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SPS Upgrade

SPS Upgrade. Study Group (BE, EN,TE), since March 2007: G. Arduini, F. Caspers, S. Calatroni, P. Chiggiato, K. Cornelis, B. Henrist , E. Mahner, E. Metral, G. Rumolo, E. Shaposhnikova (convener), M. Taborelli, C. Yin Vallgren, F. Zimmermann + …

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SPS Upgrade

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  1. SPS Upgrade Study Group (BE, EN,TE), since March 2007: G. Arduini, F. Caspers, S. Calatroni, P. Chiggiato, K. Cornelis, B. Henrist, E. Mahner, E. Metral, G. Rumolo, E. Shaposhnikova (convener), M. Taborelli, C. Yin Vallgren, F. Zimmermann + … R. Garoby, J. Bauche, P. Costa Pinto, G. Vandoni, N. Gilbert, M. Jimenez and speakers (M. Barnes, Y. Kadi, W. Hofle, …) Reports to IEAC and sLHC Main tasks: • Identify limitations in the existing SPS • Study and propose solutions • Design report in 2011 with cost and planning for proposed actions Total budget for 2008-2011: 1100 kCHF Meetings, talks, minutes: http://paf-spsu.web.cern.ch/paf-spsu/

  2. Present LHC upgrade scenarios F. Zimmermann et al.

  3. LHC injectors: present and future UNOSAT

  4. SPS: present achievements and future needs → SPS upgrade is necessary

  5. SPS: known intensity limitations • Single bunch effects: • space charge • TMCI (transverse mode coupling instability) • Multi-bunch effects: • e-cloud • coupled bunch instabilities at injection and high energy • beam loss (7-10% for 25 ns bunch spacing and 5% for 50 ns bunch spacing and nominal bunch intensity) • beam loading in the 200 MHz and 800 MHz RF systems • heating of machine elements (MKE, MKDV kickers, …) • vacuum (beam dump and MKDV outgassing), septum sparking

  6. SPSU: possible actions and cures • Higher injection energy: 25 → 50 GeV with PS2 • e-cloud mitigation • Impedance reduction (after identification!) • Damping of instabilities: • active: upgrade of beam control (transverse and longitudinal feedbacks) • “passive”: due to increased nonlinearity • 800 MHz (4th harmonic) RF system • increased longitudinal emittance (more losses at capture in LHC) • Hardware modifications: injection kickers, RF system, beam dump system, beam diagnostics, radioprotection… • New hardware: collimation?

  7. SPS with PS2 and 50 GeV injection • Sufficient improvement for space charge tune spread up to bunch intensity of 5.5 x1011 • Increase in TMC instability threshold by a factor 2.5 (needs more → transverse feedback or larger longitudinal emittance) • Shorter injection plateau (2.4 s instead of 10.8 s) and acceleration time (10%) – shorter LHC filling time (and turnaround time) • No transition crossing for all proton beams and probably light ions • Easier acceleration of heavy ions (lead): • smaller tune spread and IBS growth rate, • smaller frequency sweep - no need for fixed frequency acceleration • Smaller physical transverse emittance – less injection losses • …

  8. pressure rise, septum sparking, beam dump, MKDV outgassing beam losses on flat bottom transverse emittanceblow-up and instabilities: coupled bunch in H-plane single bunch in V-plane Today’s cures high chromaticity in V-plane transverse damper in H-plane scrubbing run (from 2002): SEY decrease 2.5 → 1.5 SPS limitations: e-cloud x 102 M. Taborelli et al. G. Arduini

  9. HEADTAIL simulations E-cloud build up threshold 1/g SPS limitations: e-cloudScaling with beam energy V-plane: instability threshold is decreasing with energy γ (constant emittances, bunch length and matched voltage) e-cloud build-up threshold H-plane: e-cloud instability growth time ~γ(G. Arduini) Experimental studies of the scaling law in the SPS: • 2006: measurements at different points during ramp with reduced chromaticity and damper gain – difficulties in interpretation • 2007: special cycle with flat portion at 55 GeV/c, dependence on transverse size was confirmed(G. Rumolo et al.PRL, 100, 2008)

  10. e-cloud mitigation Stainless steel • surface treatment: in-situ, no aperture reduction, no re-activation • carbon based composites: initial SEY<1, studies of ageing with venting, (M. Taborelli et al.) • rough surfaces – 2 layers • electromagnetic roughness (F. Caspers) • clearing electrodes (F. Caspers et al.) • active damping system in V-plane (W. Hofle + LARP) • grooves - (M. Pivi – SLAC) a-Carbon C-8 M. Taborelli et al.

  11. Experimental set-up in 2008 and 2009 • 4 strip-line monitors XSD: (1) St-St for reference, (2) old a-C coating, (3-4) EcEx and NEG in 2008 - two new coatings in 2009 (a-C + rough) • clearing (enamel) electrodes with button PUs • C - magnet with exchangeable samples (St-St in 2008, a-C in 2009) • 3(6) RF antennas for microwave transmission measurements (2008)

  12. Possible vacuum chamber modification for e-cloud mitigation • Experience due to installation of RF shields (1999-2001) and refurbishing of the cooling circuits of dipoles (2007-2009). Infrastructure: ECX5 cavern – ø20 m • 750 dipoles can be coated in 120 days →3 shutdowns (48 h/chamber, 6/day) with 2 Dumont machines and 2 coating benches • 2009:3 MBB spare magnetscoated by amorphous carbon and installed in SPS test area with microwave and vacuum diagnostics • Anti e-cloud coating Workshop, CERN, 12-13.10.2009 coating bench in bld. 867

  13. μw transmission – experimental set-up • Team: F. Caspers, S. Federmann, E. Mahner and • D. Seebacher • 2 driver systems, • 4 receiver systems • A lot of preparatory work (antennas, filters • fabricated at CERN), • installation in tunnel • Problems with IMD – modifications before each MD, progress in • results

  14. Pressure during scrubbing run uncoated-coated uncoated-uncoated coated-coated

  15. SPS limitations: impedance • 1999-2001: SPS impedance reduction in preparation for nominal LHC beam → no microwave instability • 2003-2006: impedance increase, mainly due to re-installation of 8 MKE (extraction kickers for LHC) • Only 50% of SPS transverse impedance budget is known (E. Metral et al.) → search for the rest • Shielding of the known impedance sources (MKE, MKDV...) • Active damping of the 800 MHz impedance (FB and FF) Quadrupole oscillation frequency as a function of bunch intensity Im Zeff ~ slope Similar measurements in V-plane(H. Burkhardt et al.)

  16. SPS limitations: impedanceMKE kicker shielding Longitudinal Re[Z] Printed strips in MKE-L10 Imaginary part of Z Interdigital comb structure 20mm spacing surface discharge Transverse Re[Zh] F. Caspers et al.

  17. Strong dependence on batch intensity, less on total (number of batches) Reduction of losses in 2004 with new working point and RF gymnastics (2 MV → 3 MV) Much smaller relative losses for 75 ns and 50 ns bunch spacing for the same bunch intensity: (5-7 % in 2008) To have the same absolute losses relative losses should be reduced for higher intensities! SPS limitations: beam losses LHC beam (25 ns bunch spacing): relative capture loss for different batch intensities

  18. Coupled bunch instabilities Bunch length (av., max-min) Beam stability • Cures: 800 MHz RF system in bunch-shortening mode and controlled emittance blow-up → 0.6 eVs (morefor upgrade intensities) G. Papotti et al.

  19. RF systems upgrade 200 MHz RF power (max LHC upgrade intensity) • Coupled-bunch (long.) instability threshold ~1/5 nominal intensity • Larger emittance needed for higher intensities ( ε~√N) • The 200 MHz RF system limits: • Voltage 7.5 MV • Power: 1.4 MW for half and 0.7 MW for full ring (Erik) • (3.3-4.5) MW/cavity (200 MHz) for max PS2 intensity → The 200 MHz and 800 MHz power plant should be increased → R&D for re-design of couplers and coaxial lines → New beam control → Cavity length (200 MHz) should be optimised : 4x3 +2x2 sections → 1.4 MW average, 10 MV (Trevor)

  20. FT/CNGS beam in SPS with PS2 • Total maximum intensity: 2 x higher → 1014 (minus losses) • Maximum injection energy: 13 GeV→ 25 GeV or 50 GeV • Pulse length at injection: 2 x longer → no flat bottom • Beam macro and micro structure in SPS: 5 times less bunches (25 ns spacing), more gaps • No transition crossing, bunch-to-bucket transfer with PS with PS2 ←one PS cycle→ ←one PS cycle→ ←one PS2 cycle (5-turn extract.)→

  21. SPS cycle length for CNGS SPS PS2 (examples) → Depending on PS2 physics program beam could also be injected at 26 GeV

  22. Short SPS cycle - 4.8 s(26 – 400) GeV/c Beam momentum RF voltage 200 MHz RF power 200 MHz limit limit → 50 % more RF voltage (cavities) - additional RF system ? → Twice more RF power at 200 MHz

  23. Hardware modifications • Impedance reduction (shielding, modification) – as identified • SPS magnet coating after successful tests (1/6 or 1/3 in 2013/2014 ?) • Vacuum system modification • Beam dump • 50 GeV injection: dump kickers (MKDV/H), injection kickers MKP • High intensity - RF power, cavities, beam control • Beam collimation • Radioprotection

  24. Summary • The upgraded CERN injectors should produce high intensity beam with high reliability both for LHC and other users • All machines in the LHC chain will be replaced by new ones except the SPS, which will profit from a higher injection energy • The SPS upgrade is a key element for the LHC to benefit fully from new upstream machines • A lot of work to be done in RF group! • Some measures proposed for the SPS upgrade would help for the operation with nominal and ultimate LHC beams and can be implemented earlier (e-cloud mitigation, impedance reduction)

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