Dynamics of bunches partially chopped with the MEBT chopper in the ESS linac

The front-end of a hadron linac typically has a transient time during turning on and off and bunches in the head and tail of a pulse from this period likely have wrong parameters and a risk to cause beam losses. A risk of losses must be avoidedaspossibleinahighpowermachinesothesebunches areremovedwithdeflectorscalledchoppersintheESSLinac. From experiences of other machines, a rise time of a chopper as fast as one RF period (2.84 ns for ESS) is challenging to achieve and not necessarily needed with no ring to inject like ESS, and hence a 10 ns rise time is planned for a chopper in the medium energy beam transport of ESS. This, however, means that several bunches receive intermediate deflections and may propagate with large trajectory excursions. This paper studies dynamics of such partially chopped bunches in detail to ensure no significant loss is caused by them.