The ISIS synchrotron at the Rutherford Appleton Laboratory in the UK is currently undergoing an RF upgrade. Four h=4, or second harmonic (2RF), cavities have been installed in addition to the existing six h=2, fundamental frequency (1RF), cavities and should be capable of increasing the operating current from 200 to 300µA. Two of the four cavities have been in operation for the last 2 user cycles of 2007 improving trapping losses and increasing operating currents beyond 200µA. The remaining two cavities were commissioned in the spring of 2008. This paper reports on hardware commissioning, beam tests and beam simulation results.

The ISIS Facility is the pulsed neutron and muon source based at the Rutherford Appleton Laboratory in the UK. Operation centres on the 50 Hz synchrotron, which accelerates ~3x10 13 protons per pulse from 70 to 800 MeV, providing a mean power of about 0.2 MW. As commissioning of a second harmonic RF system is completed, it is expected that the main loss mechanisms will be related to transverse space charge forces, which are particularly strong during the multi-turn injection and trapping processes. Here, we describe progress in ongoing studies to understand more about what drives loss and thus limits intensity. Results from simulations and application of relevant theory are presented, concentrating on the effects thought most important for the ISIS ring. Progress on work looking at the half integer resonance and image effects in the rectangular vacuum vessels is reported, along with work for experimental studies.

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