Speaker
Description
ISIS is the pulsed, spallation neutron and muon source at the Rutherford Appleton Laboratory in the UK. Its rapid cycling synchrotron accelerates 3e13 protons-per-pulse from 70 to 800 MeV at 50 Hz, delivering a mean beam power of 0.2 MW to its two target stations. The intensity of ISIS is beam-loss limited, so increasing its neutron and muon output requires beam-loss mechanisms to be well understood and alleviated.
Despite mitigation efforts, a vertical head-tail instability is often one of the main sources of beam-loss during high-intensity operations at ISIS. Finite-element simulations and probe-coil measurements have identified a series of low-frequency resonator impedances from the RF screens in the AC magnets. New bench measurements of RF screens will be presented that provide further evidence of them being responsible for the beam instability, and have been used to inform an update to the impedance model. A comparison between this model and beam-based impedance measurements will be presented, as well as analytical predictions for beam stability at ISIS. A possible method to mitigate the RF screen resonator impedances will also be introduced.
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