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Tevatron Modeling and Beam-Beam Simulations

Tevatron Modeling and Beam-Beam Simulations. Alexander Valishev DOE Tevatron Operations Review March 27, 2007. Outline. Linear optics model Orbit Response Analysis Turn-By-Turn Beam-Beam effects Improved Collision Helix Luminosity evolution model Weak-strong simulations

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Tevatron Modeling and Beam-Beam Simulations

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  1. Tevatron Modeling and Beam-Beam Simulations Alexander Valishev DOE Tevatron Operations Review March 27, 2007

  2. Outline • Linear optics model • Orbit Response Analysis • Turn-By-Turn • Beam-Beam effects • Improved Collision Helix • Luminosity evolution model • Weak-strong simulations • Strong-strong simulations 2007 DOE Tevatron Operations Review – A.Valishev

  3. Linear Optics from Closed Orbit (LOCO*) • Model Orbit Response Matrix is a function of • Quadrupole gradient errors • Steering magnet calibrations • BPM gains • Quadrupole tilts • Steering magnet tilts • BPM tilts • Energy shift associated with steering magnet changes Fit Mmodel to Mmeasured rms of difference=15mm 2007 DOE Tevatron Operations Review – A.Valishev * V.Sajaev, ANL

  4. Independent Component Analysis of TBT data • Kick the beam and record turn-by-turn positions at all BPMs • Decompose the signal into modes • Azimuthal distribution of modes gives b-functions 2007 DOE Tevatron Operations Review – A.Valishev

  5. Improvement of the Collision Helix Yu.Alexahin 2007 DOE Tevatron Operations Review – A.Valishev

  6. Improvement of the Collision Helix 2007 DOE Tevatron Operations Review – A.Valishev

  7. Luminosity Evolution Model * • The model describes evolution of the beam emittances and intensities taking into account the following factors: • Scattering at IP (luminosity) • Scattering on residual gas • RF noise • Intra Beam Scattering • Initial parameters (bunch by bunch intensity, transverse and longitudinal emittances) are taken from SDA • Main free model parameters are: • Gas pressure • RF noise power • IBS enhancement factor • The model does not include beam-beam effects * V.Lebedev 2007 DOE Tevatron Operations Review – A.Valishev

  8. Luminosity Evolution Store 4581, L=172 Old Helix Bunch 7 2007 DOE Tevatron Operations Review – A.Valishev

  9. Head-on Beam-Beam Tuneshifts. Store 4581 2007 DOE Tevatron Operations Review – A.Valishev

  10. Luminosity Evolution Store 4859, L=170New Helix Bunch 6 2007 DOE Tevatron Operations Review – A.Valishev

  11. Head-on Beam-Beam Tuneshifts. Store 4859 2007 DOE Tevatron Operations Review – A.Valishev

  12. Luminosity Evolution Store 5245, L=292 (Record)New Helix Bunch 6 2007 DOE Tevatron Operations Review – A.Valishev

  13. Head-on Beam-Beam Tuneshifts. Store 5245 2007 DOE Tevatron Operations Review – A.Valishev

  14. Luminosity Evolution Store 5008, L=207New Helix. High Proton Tune 2007 DOE Tevatron Operations Review – A.Valishev

  15. New Tevatron Working Point • Currently operating between 4/7 and 3/5 with beam-beam x = 0.02 • To increase number of particles need more tune space – WP near ½ should allow 40% more! • However, vicinity of half-integer increases sensitivity to quadrupole errors, especially chromatic • Moreover, large chromatic b-function is detrimental to beam-beam effects even at present WP 2007 DOE Tevatron Operations Review – A.Valishev

  16. Horizontal Chromatic Beta Function 2007 DOE Tevatron Operations Review – A.Valishev

  17. Horizontal Chromatic Beta Function Dots – measurement. Line - model

  18. Correction of b-function Chromaticity • Reconnection of sextupoles into new families 2007 DOE Tevatron Operations Review – A.Valishev

  19. WS Beam-Beam Simulation for Antiproton Bunch 6: Effect of Corrected C2, Present Working Point 2007 DOE Tevatron Operations Review – A.Valishev

  20. WS Beam-Beam Simulation for Proton Bunch 6: Effect of Corrected C2, Present Working Point 2007 DOE Tevatron Operations Review – A.Valishev

  21. Strong-Strong Simulation • Weak-Strong simulation addresses long-term (~hours) beam life time and emittance growth • With increased antiproton beam intensity fast (~1E4 turns) coherent beam-beam effects may appear • To address the possible issues with coherent stability of high intensity beams we developed a strong-strong simulation code with the following features • Strong-strong beam-beam interactions taking into account longitudinal effects (base is 3D PIC by Ji Qiang, LBL) • Machine impedance (resistive wall) • Multi-bunch, multiple collision points (72 IP’s per bunch) • Realistic machine optics and helices E.Stern, AD 2007 DOE Tevatron Operations Review – A.Valishev

  22. Strong-Strong Code Validation. Beam-Beam Not the Tevatron case! BBSS by K.Ohmi Synchrobetatron beam-beam modes can be excited in a model experiment* Data taken at VEPP-2M e+e- collider Good test for a 3D code BB3D by E.Stern * E.Perevedentsev, A.Valishev, Phys. Rev. ST Accel. Beams 4 (2001) 024403 2007 DOE Tevatron Operations Review – A.Valishev

  23. Strong-Strong Code Validation. Impedance Strong head-tail (TMCI) Head-tail Intensity Head-tail phase 2007 DOE Tevatron Operations Review – A.Valishev

  24. Strong-Strong Simulation Results • 1x1 bunch with head-on interaction only. Na=Np=2e11 – no instability • Currently working on 3x3 with 1 head-on and 2 long-range collision points Dipole moment vs. turn Horizontal dipole oscillation spectrum 2007 DOE Tevatron Operations Review – A.Valishev

  25. Conclusions #1 • Model of the Tevatron linear optics is mature. Two methods provide b-function measurement accuracy of 5% • Implementation of the new collision helix with increased separations at particular LR collision points gave predicted improvement of the luminosity life time (~16%) • Luminosity evolution model is an important tool for analysis of strength of beam-beam effects • Weak-strong simulations confirm that present working point allows little space for increasing beam intensities • Betatron tune near half-integer resonance has high potential for larger luminosity 2007 DOE Tevatron Operations Review – A.Valishev

  26. Conclusions #2 • Operation near Q=0.5 is impossible without correction of b-function chromaticity • The new sextupole circuits are being commissioned • According to beam-beam simulations correction of chromatic beta will improve situation at present WP • Strong-strong simulation code has been developed • First simulations with high antiproton intensity do not show coherent instability in the single-bunch case • Multi-bunch mode is being studied 2007 DOE Tevatron Operations Review – A.Valishev

  27. Backup slides 2007 DOE Tevatron Operations Review – A.Valishev

  28. Comparison of Antiproton Bunch 6 Parameters for 3 Working Points: Present Proton Intensity 2007 DOE Tevatron Operations Review – A.Valishev

  29. Comparison of Antiproton Bunch 6 Parameters for 3 Working Points: Proton Intensity Increased by 30% 2007 DOE Tevatron Operations Review – A.Valishev

  30. Antiproton Bunch 6 Parameters in Present Optics with Corrected and Uncorrected Second Order Chromaticity +30% Protons 2007 DOE Tevatron Operations Review – A.Valishev

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