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RF measurements during floating MD in Week 45 5 th of November 2012

RF measurements during floating MD in Week 45 5 th of November 2012. Participants : T. Argyropoulos , H. Bartosik , T. Bohl , J. Esteban Müller , H. Timko , E. Shaposhnikova CCC: G. Iadarola , Y. Papaphilippou , G. Rumolo Thanks to all SPS OP on shift. LIU-SPS BD WG 22/11/2012.

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RF measurements during floating MD in Week 45 5 th of November 2012

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  1. RF measurements during floating MD in Week 45 5th of November 2012 Participants: T. Argyropoulos, H. Bartosik, T. Bohl, J. Esteban Müller, H. Timko, E. Shaposhnikova CCC: G. Iadarola, Y. Papaphilippou, G. Rumolo Thanks to all SPS OP on shift LIU-SPS BD WG 22/11/2012

  2. General • MD title: • Longitudinal set up of the 25 ns LHC beam with Q20 optics (nominal • ~1.25x1011 pb and higher >1.4x1011 p/b injected intensities) • MD aim: • Beam stability and acceptable (for the LHC) beam parameters on flat top • Beam conditions: • 1 or 4 batches of 72 bunches • Intensities at injection: Np~(1.28 -1.6) x1011 p/b • Varying parameters @SPS: • RF voltage amplitudes at FB (V200 - operation always in double RF) • Longitudinal emittance at PS • Increase horizontal chromaticity at flat bottom

  3. Outline • Losses • Voltage programs • Stability • Bunch lengths at injection • Dipole oscillations at FT • Quadrupole oscillations at FT • Examples • Comparing with MD@2012-10-03 • Before the low level set-up • Summary

  4. Losses • Transmission (from BCT and Larger) ~ 85-89 % for single batch • 90-92 % for 3 or 4 batches  continuous losses along flat bottom • Big losses in the last part of the 4th batch Losses after injection Injected like this Larger emittance from PS - similar intensities

  5. Voltage programs • 200 MHz voltage program settings: • 2.5 to 4.5 MV - 4 dips at injections • 4.5 MV constant • 3.5 to 4.5 MV – 1st injection and 2.5 to 4.5 MV – for the rest • As in III + 500 kV at acceleration and flat top (avoid losses for higher intensities) • As in IV but no first dip • 5 MV constant (only one file) optimal

  6. Stability – Bunch lengths at injection • During the MD we asked to increase the longitudinal emittance of the • incoming bunches in the PS  change of about 100 ps • After the second increase beam was stable with good quality for • intensities up to 1.3x1011 p/b • Similar bunch lengths for the operational beam of 50 ns. εl ~ 0.31-0.33 eVs

  7. Stability – Dipole oscillations at FT • Maximum dipole oscillation only of the first batch is shown: smaller emittance • due to phase loop  more unstable than the others • Vertical lines indicate the long. emittance increase from the PS Stable conditions for intensities Np ~ 1.3x1011 p/b on FT

  8. Stability – Quadrupole oscillations at FT • Maximum Quadrupole oscillation for all 4 batches • Vertical lines indicate the long. emittance increase from the PS • Similar results as for the dipole oscillations Stable conditions for intensities Np ~ 1.3x1011 p/b on FT

  9. Examples • High intensity: Np = 1.36x1011 p/b at FT • TWC 200 MHz voltage program: case III

  10. Examples • Iintensity: Np = 1.3x1011 p/b at FT • TWC 200 MHz voltage program: case V

  11. Comparing with MD@2012-10-03 • The MD@2012-10-03 was before the low level set-up • Only 4 files to compare with: • Similar RF voltages at FB (V200 = 4.5 MV and V800 = 0.45 MV) • Longitudinal damper gains • Differences in machine conditions: • V200 calculated for bucket area of 0.65 eVs (0.6 eV) • Long. Emit. BUP: • Margin High: 1.1 (1.1) • Margin Low: 0.85 (0.8) • Scaling: 0.85 (0.83) • Amp: 50 mV (30 mv) • Different chromaticity settings (both planes)

  12. Comparing with MD@2012-10-03 • Smaller bunch lengths at injection • Comparable bunch lengths on FB after capture for the cases with stable conditions • Lower injected intensities compared to the stable • Smaller total losses

  13. Summary • Bad transmission: • ~85-89 % with single batch • ~90-92 % with 4 batches • Optimal machine conditions for Np~1.3x1011 p/b at FT • Not yet for higher intensities • Significant improvement with longer incoming bunches (τinj ~4.2 ns) • as in the operational 50 ns beam.  more losses (1-2% ?) • It seams that for smaller bunches with higher intensities BUP is more difficult • to optimize (observed also in the past)  more induce voltage  effect on the • shape of the incoherent synchrotron frequency spread (?) • Comparison with the MD@2012-10-03 before the low level set-up (beam was unstable • for Np>1.4x1011 p/b at injection): • Smaller bunch lengths at injection • Similar at flat bottom after capture • Beam was stable in the MD@2012-11-05

  14. Higher intensities (~1.45x1011 at injection) • Increase ScaleBUP while keeping the same high VBUP (60 mV) • improved stability • Still unstable with long bunches at FT V200 = 3 MV – V800 = 0.3 MV ScaleBUP = 0.85 – VBUP = 60 mV V200 = 3 MV – V800 = 0.45 MV ScaleBUP = 0.9 – VBUP = 60 mV Change of the ratio V800/V200 to 0.1 improved the situation but not significantly

  15. Higher intensities (~1.45x1011 at injection) • Increase RF voltage at FB improved stability • Still some bunches are unstable with very long bunches at FT V200 = 3 MV – V800 = 0.3 MV ScaleBUP = 0.85 – VBUP = 60 mV V200 = 4.5 MV – V800 = 0.45 MV ScaleBUP = 0.85 – VBUP = 60 mV

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