Mega Ampere Spherical Tokamak

Mega Ampere Spherical Tokamak

Plasma in the MAST reactor.
Type Spherical tokamak
Operation date 1999–2013
Major radius ~0.9 m
Minor Radius ~0.6 m
Magnetic field 0.55 T
Heating 5 MW
Plasma current 1.3 MA

The Mega Ampere Spherical Tokamak (MAST) experiment was a nuclear fusion experiment in operation at Culham, Oxfordshire, United Kingdom from December 1999 to September 2013. It followed the highly successful Small Tight Aspect Ratio Tokamak (START) experiment (1991 - 1998) and is followed by MAST-Upgrade (2016 - ), which re-uses many of MAST's components and services. MAST used the same innovative spherical tokamak design as START, which has shown itself to be more efficient than the conventional toroidal design, adopted by Joint European Torus (JET) and ITER. START proved to exceed even the most optimistic predictions and the purpose of MAST is to confirm the results of its forerunner by using a larger more purpose-built experiment.

It was fully commissioned by EURATOM/UKAEA and took two years to design and a further two years to construct. It includes a neutral beam injector similar to that used on START and uses the same merging compression technique instead of the conventional direct induction. Merging compression provides a valuable saving of central solenoid flux, which can then be used to further ramp up the plasma current and/or maintain the required current flat-top.

Its plasma volume is about 8 m3. Density ~ 1020/m3.

Image to right shows plasma in the MAST reactor. Note the almost circular outer profile of the plasma. The extensions off the top and bottom are plasma flowing to the ring divertors, a key feature of modern tokamak designs.


  • Objectives 1
  • Timeline 2
  • Design 3
  • Operation 4
  • Upgrades 5
  • See also 6
  • References 7
  • External links 8


  • Studies in a new regime, to provide improved understanding of tokamaks, and improved ITER design (e.g., effects of plasma shaping).
  • To investigate the potential of the spherical tokamak route to fusion power.


  • ~1995 design starts
  • ~1997 construction starts
  • 1999 First plasma
  • 2013 Oct. Final plasma (#30471) before shutdown for upgrade.[1]


The magnetic field coils are not superconducting and (for longer runs after upgrade 1a) need to be cooled to -20 C before each pulse.[2]


From 1999 to 2013 it made 30471 plasmas (in pulses up to 0.5 sec).


The device is planning a major upgrade to significantly enhance its capabilities to address its primary objectives. (listed above). The first stage "1a" should be complete by 2016.[3] During the first upgrade '1a' :

  • Toroidal magnetic field will be increased from 0.55 Tesla to 0.84 Tesla
  • Energy deposited in plasma at high current will be increased from 2.5 megajoules to 10-20 megajoules
  • Max Pulse length at high current/field will be increased from 0.5 seconds to 2-4 seconds
  • Plasma current will be increased from 1,300,000 amps to 2,000,000 amps

It will be the first tokamak to use a Super-X divertor.

As of Jan 2015 further upgrades are not funded.

See also


  1. ^ It's goodbye to MAST - and hello to MAST-Upgrade | 01/10/2013
  2. ^ MAST-Upgrade model
  3. ^ MAST Upgrade

External links

  • MAST Main Page
  • Photos of MAST
  • First results from MAST. 2001 Summary of first 6 months