News and events
New light being shed on the secrets of fusion plasmas | 30/11/2009
A £2million upgrade to the MAST tokamak's Thomson scattering laser diagnostic will give UK physicists unprecedented insights into the behaviour of fusion plasmas.
The MAST experiment, located at Culham Centre for Fusion Energy (CCFE) in Oxfordshire, now has the world's most advanced system for recording the plasma temperature and density profiles, aiding research into nuclear fusion as a future energy source. The upgrade, part-funded (£400,000) by the University of York and the Northern Way collaboration of Regional Development Agencies, was completed in September 2009 and the diagnostic is already providing data exceeding its design specifications.
Thomson scattering is used to obtain local measurements of electron temperature and density inside the hot plasma – which can reach over 20 million degrees Celsius in MAST – by measuring the scattering of light from laser beams fired into the plasma. The upgrade has increased the number of measurements that can be made during a MAST plasma pulse by doubling the amount of lasers used to eight. This allows over 150 separate time points to be captured during the lifetime of a plasma, from 130 different locations. A triggering device can synchronise lasers to the exact time of specific ‘events' during the pulse, such as the formation of the plasma or the injection of fuel pellets.
A better understanding of the processes happening in plasmas will help to improve the performance of future fusion devices such as ITER, the industrial-scale tokamak being built at Cadarache, France. The MAST Thomson scattering diagnostic will give researchers an extremely detailed view of the evolution of the plasma, as CCFE project leader Dr Mike Walsh explains:
“We expect the system to throw up new physics and allow us to observe effects we have never been able to see in plasmas before,” says Walsh. “We can also get a more accurate picture of occurrences we already know about; for example, the formation of ‘magnetic islands' that affect confinement of the plasma and reduce fusion energy output.”
Researchers from the University of York's Plasma Physics and Fusion Group, in collaboration with CCFE, will exploit the upgraded system to confirm theoretical principles of plasma behaviour. They will run experiments on MAST direct from York, using a new remote control room recently installed at the university. Professor Howard Wilson of the University of York says:
“It is early days, and there is still work to be done to interpret the first data, but already this world-leading Thomson system is revealing tantalising glimpses of plasma physics phenomena in unprecedented detail.”
The MAST upgrade demonstrates how far plasma diagnostic techniques have advanced since the pioneering Thomson scattering measurements by Culham scientists 40 years ago, which confirmed the performance of the Soviet Union's T-3 tokamak – leading fusion researchers around the world to adopt the tokamak concept. Dr Mike Forrest, who was a member of the Culham team that travelled to the Kurchatov Institute in Moscow in 1969, comments:
“In 1969 we made great advances with a system that could only give one measurement of temperature at one position in the plasma. At MAST today, 30,000 measurements can be generated in one pulse, so Culham is still leading the way in laser scattering techniques 40 years on.”
