Beyond the Sun: Inside a Fusion Reactor

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. 

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. 

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. 

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

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.

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.

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.

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.

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.

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.

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. 

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.

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

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.

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. 

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.