Observation of a Synchro-betatron Instability in Fermilab Booster

TL;DR

This paper reports the observation of a synchro-betatron instability in the Fermilab Booster during high-current operation, highlighting a threshold for dipole instability linked to collective effects near transition crossing.

Contribution

It provides the first experimental observation of a synchro-betatron instability in the Fermilab Booster, advancing understanding of collective beam instabilities at high intensities.

Findings

Identified an intensity threshold for instability onset.

Observed losses concentrated in the bunch tail.

Linked the instability to convective instability mechanisms.

Abstract

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.