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What is a tokamak?

‘Tokamak’ is the name of the type of machine that uses large magnets and high pressure to create fusion energy like a tiny version of a star. 

The inside walls of the tokamak are coated with materials with a high melting temperature such as tungsten and beryllium. This is to minimise damage caused while holding a fusion plasma. 

Plasma is the fourth state of matter. Heating a solid will turn it into a liquid, heating a liquid will turn it into a gas and heating a gas to a high enough temperature will cause it to ‘ionise’ and turn it into a plasma. The plasma inside our tokamaks can glow pink and reach 150 million °Celsius (that’s 10x hotter than the core of the sun!). A plasma is made up of charged ions, meaning, it can be held and confined using magnetic fields. 

The plasma is created using hydrogen isotopes, deuterium and tritium. Once heated to extremely high temperatures, the atomic nuclei (positively charged core of the atom) fuse creating helium releasing a high energy neutron. This release of energy can be captured and converted into a safe, usable, and sustainable source of power 

The magnets produce a large magnetic field which pushes and holds the plasma in the centre of the machine. To help then run efficiently the magnets are held at cryogenic temperatures around -269°C! 

The tokamak is held in a vacuum so that air does not contaminate the fusion fuels, this helps to give us the best reaction possible and therefore produce energy more efficiently. 

The ‘blanket’ wraps around the machine and is used to produce fuel. As neutrons leave the machine from the fusion reaction, they will hit the blanket and react with the lithium inside.  This reaction produces tritium which is a fusion fuel. We can channel this tritium back into the plasma which helps to make the machine self-sufficient. 

The divertor is also called the ‘exhaust’ and it works similarly to the exhaust pipe of a car, it takes hot waste gas that is no longer needed and channels it out of the system. The STEP tokamak will have two of these divertor channels, one at the top and one at the bottom. 

The central solenoid is placed through the centre of the tokamak. It induces a current inside the plasma which helps to heat it and creates a magnetic field which directs the plasma around the tokamak.