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Update of the Sixtrack scattering routine

Update of the Sixtrack scattering routine. Claudia Tambasco, Belen Salvachua, Stefano R edaelli, Roderik Bruce, Daniele Mirarchi. Collimation Working Group 31/03/2014 . Acknowledgements. Thanks to whole the collimation team , in particular to L.Lari , A.Marsili , G.Cavoto .

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Update of the Sixtrack scattering routine

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  1. Update of the Sixtrack scattering routine Claudia Tambasco, Belen Salvachua, Stefano Redaelli, Roderik Bruce, Daniele Mirarchi Collimation Working Group 31/03/2014

  2. Acknowledgements Thanks to whole the collimation team, in particular to L.Lari, A.Marsili, G.Cavoto. Thanks to A. Lechner and the FLUKA team: Providing FLUKA cross sections: Comparison FLUKA/Sixtrack cross sections will continue (R.Bruceet al.) Ionization losses: Implementation of the Landau tail for the Ionization energy loss (D.Mirarchi et al.) Thesis on Cern Library at: https://cds.cern.ch/record/1690529/files/CERN-THESIS-2014-014.pdf

  3. Contents • SixTrack scattering routine updates: • Carbon density • Ionization losses • Coulomb scattering correction • Nuclear interactions • Results: • 3.5 TeV global losses • 3.5 TeV data/simulations comparison at TCTs • 7 TeV impacts at collimators • 7 TeV Cleaning Efficiency • Ongoing work • Conclusions

  4. Why do we need to update the SixTrack scattering routine? • Scattering routine developed in 1990’s (by T. Tranker and J.B Jeanneret) • Recent measurements of cross section processes Better description of interaction with matter After the long shutdown, LHC will reach the designed proton energy of 7 TeV and the luminosity peak of 10^34 [cm-2 s-1] : Higher Luminosity and Energy More beam losses, more energy deposition on the machine equipment quench of the superconducting magnets Even more important Collimation System: More accurate prediction of the Cleaning efficiency • Improving the physics model of the scattering routine allows to increase the power of predictions for higher energy simulations

  5. SixTrack scattering routine • Simulates scattering mechanisms of the protons within the collimator jaws • developed in 1990’s (by T. Tranker and J.B Jeanneret) Ionization (Bethe-Bloch equation) Electromagnetic processes Small angle: Multiple Coulomb scattering Large angle: Rutherford Scattering Coulomb scattering: Nuclear interactions scattering with the nucleons Effective number of nucleons

  6. Scattering routine changes: Nuclear Interactions: • Proton-proton SD cross section • Proton-proton elastic cross section • Proton-proton total cross section • Proton-Nucleus inelastic cross section • Proton-Nucleus total cross section • Proton-Nucleus elastic cross section • updated according to recent experimental data Review of electromagnetic processes: • Ionization • Coulomb scattering and Carbon density (see next slide for the value implemented)

  7. Update Carbon density Previous Carbon in SixTrack AC150K Carbon New! TCP and TCSP collimators Used as TCP/TCSG Carbon jaw by default Graphitic carbon, but its compaction rate is far from full so its nominal density is significantly lower, i.e. 1.65 g/cm^3.

  8. Update of ionization energy loss In many Monte Carlo programs the ionization energy loss is simulated by implementing a continue loss that is described by the Bethe-Bloch equation: Previous SixTrack version: used a constant value to describe the energy lost by ionization which was an approximation of the Bethe-Bloch. New SixTrack version: implemented the Bethe-Bloch equation for the complete list of collimator materials. Used before for simulations at all energies

  9. Multiple Coulomb Scattering correction Multilple Coulomb Scattering: added logarithmic part in rms angle formula: Old SixTrack version: the logarithm part in the rms angle formula was missing New SixTrack version: added missing logarithmic part Adding the logarithmic part increases the rms of the scattered angle distribution With the new implementation the difference on the rms reaches up 20% for Tungsten Carbon 60 cm RMS: 0.00292 RMS: 0.00242 New SixTrack Old SixTrack

  10. Proton-proton scattering • Experimental data from LHC experiments are available for p-p total and elastic cross sections at 3.5 TeV and 4 TeV beam energy • New SixTrack version: implemented recent parameterizations from COMPETE collaboration New parameterizations: Before: linear fit used 7 TeV Differential pp ELASTIC cross-section: Slope Parameter New parameterization:

  11. Single diffractive cross section Old SixTrack version: implementation from an old theory of K. Goulianos (1983) Further experimental data showed the necessity to develop a new theory New SixTrack version: implementation from updated theory from same author “Renormalization of hadronic diffraction and the structure of the pomeron”, K. Goulianos Physic Letters B 358 1995 New parameterization: Larger momentum change w.r.t. elastic scattering pp SD cross section The previous version underestimated the total proton-proton SD cross section

  12. Minor Updates: p-Nucleus cross sections • Proton-Nucleus total cross section: • new collision length from PDG (max variation ~2% ) • Proton-Nucleus inelastic cross section: • new interaction length from PDG (max variation ~3% ) Proton-Nucleus elastic cross section: automatically updated since it is calculated by subtracting the other contributions

  13. Results: Global losses at 3.5 TeV Impacts at collimators and aperture Change on Cleaning Q8-Q11 Old SixTrack 3.5 TeV New SixTrack 3.5 TeV TCSG IP6 new: ~1.5 e-4 old: ~4 e-5

  14. Results: Check improvement with data • Look at the TCT losses in IP1 and IP5 • SixTrack gives the primary impacts at collimators, then BLM response factors from FLUKA are needed [E.Skordis, R.Bruce] 3.5 TeV Experimental Data vs simulation at TCTs Perfect machine Thanks to R.Bruce for experimental data Thanks to FLUKA For BLM response factors FLUKA+Sixtrack Only Sixtrack By a factor of ≈3 closer to data w.r.t. the old routine The new SixTrack version provides a better agreement with the experimental data A new estimation of the cleaning inefficiency at 7 TeV has been carried out

  15. New predictions of the losses at 7 TeV: impacts at collimators B1 horizontal halo case TCTH-V IP1 TCTH-V IP5 ~by a factor 4 more losses in TCSG in IP6

  16. New predictions of the losses at 7 TeV New SixTrack at 7TeV Beam 1 Horizontal halo distribution r1 r2

  17. New predictions of the losses at 7 TeV (DS region) DS regions: r1=20270-20350 r2=20370-20450 More losses on the cold magnets by a factor of≈ 1.8 w.r.t. the previous routine

  18. Ongoing work • Paper in preparation includes: • Description of all the updates • 7 TeV predictions of the new simulations • Parametric study of cleaning and impacts at TCTs and TCSG in IP6 for: • Ionization energy Bethe-Bloch vs most probable value of the Landau Distribution and the tails • Singe Diffractive cross section variation: ±10%, ±20, …, ±90% Preliminary! From PDG

  19. Conclusions • The physics model of the SixTrack scattering routine has been updated and improved • The effects of the new SixTrack version has been studied by data-simulation comparison at 3.5 TeV 3 times closer to the data w.r.t. the old SixTrack version • A study on the cleaning inefficiency prediction at 7 TeV has been carried out 1.8 times more losses on the cold magnets w.r.t. the old SixTrack version • Data-simulations comparison at 3.5 TeV in the imperfect machine case further agreement expected (see R. Bruce talk) Follow up of the work in the team: Further comparisons with other codes (FLUKA/SixTrack/Merlin/Geant) Further physics model improvement (Bethe-Bloch/Landau tails) New SixTrack release contains already the presented changes (R.Bruce, D.Mirarchi, A.Rossi)

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