ps-to-sps beam transfer studies

PS-to-SPSBeam Transfer Studies

Helga Timkó BE-RF-BR

in collaboration withTheodoros Argyropoulos, Thomas Bohl, Heiko

Damerau, Steven Hancock, Juan Esteban Müller, Elena Shaposhnikova

LIU-SPS WG on Beam loss… 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

16th May 2012

MOTIVATIONPS-TO-SPS TRANSFER:

Motivation for the transfer studies – Earlier…

A few years ago still, losses were very high Typically around 10-20 %

Þ The currently operational SPS flat-bottom (FB) scheme and many other settings were optimised through these studies

2004

E. Shaposhnikova et al.: Capture loss of the LHC beam in the CERN SPS

Nominal LHC intensity (~1.1-1.3 1011 ppb), 25 ns

LIU-SPS WG on Beam loss… 5

…as a function of intensity…

Losses increase significantly with intensity Þ will be a problem in future

Why do losses increase with intensity? Higher intensity εL more

losses Beam loading deformation

of bucket more losses

16th May 2012

J. Esteban Müller

Losses increase with bunch intensity

…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!

PREVIOUS MEASUREMENTS

PS-TO-SPS TRANSFER:

LIU-SPS WG on Beam loss… 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

16th May 2012

SIMULATION HIGHLIGHTSPS-TO-SPS TRANSFER:

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

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Emittance blow-up

There is an emittance blow-up (due to the synchronisation loop) in the PS included also in the simulations

16th May 2012

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

16th May 2012

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

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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

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SPS

OPTIMISATION STUDIESPS-TO-SPS TRANSFER:

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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 MHz is

optimised based on transmission, t80 MHz is optimised based on bunch length

16th May 2012

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Optimised bunch shapes

… now improved:tails less populated

16th May 2012

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Effect on transmission

With optimised timing and 900 kV in the PS: Losses are reduced, despite having longer bunches

16th May 2012

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SPS capture voltage

Using the SPS voltage & momentum programme for the acceleration ramp, we simulated injection & acceleration:

16th May 2012

23 MV has 3-4 % better transmission than 3 MV No difference between 2 MV and 23 MV is seen in our sims 23 MV stands for: 2 MV at batch injections, 3 MV in-between injections

ONGOING MDSPS-TO-SPS TRANSFER:

Verification of our results

2012-03-29 MD: optimising the PS bunch rotation timing Preliminary results, need further measurements (beam

conditions were changing)

LIU-SPS WG on Beam loss… 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

16th May 2012