Other Means to Increase the SPS 25 ns Performance - Longitudinal Plane

Abstract

At the end of the LHC run 2 in 2012 the 25 ns beam with an intensity of 1.3×10¹¹ p/b was successfully accelerated in the SPS. Further significant increase of bunch intensity in the SPS requires that all LIU baseline upgrades are in place (for 200 MHz and 800 MHz RF systems and ecloud mitigation), but even then the bunch intensity could be limited below the HL-LHC  value of 2.5×10¹¹ by beamloading and longitudinal beam instabilities. In this paper other means to increase the 25 ns beam performance are considered. In particular, we study the  potential gain in stability for bunches with larger longitudinal emittance at the SPS extraction, possible in the scenario with a 200 MHz RF system in the LHC. The expected longitudinal  limitations (coupled-bunch instability, loss of Landau damping, microwave instability and RF power during the ramp) are analyzed for a single and double RF operation and different optics (Q20, Q26 and intermediate one). Bunch rotation before extraction to the LHC is also addressed as a potential technique to decrease capture losses of long bunches in the LHC.