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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

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

outline
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…

motivation for the transfer studies earlier
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

as a function of intensity
…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…

and today
…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!
mds 25 ns and 50 ns beam
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…

our model
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
emittance blow up
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…

simulating the 50 ns case
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…

so why is the transmission not improved
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…

ps rotation timing
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…

optimising the bunch rotation
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…

optimised bunch shapes
Optimised bunch shapes

… now improved:

tails less populated

LIU-SPS WG on Beam loss…

effect on transmission
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…

sps capture voltage
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…

verification of our results
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

conclusions outlook
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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