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Injector beam requirements and options

Injector beam requirements and options. Giovanni Rumolo and Hannes Bartosik

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Injector beam requirements and options

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  1. Injector beam requirements and options Giovanni Rumolo and HannesBartosik Acknowledgments: G. Arduini, T. Bohl, H. Damerau, J. Esteban-Müller, A. Findlay, R. Garoby, S. Gilardoni, B. Goddard, S. Hancock, G. Iadarola, B. Mikulec, Y. Papaphilippou, E. Shaposhnikova, R. Tomás PS & SPS Operation crews LBOC, 8 April 2014

  2. Proposed LHC start up in 2015 6.5 – 7 TeV 450GeV LHCPROBE LHCINDIV LHC50 (std) up to 1.5 x 1011 p/b LHC25 (std) 1.2 x 1011 p/b LHC50 (std/BCMS) up to 1.7 x 1011 p/b Intensity ramp up & physics with 25ns 6.5 – 7 TeV 450GeV LHC25 (std) 1.2 x 1011 p/b LHC25doublet 1.6 x 1011 p/doublet LHC25 (std/BCMS) up to 1.3 x 1011 p/b Use of low e-cloud filling patterns Or, if scrubbing not sufficient Possible alternative LHC25 (8b+4e) up to 1.8 x 1011 p/b LHC25 (BCMS) up to 1.3 x 1011 p/b From LMC, 27 November 2013 LBOC, 8 April 2014

  3. LHCPROBE & LHCINDIV – specs @LHC injection • LHCPROBE usually below or about 1010 p/b, transverse emittance not critical • LHCINDIV parameter range also extended in MDs to produce single bunches with up to 4 x 1011 p/b and/or with lower longitudinal emittances (down to 0.15 eVs) at SPS injection • Accelerate and extract high intensity variants for possible impedance or beam-beam studies ? LBOC, 8 April 2014

  4. LHCPROBE & LHCINDIV – 2013 status • Since 2013, new production mechanism in the PSB to cover parameter range for both these beams (S. Hancock, CERN-ATS-Note-2013-040 MD) • Based on longitudinal blow up (C16 voltage) during the first part of the cycle for intensity setting • It provides unprecedented intensity shot-to-shot reproducibility and preserves the 6D phase space unchanged for different intensity values LBOC, 8 April 2014

  5. LHCINDIV VdM – 2012 status • In 2012, a new single Gaussian bunch was produced for Van der Meer scans (H. Bartosikand G. Rumolo, CERN-ACC-NOTE-2013-0008 MD) • Based on longitudinal AND transverse shaving in the PSB to obtain “large” emittance single bunches with less than Gaussian tails • Provides Gaussian bunches with the desired intensities in the SPS after scraping LBOC, 8 April 2014

  6. LHC50 (std & BCMS) – pre-LS1 status • 50 ns beam at the SPS extraction in 2012/13 (Q20) • Combined wire-scans at end of SPS flat bottom (values cross-checked with LHC) • Error bars include spread from measurements as well as systematic uncertainty (10%) • Intensity measured at SPS flat top after scraping • Transport through PS and SPS within intensity loss and emittance blow up budgets • Four trains of 36 bunches • Routinely used for physics in 2012 • Three trains of 24 bunches • Sent to LHC only for test to prove luminosity gain LBOC, 8 April 2014

  7. LHC25 (std & BCMS) – pre-LS1 status • 25 ns beam at the SPS extraction in 2012 (Q20) • Combined wire-scans at end of SPS flat bottom (values cross-checked with LHC) • Error bars include spread from measurements as well as systematic uncertainty (10%) • Intensity measured at SPS flat top after scraping • Transport through PS and SPS 15% above budgets for std beam • Four trains of 72 bunches • Used for the LHC scrubbing run in 2012 • Three trains of 48 bunches • Used for the LHC pilot physics run in 2012 LBOC, 8 April 2014

  8. Pre-LS1 performance • 50 ns beam (both standard production and BCMS) already very close to the limits in injectors • Intensity per bunch: close to the limit of longitudinal instability in the PS • Brightness: BCMS at the present space charge limit in the SPS • 25 ns beam (both standard production and BCMS) already very close to the limits in injectors • Intensity per bunch:10% from the limit due to RF power and longitudinal instability in the SPS • Brightness:At the present space charge limit in the PS LBOC, 8 April 2014

  9. Post-LS1: Expected performance • Higher intensity • Extended reach thanks to the upgraded longitudinal feedback in the PS • 25 ns expected to be limited to 1.3 x 1011 p/b because of RF power and longitudinal instabilities in the SPS • Higher brightness • RF manipulations in the PS @2.5 GeV (instead of 1.4 GeV) – PS extraction time moved to c2850 for all 3bp LHC cycles • Larger longitudinal emittance from the PSB • Space charge alleviated by both longer bunches and larger momentum spread • PSB control of longitudinal parameters along the cycle • Controlled longitudinal emittance blow up to produce the required longitudinal emittances • Use of h1+2 in phase at the PSB extraction to keep these larger longitudinal emittance bunches within a certain length (recombination kicker rise time constraint) LBOC, 8 April 2014

  10. Post-LS1: PSB – PS transfer Recombination kicker rise time: Longitudinal emittance per bunch at PS injection should not exceed • [Total Split Factor x 0.35 eVs]/1.1 (includes 10% margin for blow-up) • About 3 eVs (h=7) and 2 eVs (h=9) for RF manipulations at Ekin=2.5 GeV • [FB Split Factor x 1 eVs] for transition crossing in h=21 • Matched value in the PSB (h1+2) to obtain the above bunch lengths LBOC, 8 April 2014

  11. Post-LS1: PSB – PS transfer Recombination kicker rise time: Longitudinal emittance per bunch at PS injection should not exceed • [Total Split Factor x 0.35 eVs]/1.1 (includes 10% margin for blow-up) • About 3 eVs (h=7) and 2 eVs (h=9) for RF manipulations at Ekin=2.5 GeV • [FB Split Factor x 1 eVs] for transition crossing in h=21 • Matched value in the PSB (h1+2) to obtain the above bunch lengths LBOC, 8 April 2014

  12. Post-LS1: LHC25 (std & BCMS) BCMS with new longitudinal parameters Std with new longitudinal parameters 2012 2012 LBOC, 8 April 2014

  13. Post-LS1: LHC25 and LHC50 (std & BCMS) • Achievable beam parameters at the LHC injection after LS1 • Assuming: • Transport in the PS and SPS within budgets • Benefits from reviewed longitudinal parameters in the PSB – PS transfer • Successful SPS scrubbing after exposure to air during LS1 • Summary tables LBOC, 8 April 2014

  14. LHC25doublet (scrubbing beam) • Machine tests in the SPS at the end of 2012-13 run • Doublet production scheme at SPS injection validated • E-cloud enhancement experimentally demonstrated • The production scheme is based on splitting of long bunches at SPS injection • Injection of trains of 72 x 10ns long bunches with 1.7e11 p/doublet on unstable phase and capture in two neighboring buckets • Should be fine in LHC  only interlocked BPMs to be checked with doublets 4 3 1st inj. 200 MHz RF Voltage [MV] 2 1 0 4 -2 0 8 2 6 Time [ms] LBOC, 8 April 2014

  15. LHC25doublet (scrubbing beam) • We need to accelerate 1.6 x 1011 p/doublet in the SPS • ex,y ~3 μm at best at injection • RF power and longitudinal instability limitation in the SPS  intensity perhaps achievable with a 3x slower ramp rate, tentatively on Q20 • Longitudinal emittance about 0.4 eVs at injection from simulations (J. Esteban-Müller) • Beam quality possibly degraded due to e-cloud and longitudinal limitations • Need to gain experience in the SPS with dedicated MDs in 2014 for complete parameter list at flat top LBOC, 8 April 2014

  16. 8b+4e scheme • Creates trains with 4 missing bunches every 8 bunches (H. Damerau, RLIUP) • Allows for larger intensity per bunch • Is expected to reduce e-cloud effects • Production • Std scheme  Unbalanceh = 7  21 triple split into a double split, leaving empty bucket – bunch pattern 6x(8b+4e) + 8b • BCMS merging and triple splitting suppressed – bunch pattern 3x(8b+4e) + 8b Ekin = 2.5 GeV Ekin = 2.5 GeV • Simulation • Simulation Standard scheme BCMS LBOC, 8 April 2014

  17. 8b+4e scheme • Limited to 1.8 x 1011 p/b in the SPS because of longitudinal instabilities • Brightness limited by • PSB brightness for standard scheme • No outstanding bottleneck for BCMS Standard scheme BCMS LBOC, 8 April 2014

  18. 8b+4e scheme • Limited to 1.8 x 1011 p/b in the SPS because of longitudinal instabilities • Brightness limited by • PSB brightness for standard scheme • No outstanding bottleneck for BCMS Standard scheme BCMS LBOC, 8 April 2014

  19. Summary • LHC start up • LHCPROBE and LHCINDIV with new production mechanism in the PSB for the bunch intensity control • LHC50 standard (first phase Scrubbing I) • Up to 1.7 x 1011 p/b with ex,y=1.6 mm • Possibly LHC25 standard (last phase Scrubbing I) • Up to 1.3 x 1011p/b with ex,y=2.4 mm • Physics and 25ns operation • LHC50 (standard and BCMS) for first phase physics operation • BCMS up to 1.7 x 1011 p/b with ex,y=1.1 mm • LHC25 standard (first phase Scrubbing II) • LHC25 doublet (last phase Scrubbing II) • Up to 1.6 x 1011p/doublet with ex,y>3.0 mm • LHC25 BCMS for physics operation • Up to 1.3 x 1011p/b with ex,y=1.3 mm • 8b+4e as alternative if scrubbing is not enough to run with LHC25 BCMS • Up to 1.8 x 1011p/b with ex,y=2.3/1.4 mm (std/BCMS) LBOC, 8 April 2014

  20. Thank you for your attention LBOC, 8 April 2014

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