LONGITUDINAL EMITTANCE BLOW-UP AND PRODUCTION OF FUTURE LHC BEAMS

Abstract

During Long Shutdown 2 the RF systems of the PSB will be replaced with broadband Finemet systems, there will also be an energy increase and many other modifications. This note summarises studies that were done to investigate how to meet the emittance requirements for the LIU-PSB baseline and a possible use of the broadband cavities to improve the capture process. The LIU-PSB baseline requires longitudinal emittance blow-up to 3 eVs with 205 ns bunch length at extraction. The current ferrite RF systems were used, with phase  modulation of a high harmonic, to produce 2.8 eVs bunches with 220 ns bunch length, as this is the largest that can currently be transferred to the PS. Larger emittances were possible,
demonstrating the ability to reach the LIU-PSB baseline in the future, which is confirmed in simulation. The broadband impedance of the Finemet was exploited to allow RF voltage to be supplied on three harmonics (h=1, h=2, h=3), as opposed to the usual 2. For high intensity beams this lead to an improved capture efficiency for the same total voltage, and future studies are planned to demonstrate if there is an effect on extracted transverse emittance.