The ISIS accelerator paves the way
27 Aug 2009



After over twenty years of operation ISIS is still the world’s leading pulsed neutron and muon source.

Part of the FETS Radio Frequency Quadrupole (RFQ), which focuses, bunches and accelerates the beam. This 'model' RFQ has been made by Imperial COllege. The final RFQ will be 4m long and this represents about 1/10 of that as a design and machining test.​

But future accelerators needed for new neutron sources or a neutrino factory require even more powerful machines. Accelerator physicists at ISIS, working in collaboration with other UK colleagues, are helping to develop the technology for these next generation sources.

Essential to any accelerator is the ‘front end’. This, as the name suggests, is the first part of the acceleration process and is responsible for initial production of the proton beam which eventually becomes the source for neutrons and muons in ISIS.
To demonstrate production of beams for new, high intensity sources, ISIS scientists are collaborating with the Accelerator Science and Technology Centre (ASTeC), Imperial College London and the University of Warwick to build a ‘Front End Test Stand’ (FETS) at RAL. The idea is to create something that can be used to produce a pulsed proton driver of up to 5 MW power. Considering that ISIS has a pulsed proton driver of 0.16 MW, this is a considerable challenge.
“One of the biggest considerations is to increase the beam current, without increasing the beam loss,” explains Alan Letchford, one of the ISIS scientists working on the FETS. To achieve this a beam chopper is being developed which creates gaps in the proton chain, ensuring that there isn’t a ‘pile-up’ as the beam enters the synchrotron.
When it is up and running the new FETS will produce a 60 mA beam current – three times greater than the one produced by ISIS now. The test stand could serve as the front end of an upgraded ISIS machine. The increased proton flux on to the target would produce significantly more neutrons, increasing the throughput of experiments and allowing more sensitive experiments to be carried out.
As well as providing a future upgrade for ISIS the FETS could have a number of other applications. It could provide the starting source for a ‘Neutrino Factory’ which would produce the most intense and focused beam of neutrinos ever achieved. There is also interest in an acceleratorbased source for the transmutation of long-lived nuclear waste products. Already the FETS has its own special building at RAL, and construction of the machine is due to begin soon. The scientists hope to have the FETS up and running by 2011, ensuring that ISIS stays at the forefront of the field of pulsed accelerator sources.

Engineering model of the FETS

Engineering model of the FETS chopper components and associated focusing magnets and bunching cavities
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Alan Letchford (ISIS)

Research date: December 2007

Further Information

Status report on the RAL front end test stand, A Letchford et al, Proceedings of the 22nd Particle Accelerator Conference, Albuquerque, NM, USA, June 2007. Imperial College FETS webpage, ep/research/fets.htm