Initially, the upgrades on the Mega Amp Spherical Tokamak (MAST) facility at Culham Centre for Fusion Energy will focus on developing a compact fusion source. This will hopefully enable the construction of a cost-effective component test facility to study the engineering of commercial fusion reactors.
Further upgrades will lead to studies on the physics and control of high-performance plasmas to improve the future operation of ITER – an international project to design and build an experimental fusion reactor based on the ‘tokamak’ concept.
The spherical tokamak is a compact alternative to the JET-ITER-style magnetic-confinement fusion configuration. Spherical tokamak innovations promise to deliver more efficient energy production in fusion reactors.
The final round of upgrades will prepare the machine to be the first to trial the Super-X divertor, an innovative plasma exhaust system capable of handling the huge power loads of future commercial reactors.
It is expected that the upgrades will be completed by 2015. These upgrades follow the recommendations of an independent review of the fusion programme for Research Councils UK, published in February 2010, which endorsed MAST Upgrade as part of a long-term funding strategy for UK magnetic-confinement fusion research.
Prof Steve Cowley, head of Culham Centre for Fusion Energy, said: ‘MAST Upgrade is going to be a very important device in fusion research, both for the world and for the UK. We will get near-fusion conditions in a very compact device and provide the basis of a whole slew of important experiments in physics and technology – important for fusion but also for basic understanding of plasmas and their interactions with materials. It will guarantee that, on the Culham site, we will have world-leading research for the next generation, making a vital step towards commercial fusion power.’
Fusion energy
Fusion is the process that powers the sun and the stars. When light atomic nuclei fuse together to form heavier ones, a large amount of energy is released.
To utilise fusion as an energy source, gaseous fuel is heated to extreme temperatures, hotter than the centre of the Sun, forming a plasma in which fusion reactions take place. A commercial power station will use the energy from neutrons produced by fusion reactions to generate electricity.
Research is focused on delivering the huge potential of fusion as an energy source that is safe, environmentally responsible, economically viable, with abundant and widespread fuel resources. In Europe, fusion research is organised in a coordinated programme that provides for intensive use of pan-European R&D resources in collaborations on major research topics.
The magnetic-confinement fusion programme’s objectives are to obtain and study conditions approaching those needed in a power plant using the ‘tokamak’ machine concept – effectively a magnetic bottle that contains the hot plasma. The next step is ITER, an international tokamak experiment that should provide a full scientific demonstration of the feasibility of fusion in power-plant-like conditions. ITER is now being constructed at Cadarache in the south of France. ITER will be followed by a demonstration fusion power station, DEMO.
Spherical tokamaks
Since tokamaks were developed in Russia in the 1960s, research has mainly concentrated on machines that hold the plasma in a doughnut-shaped vacuum vessel around a central column, with very successful results. JET and the next-generation ITER device are designed with this configuration, known as the ‘conventional tokamak’.
Spherical tokamaks’ (STs) hold plasmas in tighter magnetic fields, forming a more compact, cored apple shape. Topologically the same as conventional tokamaks, spherical tokamaks get their name from the natural shape of the plasma that forms as width of the centre column is minimised. The ST’s design produces a device where plasmas are confined at higher pressures for a given magnetic field. This could result in more efficient power plants, which will cost less to build as they do not need to be as large as conventional machines for the same performance.
The world’s first hot spherical tokamak, START, was built at Culham and operated from 1991 before being succeeded by the larger MAST experiment in 1999.
Source: CCFE
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