Harmonic Based Beam Position Measurements on Debunched Beams

In some accelerator environments, e.g. in linear accelerator (LINAC), the beam position is measured with a BPM operating at one particular strong harmonic component present in the beam signal. This approach has limitations once the beam gets debunched and the harmonic components drops. Nevertheless, from a signal processing point of view the signal-to-noise ratio can be still acceptable with highly debunched beams, leading, in principle, to a reasonable, even if degraded, position measurement. A simplified beam transport model developed for the CERN BI transfer line between LINAC4 and the PS Booster demonstrates, that in some case, the harmonic component cannot be used anymore for position measurement despite the fact it is still significative in amplitude.