Transverse emittance growth due to rf noise in crab cavities: Theory, measurements, cure, and high luminosity LHC estimates

Journal Article · 05 May 2024 · Physical Review Accelerators and Beams

DOI: https://doi.org/10.1103/PhysRevAccelBeams.27.051001 · OSTI ID:2345954

Baudrenghien, P.; Mastoridis, T.

The High-Luminosity LHC (HL-LHC) upgrade with planned operation from 2029 onward has a goal of achieving a tenfold increase in the integrated number of recorded collisions thanks to a doubling of the intensity per bunch ( $2.2\times {10}^{11}$ protons) and a reduction of ${\beta }^{*}$ (the $\beta$ value in the two high luminosity detectors, namely ATLAS and CMS) to 15 cm. Such an increase in recorded collisions would significantly expedite new discoveries and exploration. Crab cavities are an important component of the HL-LHC upgrade and will contribute strongly to achieving an increase in the number of recorded collisions. However, noise injected through the crab cavity radio frequency (rf) system could cause significant transverse emittance growth and limit luminosity lifetime. We presented a theoretical formalism relating transverse emittance growth to rf noise in an earlier work. In this follow-up paper, we summarize measurements in the super-proton synchrotron (SPS) at CERN that validate the theory, we present estimates of the emittance growth rates using state-of-the-art rf and low-level rf (LLRF) technologies, and we set the rf noise specifications to achieve acceptable performance. A novel dedicated feedback system acting through the crab cavities to mitigate emittance growth will be required. In this work, we develop a theoretical formalism to evaluate the performance of such a feedback system in any collider, identify limiting components, present simulation results to validate these studies, and derive key design parameters for an HL-LHC implementation of such a feedback system. Published by the American Physical Society 2024

• Research Organization: California Institute of Technology (CalTech), San Luis Obispo, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: SC0019287
• OSTI ID: 2345954
• Journal Information: Physical Review Accelerators and Beams, Journal Name: Physical Review Accelerators and Beams Journal Issue: 5 Vol. 27; ISSN 2469-9888; ISSN PRABCJ
• Publisher: American Physical SocietyCopyright Statement
• Country of Publication: United States
• Language: English