After all that has been said, there is obviously a future for nuclear fusion. We have come much closer to achieving this, and it may actually be just 30 years away, maybe a decade less. This of course is talking about a successful nuclear fusion reactor that can power cities - not a model, not a demonstration, but an actual reactor. With that being said - let’s dive into the technologies that are being developed for nuclear fusion.
Technologies
Before I get into the reactors being developed, it is important to understand the two main ways of harnessing energy. So, you do remember when temperature and pressure are extremely high, elements tend to turn into plasma. Plasma is the fourth state of matter after solid, liquid, and gas. Gases at extremely high temperatures - like in the Sun - turn into plasma, but this does not mean that they have the same properties...well there is one similarity. Like a gas, plasma does not have a definite shape or volume.
Unlike gas, plasma is electrically conductive, produces magnetic fields and electric currents, and responds strongly to electromagnetic forces. Now in the reactors, when plasma is formed, it’s extremely difficult to control due to these properties, and hence harnessing energy becomes a big problem. It’s like when you have a very hot plate - how are you going to carry it from one place to another? This is why we have come up with two ways of trying to control this plasma - magnetic and inertial confinement.
Magnetic Confinement
Firstly, this type of confinement makes use of a particle accelerator. This accelerator is a machine that uses electromagnetic fields (you can look at this as a powerful electric magnet) to propel charged particles to very high speeds and energies, which are used to heat up hydrogen gas, turning it into plasma.
Magnetic confinement, as the name suggests, uses magnetic properties. However, it uses electric fields as well which are mostly used in superconducting magnets, because as mentioned before, the state plasma, has electrical properties too and hence you would need a much much stronger magnet.
They can generate magnetic fields that are up to ten times stronger and there isn’t any resistance to electrical currents. This basically controls the flow of plasma but it isn’t that simple since plasma can move in any direction - there will have to be a specific design and placement of magnets such that plasma doesn’t hit the walls of the reactor.
Inertial Confinement
A tiny solid pellet of fuel, such as deuterium-tritium (D-T) is compressed to an extremely high density, while being heated to a high temperature so that fusion power is produced in the few nanoseconds before the pellet blows apart. This ’heating’ is done through using a high energy laser beam that heats the pellet to high temperatures however, the pellet has to be heated equally, every area/section of the fuel must be the same temperature throughout. The laser uniformly heats the outer layer, causing materials to blow off. This is where Newton’s 3rd law comes in handy - every action has an opposite reaction. Hence when the outer layers blow off (upwards) the inner layers get blown downwards, getting compressed.
Tokamak.. ITER
To make it clear, tokamak is a type of magnetic confinement design for a fusion reactor. Tokamak is a Russian name and it translates to toroidal chamber which basically is a doughnut-shaped vacuum chamber . The design of tokamak is looked as the most successful and hence I will be briefly introducing the latest tokamak.
ITER is considered as a tokamak reactor, and with over 200 tokamaks over the globe, ITER will be the world's largest tokamak, with ten times the plasma volume of the largest tokamak operating today. ITER is also conceived as the last experimental step to prove the feasibility of fusion as a large-scale and carbon-free source of energy,
Figure 1: Tokamak
To start the process, air and impurities are first evacuated from the vacuum chamber. Next, the magnet systems that will help to confine and control the plasma are charged up and the gaseous fuel is introduced. As a powerful electrical current is run through the vessel, the gas breaks down electrically, becomes ionised (electrons are stripped from the nuclei) and forms a plasma.
Inside, under the influence of extreme heat and pressure, gaseous hydrogen fuel becomes a plasma. In a star as in a fusion device, plasmas provide the environment in which light elements can fuse and create energy. This plasma temperature is at about 150 million degree Celsius. That is ten times the temperature of the sun..
As the plasma particles become energised and collide they also begin to heat up. At extremely high temperatures, particles ”energised” to such a degree can overcome their natural electromagnetic repulsion on collision to fuse, releasing huge amounts of energy. With a huge amount of energy, there can be safety concerns and hence the flow of plasma needs to be controlled.
The charged particles of the plasma can be shaped and controlled by the massive magnetic coils placed around the vessel; physicists use this important property to confine the hot plasma away from the vessel walls.
This of course is a brief intro to a fusion reactor. To dwell into the major components of this system might get confusing so I’ll be diving into them further in my next blog posts. Keep reading.
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