Mega Ampere Spherical Tokamak (MAST) was a

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...

experiment, testing a

spherical tokamak A spherical tokamak is a type of fusion power device based on the tokamak principle. It is notable for its very narrow profile, or '' aspect ratio''. A traditional tokamak has a toroidal confinement area that gives it an overall shape similar to ...

nuclear fusion reactor Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions. In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices de ...

, and commissioned by

EURATOM The European Atomic Energy Community (EAEC or Euratom) is an international organisation established by the Euratom Treaty on 25 March 1957 with the original purpose of creating a specialist market for nuclear power in Europe, by developing nucl ...

UKAEA The United Kingdom Atomic Energy Authority is a UK government research organisation responsible for the development of fusion energy. It is an executive non-departmental public body of the Department for Business, Energy and Industrial Strategy ( ...

. The original MAST experiment took place at the

Culham Centre for Fusion Energy The Culham Centre for Fusion Energy (CCFE) is the UK's national laboratory for fusion research. It is located at the Culham Science Centre, near Culham, Oxfordshire, and is the site of the Joint European Torus (JET), Mega Ampere Spherical Tokam ...

Oxfordshire Oxfordshire is a ceremonial and non-metropolitan county in the north west of South East England. It is a mainly rural county, with its largest settlement being the city of Oxford. The county is a centre of research and development, primarily ...

, England from December 1999 to September 2013. A successor experiment called MAST Upgrade began operation in 2020.

Design

A spherical tokamak is shaped more like a cored apple than the conventional, doughnut-shaped toroidal design used by experiments such as

ITER ITER (initially the International Thermonuclear Experimental Reactor, ''iter'' meaning "the way" or "the path" in Latin) is an international nuclear fusion research and engineering megaproject aimed at creating energy by replicating, on Earth ...

. Spherical tokamaks are more efficient in their use of the magnetic field. MAST included a

neutral beam injector Neutral-beam injection (NBI) is one method used to heat plasma inside a fusion device consisting in a beam of high-energy neutral particles that can enter the magnetic confinement field. When these neutral particles are ionized by collision with ...

for plasma heating. It used a merging compression technique for plasma formation instead of the conventional direct induction. Merging compression saves central

solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...

flux, which can then be used to increase the plasma current and/or maintain the required current flat-top. MAST's plasma volume was about 8 cubic meters. It confined plasmas with densities on the order of 10²⁰/m³. MAST's plasma had an almost circular outer profile. The extensions off the top and bottom are plasma flowing to the ring

divertor In nuclear fusion power research, a divertor is a device within a tokamak or a stellarator that allows the online removal of waste material from the plasma while the reactor is still operating. This allows control over the buildup of fusion prod ...

s, a key feature of modern tokamak designs.

Experiments

MAST confirmed the increased operating efficiency of spherical tokamaks, demonstrating a high

beta Beta (, ; uppercase , lowercase , or cursive ; grc, βῆτα, bē̂ta or ell, βήτα, víta) is the second letter of the Greek alphabet. In the system of Greek numerals, it has a value of 2. In Modern Greek, it represents the voiced labiod ...

(ratio of plasma pressure to the pressure from the confining magnetic field). MAST performed experiments on controlling and mitigating instabilities at the edge of the plasma – so-called Edge Localised Modes or ELMs.

History

MAST

MAST was designed to confirm the results of the earlier

Small Tight Aspect Ratio Tokamak The Small Tight Aspect Ratio Tokamak, or START was a nuclear fusion experiment that used magnetic confinement to hold plasma. START was the first full-sized machine to use the spherical tokamak design, which aimed to greatly reduce the aspect ...

(START) experiment (1990-1998) in a larger, more purpose-built experiment. The MAST design phase occupied 1995-1997, with construction beginning in 1997, and the first plasma obtained in 1999. The first results of the MAST demonstrate that mode-H is reached with more ease and less energy than expected with a considerable improvement in confinement, a fundamental point for any energy production scenario. Finally, different scenarios have been successfully tested to decrease the energy flow in the central solenoid vs plasma current, which represents another fundamental point for designing a demo spherical tokamak. Over its lifetime MAST produced 30,471 plasmas (in pulses up to 0.5 sec). In October 2013 the reactor was shut down for the upgrade to MAST Upgrade.

MAST Upgrade

MAST Upgrade is the successor experiment to MAST, also at Culham Centre. The upgrade, which cost £45M, started in 2013 and was expected to significantly exceed MAST’s heating power, plasma current,

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

and pulse length. MAST Upgrade began operation on 29 October 2020. One of MAST Upgrade's most notable features is the Super-X divertor. The divertor removes excess heat and impurities from the plasma. Conventional divertor designs, at powerplant scale, will experience high heat loads and will need to be regularly replaced. The Super-X divertor was expected to produce heat loads that are lower by around a factor of ten and has been seen as initially successful.

Spherical Tokamak for Energy Production

The design of the next generation

Spherical Tokamak for Energy Production Spherical Tokamak for Energy Production (STEP) is a spherical tokamak fusion plant concept proposed by the United Kingdom Atomic Energy Authority and funded by UK government. The project is a proposed DEMO-class successor device to the ITER tokamak ...

(STEP) began in 2019 with £220 million in government funding. The plan is to begin operations in the 2040s. The current plan does not include a tritium generation facility.

References

External links

MAST Main PagePhotos of MASTFirst results from MAST. 2001
Summary of first 6 months
MAST Upgrade Research Plan, November 2019
{{authority control Tokamaks Culham Centre for Fusion Energy