Philip Burrows

Abstract:

The ATF2-3 beamline is the only facility in the world for testing the Final Focus Beamline of linear colliders and is essential for the ILC and the CLIC projects. A vertical electron beam size of 41 nm (within 10% of the target), a closed-loop intra-bunch feedback of latency 133 ns, and direct stabilization of the beam position at the Interaction Point to 41 nm (limited by IP BPM resolution) have all been achieved at ATF2. These results fulfilled the two main ATF2 design goals, but were obtained with reduced aberration optics and a bunch population of approximately 10% of the nominal value of 10^10 electrons. Recent studies indicate that the beam degradation with the beam intensity is due to the effects of wakefields. To overcome this intensity limitation, hardware upgrades including new vacuum chambers, magnets, IP-Beam Size Monitor laser, cavity BPMs, wakefield mitigation station, as well as a comprehensive R&D program to maximize the luminosity potential are being pursued in the framework of the ILC Technology Network. This new R&D program focuses on the study of wakefield mitigation techniques, correction of higher-order aberrations, tuning strategies, including AI techniques, as well as beam instrumentation issues, such as the BPMs, advanced Cherenkov Diffractive Radiation monitors, and fast feedback systems, among others. This paper summarizes the hardware upgrades, the R&D program and the results of the Fall 2023-Winter 2024 experimental campaign performed in ATF2-3.

Abstract:

A beam position monitor based on Cherenkov diffraction radiation (ChDR) is being investigated as a way to disentangle the signals generated by the electromagnetic fields of a short-pulse electron bunch from a long proton bunch co-propagating in the AWAKE plasma acceleration experiment at CERN. These ChDR BPMs have undergone renewed testing under a variety of beam conditions with proton and electron bunches in the AWAKE common beamline, at 3 different frequency ranges between 20-110 GHz to quantify the effectiveness of discriminating the electron beam position with and without proton bunches present. These results indicate an increased sensitivity to the electron beam position in the highest frequency bands. Furthermore, high frequency studies investigating the proton bunch spectrum show that a much higher frequency regime is needed to exclude the proton signal than previously expected.

Abstract:

Most particle accelerators utilize beams with a charge density concentrated in the center of the bunch in real 3-dimensional space and the 6-dimensional phase space. In this work, by enhancing the space-charge forces in the photo-cathode injector of the Compact Linear Electron Accelerator for Research (CLEAR) at CERN, we produce electron bunches with a “bubble-like” shape, with a charge density mostly concentrated on the outside shell. We demonstrate that the dynamics of such beams can be tailored to achieve stable uniformity in the coordinate and momentum transverse planes simultaneously. This would allow reaching a uniform dose distribution without a severe loss of particles which is of the great interest in the irradiation community. Additionally, we investigate the potential benefits of bubble-beams across several accelerator pillars: for driving light sources, for advanced acceleration technologies, and for particle colliders.

Abstract:

During operation, the Future Circular electron-positron Collider (FCC-ee) will be subject to vibrations from mechanical sources and ground motion, resulting in errors with respect to the closed orbit. To achieve physics performance, luminosity and beam lifetime must be kept to design specifications. To correct for errors at the IPs, a fast feedback system is required. In this paper, we present the tolerances for the allowable beam offsets at the interaction points (IPs) and propose a fast feedback system to address these errors, with the methods of detecting and correcting errors discussed.

Abstract:

During 2023, examination of the action dependence of sextupolar resonance driving terms (RDT) in the LHC at injection, as measured with an AC-dipole, demonstrated that a robust measurement of the RDTs could still be achieved even with very small amplitude kicks, typically used for linear optics studies. Consequently, analysis of optics measurements from 2022 to 2024 during the LHC energy ramp allowed a first measurement of the sextupole resonance evolution. A large asymmetry was observed between the two LHC beams, with the clockwise circulating beam (LHCB1) being significantly worse than the counter-clockwise circulating beam (LHCB2), and a clear increase in the RDT strength during the ramp was observed. During 2024 commissioning, a first attempt was made to correct the 𝑓1020 RDT of LHCB1 at injection. Results are presented in this report.