The UK is working on their own approach to nuclear fusion for power production. Their Mega Amp Spherical Tokamak (Mast) Upgrade has taken seven years to construct at a cost of seventy-one million dollars to date. It utilizes an innovative design known as a spherical tokamak. The tokamak is a popular approach for fusion devices that use magnetic fields to confine the plasma inside a vessel. The plasma consists of a hot ionized gas in which nuclear fusion takes place. Most of them are shaped like a donut. However, in the Mast Upgrade, the size of the donut hole has been shrunk as much as possible leading to a more spherical shape.
Prof Ian Chapman is the chief executive of the U.K. Atomic Energy Authority (UKAEA). When the Mast Upgrade was switched on for the first time recently, he said that it was "a really momentous occasion".
The occurrence of what is called “first plasma” signals the start of this pioneering effort to move the U.K. closer to building a commercial fusion power plant. While it is relatively easy to control a plasma and perform fusion, it is another matter to achieve the Lawson criterion where the amount of energy being pumped into the fusion reactor is less than the amount of energy generated by the reactor.
The Culham Center for Fusion Energy is currently home to both the Mast Upgrade and another fusion reactor project called the Joint European Torus (JET). The JET is based on a more conventional fusion reactor design. It was the precursor for the international, multi-billion-euro being built in France called the ITER. It is hoped that the ITER project, which is one of the biggest science experiments in the world, will be able to demonstrate nuclear fusion at a scale that could be used for energy production.
In addition to the JET, the Culham researchers have been pursuing a parallel project with the Mast Upgrade. Professor Chapman said in an interview, “We've been thinking about a pathway to fusion power plants which allowed for smaller, and therefore cheaper builds. That will hopefully allow quicker penetration into energy markets. That's the genesis behind the spherical tokamak.”
However, Chapman says that “the big challenge behind the spherical tokamak is that the boundary conditions behind making fusion happen is that you need the fuel to be 10 times hotter than the Sun. If you put that into a much smaller box... the chances of melting the walls of the box are much higher. So you need a really clever way of getting the heat out.”
The scientists at Culham have designed a very complex and technically challenging exhaust system. The next step in their research is to test this new exhaust system which is called the Super-X divertor in the Mast Upgrade. It is designed to channel plasma out of the reactor at temperatures that are low enough for the materials in the reactor to cope with. This means that the components of the reactor will last much longer. Chapman said, “If it works, it really does offer a path to much more compact fusion power plants, in a much more cost-competitive way to delivering fusion here on Earth.”
Amanda Solloway is the UK Science Minister. She said, “We want the UK to be a world leader in fusion energy and to capitalize on its amazing potential as a clean energy source that could last for hundreds of years. Backed by £55m of government funding, powering up the Mast Upgrade Device is a landmark moment for this national fusion experiment and takes us another step closer towards our goal of building the UK's first fusion power plant by 2040.”