Spherical tokamak could take major steps towards fusion power

CCFE 24/08/2016

A concept for a device to tackle some of the main hurdles standing in the way of commercial fusion power has been drawn up by Princeton Plasma Physics Laboratory with input from CCFE.

The Fusion Nuclear Science Facility would for the first time integrate systems for electricity production, materials and component testing, and fuel breeding in one plant. This could offer a route in addition to the international ITER experiment – now under construction in France – to the first fusion power stations.

By generating a small amount of net electricity, the facility would also act as a pilot plant to demonstrate nuclear fusion as a practical energy source – a long-awaited and symbolic moment.

The concept is based on the spherical tokamak design – a compact type of fusion device pioneered by Culham’s START and MAST experiments and Princeton’s NSTX machine. The spherical tokamak can produce the high performance plasmas needed for fusion reactions in comparatively small, cost-effective machines, making it a good choice for prototyping power plant technology.

The proposal is outlined in a paper published in Nuclear Fusion journal, with research led by Jonathan Menard, program director for Princeton’s NSTX Upgrade tokamak (which is pictured). CCFE’s Tim Hender is one of the co-authors.

The design would incorporate innovations developed at CCFE; notably, the exhaust system designed to steer hot plasma out of the reactor without damaging its walls is based on the ‘Super-X divertor’ being trialled on Culham’s new MAST Upgrade tokamak.
CCFE’s Fusion Programme Manager Ian Chapman (who will take over as CEO in October) said: “We are very supportive of the proposal. It could drive the fusion technology programme forward in several crucial ways, and if it also puts fusion power on the electricity grid that would be a fantastic achievement.

“In particular, a device that can test materials and components at full scale is a necessary step for fusion. Although a lot of work is being done on materials at the microscopic level, including at Culham, we have long advocated a component test facility that replicates the conditions inside a commercial fusion reactor.

“As the Nuclear Fusion paper suggests, the spherical tokamak is the ideal machine for this role. The new UK experiment MAST Upgrade will be a major part of taking this work forward along with NSTX Upgrade at Princeton. The innovative technology being developed on these tokamaks, such as MAST Upgrade’s Super-X plasma exhaust system, can form the basis for this exciting next step.”

See the Princeton Plasma Physics Laboratory website for more detail on the Fusion Nuclear Science Facility and pilot plant concept.

NSTX Upgrade image courtesy of PPPL.