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SPS Upgrade plan and coating requirements AEC’09: anti e-cloud coating workshop 2009 (ACCNET)

SPS Upgrade plan and coating requirements AEC’09: anti e-cloud coating workshop 2009 (ACCNET). E. Shaposhnikova (CERN/BE/RF) for SPSU Study Team. SPS upgrade plan e-cloud issues coating requirements. Motivation for CERN injector upgrade. Future LHC upgrade:

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SPS Upgrade plan and coating requirements AEC’09: anti e-cloud coating workshop 2009 (ACCNET)

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  1. SPS Upgrade planand coating requirementsAEC’09: anti e-cloud coating workshop 2009 (ACCNET) E. Shaposhnikova (CERN/BE/RF) for SPSU Study Team SPS upgrade plan e-cloud issues coating requirements

  2. Motivation for CERN injector upgrade • Future LHC upgrade: • radiation damage of LHC IR Quads • statistical error reduction saturates after a few years of nominal operation • physics motivation for 10 times higher ℒ • 25% more discovery range in particle mass • 2 times higher precision ►new beam requirements • Age of the present injectors and need for reliable operation for the next X(?) years • Linac2 1978 • PSB 1975 • PS 1959 • SPS 1976 • New experiments at low beam energy

  3. Today’s performance of the LHCinjector chain (nominal parameters)

  4. CERN future accelerators New injectors • Linac4 (2014) → 160 MeV • LPSPL → 4 GeV • PS2 → 50 GeV

  5. Planning and milestones • Linac4 project start: 2008; commissioning: 2013 • Beam from modified (2012/2013) PS Booster: 2014 → Shorter PS cycle and LHC filling time, ultimate LHC intensity, more beam for low energy physics Ultimate beam from SPS: 2015? • Project proposal for SPL, PS2 and SPSU: 2011 → More reliable operation, shorter LHC filling time with higher intensity, high proton flux from LPSPL, PS2 and SPS → Potential for DLHC with SPS+ (new magnets 50 GeV → 1 TeV) • Nominal LHC beam for physics with new SPS injectors: 2018? • High intensity beam for physics: depends on the SPS upgrade

  6. SPS beams with PS2 andpresent achievements → SPS upgrade is necessary e-cloud

  7. SPS→SPSU(pgrade) Study Group http://cern.ch/spsu/ Exists since March 2007 Active members: (BE, EN,TE): G. Arduini, F. Caspers, S. Calatroni, P. Chiggiato, P. Costa Pinto, K. Cornelis, E. Mahner, E. Metral, G. Rumolo, E. Shaposhnikova (convener), M. Taborelli, C. Yin Vallgren, F. Zimmermann + R. Garoby, J. Bauche, G. Vandoni, N. Gilbert… and speakers Main tasks: • Identify limitations in the existing SPS • Study and propose solutions • Design report in 2011 with cost and planning for proposed actions

  8. SPS: known intensity limitations • Single bunch effects: • space charge • TMC (Transverse Mode Coupling) instability • Multi-bunch effects: • e-cloud • beam loss • vacuum: pressure rise, outgassing, septum sparking • longitudinal coupled bunch instabilities • beam loading in the 200 MHz and 800 MHz RF systems • heating of machine elements (e.g. MKE, MKDV kickers)

  9. 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 • “passive”: due to increased nonlinearity • 800 MHz (4th harmonic) RF system • increased longitudinal emittance • hardware modifications: injection kickers, RF system, beam dump system, collimation, beam diagnostics, radioprotection

  10. 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 • 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

  11. pressure rise beam losses transverse emittance blow-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 G. Arduini M. Taborelli

  12. LHC batch (72 bunches) after 30 min of coast at 26 GeV/c SPS limitations: beam losses • Bunch peak amplitude in the head and tail of LHC batch during cycle head tail head tail horiz. time 2 s/div Possible loss mechanism connected with e-cloud (G. Franchetti et al.) T. Bohl et al.

  13. Strong dependence on batch intensity, much less on total (number of batches) Higher losses at the beginning of run – up to 20%, less at the end (typically ~ 10 %) Much smaller relative losses for 75 ns and 50 ns bunch spacing for the same bunch intensity: (5%) – not single bunch effect →e-cloud? SPS limitations: beam losses LHC beam (25 ns bunch spacing): relative capture loss for different batch intensities

  14. SPS limitations: e-cloudScaling with bunch spacing and intensity 25 ns spacing, SEY=1.4 50 ns spacing, SEY=1.6 e-cloud build-up - results from ECLOUD simulations (G. Rumolo): non-monotonic dependence on bunch intensity for fixed spacing and SEY → for 50 ns spacing a higher intensity is always better

  15. HEADTAIL simulations E-cloud build up threshold 1/g SPS limitations: e-cloudScaling with beam energy V-plane:instability threshold isdecreasing 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: • measurements at different points during ramp with reduced chromaticity and damper gain – difficulties in interpretation • special cycle with flat portion at 55 GeV/c, dependence on transverse size was confirmed(G. Rumolo et al.PRL, 100, 2008)

  16. e-cloud mitigation SPS requirements: • SEY < 1.3 • applicable to the existing stainless steel vacuum chamber inside 6 m long magnets without dismantling • no aperture reduction (thickness < 0.5 mm) • no bake-out above 120 deg • no re-activation • no ageing with venting • low impedance • long-term stability • good vacuum properties, no (small) outgassing

  17. e-cloud mitigation • Coatings • low SEY a-C (talk by M. Taborelli, S. Calatroni) • rough surfaces (talk by I. Montero) • Clearing electrodes all along the beam pipe (F. Caspers, T. Kroyer, E. Mahner) • fixing (needs 600-800 deg) • impedance • Grooves (talk by M. Pivi) • manufacture, test with beam, aperture, impedance • Active damping system in V plane (W. Hofle and LARP) • feasibility (instability growth rate, frequency) • large bandwidth • incoherent effects

  18. SPS experimental set-up in 2008-2009 aC-8 • 4 strip-line monitors XSD: • (talk by C. Yin Vallgren) • (1) St-St for reference • (2) old a-C coating • (3-4) two new coatings (a-C , a-C&rough) • clearing (enamel) electrodes with button PUs • C - magnet with exchangeable samples (St-St in 2008, a-C in 2009)

  19. SPS vacuum chamber coating • Special magnet coating system was designed and during 2008/2009 shutdown 3 spare SPS dipoles were successfully coated (top&bottom)by amorphous carbon (talk by P. Costa Pinto) and installed in the SPS test area with microwave (talk by S. Federmann) and vacuum (talk by M. Taborelli) diagnostics • → very promising results • → real implementation coating bench in bld. 867

  20. Possible vacuum chamber modification • Implementation in the SPS • (from 2013?) • 750 vacuum chambers inside dipoles can be treated in 3-4 shutdowns (talk by J. Bauche) • Experience due to installation of RF shields (1999-2001) and refurbishing of the cooling circuits of dipoles (2007-2009) • Infrastructure partially exists S. Sgobba

  21. a-C coating • Open questions: • Long-term (> 10 years) behavior (ageing with venting and beam scrubbing) • Quality control of results, diagnostics • Pressure (outgassing) • What should be coated? • (talk by G. Rumolo)

  22. e-cloud signal in SPS dipoleand outside • e-cloud trace more visible at the magnet edges • and outside • effect of the fringe field or optical illusion? • - more clean surface – less protected by dust? K. Cornelis

  23. Summary • In the present CERN upgrade scenario (under discussion) all machines in the LHC injector chain will be replaced by new ones except the SPS, which will have a higher injection energy • The SPS upgrade is a key element for the LHC to benefit fully from new upstream machines • E-cloud is one of the main SPS limitations even for the present performance and it will not be improved at higher injection energy • At the moment amorphous carbon coating seems to be the most promising solution for e-cloud mitigation in the SPS and can be implemented earlier (from 2013?) to improve machine performance for nominal and ultimate LHC beams

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