Bunch-by-Bunch Analysis of the LHC Heavy-Ion LuminosityĀ Ā· the last bunch in a train. ššµ...
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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).
šµš increase from 1st to the last bunch in a train.
ššµ decreases from 1st to last bunch in a train.
šš shows similar behaviour as šµš.
Footnotes: 1) 2)
Bunch-by-Bunch Differences
ā¢ 3 simulation runs with varying initial šš to account for calibration uncertainties. ā¢ Losses in šš are overestimated by the simulation, due to assumption of
Gaussian longitudinal profile. ā¢ The calibrated šš seems to be underestimated by about 10%. ā¢ š³, ššµ and šš fit very well to the simulation for +10% initial ššµ.
ā¢ Heavy-ion operation in the LHC: [1] 2010: Pb-Pb, [2] 2011: Pb-Pb, [3] 2013: p-Pb. ā¢ Beam dynamics of high intensity Pb (lead) beams are strongly influenced by IBS. ā¢ Pb ions injection chain: source ā LINAC3 ā LEIR ā PS ā SPS ā LHC. ā¢ Each train injected from SPS spends a different time at the LHC injection plateau, introducing significant changes from train to train. ā¢ Within a LHC train an even larger spread is imprinted from bunch to bunch by
the SPS injection plateau: ā¢ Inject 2 bunches from PS ā SPS: 12 injections to construct LHC train. ā¢ While waiting for remaining injections form PS, bunches are strongly affected by IBS (ā šøāš) at low energy.
ā Emittance growth and particle losses.
ā¢ This results in a spread of the luminosity šæ, produced in each bunch crossing.
ā¢ Running conditions after LS1: ā higher E = 6.5Z TeV and lower š·ā = 0.5m. ā¢ Estimate peak luminosity at start of collisions: ā Model based on 2011 bunch-by-bunch luminosity, predicts peak šæBunch as a function of position inside the beam. ā Assumption: 2011 beam conditions. ā 2011 filling scheme & scaling to E = 6.5Z TeV yields š³šššš = š.š Ć šššššš¦āšš¬āš = š.š š³ššš¬ššš. ā¢ Alternating 100/225ns bunch spacing to
increase total number of bunches. ā Possible to reach š³ > š Ć šššššš¦āšš¬āš. ā¢ In 2013 p-Pb run šµš could be increased by 30%.
Evolution of Colliding Bunches
Luminosity Projections for after LS1
In LHC right after injection
ā¢ Collisions of equivalent bunches (with similar šš and šš). ā¢ šæBunch varies by a factor 6 along a train - introducing different lifetimes. ā¢ Slope between last bunches of trains introduced by IBS at LHC injection plateau. ā¢ Particle losses during collisions are dominated by nuclear EM processes, ā leading to non-exponential šš decay and short lifetimes at E = 3.5Z TeV.
1),2)
Acknowledgments: ā¢ R. Bruce. ā¢ Wolfgang-Gentner-Programme of the Bundes-
ministerium fĆ¼r Bildung und Forschung (BMBF).
ššµ: normalised emittance šš: bunch length
LHC: Large Hadron Collider IBS: intra-beam scattering š³: luminosity šµš: bunch intensity
Single Bunch Evolution at Injection
dots ā data lines ā tracking simulation
ā¢ Simulation Code: Collider Time Evolution (CTE) [4]. ā¢ Tracking of 2 bunches of macro-particles in time in a collider. ā¢ Simulation of IBS, radiation damping, but, eg, no beam-beam. ā¢ Evolution of 4 single Pb bunches at injection (E = 450GeV). ā¢ Horizontal IBS growth stronger than vertical due to horizontal dispersion, ā no vertical dispersion in model (for speed). ā¢ Additional growth in vertical šš due to coupling.