fusion research and development focus on minimising the generation of radioactive waste and designing materials and systems that can handle the challenges of fusion environments. Unlike nuclear fission, where long-lived radioactive waste is a significant concern, the radioactive waste produced in fusion is generally less problematic and has shorter half-lives.
Efforts are made to use materials that are compatible with fusion environments, and research is ongoing to find ways to manage and recycle materials in a way that minimizes waste production and environmental impact. As fusion technology advances, waste management practices will continue to be an important aspect of ensuring the safety and sustainability of fusion power generation.
The main Current problems with the Tokamak
Fusion reactions do not produce the long-lived radioactive waste associated with nuclear fission. The fuels, deuterium and tritium, can be obtained from abundant sources and are not as dangerous as the fuels used in nuclear fission. One of the biggest challenges in achieving practical fusion on Earth is confining the hot plasma at the required high temperatures and densities for a sufficient duration. Magnetic confinement (using strong magnetic fields) and inertial confinement (using intense lasers or other methods) are two primary approaches.
Companies building the Tokamak at the moment:
While ITER is not a company, it is a major international collaboration to build the world’s largest experimental tokamak. Located in Cadarache, France, ITER aims to demonstrate the feasibility of sustained nuclear fusion and produce a significant amount of fusion energy. It’s a collaboration among 35 countries, including the European Union, the United States, Russia, China, Japan, India, and others.
TAE Technologies, based in the United States, is working on an advanced field-reversed configuration (FRC) tokamak known as “Norman.” TAE focuses on a different magnetic confinement approach than traditional tokamaks, aiming to achieve net energy gain from fusion.
General Fusion, also based in the United States, is developing a fusion system called “Magnetized Target Fusion.” While not a traditional tokamak, their approach involves using compression techniques to achieve fusion conditions.
A collaboration between MIT (Massachusetts Institute of Technology) and the private company Commonwealth Fusion Systems, SPARC aims to develop a high-field, compact tokamak to demonstrate net energy gain.
East
While not a company, EAST is a tokamak located in China that has been actively conducting research in the field of nuclear fusion. It’s a part of the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP).
K-STAR
K-STAR is located in South Korea and is dedicated to studying and advancing nuclear fusion through a superconducting tokamak design.
ASDEX
Located in Germany, ASDEX Upgrade is operated by the Max Planck Institute for Plasma Physics and is involved in various fusion research activities using a tokamak configuration.
So is it the future of clean energy?
After doing deep research into this topic of fusion energy I definitely feel like fusion is the way forward, with the minimum amount of waste being produced and the potential of large amounts of energy/electricity. There is a very small amount of waste that will be produced and it won’t contribute to global warming. There are challenges and we are constantly getting closer to the breakeven point and getting past the challenges.
With the amount of money and resources being used to try and achieve the break-even point I think we will reach it by 2030. This will only happen if we keep on putting in the resources and effort, We need more people to help out than ever before as we are reaching a time where cancer and poverty is not a problem but climate change is as if we don’t solve climate change there will be no humans.
So yes, the future of clean energy, fusion is potentially here. Let’s keep on striving for greatness.
Check out my video bellow on on Fusion Energy!
Thanks for Reading
