1. SPS Scrubbing Runs 2014 week 45 and week 50 (part I) H. Bartosik, G. Iadarola, K. Li, L. Mether, G. Rumolo, M. Schenk Thanks to: SPS OP crew, G. Arduini, T. Argyropoulos, : T. Bohl, E. Carlier, K. Cornelis, H. Damerau, J. Esteban Muller, A. Findlay, S. Gilardoni, B. Goddard, A. Guerrero, S. Hancock, W. Höfle, V. Kain, G. Kotzian, A. Lasheen, M. Meddahi, E. Métral, B. Mikulec, G. Papotti, E. Piselli, A. Romano, R. Salemme, B. Salvant, E. Shaposhnikova, M.Taborelli … and thanks to the PS complex for the preparation of the challenging beams!! LIU SPS intermediate scrubbing review, 23 February, 2015

2. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

3. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

4. Scrubbing run Scrubbing run Injector schedule 2014 Originally 2 weeks foreseen for SPS scrubbing, then reduced to two blocks of 7 and 2.5 days in Week 45 and 50, respectively Some goals (or desired outcome) of SPS scrubbing in 2014  Recover 2012 performance with LHC 25 ns beams and qualify machine behavior with LHC beams after long shutdown  Test doublet beams for SPS scrubbing and in preparation for LHC scrubbing in 2015  Study high intensity 25 ns beams at 26 GeV/c to gain information to steer LIU decision coating vs. scrubbing in 2015  Test new LHC-type beam variants

5. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

6. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days MD3: 26.4 s, long flat bottom cycle 26 GeV/c MD1: 7.2 s, short flat bottom cycle 26 GeV/c LHC25NS: 22.8 s, nominal LHC filling cycle to 450 GeV/c

7. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days MD3: 26.4 s, 26 GeV/c Monday Prepared machine for scrubbing (Fast vac. valves blocked open, extraction elements off, ZSs at -30 kV) In agreement with TE-ABT increased MKP4 SW pressure interlock to 4e-7 mbar Setup of scrubbing cycles (early dump to control pressure in MKP and TIDVG) COLDEX moved into IN position (observed no impact on beam lifetime) Started maximizing integrated beam intensity on scrubbing cycle −limited by TIDVG vacuum interlock  in agreement with TE-ABT and EN-STI interlock level raised from 4e-7 mbar to 6e-7 mbar (while the pressure in MKP4, initially lower, was slowly creeping up….)

8. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days MD3: 26.4 s, 26 GeV/c Tuesday Continued scrubbing at 26 GeV (MD3 cycle, inject more, move the dump later in the cycle) In parallel, setup of 200 MHz LL RF on acceleration cycle −6h in the afternoon, mostly without beam, reduced the duty cycle Reached 4 batches on FB with dump at 13s Limited by MKP4 vacuum (mainly related to increase of static pressure due to heating) −Had to go back to 3 batches during the night for cool down

9. Wednesday Dedicated MD on new 800 MHz LLRF (from 10:00 to 00:45, fully dedicated in first part, then in parallel with setting up of doublet) Agreed with TE-ABT and EN/STI about the MKP4 and TIDVG thresholds −Raise MKP4 SW interlock to 5e-7 mbar −Raise TIDVG interlock to 1.2e-6 mbar Started setting up the doublet beam on MD1 −1 batch of 72 bunches from PS split into 72 doublets, low intensity (~1.2e11 p/doublet) −Observed strong pressure rise in the arcs (but none in a-C coated cells and in sensitive elements) Mains tripped during the night (4h no beam) Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days MD3: 26.4 s, 26 GeV/c MD1: 7.2 s, 26 GeV /c LHC25NS: 22.8s, 450 GeV/c

10. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days Thursday Continued scrubbing with standard 25 ns beam (injected up to 5 batches of 72 bunches) In parallel, LHCPILOT cycle for LHC mastership and RF synchronization tests, and TI2 polarity checks Continued transverse damper setup for doublet beams Tests with multiple batches on cycle with acceleration (longitudinal instabilities observed, since longitudinal damper was still not functional on the ramp) In the night, scrubbing exclusively with doublet beam to allow for MKP4 cool down MD3: 26.4 s, 26 GeV/c MD1: 7.2 s, 26 GeV/c LHC25NS: 22.8s, 450 GeV/c

11. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days Friday No beam in the morning due to PS problems (TT2 quad and then RF) Continued setup of the 200 MHz longitudinal dampers In parallel scrubbing with doublet beam on MD1 cycle −Further transverse damper setup −Observed transverse instabilities on the trailing bunches of the train (no vertical instability observed on standard 25 ns beam, even with low chromaticity) In the night acceleration of 4 batches of 72 bunches up to 450 GeV/c Scrubbing with 4 batches accelerated (interleaved with doublet scrubbing when pressure in TIDVG became too high) MD1: 7.2 s, 26 GeV/c LHC25NS: 22.8s, 450 GeV/c

12. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days Saturday Scrubbing with standard 25 ns at 26 GeV/c and with acceleration Optimized closed orbit on the energy ramp to reduce losses Tested multiple injections (up to 4) of doublet beam on the long 26 GeV/c cycle −Beam quality initially quite poor, could be later improved by fine tuning −RF voltage ramped to 7 MV after the last injection to increase scrubbing −Left in for scrubbing over night MD3: 26.4 s, 26 GeV/c MD1: 7.2 s, 26 GeV/c LHC25NS: 22.8s, 450 GeV/c

13. Monday TuesdayWednesdayThursdayFridaySaturdaySunday Scrubbing week 45: overview days Sunday Characterization of the 25 ns beam (4x72b.) at 26 GeV (to be compared against 2012 meas): −Emittance measurements, bunch-by-bunch tune measurements −Lifetime as a function of vertical chromaticity Characterization of the doublet beam (4x72doublets) at 26 GeV: −Emittance measurements, bunch-by-bunch tune measurements −Lifetime as a function of vertical chromaticity Few tests with orbit bumps to localize the scrubbed region Monday 5.00: beam stopped for cool down and access to move COLDEX out MD3: 26.4 s, 26 GeV/c

14. MKP pressure and temperature evolution

15. Increase of MKP4 SW pressure interlock to 4e-7 mbar, then 5e-7 mbar necessary to advance with scrubbing Relatively low dynamic pressure rise, but static vacuum following the temperature profile MKP heating due to impedance with nominal 25 ns beams, but cool down with low intensity doublets (consistent with the impedance model)

16. TIDVG pressure and temperature evolution

17. Increase interlock level from 4e-7 mbar to 6e-7 mbar was necessary to advance with scrubbing. Increase to 1.2e-6 mbar needed when dumping beam on TIDVG Conditioning visible over scrubbing run Temperature rise by more than 4 degrees when dumping consecutive shots on TIDVG

18. Important facts of Scrubbing Run I (1/2) 1 full week (week 45) high efficiency scrubbing with very good beam availability (only minor hiccups) and main limitations coming from vacuum in MKP4 and TIDVG (not the arcs) Large use of long flat bottom (26 GeV/c) cycle, gradually increasing number of batches injected and moving the dump later in the cycle (as vacuum in TIDVG or MKP4 permitted) Successfully deployed low intensity doublet beam (up to four batches at 26 GeV/c with no more than 1.4 x 10 11 p/doublet) Enhanced electron cloud in high-field non a-C coated regions and none in a-C coated regions and field free regions  Experimental evidence of electron cloud suppression with a-C coating No MKE heating, but significant heating on MKP4 leading to outgassing and pressure above interlock value Lower MKP heating (as expected from C. Zannini’s kicker impedance model) with doublet beam, which allowed scrubbing while recovering MKP4 vacuum

19. Important facts of Scrubbing Run I (2/2) Recovered nominal LHC beam (4 batches 72b) at 450 GeV/c Commissioned the new TIDVG with standard 25 ns beam at 450 GeV/c, data taken for thermal response Measured transverse emittances below 3  m Minor fine tuning yet to be done ε v ≈ 2.4 μm

20. Important facts of Scrubbing Run I (2/2) Recovered nominal LHC beam (4 batches 72b) at 450 GeV/c Commissioned the new TIDVG with standard 25 ns beam at 450 GeV/c, data taken for thermal response Measured transverse emittances below 3  m Minor fine tuning yet to be done Vertical electron cloud instabilities hard to reproduce with Q20 optics! Observed only with doublets due to high electron cloud operation Standard 25 ns beam was stable even with low vertical chromaticity setting Further studies including comparison with Q26 optics planned Important conditioning of both newly installed elements (e.g., MKP4, TIDVG) and pressure in arcs →Scrubbing overall successful so far, re-conditioning is always easier than first conditioning…

21. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

22. Scrubbing run in week 50: overview MD3: 26.4 s, long flat bottom cycle 26 GeV/c LHC25NS: 22.8 s, nominal LHC filling cycle to 450 GeV/c LHCMD4: 31.2 s, long cycle with 3x slower ramp to 450 GeV/c days

23. Scrubbing run in week 50: overview MD3: 26.4 s, 26 GeV/c: High intensity 25 ns beam Monday (08/12/2014) High intensity 25 ns beam (up to 1.9e11 p/b injected) on flat bottom cycle −Lifetime quite poor −Horizontal instability after injection of 2 nd batch −Emittance blow-up in last part of trains (starting from 2 nd batch), especially horizontal Intensity scan during the night (but problems in PSB RF) → Back to strong and visible electron cloud effects: −Stronger electron cloud in drift regions due to higher intensity, in dipoles due to different stripe position −Beam more sensitive to collective effects due to high intensity days

24. Scrubbing run in week 50: overview Tuesday (09/12/2014) Slow acceleration cycle (initially, cycle setup with 12 bunches) −Doublet beam (up to 1.5e11 p/b injected) −Instabilities and losses on the ramp −High losses on flat bottom and beginning of ramp, increasing significantly with the amount of beam injected Doublets also on cycle with nominal LHC filling ramp in parallel −Maximum intensity on flat top of about 1.4e11 p/doublet, large emittance growth at the tails of the doublet trains TT10 quad trip + RF problems in PS during the night →Many issues due to enhanced electron cloud. Improvement needed with scrubbing, but also with systematic work on set up (working point, transverse damper, LLRF, longitudinal settings) −2015 doublet cycle from MD to ‘operational’ to prepare beam for LHC MD3: 26.4 s, 26 GeV/c LHC25NS: 22.8 s, 450 GeV/c: Doublet LHCMD4: 31.2 s, slow ramp to 450 GeV/c: Doublet days

25. Scrubbing run in week 50: overview Wednesday (10/12/2014) Two parallel cycles −Long flat bottom cycle for scrubbing with high intensity standard beam −Nominal LHC filling cycle (with acceleration to 450 GeV/c) to test LHC beam variants 8b+4e beam on LHC cycle (1.7e11 p/b injected, 1.4e11 p/b at flat top) −Well behaved electron cloud-wise, i.e. no signal on e-cloud monitors (as predicted) −Pressure spike on ZS (impedance?), however quickly conditioning while running with this beam −Large losses at beginning of ramp BCMS in rather good shape (1.4e11 p/b injected, 1.15e11 p/b at flat top), but still large losses at beginning of ramp LHC25NS: 22.8 s, 450 GeV/c: 8b+4e BCMS MD3: 26.4 s, 26 GeV/c: High intensity 25 ns beam days

26. Important facts of Scrubbing Run II High intensity LHC beam (4 batches 72b) at 26 GeV/c  Strong electron cloud effects o Poor lifetime, strong emittance blow up at the tails of the batches o Clear coherent instabilities contributing to the blow up (in spite of the transverse damper and/or high chromaticity) Doublet beam accelerated to 450 GeV/c  Many transverse instabilities observed on the slow ramp  Maximum intensity at flat top limited to 1.4e11 p/doublet on nominal LHC filling ramp, lower on slow cycle (but with 3.6 s injection plateau). Strong emittance blow up.  In general, beam quality strongly and quickly degraded by electron cloud, but room for improvement if taken on ‘operational’ basis (scrubbing, better set up) Other LHC beam variants tested  8b+4e well behaved in terms of electron cloud (as expected), but sparking and outgassing on ZS (however quick conditioning was observed), up to three batches accelerated to 450 GeV/c  BCMS in rather good shape, less electron cloud thanks to shorter batches, up to three batches accelerated to 450 GeV/c  For both cases, no clear beam degradation due to electron cloud, but quite large losses at start of the ramp

27. Comparison of integrated BCT 2012 scrubbing run limited by MKE kicker heating 2014 scrubbing run W45 and W50 limited by MKP4 pressure (hopefully only temporary problem since kicker was newly installed)

28. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

29. Pressure evolution (normalized): Arc 5 DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests clear conditioning clear conditioning and very high efficiency with doublet

30. Pressure evolution: Arc 5 Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Scrubbing W45 (~1.2 x 10 11 ppb) conditioning conditioning with doublet similar pressure at beginning conditioning high intensity

31. Pressure evolution: a-C coating DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests No pressure rise with doublet beam residual pressure rise from neighboring elements

32. Outline Introduction Overview Scrubbing Run Week 45 MKP, TIDVG temperatures and pressures Overview Scrubbing Run Week 50 Vacuum pressure evolution (arcs vs a-C coated cells) Scrubbing observations in the e-cloud monitors Main observations with different beam configuration 25 ns beam – standard scheme 25 ns beam – BCMS 8b+4e – low e-cloud pattern High intensity 25 ns beam Doublet beam Some comparison against simulations Doublets: MBA vs MBB Doublets: Dipoles vs field free

33. ECM 1a (MBA StSt) at 1 s DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests Nov. 2012 (Nominal beam) Stronger E-cloud with doublet less e-cloud with high intensity no e-cloud with other beams

34. ECM 1a (MBA StSt): maximum signal DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests e-cloud not completely suppressed when many batches in the machine (for standard and BCMS)

35. ECM 1b (MBB StSt): at 1 s DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests Nov. 2012 (Nominal beam) Some conditioning, but e-cloud never completely suppressed even at 1 s

36. ECM 1b (MBB StSt): maximum signal DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests Conditioning is less obvious No e-cloud with 8b+4e

37. ECM 2a (MBB Cu): at 1 s DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests Nov. 2012 (Nominal beam) Strong deconditioning since 2012 but also quick re-conditioning

38. ECM 2a (MBB Cu): maximum signal DoubletStd. 25 nsDoubletStd. 25 ns8b+4e / BCMS Scrubbing W45 (~1.2 x 10 11 ppb) Scrubbing W50 (~1.5-2.0 x 10 11 ppb) Std 25 nsDoublet25 ns (450 GeV)DoubletFinal tests (Re)-conditioning Conditioning with high intensity e-cloud with short bunches No e-cloud with 8b+4e

39. Thank you for your attention!