Prepared by M. JimenezAT Dept / Vacuum Group, ECloud’04

Future Needs and Future DirectionsMaximizing 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. JimenezAT 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 DirectionsCase of the SPS as the LHC

Injector

Prepared by M. JimenezAT Dept / Vacuum Group, ECloud’04

Future Needs and Future DirectionsCase 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 1st 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. JimenezAT Dept / Vacuum Group, ECloud’04

IntroductionSPS Running with LHC-type

beams

Decrease observed

4th batch no captured correctly

Prepared by M. JimenezAT Dept / Vacuum Group, ECloud’04

1.0

1.5

2.0

2.5

3.0

3.5

25 30 35 40 45Time (s)

P

/P

0

100

200

300

400

500

Bea

m E

nerg

y (G

eV)

HP500

HP517

HP520

Beam Energy (GeV)Dipole field region

Field-free region

Main Results at 25 ns Bunch SpacingDetrimental effect of the ramp

in EnergyPressure Variations

Decrease observedRF adjustment

Prepared by M. JimenezAT Dept / Vacuum Group, ECloud’04

Future Needs and Future DirectionsCase 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