Optical fibre beam loss monitors (oBLMs) are in use at several accelerator facilities worldwide as an online, low-cost, and reliable beam loss monitoring solution. They measure beam loss locations through time-of-flight analysis of Cherenkov radiation produced in optical fibres by relativistic particle showers from beam loss events. They offer continuous accelerator coverage and can attain a beam loss location precision of 1 m or better. The recirculating multi-energy particle beams of energy recovery LINACs present difficulties in tracking losses from beam bunches throughout their journey in the machine. A potential solution is offered through estimation of the beam loss energy from the measured intensity of the oBLM signal, which could be used to determine the beam bunches associated with each loss signal. Monte Carlo simulations of beam loss interaction with the oBLM were performed in Geant4 to qualitatively investigate the feasibility of this method. The most feasible scenario occurs when the percentage change in the number of lost particles (loss intensity) from two beam losses is less than half of their corresponding percentage energy change. Otherwise, a complementary means of determining loss intensity is recommended for this method. Additionally, the relationship between beam energy and oBLM signal intensity was found to vary strongly with beam loss position relative to the fibre. Measurements were collected from the oBLM system installed at CLEAR, CERN; qualitative agreement was observed with the simulations, although quantitative analysis was not possible. Simulations were therefore identified as a critical component of oBLM energy estimation—to determine the expected behaviours of the oBLM signal on an accelerator and guide the analysis and interpretation of the intensity measurements.
Jones et al. (Fri,) studied this question.