Observation of a Synchro-Betatron Instability in Fermilab Booster

In preparation for PIP-II, there has been interest in running the Fermilab Booster at a higher current more indicative of the PIP-II era operation.In July 2023, an experiment was performed to study collective instabilities over the transition crossing at the Fermilab Booster.Over the transition crossing, the synchrotron tune becomes small and synchro-betatron instabilities become possible.During the experiment, an intensity threshold was observed, above which a dipole instability with losses concentrated in the tail of the bunch.These losses are consistent with the Convective Instability.