Bryan Jones

Injection studies on the isis synchrotron

The ISIS Facility at the Rutherford Appleton Laboratory in the UK produces intense neutron and muon beams for condensed matter research. It is based on a 50 Hz proton synchrotron which, once the commissioning of a new dual harmonic RF system is complete, will accelerate about 3.5 x 1013 protons per pulse from 70 to 800 MeV, corresponding to mean beam powers of 0.2 MW. The multi-turn charge-exchange injection process strongly affects transverse beam distributions, space charge forces, beam loss and therefore operational intensity. The evolution of longitudinal distributions and subsequent trapping efficiency is also intimately linked with injection. Optimising injection is therefore a key consideration for present and future upgrades. Work is now under way looking at this process in more detail, and relates closely to other transverse space charge studies on the ring. This paper presents work including: space charge simulations of the present machine and comparison with observations; assessment of related loss mechanisms; and study of optimal painting schemes. Plans and preparations for more detailed experimental work are also summarised.

Development of Physics Models of the ISIS Head-Tail Instability

ISIS is the pulsed spallation neutron and muon source at the Rutherford Appleton Laboratory in the UK. Operation centres on a rapid cycling proton synchrotron which accelerates 3×10 protons per pulse from 70 MeV to 800 MeV at 50 Hz, delivering a mean beam power of 0.2 MW. As a high intensity, loss-limited machine, research and development at ISIS is focused on understanding loss mechanisms with a view to improving operational performance and guiding possible upgrade routes. The head-tail instability observed on ISIS is of particular interest as it is currently a main limitation on beam intensity. Good models of impedance are essential for understanding instabilities and to this end, recent beambased measurements of the effective transverse impedance of the ISIS synchrotron are presented. This paper also presents developments of a new, in-house code to simulate the head-tail instability and includes benchmarks against theory and comparisons with experimental results.