# How a Tokamak Works By Aaron Feigenbaum Topic: Physics & Chemistry [Open the interactive Jig](https://ask.jig.com/j/44WM85xn1cQJ) ## Guide ### 1. A star in a ring A tokamak is a machine that tries to make energy the way the Sun does, by joining tiny atoms together\. Inside this ring floats a gas far hotter than the Sun, touching nothing at all\. Drag to look around the cutaway\. Tokamak is a Russian word for a ring\-shaped chamber with magnetic coils\. ### 2. Fusion: atoms join The fuel is two heavy kinds of hydrogen, called deuterium and tritium\. When their centres, the nuclei, crash together fast enough, they fuse into helium and fling out a speedy neutron\. A tiny bit of mass turns into a lot of energy\. Red balls are protons and grey balls are neutrons\. Gram for gram, this fuel holds about four million times more energy than coal\. ### 3. Hotter than the Sun Nuclei push each other away, so they only fuse when they move incredibly fast\. That means heating the fuel to about 150 million degrees Celsius\. At that heat atoms break apart into nuclei and electrons, tiny bits that carry electric charge\. This glowing soup is called plasma\. That is about ten times hotter than the centre of the Sun\. The real plasma is so thin it barely glows; here it is coloured so you can see it\. ### 4. A cage of magnets No wall could hold something so hot, so the tokamak uses magnets instead\. Eighteen giant D\-shaped coils wrap around the ring\. Their field runs the long way round, and the charged particles spiral along it like beads on a wire\. The coils are superconductors: chilled to minus 269 degrees Celsius, they carry huge currents with no resistance, just a few metres from the hottest place in the solar system\. ### 5. Add a twist A field that only goes round the ring is not enough: the particles slowly drift up or down and escape\. The tall magnet in the middle drives an electric current through the plasma itself, and that current twists the field into a spiral\. Try both and watch the particles\. The twist keeps carrying each particle from the top of the ring to the bottom and back, so its drift cancels out\. ### 6. Shape it and heat it Six ring\-shaped magnets outside the coils hold the plasma in place and give it its D shape\. Beams of fast particles and radio waves then pour in heat\. Press the button to heat the plasma until fusion begins\. The current flowing through the plasma heats it too, a bit like the wire in a toaster\. ### 7. Catching the energy Neutrons have no electric charge, so the magnets cannot hold them\. They fly straight out into the blanket, a wall of steel blocks lining the chamber, which turns their energy into heat\. A power plant would use that heat to boil water and make electricity\. The divertor along the bottom works like an exhaust pipe, removing helium ash and other waste from the plasma\. ### 8. Building a star on Earth This model follows ITER, the largest tokamak ever built, now being assembled in France by many nations together\. It stands about 30 metres tall and weighs 23,000 tonnes\. Its goal is to make ten times more fusion power than the heat put in\. Fusion stops by itself if anything goes wrong: the plasma simply cools down\. Find the tiny person by the base for scale\.