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PS-to-SPS Beam Transfer Studies

PS-to-SPS Beam Transfer Studies. Helga Timkó BE-RF-BR in collaboration with Theodoros Argyropoulos , Thomas Bohl, Heiko Damerau , Steven Hancock, Juan Esteban Müller, Elena Shaposhnikova. Outline. Motivation for the beam transfer studies Earlier Today Measurement results

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PS-to-SPS Beam Transfer Studies

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  1. PS-to-SPSBeam Transfer Studies Helga Timkó BE-RF-BR in collaborationwith Theodoros Argyropoulos, Thomas Bohl, Heiko Damerau, Steven Hancock, Juan Esteban Müller, Elena Shaposhnikova

  2. Outline • Motivation for the beam transfer studies • Earlier • Today • Measurement results • Why we did not understand them • A few highlights of our simulation results • Explaining past observations • New ideas for optimisation • On-going work LIU-SPS WG on Beam loss…

  3. PS-TO-SPS TRANSFER: MOTIvation

  4. Motivation for the transfer studies – Earlier… • A few years ago still, losses were very high • Typically around 10-20 % • The currently operational SPS flat-bottom (FB) scheme and many other settings were optimised through these studies 2004 Nominal LHC intensity (~1.1-1.3  1011 ppb), 25 ns Up to 40 % losses!! E. Shaposhnikova et al.: Capture loss of the LHC beam in the CERN SPS

  5. …as a function of intensity… • Losses increase significantly with intensity  will be a problem in future • Why do losses increase with intensity? • Higher intensity  εL  more losses • Beam loading  deformation of bucket  more losses Losses increase with bunch intensity J. Esteban Müller LIU-SPS WG on Beam loss…

  6. …and today • Today, losses are down to ~5 % for nominal intensity (due to scrubbing) • When we’ll increase intensity, losses will be significant again • The SPS bucket is already very full at injection • Would like to use a larger εL, which is good for • Stability in the PS & SPS • Higher intensity beam – planned for future LHC operation • The PS has been upgraded many times over the past 50 years and will be pushed to its limits with the future intensity requirements • Minimising the losses in the injector chain is essential in order to deliver the required intensity to the LHC!

  7. PS-TO-SPS TRANSFER: Previous measurements

  8. MDs: 25 ns and 50 ns beam • 50 ns: 4th July 2011 • 25 ns: 7th November 2011 • Transmission didn’t improve using 900 kV for the bunch rotation in the PS But the transmission stays the same Bunch length does down when 900 kV is applied LIU-SPS WG on Beam loss…

  9. PS-TO-SPS TRANSFER: Simulation Highlights

  10. Our model • In our simulations, we use • Real, averaged phase-space distributions of the bunches • From tomography measurements at the PS FT • Real voltage programmes in PS and SPS • Single bunch simulations, no intensity effects have been taken into account

  11. Emittance blow-up • There is an emittance blow-up (due to the synchronisation loop) in the PS  included also in the simulations Measured bunch lengths are shorter than the simulated LIU-SPS WG on Beam loss…

  12. Simulating the 50 ns case • Transmission measured at SPS FB, before the acceleration • V200 MHz = 2 MV, V800 MHz = 0.34 MV in bunch-shortening mode • Reproduce exp. results when emittance blow-up is added Bunch lengths are matched by ε blow-up Transmission becomes very realistic LIU-SPS WG on Beam loss…

  13. So, why is the transmission not improved? • There is no improvement with larger voltage, because • Bunches have a particular shape and • Buckets are very full; • To improve the transmission, need to improve the shape LIU-SPS WG on Beam loss…

  14. PS rotation timing • However, in the MDs above we adjusted only t80 MHz • t40 MHz = 150 μs was kept the same for both 600 kV and 900 kV cases SPS LIU-SPS WG on Beam loss…

  15. PS-TO-SPS TRANSFER: OPTIMISATION STUDIES

  16. Optimising the bunch rotation • For 1+2 cavities, optimal timing reduces losses: 4.4 %  3.5 % • Using 2+3 cavities instead of 1+2: 3.5 %  1.3 % • N.B. only t40 MHzis optimised based on transmission, t80 MHz is optimised based on bunch length Current operational point LIU-SPS WG on Beam loss…

  17. Optimised bunch shapes … now improved: tails less populated LIU-SPS WG on Beam loss…

  18. Effect on transmission • With optimised timing and 900 kV in the PS: • Losses are reduced, despite having longer bunches Transmission is considerably improved LIU-SPS WG on Beam loss…

  19. SPS capture voltage • Using the SPSvoltage &momentum programme for the acceleration ramp, we simulated injection & acceleration: Capture + FB losses Capture + FB + acceleration ramp losses • 23 MV has 3-4 % better transmission than 3 MV • No difference between 2 MV and 23 MV is seen in our sims • 23 MV stands for: 2 MV at batch injections, 3 MV in-between injections LIU-SPS WG on Beam loss…

  20. PS-TO-SPS TRANSFER: ONGOING MDS

  21. Verification of our results • 2012-03-29 MD: optimising the PS bunch rotation timing • Preliminary results, need further measurements (beam conditions were changing) Currently operational Optimum in simulations

  22. Conclusions & outlook • Earlier, transmission was not improved with V80 MHz,PS= 900 kV, due to the ‘S-shape’ of the bunch and a full SPS bucket • Bunch shape has to be optimised during the PS rotation • Simulations predict a gain of a few % by optimising the PS bunch rotation timing • First MD results are encouraging • The SPS FB voltage influences the losses in the beginning of the acceleration ramp • We can expect significant increase in losses for higher emittances (intensities) • Simulations including intensity effects are planned LIU-SPS WG on Beam loss…

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