Major upgrade of the MAST tokamak will pave the way towards future fusion power station

Last artificial star in tokamak MAST before major upgrade

Scientists at the UK’s Culham Centre for Fusion Energy (CCFE) have run final experiments on the MAST tokamak before starting a major overhaul of the device that will pave the way for a prototype fusion plant.

“It’s a bittersweet moment for us because we are saying goodbye to the old machine but at the same time, we are already looking forward to the new one,” said the CCFE spokesman Nick Holloway.

“At 4pm today, we will run the last plasmas and within minutes after that, engineers will move in to shut down the tokamak for the next 18 months. By Monday, the roof beams in the MAST machine area will have been taken off before the 25-tonne MAST vessel will be lifted on a big crane and moved to the assembly hall.”

The £30m upgrade is set to make MAST (the Mega Ampere Spherical Tokamak), a cutting edge facility. It will increase its power and enable testing technologies that will improve the knowledge base needed for the construction of ITER, but also to test systems for the DEMO prototype fusion power plant.

“To take fusion forward to ITER and through to commercial power, we need to keep improving our research facilities. In 2015, CCFE will have a machine that we and our collaborators from around the world can use to explore exciting new areas of plasma physics and test innovative concepts for fusion technology. We can’t wait,” said Dr Brian Lloyd, Head of CCFE Experiments Department.

One of the key technologies the upgraded MAST will be equipped with is the Super-X divertor, an innovative high-power exhaust system that will reduce the power loads from particles leaving the plasma.

The divertor is an exhaust system at the bottom of the fusion chamber, through which waste rejected from the plasma leaves the reactor. The particles being exhausted are extremely energetic, resulting in extreme power loads on in this part of the reactor. The idea of Super-X is to steer the particles along a longer exhaust path, allowing them to cool down and spreading them over a larger area, so that the power loads on materials are significantly reduced. 

“This technology could actually pave the way towards future fusion power stations. It will be the very first time anyone will be using this technology,” Holloway said.

Since 1999, MAST, an innovative spherical tokamak, a successor of UK’s earlier venture called START, has created over 24,000 man-made stars, providing a wealth of data. The knowledge gathered during the MAST experiments has helped advance understanding in many key areas including plasma instabilities and start-up methods.

The spherical concept that MAST inherited from START, has proven over the years to be more efficient than the conventional toroidal design, adopted by JET and ITER.

MAST has originally been commissioned by Euroatom and the UK Atomic Energy Agency, the current upgrade, however, is funded by the Engineering and Physical Sciences Research Council.

Apart from the Super-X divertor, the tokamak will receive a new centre column, better divertor coils, and a cryopump and power supplies that will provide pulse lengths up to ten times that of the existing machine.

As Holloway said, the MAST engineers and physicist are definitely not going on a 18-month vacation. They will be busy analysing the data the tokamak has provided previosly and will have to prepare new experiments for the improved machine.

“There will also be a lot of work developing the new systems and also a lot of theoretical work to do that will be put to practice later,” Holloway concluded.


VIDEO: A fusion experiment inside the MAST device


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