Experimental and simulation studies of the PS-to-SPS beam transfer efficiency

Larger longitudinal emittance for the LHC-type beams is desirable at the end of the cycle in the PS and on the flat bottom in the SPS for longitudinal beam stability and for high-intensity beams. However, current beam losses during longitudinal bunch-to-bucket transfer are at the limit of the acceptable. Hence, reducing transfer losses is inevitable to create the necessary margin for increasing the longitudinal beam emittance. Experimentally, the losses in the SPS could not be reduced so far, despite of producing shorter bunches by using a higher 80 MHz voltage in the PS for the bunch rotation. The simulations presented here show why experiments did not succeed to improve the transmission, and demonstrate that there is still room for improvement. Systematic studies of several PS rotation and SPS injection parameters revealed the sensitivity of the transmission to these parameters. As a result, it is suggested to increase the 80 MHz rotation voltage and optimise the 40 MHz and 80 MHz bunch rotation timings in the PS. Furthermore, as seen both in operation and simulations, the SPS capture voltage can considerably influence the losses in the beginning of the acceleration ramp.