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First plasma for upgraded UK spherical tokamak

30 Oct 2020 Michael Banks
First plasma at the Mega Amp Spherical Tokamak
Hot stuff: The first plasma has been recorded at the upgraded Mega Amp Spherical Tokamak. (Courtesy: Culham Centre for Fusion Energy)

Officials at the Culham Centre for Fusion Energy (CCFE) in Oxfordshire, UK, have announced that they have achieved “first plasma” on the upgraded Mega Amp Spherical Tokamak (MAST). Following seven year of upgrade work on MAST at a cost of £55m, the machine was fully powered up for the first time yesterday allowing the experimental programme to begin. Over the coming years, MAST-U will seek to demonstrate that high plasma performance could be scalable to an actual fusion reactor.

Operated by the United Kingdom Atomic Energy Authority (UKAEA), the CCFE is already home to the Joint European Torus (JET) tokamak. This is involved in testing the materials that are to be used in the ITER fusion experiment, which is currently being built in Cadarache, France. Whereas JET – like ITER – has a doughnut-shaped plasma, MAST on the other hand has a spherical plasma, shaped much like a cored-out apple. This design allows for a much more compact – and cheaper – device and it is hoped that this kind of tokamak could one day be used as a potential fusion reactor.

The MAST tokamak was operational between 1999 and 2013 before being shut down for the upgrade, which was completed last year. Known as MAST-U, it is expected to be able to create a plasma of deuterium with a timespan of around 2–4 s, compared with just 0.5 s before. A major feature of the upgrade is a new exhaust system – known as a divertor – that it is hoped will show that the tokamak is able to handle the intense exhaust heat emerging from the plasma more effectively than existing designs, including that used on ITER. The MAST-U divertor is intended to take a 50 MW/m2 heat load and reduce it to just 5 MW/m2.

The CCFE has also received £21m from the European Fusion Research Consortium and the UK’s Engineering and Physical Sciences Research Council to further enhance the upgrade. This will include doubling the neutral beam injection into the plasma from 5 MW with MAST-U to 10 MW. Work on that is expected to be complete by the end of next year.

A step up

Research on MAST is also expected to inform the conceptual design of the UK’s prototype fusion power plant – Spherical Tokamak for Energy Production (STEP). Work on the design is set to be complete by 2024 with the aim to build STEP by 2040. “MAST Upgrade ensures the UK is in the premier league of countries working on fusion – and will be vital in achieving UKAEA’s goal of building the STEP fusion power plant,” says Ian Chapman, UKAEA chief executive. 

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