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Large Piwinski Angle MD

This document investigates the Piwinski angle's role in influencing luminosity and beam-beam limits in high-energy colliders, focusing on scenarios for the High-Luminosity Large Hadron Collider (HL-LHC) and the Large Hadron Electron Collider (LHeC). It discusses the effects of varying crossing angles, the significance of geometric overlap in collisions, and historical experiments at SPS, RHIC, and Tevatron. The findings emphasize the potential for enhanced luminosity through strategic angle adjustments and improved emittance in particle beams.

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Large Piwinski Angle MD

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  1. Large Piwinski Angle MD J. Abelleira, R. Assmann, P. Baudrenghien, C. Bhat, T. Bohl, O. Brüning, R. Calaga, R. De Maria, O. Dominguez, S. Fartoukh, M. Giovannozzi, W. Herr, J.-P. Koutchouk, M. Meddahi, E. Metral, K. Ohmi, G. Papotti, T. Pieloni, S. Redaelli, L. Rossi, E. Shaposhnikova, R. Tomas, F. Zimmermann LSWG, 16 August 2011

  2. Piwinski angle primary motivation for HL-LHC & LHeC “Piwinski angle” “luminosity reduction factor” without crab cavity qc/2 nominalLHC effective beam size: s*x,eff≈ sx*/Rf “LPA” upgrade • Piwinski angle: • geometric overlap • tune shift • syn.beta resonances • symmetry breaking “FCC” upgrade

  3. motivation • for e+e- colliders crossing angle could lead to large reduction in beam-beam limit & luminosity (DORIS-I→“Piwinski angle” f, KEKB → crab cavities) • little is known about hadron collider beam-beam limit with crossing angle; RHIC & Tevatron: head-on collisions • the only controlled experiment was done at SppbarS • nominal LHC was pushed to f~0.64 • fwill futher increase for smaller-than-design emittance • HL-LHC scenarios consider f up to 2.5 • beam-beam limits experiments so far were done for head-on collisions or very small Piwinski angle

  4. historical experiments at SPS collider K. Cornelis, W. Herr, M. Meddahi, “Proton Antiproton Collisions at a Finite Crossing Angle in the SPS”, PAC91 San Francisco f~0.45 qc=500 mrad SPS tests up to f>0.7 showed some additional beam-beam effect present nominal LHC: f~0.64, ATS upgrade: f~2.5! f>0.7 qc=600 mrad small emittance

  5. simulations for nominalLHC with higher bunch charge collisions with 285 mrad crossing angle no crossing angle K. Ohmi 2 IPs 2 IPs simulated luminosity lifetime with no crossing angle is 10 times better than with 285 mrad angle (f≈0.65, b*=0.55m, ge=3.75 mm, E=7 TeV)

  6. MD plan • transient losses going into collision, beam lifetime and luminosity lifetime for large and zero Piwinski angle • beam parameters that correspond to x≥0.03 for q=0 • injection energy, collision tunes • 2 or 3ultimate low-emittance bunches per beam • 3 bunches would be at/above safe beam limit (5e11) • one bunch of each beam collides in IP1, IP5, (IP2) and IP8 • Piwinskiangle is varied by changing q at maximum bunch length longit. blow up in SPS and injected into a 3 MV RF voltage in LHC to obtain 4sigma_z~1.6 ns (times c) • nominal & zero spectrometer strength in IP8 • orbit correction when changing spectrometer strength • beams also have to be brought into collision • TCT adjustment needed in IP8 (& IP2)?

  7. MD table - details

  8. Simulations of the LPA MD K. Ohmi, KEK

  9. 2 IPs not feasible! K. Ohmi

  10. 3 or 4 IPs feasible! difference very clear for 4 IPs K. Ohmi

  11. A difference due to crossing angle is seen with 4IPs, but weak for 3 IPs doing the experiment with 4 Ips would be preferred K. Ohmi

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