Barrier Buckets and Transient Beam Loading in the SPS

Using long bunches held in place by barrier buckets to overcome the limitations associated with peak density in high intensity bunched beams could be a promising scheme for increasing the luminosity of LHC. In the SPS at CERN an initial barrier bucket machine development(MD) study was done in 1999 to check the capabilities of 200 MHz thick barriers generated by the travelling wave system. A second experiment took place on 5th of August 2003 to examine high intensity effects. In this experiment a flat and stable long bunch of @ 3 µs bunch length was obtained and kept for more than 80 minutes without developing a significant line density modulation. However, strong beam loading effects were observed during the injection process, causing a coherent, non-negligible energy transfer from the beam to the RF cavities, and significant fraction of the injected beam was lost to a coasting beam background. The beam intensity that could be confined in between the barriers suffered emittance increase and was not high enough to observe possible beam instabilities. An analysis of these transient beam loading effects is presented in this paper with the conclusion that the use of barrier buckets in the LHC will require particular attention to be paid to the use of any RF gymnastics in their presence. In addition to the analysis of the data obtained in the SPS, possible future experiments that can be carried out are also proposed.