Although ISIS will continue to operate for many years to come, plans for a new facility will be developed over the next decade to be ready for construction sometime after 2030. This will maintain and enhance the UK's neutron and muon provision, in a way complementary to the ESS and in support of the UK research community.
A project is underway to consider the requirements for an ISIS-replacement facility, and to explore the technologies that might underpin this, including different accelerator technologies.
One accelerator option being considered is a low energy linear accelerator combined with a Fixed Field Alternating gradient accelerator (FFA), which could accelerate protons up to 1.2 GeV. An FFA uses DC magnets that hold a constant field rather than AC magnets like those used in a synchrotron, with the protons travelling in a spiral as in a cyclotron.
Since they are free from magnet ramping, they can operate at a much higher repetition rate than synchrotrons. They also enable beam stacking, where an initial bunch of particles is injected and accelerated to high energy. This bunch continues to circulate, while a second and subsequent bunches are accelerated to merge into the first. This leads to a higher peak beam current and can also separate the user pulse rate from the acceleration injection pulse rate. Using an FFA could also reduce operating costs, as DC magnets are usually cheaper to operate and more reliable.
The drawbacks of such machines are the need for bigger and more complex magnets. No high power FFAs have been built before, although a project using an FFA for high power muon production is currently under study at the Chinese Spallation Neutron Source. The intense beams group at ISIS is looking to build a proof-of-principle ring to demonstrate whether FFAs are suitable for the high-power operation required for ISIS-II.
After four years of design work, this month saw the delivery of a magnet that is the prototype of a prototype of what would be needed for such an FFA. A tenth of the size of the final version, it's a complex build of nested metal coils and has taken the manufacturer a year to build.
The team were very excited to see the magnet delivered, and they are looking forward to the next stage of the project. This will involve characterising the magnet in different settings corresponding to specific beam configurations and investigating ways to correct errors coming from misalignments and manufacturing errors.
The magnet was designed by PhD student Ta-Jen Kuo from Imperial College London who has been jointly supervised by ISIS' Jean-Baptiste Lagrange and Jaroslaw Pasternak from Imperial. Iker Rodriguez, Jon Speed and Siva Mohanavelu from the magnet design group have also contributed their expertise at different stages of the project, including several visits to the manufacturer. Stephen Brooks, a former ISIS scientist and FFA expert now based in Brookhaven National Lab has also greatly contributed to the project with his keen insights.
