Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Future Needs and Future Directions Maximizing the LHC Performances J.M. Jimenez …when Nature persists in doing things worst than what their can be, it uses to be much more efficient to find alternative solutions than trying suppressing the source… …Since the train already left the station… …How do we avoid the clouds ?

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 SPS shall be available for LHC injection but also for the CNGS (Neutrino) –After shutdowns, SPS will be operational after 5 days of beam conditioning –No signal in the field-free regions (long straight sections) –In the arcs (dipole field), electron cloud still “visible” –Strong vacuum cleaning (factor 100 in 4 days) –After periods without LHC-Type beams, upward drift of the SEY is not an issue since measurements confirmed that SEY recovered its initial value after 4 hours of operation with LHC beams –Beam conditioning efficiency limited to the parameters used during the scrubbing  will not be effective if running conditions become more favourable  SPS shall be used to improve the understanding of the electron cloud build up and induced instabilities and help in the benchmarking of the simulations  Keep operational the “Electron Cloud Bench”  Simulations shall be kept under pressure Future Needs and Future Directions Case of the SPS as the LHC Injector

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Future Needs and Future Directions Case of the LHC (1) What is the maximum luminosity achievable at 75 ns / 25 ns bunch spacing assuming the cryogenic limitations ? Build up in dipole, quadrupole and field free regions  Why RHIC behave differently ? Are e - induced heat loads the only 1 st order limitations ? What about emittance growth and e-p instabilities since they limit PSR, KEKB and PEPII Beam conditioning efficiency on the cold surfaces in field free and dipole field  Dose effect required Beam conditioning time will increase in presence of: –Emittance growth and e-p instabilities –Pressure rises at collimators –Higher radiation levels and background unacceptable for Experiments Influence of the reduced bunch length in LHC versus SPS? –Detrimental effect of the ramp in energy Filling scheme modification more efficient than the decrease of the bunch intensity (displacement of the lateral strips in the dipoles) Simul.Simul. & Experim.Experim.Other Colours tell you the type of actions required: Simulations, Experiments, others

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Introduction SPS Running with LHC-type beams Decrease observed 4 th batch no captured correctly

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Main Results at 25 ns Bunch Spacing Detrimental effect of the ramp in Energy Pressure Variations Decrease observed RF adjustment

Prepared by M. Jimenez AT Dept / Vacuum Group, ECloud’04 Future Needs and Future Directions Case of the LHC (2) …How reliable are the extrapolations from the SPS to the LHC ? –NEG coating behavior with seeding of electrons (photoelectrons) –Edge effects in the SPS when studying the beam conditioning (limited length) –Unexpected electron cloud enhancement or triggering in the LHC ? Consequences of the collimators halo –Are the electron build-up thresholds the same as for SPS ? –Bunch length Effect (0.25 instead of 1.7 ns rms at injection) –Filling pattern of the LHC Can Electron survive the LHC gaps (injection and dump kickers rise time 1-3  s) ? How to play with the filling pattern ? Simul.Simul. & Experim.Experim.Other