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MAST Upgrade is the UK’s national fusion experiment.

It is tackling one of fusion energy’s biggest challenges: plasma exhaust.

The device is based on the original MAST (Mega Amp Spherical Tokamak) machine, which ran from 2000 to 2013. It has been rebuilt to enable higher performance – longer pulses, increased heating power and a stronger magnetic field – and an innovative new plasma exhaust system.

MAST Upgrade is exploring the route to compact fusion power plants, testing reactor technology and addressing physics issues for the international ITER fusion project. It keeps the UK at the forefront of global research into fusion energy.

Plasma exhaust: the Super-X factor

MAST Upgrade particularly focuses on plasma exhaust – a key issue that must be solved to achieve commercial fusion power.

The tokamak’s exhaust system (known as the ‘divertor’) processes spent fuel and heat ejected from the plasma. The plasma must be cool enough where it meets surfaces in the divertor to ensure that any damage is minimal.

Present divertors are not designed to withstand the intense power loads that will be created in the large fusion machines in future power plants. Divertor components would require replacement every few years, making it difficult for fusion to become an economically competitive energy source. The challenge is to develop a divertor with a manageable power load; about the same as in a car engine.

MAST Upgrade is the first tokamak to trial the ‘Super-X divertor’. This is an exhaust system designed to reduce heat and power loads from particles leaving the plasma, which should mean divertor components will last much longer. If successful, Super-X could be used in prototype power plants and commercial fusion reactors. MAST Upgrade can also operate with a variety of other divertor configurations to compare their effectiveness and inform design choices for future fusion reactors.

Advancing the spherical tokamak design

MAST Upgrade continues Culham’s pioneering research into spherical tokamaks. With a tighter magnetic field than the conventional JET – ITER-style tokamak, the spherical plasma configuration can achieve more efficient performance. This has excellent potential for building compact test reactors and could also offer a long-term route to smaller and cheaper fusion power plants.

Diagram of conventional tokamak and spherical tokamak

A user facility for fusion scientists from around the UK and the rest of the world

Researchers from CCFE and from our partners at universities and other European fusion laboratories use MAST Upgrade to study many areas of plasma physics. MAST Upgrade’s excellent diagnostics and plasma viewing capabilities make it one of the best tokamak experiments for understanding the physics of fusion plasmas. Data from MAST Upgrade will feed into international preparations for the ITER project, due to go into operation in the mid 2020s.

MAST Upgrade is funded by the UK Engineering & Physical Sciences Research Council, and by EUROfusion as part of the European Medium-Sized Tokamak programme.

MAST Upgrade Research Plan, issued November 2019

MAST Upgrade Users’ website
Information and tools for MAST Upgrade collaborators and users, including machine and data access information, operational logs and experiment planning. The site requires a login – please contact us if you are a collaborator who would like to apply for access.

Scientists in the MAST Upgrade control room
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