Pros and cons interleaving the filling of the LHC S. Fartoukh AB/ABP, LHCCWG 9 October 2007 Pre-requisite for any filling scheme Arguments in favor of an interleaved filling scheme Arguments against “Conclusions” S. Fartoukh, LHCCWG, 9 October 2007

Pre-requisites for any filling scheme   A circulating “measurable” beam before the injection of any nominal bunches, e.g. a pilot bunch, for optics checks (orbit, Q, Q’, eventually coupling and beta’s). A check and readjustment, if needed, of the main beam observables on the injection plateau before re-injecting new nominal bunches. S. Fartoukh, LHCCWG, 9 October 2007

Arguments (LHC related) in favor an interleaved filling scheme   RF : none BT : none BI : none ABP : none, except LEPII experience where it was impossible to stack one beam when the 4 buckets of the other beam was full, but … parasitic beam-beam effect was much stronger (e.g. very small separation due to limited strength in the electrostatic separators). S. Fartoukh, LHCCWG, 9 October 2007

Arguments (LHC related) against an interleaved filling scheme   RF : none BT : weak preference for the sequential filling scheme in case one given beam is aperture limited by the TDI of the other beam (e.g. inject beam1 with TDI of beam2 retracted, but then at some point the TDI of beam2 will have to go back in the vacuum chamber with beam1 circulating…) BI : none  ABP : two weak arguments against Life time for ions in proton-ion operation (ions must be injected after protons …if no beam-beam related limitations, see previous slide). Aperture bottle-neck in D2 (IP-side) for off-bucket particles (and pilot), getting the full kick by the MKI at each injection, see SF, LTC 2006-15 (with the interleaved scheme the number of such particles will be at least doubled …assuming no RF cleaning of the window foreseen for the next injection). S. Fartoukh, LHCCWG, 9 October 2007

“Conclusions” “Indécidable” Better to keep both options available   “Indécidable” Better to keep both options available The final answer will certainly come from turn around and average lumi optimization, e.g. What to do if Ring1 is full and the injector chain is erratically not operational to complete the filling of Ring2? … Ramp with strong current asymmetry, i.e. with a huge number of super packman bunches? … Or dump and refill in interleaved mode, if available? S. Fartoukh, LHCCWG, 9 October 2007