Philip Burrows

Abstract:

A system of three lowQ cavity beam position monitors (BPMs), installed in the interaction point (IP) region of the Accelerator Test Facility (ATF2) at KEK, has been designed and optimised for nanometre-level beam position resolution. The BPMs are used to provide an input to a low-latency, intra-train beam position feedback system deployed in single-pass, multi-bunch mode with the aim of demonstrating intra-train beam stabilisation on electron bunches of charge ~1 nC separated in time by 280 ns. In 2016 the BPM resolution was demonstrated to be below 50 nm using the raw measured vertical positions at the three BPMs. New results will be presented utilising integrated sampling of the raw waveforms, improved BPM alignment and modified cavities to demonstrate a vertical position resolution on the order of 20 nm.

Abstract:

The International Linear Collider (ILC), as described in its Technical Design Report (TDR), must maintain strict control of its electron and positron beams in order to achieve the desired luminosity at each of its proposed center-of-mass energies. Controlling the beam parameters requires a dynamic system, capable of adjusting to a myriad of perturbations and errors. One of the components used to control the beam is the Interaction Point (IP) feedback system, which is used to dynamically steer the beams back into collision within nanoseconds. This work will show the simulation of the IP feedback system's compensation for ground motion model K at the ILC.

Abstract:

The high luminosity requirement for a future linear collider sets a demanding limit on the beam quality at the Interaction Point (IP). Even the natural motion of the ground could misalign the quadrupole magnets to such an extent that the resulting dipole kicks would require compensation. The novel technique described in this paper uses seismometers to measure the positions of the quadrupole magnets in real time and a kicker to counteract the effect of their misalignment. The prototype system deployed at the Accelerator Test Facility (ATF) at KEK in Japan has already demonstrated a reduction in the pulse-to-pulse vertical position jitter of the beam by about 10%. Based on the observed correlation of the beam position to the quadrupole positions the maximum possible jitter reduction from such a system is estimated to be about 25%. This paper details the latest improvements made to the system with the aim of achieving this limit.

Abstract:

A high-resolution, low-latency beam position monitor (BPM) system has been developed for use in feedback systems at particle accelerators and beamlines that operate with trains of particle bunches with bunch separations as low as several tens of nanoseconds, such as future linear electron-positron colliders and free-electron lasers. The system was tested with electron beams in the extraction line of the Accelerator Test Facility at the High Energy Accelerator Research Organization (KEK) in Japan. The fast analogue front-end signal processor is based on a single-stage RF down-mixer, with a measured latency of 15.6 ± 0.1 ns. The processor has been optimised, doubling the maximum operating beam intensity up to 1.6 nC, and the signal processing in the custom digital acquisition board has been upgraded in order to improve the resolution beyond the 300 nm level measured previously. The latest results, demonstrating a position resolution of order 150 nm with single-pass beam, will be presented.

Abstract:

A lowlatency feedback system has been designed and tested to achieve interbunch position stabilisation at the final focus of the Accelerator Test Facility (ATF2) at KEK. This system has now been enhanced through the use of position information from two cavity beam position monitors (BPMs) to enable beam stabilisation at a third, intermediate location where a witness BPM measures the correction. LowQ cavity BPMs were used, along with custom signal processing electronics designed for low latency and optimal position resolution. A custom stripline kicker, power amplifier and digital feedback board were used to provide beam correction and feedback control. The system was tested in singlepass, multibunch mode with the aim of providing interbunch beam stabilisation on electron bunches of charge ~1 nC separated in time by 280 ns. In 2015 a single BPM feedback system demonstrated beam stabilisation to below 75 nm. To date the two BPM input feedback system has demonstrated beam stabilisation to 83 ± 6 nm. This performance is limited by the current understanding of the cavity BPM resolution. Work will be described with the aim of improving this result.