Issue 76

Beam Dynamics Newsletter

5.4 Development of high-resolution cavity beam position monitors for use in low-latency feedback systems

CANDIDATE: Talitha Bromwich, University of Huddersfield, U.K.
SUPERVISOR: Prof. P. Burrows
GRADUATION: June 2018



The thesis work was carried out with the Feedback On Nanosecond Timescales (FONT) group at the John Adams Institute for Accelerator Science at the University of Oxford. The FONT intra-train feedback system is designed to provide beam position stabilisation in single-pass accelerators. The studies focused on a feedback system utilising beam position information from three high-resolution cavity beam position monitors (BPMs) at the interaction point (IP) of the Accelerator Test Facility 2 (ATF2) at KEK, Japan, with the goal of stabilising the low-emittance electron beam to the nanometre level. The operation, optimisation and resolution performance of this IP system formed the subject of the thesis.

The work achieved an improvement in the cavity BPM resolution estimate from 50 nm to 20 nm using waveform integration in analysis of the BPM signals. A multi-parameter fit was used to address inaccuracies in calibration methods and unwanted charge-dependencies to achieve more consistent resolution performance and produce a best-ever resolution estimate for the BPMs of 17.5\( \pm \)0.4 nm. A novel mode of IP beam position stabilisation using two BPMs as input to the feedback was also successfully demonstrated. The beam position was stabilised to 57\( \pm \)4 nm, as measured at an independent BPM. The analysis suggested correction capability could be enhanced by feedback firmware waveform integration to achieve a measurable beam stabilisation of the order of 40 nm in the future. This work will be continued by the FONT group and collaborators at the ATF2.

Any future accelerators, including linear colliders like the ILC and CLIC, and X-ray free electron lasers, will require BPMs for diagnostic purposes and orbit feedback to enable very precise beam handling. High-resolution beam position measurements and low-latency feedback systems capable of nanometre-level position stabilisation will be vital to realise this precise beam handling. The PhD work is expected to contribute towards the advancement of these future endeavours.