• C.M. Warsop, D.J. Adams, B. Jones, S.J. Payne, B.G. Pine, R.E. Williamson
  STFC/RAL/ISIS, Chilton, Didcot, Oxon

ISIS is the spallation neutron source at the Rutherford Appleton Laboratory in the UK. Operation centres on a 50 Hz proton synchrotron, which accelerates ~3·10¹³ ppp from 70 to 800 MeV, corresponding to beam powers of 0.2 MW. Beam loss imposes limits on operational intensity, and a main contributing mechanism is the action of half integer resonance under high space charge. The same loss mechanism is also a potential problem in ISIS upgrade scenarios involving either higher energy injection into the existing ring, or the addition of a new 3 GeV, high intensity RCS. Progress on particle in cell simulation studies investigating the effects of the driven coherent envelope motion, the associated parametric halo, along with implications of momentum spread, dispersion and longitudinal motion, is reported. Where possible, comparisons are made with relevant theoretical models. Closely related benchmarking work, experimental studies and plans are also summarised.

• R.E. Williamson, B.G. Pine, C.M. Warsop
  STFC/RAL/ISIS, Chilton, Didcot, Oxon

ISIS is the pulsed neutron and muon source based at the Rutherford Appleton Laboratory in the UK. Operation is centred on a loss-limited 50 Hz proton synchrotron which accelerates ~3·10¹³ protons per pulse from 70 MeV to 800 MeV, corresponding to mean beam powers of 0.2 MW. A number of ISIS upgrades are currently under study. One option replaces the linac for higher energy injection into the existing ring, potentially increasing beam current through reduction in space charge. The other main option adds a new 3 GeV RCS, boosting the energy of the beam to provide higher beam power. For both these upgrade routes, longitudinal dynamics of the existing and proposed new rings play a crucial role in achieving high intensity with low loss. This paper outlines longitudinal beam dynamics studies in the rings for both these cases, including development of a new longitudinal space charge code, comparison of different algorithms and codes and treatment of the key beam dynamics issues for each case. The influence of non-space charge impedances is also considered.