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T ransverse beam dynamics issues in the PS

T ransverse beam dynamics issues in the PS. R. Wasef , S. Gilardoni , A. Huschauer , G. S terbini on behalf of PS-LIU team. LIU Day 11/04/2014. Outline. Transverse challenges Space Charge at injection Injection oscillations Transverse damper and feedback Summary and Conclusions.

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T ransverse beam dynamics issues in the PS

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  1. Transverse beam dynamics issues in the PS R. Wasef, S. Gilardoni, A. Huschauer, G. Sterbini on behalf of PS-LIU team LIU Day 11/04/2014

  2. Outline • Transverse challenges • Space Charge at injection • Injection oscillations • Transverse damper and feedback • Summary and Conclusions

  3. Transverse Challenges in the PS • Acceleration: • Transition crossing • Flat top: • Electron cloud • Transverse instabilities • Injection flat bottom: • Injection oscillations • Space charge • Headtail instability

  4. Space Charge at injection 1st Injection 170ms 4 bunches • Current injection energy: 1.4 GeV • Typical tune-spread of current operational beam~(-0.2 ; -0.28) • LHC double batch injection:Long flat bottom: 1.2s • LIU Budgets: 5% beam loss, 5% emittancegrowth • Requests @2GeV: LIU -> ΔQ~(-0.19 ; -0.31) HL-LHC -> ΔQ~(-0.18 ; -0.30) 2nd Injection 1370ms 2 bunches 1.2s Current operation area

  5. Space Charge at injection hallow particles Core of the beam • The beam tune-spread is trapped between the 4qy=1 and the integer resonances. • The choice of the working point is a compromise between losses and emittance blow-up • To respect the LIU budgets of beam loss and emittance growth, ΔQmax≈-0.31

  6. Resonance Compensation Vertical tune scan 2Qx+Qy compensation 3Qy compensation  Successful implementation of a resonance compensation scheme

  7. Space Charge at injection • The resonance compensation would empty larger area for the working are, but the 4Qy=25 resonance is still limiting this area. • Solutions for 4Qy resonance: • A study of changing the vertical integer tune shows promising results to avoid the 4Qy resonance • Changing the optics: larger horizontal dispersion & larger vertical dispersion • Longitudinally hollow bunch

  8. Injection Oscillations measurement • At injection of high intensity beams, intra-bunch oscillations were observed. • No unstable behavior observed • A study revealed that the cause of theseoscillations is indirect space charge. • Problem first observed in 1998.Explained in 2013 • The effect of these oscillations on the emittance of future beams (HL-LHC:32.5 1011 ppb, LIU :281011 ppb) hasto be studied. • TFB damp it effectively. Effect on the emittance to be studied simulation

  9. Transverse Damper and Feedback Injection oscillation • The TFB was designed to damp injection orbit errors of 3mm (peak to peak) within 50 turns, to limit the caused emittancegrowth: • It also has been used as feedback to dump Headtail instabilities at injection. (Chromaticity should be controlled at 2GeV)

  10. Transverse Damper and Feedback • Using the TFB at flattop, it wasable to delay the observed instability by ~10ms • It could not cure instabilities at transition (700MHz instabilities).These instabilities are not to be expected for LHC beams. • E-Cloud

  11. Summary and conclusions • Injection flat-bottom: • Injection oscillations:  TFB, effect on the emittance? • Space charge:  2GeV injection upgrade, Resonance compensation, studies on going (change of vertical integer, new optics, hollow bunches…etc) • Headtail instability:  TFB • Transition instabilities: no limitation expected • Flat-top: • Electron Cloud:  TFB • Transverse instabilities:  TFB

  12. Backup slides

  13. BCMS scheme (48 bunches / PS batch) • LIU upgrades • SPS 200 MHz upgrade • SPS e-cloud mitigation • PSB-PS transfer at 2 GeV • Limitations BCMS scheme • SPS: longitudinal instabilities + beam loading • PS: space charge • SPS: space charge • Performance reach • 2.0x1011p/b in 1.37μm (@ 450GeV) • 1.9x1011p/b in 1.65μm (in collision) HL-LHC LIU-Std LIU-BCMS

  14. Injection oscillations measurement simulation max. tune shift in this simulation is approx. 0.01 larger than in the measurement  effect very sensitive to the longitudinal distribution

  15. 4thorder Resonance Horizontal tune fixed at 6.23 Vertical tune: 6.24->6.3->6.24 • Maximum detuning due to space charge: • Beam 1 : (-.22 ; -.4) • Beam 2 : (-.18 ; -.37) • Beam 3 : (-.08 ; -.07) • Beam 4 : (-.01 ; -.01) 6.3 6.24  The 4th order resonance seems to be excited by space charge

  16. Resonance compensation Horizontal tune scan 2Qx+Qy compensation 3Qy compensation

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