ISIS megawatt upgrade plans

The ISIS spallation neutron source has been running successfully for more than 15 years and at 160 kW remains the most powerful source of its kind in the world. With machines due to operate at or near the megawatt level under construction in the United States and Japan and expected to come on line within the next decade, advances in Europe have not progressed at the same rate. A positive decision on the European Spallation Source (ESS) looks unlikely and one is led to consider the feasibility of alternative options. An ISIS upgrade is one such possibility. The current installation of a radio frequency quadrupole (RFQ) in the linac and a dual harmonic RF system in the synchrotron should lead to an increase in intensity of up to 50%, but plans are also under way to increase the beam power to 1 MW with the possibility of going to 4-5 MW in the longer term. The 1 MW option is based on an increase in energy to 3 GeV by means of a second synchrotron using ISIS as a booster. Details of the new ring and studies of the accelerating system are given in this paper. The ring also has the option of accelerating to 8 GeV at reduced frequency and this could be used as a test bed for the nanosecond bunch compression needed for the proton driver for a neutrino factory (NF). The cost of these proposals is relatively modest compared with a completely new facility. In the longer term, a combination of two such rings with a new synchrotron booster (replacing the existing ISIS) would give several options, for example: 4 MW for neutrons, or 2 MW for neutrons plus 2 MW for neutrino/muon studies, or 4 MW for a neutrino facility.