A sub-micron resolution, bunch-by-bunch beam trajectory feedback system and its application to reducing wakefield effects in single-pass beamlines

TL;DR

This paper presents a high-precision, bunch-by-bunch beam trajectory feedback system that significantly reduces beam jitter and wakefield effects in single-pass beamlines, improving beam stability and size control.

Contribution

The development and experimental validation of a sub-micron resolution, bunch-by-bunch feedback system for stabilizing beam trajectories in accelerator facilities.

Findings

Beam offset stabilized to better than 350 nm.

Trajectory angle corrected within 250 nrad.

Beam jitter reduced by a factor of 4, decreasing beam size variation.

Abstract

A high-precision intra-bunch-train beam orbit feedback correction system has been developed and tested in the ATF2 beamline of the Accelerator Test Facility at the High Energy Accelerator Research Organization in Japan. The system uses the vertical position of the bunch measured at two beam position monitors (BPMs) to calculate a pair of kicks which are applied to the next bunch using two upstream kickers, thereby correcting both the vertical position and trajectory angle. Using trains of two electron bunches separated in time by 187.6~ns, the system was optimised so as to stabilize the beam offset at the feedback BPMs to better than 350~nm, yielding a local trajectory angle correction to within 250~nrad. The quality of the correction was verified using three downstream witness BPMs and the results were found to be in agreement with the predictions of a linear lattice model used to propagate the beam trajectory from the feedback region. This same model predicts a corrected beam jitter of c.~1~nm at the focal point of the accelerator. Measurements with a beam size monitor at this location demonstrate that reducing the trajectory jitter of the beam by a factor of 4 also reduces the increase in the measured beam size as a function of beam charge by a factor of c.~1.6.