Beyond the Sun: Inside a Fusion Reactor

The future's bright, the future's fusion!

This story was created for the Google Expeditions project by Twig World, now available on Google Arts & Culture

Making Energy

Travel inside the world's most revolutionary fusion reactor and discover how the energy of a sun can be recreated inside a secret building locked away from prying eyes.

Making the Sun on Earth

Welcome to the JET control room at the Culham Centre for Fusion Energy. Oil and coal supplies are running out. At Culham, scientists are trying to develop a new way of making energy by copying the process that occurs in the Sun, known as fusion.

When the process is fully developed, it will be non-polluting, using seawater as a fuel source to produce lots of energy. In the control room, an experiment – or “pulse” – is about to happen. 

Scientific Coordinator

The scientific coordinator is responsible for deciding the question that will be investigated during today’s 15 experiments. The problem the scientific coordinator is trying to solve is how to get more energy out of the JET reactor than is put in. 

At the moment, the reactor uses more energy than it produces. 

The Engineer in Charge

The lead scientist makes sure JET works as it should during each experiment. This is difficult, as the reactor is experimental and the temperatures inside reach 150 million degrees Celsius – making it the hottest place in the Solar System! 


The shift technician starts each pulse. Powerful magnets create a magnetic field, which acts like a bottle to contain the dangerously hot gas known as plasma. Protective tiles line the walls of the reactor in case the magnets fail. The reactor heats up. 

A tiny amount of hydrogen fuel – around the mass of a postage stamp – is put into the reactor. 


This is a European project and all partners must agree on the questions that need to be answered. The scientists and engineers work as a team to collect 60 gigabytes of data that will help them answer the agreed questions.

Understanding Fusion

To understand the JET and MAST fusion reactors at Culham, you need to understand how fusion works. Try to picture the process in your mind as you look around. 

What You Need is Heat

Like any substance, gas particles move faster and have more energy when they are heated. The fusion reactors heat up hydrogen, making its particles move faster and faster with enormous amounts of energy.



Eventually, the particles in the gas break down a little and become a soup of protons and electrons. This soup is called plasma. Many people think that plasma looks very beautiful.


When the hydrogen particles are heated up to more than 150 million degrees Celsius, they move so quickly that they crash into each other.


When two hydrogen particles collide at high speed, they fuse together to make a new substance called helium. This is nuclear fusion. If the reaction is large enough, it generates its own heat and becomes self-sustaining, like the Sun.


Nuclear fusion has fuelled the Sun for 4.5 billion years! The opposite of fusion is fission, where particles break up. Fusion reactors are an attempt to make fusion happen on Earth, which could help meet future energy needs.

Underneath the MAST Fusion Reactor

In any experiment, scientists must measure some variables (dependent variables) and control other variables to make the experiment a fair test. The same is true here. 

A full-size reactor built using data from these experiments might not work properly if the results were unreliable. Scientists control experiments to ensure accurate measurements and results that can be used to build bigger reactors.

Ports for Diagnostics

These ports are used for the diagnostics, or measuring tools. Lasers are used to measure the temperature of the hot plasma, which is one of the variables. The plasma needs to be at a stable temperature, between 100 million and 150 million degrees Celsius.

Wires on the Base

There are wires all over the bottom of the reactor vessel. These are used to create heat and bake off any impurities or moisture that could affect the results before the experiment starts. 

Martin Simmonds

Martin is an engineer working at the centre. One of his jobs is to make sure that the UK’s MAST fusion reactor is built according to the specification in its design.

Inside JET Reactor

This is the in-vessel training facility, and it looks very much like the real JET fusion reactor. It is used to train scientists to carry out many of the maintenance activities that will be needed during an experiment. 

The Base of the Vessel

During an experiment, the air is pumped out of the reactor, leaving a vacuum. The base of the vessel is made of very strong stainless steel, which allows it to resist the vacuum. 


The sides of the reactor are lined with tiles made of tungsten, which is heat resistant, and beryllium, which is light and does not react with the plasma.

Robotic Arm

A robotic arm means that humans do not have to enter the reactor, which contains toxic beryllium and radioactivity. The arm is controlled by a technician outside the reactor. Technicians practise using the robotic arm by playing Jenga with it.

The Channel

At the bottom of the reactor is a channel that acts as an exhaust pipe. The waste product is a very small amount of helium, which is an unreactive gas.

Controlling the Robotic Arm

The robotic arm enters the reaction vessel between experiments to carry out maintenance and conduct tests. A toolbox also enters the reactor from the other side so that all of the equipment and other materials are close by. 

Technically, the arm is not a fully automated robot, because the technician controls it.

Engineering Technician

The control of the robotic arm is a delicate job. The technician must learn to visualise the robotic arm operating inside the reactor. A movement of the technician’s arm will trigger the same movement in the robotic arm. 

Force Feedback Loop

The robotic arm is very sophisticated. The technician receives physical feedback from it, similar to feeling resistance from an object, or haptic feedback from a game controller. Using the arm is almost like being inside the reactor, doing the work. 


The engineering technician can see what the robotic arm is doing via these screens, which include a real-time, virtual-reality view of inside the reactor. This helps the technician move the arm accurately. 

Solving Engineering Problems

This is the materials research facility, set up to help solve some of the engineering problems faced in making a full-size reactor. The environment inside the reactor is harsh, and no one knows what will happen to materials when they are put under stress.

Hot Cells

The metals that come out of the reactors are toxic and radioactive. Tiny fragments are cut out, polished and mounted, ready to be examined in the “hot cells”, which are the windows you can see.

Alex Operates the Scanning Electron Microscope

Alex is an experimental materials scientist, currently doing her PhD on the impact of length-scales when measuring mechanical strength. 


Samples placed in the Scanning Electron Microscope can be magnified up to 100,000 times. Scientists can see, for example, if tungsten in the reactor has become fragile or broken over time.

How Does a Fusion Reactor Work?

There are two different types of fusion reactor in the fusion centre: JET and MAST. 

They both have to solve the same problems: Heating the hydrogen to millions of degrees Celsius to make plasma.Controlling the super-heated plasma to keep it away from the vessel walls using electromagnetic fields.Producing more energy than they consume.

Here, you can see the outside of the JET fusion reactor.

Heating the Plasma

This is the neutral beam injector. In this machine, hydrogen is split, heated and given massive amounts of electrical energy. It is then pushed into the plasma, passing on its energy to heat the plasma. 

The way the plasma is heated by the neutral beam injector is similar to the way steam can be used to heat milk: water is heated to make steam and then pushed into the milk, transferring heat energy. 

Controlling the Plasma

Controlling the Plasma

When the plasma reaches 100 million degrees Celsius, coming into contact with anything colder, such as the sides of the reactor, cools it, preventing fusion. But plasma is charged, like a magnet, and is held in the middle of the reactor by strong electromagnets surrounding it.

Making Energy

Making Energy

The Sun’s fusion reactions take place continuously because it is very large and does not run out of hydrogen. The fusion reactions inside MAST and JET are much smaller, and work in just 30- or 40-second pulses. On the right you can see a pulse inside JET. 



ITER is a fusion reactor being built in the south of France. Much bigger than JET or MAST, it will produce more energy than it uses. It is hoped that within 100 years, every country will use fusion reactors to generate huge amounts of electricity without polluting the environmen

How to Build a Fusion Reactor

The JET reactor is a tokamak, which contains the fuel in a doughnut-style metal ring, where it is heated to 10 times the temperature of the Sun’s core to form plasma. The reactor has 4 main functional parts.


Plasma is the essential fuel of the fusion reaction. In the plasma, some electrons are freed from their atoms, enabling electricity to flow.

Central Column

This column drives a current in the plasma in a given direction. It is constructed with poloidal field coil magnets and is the primary transformer circuit.

Magnetic Fields

The magnetic fields are used to position and shape the plasma inside the reactor. This keeps the hottest plasma in the Solar System away from the reactor vessel.

The Reactor Is Complete

The reactor needs tiles to protect its walls and magnets, as well as heating elements, measuring instruments and fuel. When the reactor runs a “pulse” or experiment, lighter elements can fuse and release energy.

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The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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