bunch-by-bunch analysis of the lhc heavy-ion luminosityΒ Β· the last bunch in a train. ππ΅...
Post on 24-Jul-2020
4 Views
Preview:
TRANSCRIPT
Bunch-by-Bunch Analysis of the LHC Heavy-Ion Luminosity
M. Schaumann1,2, J.M. Jowett1
1CERN, Geneva, Switzerland; 2RWTH Aachen, Aachen, Germany
LHC: Large Hadron Collider IBS: intra-beam scattering
[1] T. Mertens et al., TUPZ017, IPAC 2011. [2] M. Schaumann et al., TUPFI025, IPAC 2013. [3] J. Jowett et al., MOODB201, IPAC 2013. [4] R. Bruce et al., Phys. Rev. ST Accel. Beams 13, 091001 (2010).
π΅π increase from 1st to the last bunch in a train.
ππ΅ decreases from 1st to last bunch in a train.
ππ shows similar behaviour as π΅π.
Footnotes: 1) 2)
Bunch-by-Bunch Differences
β’ 3 simulation runs with varying initial ππ to account for calibration uncertainties. β’ Losses in ππ are overestimated by the simulation, due to assumption of
Gaussian longitudinal profile. β’ The calibrated ππ seems to be underestimated by about 10%. β’ π³, ππ΅ and ππ fit very well to the simulation for +10% initial ππ΅.
β’ Heavy-ion operation in the LHC: [1] 2010: Pb-Pb, [2] 2011: Pb-Pb, [3] 2013: p-Pb. β’ Beam dynamics of high intensity Pb (lead) beams are strongly influenced by IBS. β’ Pb ions injection chain: source β LINAC3 β LEIR β PS β SPS β LHC. β’ Each train injected from SPS spends a different time at the LHC injection plateau, introducing significant changes from train to train. β’ Within a LHC train an even larger spread is imprinted from bunch to bunch by
the SPS injection plateau: β’ Inject 2 bunches from PS β SPS: 12 injections to construct LHC train. β’ While waiting for remaining injections form PS, bunches are strongly affected by IBS (β πΈβπ) at low energy.
β Emittance growth and particle losses.
β’ This results in a spread of the luminosity πΏ, produced in each bunch crossing.
β’ Running conditions after LS1: β higher E = 6.5Z TeV and lower π·β = 0.5m. β’ Estimate peak luminosity at start of collisions: β Model based on 2011 bunch-by-bunch luminosity, predicts peak πΏBunch as a function of position inside the beam. β Assumption: 2011 beam conditions. β 2011 filling scheme & scaling to E = 6.5Z TeV yields π³ππππ = π.π Γ ππππππ¦βππ¬βπ = π.π π³πππ¬πππ. β’ Alternating 100/225ns bunch spacing to
increase total number of bunches. β Possible to reach π³ > π Γ ππππππ¦βππ¬βπ. β’ In 2013 p-Pb run π΅π could be increased by 30%.
Evolution of Colliding Bunches
Luminosity Projections for after LS1
In LHC right after injection
β’ Collisions of equivalent bunches (with similar ππ and ππ). β’ πΏBunch varies by a factor 6 along a train - introducing different lifetimes. β’ Slope between last bunches of trains introduced by IBS at LHC injection plateau. β’ Particle losses during collisions are dominated by nuclear EM processes, β leading to non-exponential ππ decay and short lifetimes at E = 3.5Z TeV.
1),2)
Acknowledgments: β’ R. Bruce. β’ Wolfgang-Gentner-Programme of the Bundes-
ministerium fΓΌr Bildung und Forschung (BMBF).
ππ΅: normalised emittance ππ: bunch length
LHC: Large Hadron Collider IBS: intra-beam scattering π³: luminosity π΅π: bunch intensity
Single Bunch Evolution at Injection
dots β data lines β tracking simulation
β’ Simulation Code: Collider Time Evolution (CTE) [4]. β’ Tracking of 2 bunches of macro-particles in time in a collider. β’ Simulation of IBS, radiation damping, but, eg, no beam-beam. β’ Evolution of 4 single Pb bunches at injection (E = 450GeV). β’ Horizontal IBS growth stronger than vertical due to horizontal dispersion, β no vertical dispersion in model (for speed). β’ Additional growth in vertical ππ due to coupling.
top related