Very Preliminary proton MD summary G. Arduini – BE/ABP

1. Very Preliminary proton MD summary G. Arduini – BE/ABP Acknowledgements: BI, Collective effects team, Cryo, Injection Team, OP, Vacuum Team Special thanks to Massi and Experiments

2. Motivations • Complete the observations from the previous MD with 50 ns beam concerning electron cloud build-up: • Vacuum rise has been observed in all uncoated warm-warm and warm-cold transitions (where vacuum pressure measurements exist) for bunch populations > 6×1010 p/bunch and with trains of 24 bunches. Differently from 150 ns beam pressure rise is observed also in vacuum pipe with single beam. • Reduction by more than a factor 10 of the vacuum activity has been observed during “scrubbing” at 450 GeV from 29/10 to 4/11 • Clear signs of heat load due to electron cloud build-up in the arcs have been observed with 50 ns. No sign of it with 150 ns. • No clear evidence of reduction of the heat load at 3.5 TeV after scrubbing  need additional experiment (comparison with first fill performed with 50 ns, before the scrubbing) • Compare the behaviour of the 75 ns beam with 50 ns beam in terms of vacuum rise, heat load and beam stability

3. Overview

4. Issues during the test • Major stops (~9 hours): • RF PS (Wed/Thu) • MKD (Fri/Sat) • RF setting-up: some of the parameters are not yet remotely controllable and/or not cycle dependent  expert intervention required in SR4 • Preparation in the injectors could be done only at the last minute due to problem on 80 MHz cavity in the PS not allowing to run ions and protons in parallel • First asynchronous dump (beam 1). Luckily enough with pilot at 450 GeV. HW failure in the distribution of the triggers

5. 75ns – high intensity • Capture losses observed on beam 2 during Thursday are understood  Cavity 7B2 is showing some noise on the accelerating voltage in the presence of high intensity. Possible sources: • Multipacting in the antenna pot or cable connector perturbing the field measurement (and the cavity feedback). • Micro-quenches in the cavity causing a real field drop (and also perturbing the feedback). • Might be triggered by multipacting/electron cloud in the cavity. • Conditioning at higher voltage might help. A. Butterworth

6. Achieved 75ns • Filling while monitoring vacuum and cryogenics, all at 450GeV • 680 bunches/beam (8+14*48) 9 1010 p/b, batch spacing 1.85 us • Kept this beam for 2 hours for UFO investigations • 680 bunches Beam1 (8+14*48) 11 1010 p/b, batch spacing 1.85 us • 824 bunches Beam1 (8+17*48) 11 1010 p/b, batch spacing 1.005 us  realized afterwards that this spacing is not compatible with operation of the fast BCT and possibly the damper. To be enforced for the future.

7. Achieved 75ns Average bunch population ~0.9×1011 p. Total intensity ~6×1013 p/beam

8. Achieved 75ns Except for first train (8 bunches) for all the other losses are located at the tail of the batch

9. Emittances with 680 bunches Time evolution being analyzed. B1 affected by H instability at the tail of each batch  Stabilized by chromaticity  data being analyzed to understand origin. Bunch population = 1.1×1011p – batch spacing 1.85 ms Q’H,V=14 Q’H,V=24 Q’H,V=24 Q’H,V=14

10. Emittances with 680 bunches High chromaticity seems to help controlling the beam also for tighter batch spacing (1.005 ms) and nominal bunch intensity. Bunch population = 1.1×1011p – batch spacing 1.85 ms

11. Loss maps with 488 bunches for B1 (1011 p/bunch). Effect of the observed pressure rise in the straight sections? (to be further analyzed) Observed losses

12. 75 ns vs. 50 ns 75 ns (8+48 b) – 1.85 ms spacing 50 ns (12+48 b) – 1.85 ms spacing

13. 75 ns vs. 50 ns 75 ns up to 824 bunches (Beam 1). 50 ns up to 444 bunches (Beam 1) For both beams significant heat load in the beams screens of the triplets (particularly L8) L. Tavian

14. 75 ns – 824 bunches • 75 ns is certainly better than 50 ns but scrubbing is required in order to operate with large number of bunches and to ramp. V. Baglin, G. Bregliozzi, G. Lanza

15. Some results – scrubbing with 50 ns Before scrubbing (30/10): Heat load ~40 mW/m/beam After scrubbing (19/11) Heat load <10 mW/m/beam. Only B2 Same filling pattern (9x12 b) and bunch population (~1011 p). Scrubbing at 450 GeV effective also for 3.5 TeV in the arcs L. Tavian

16. Preliminary summary • Transition from ions to protons took longer than expected (RF set-up required in SR4, access for problems in the injectors)  some of the RF parameters to be made remotely controllable • Analysis ongoing several data sets • Less vacuum activity 75ns spacing as compared to 50 ns  although we will need scrubbing (or solenoids) to avoid pressure rises in the straight sections to fill up the machine • Heat load in beam screens the arcs for 75 ns beam hardly visible but important activity in the triplets in particular L8 • Comparison of 50ns at 3.5 TeVbefore and after scrubbing at 450 GeVclearly shows that the situation has improved significantly in the straight sections and in the arcs (heat load)

17. Reserve

18. Pressure rises with trains of 24 bunches • Vacuum Interlock due to pressure increase on the penning gauges VGPB.773.6L7.R on the cold-warm transition of the Q6L7.R. Beams circulating in different vacuum chambers • Unexpected (at least to me) for this number of bunches 9x12 1x12+4x24

19. E-cloud measurements & scrubbing • Moved to e-cloud measurement–scrubbing mode on Sunday afternoon until Wednesday evening (with an interruption on Monday day-time for quench test at 3.5 TeV): • Pressure rise observed in cold-warm and warm-warm (uncoated) transitions • Even stronger pressure rise when injecting trains of 36 bunches • Little or no dependence on bunch length • Cleaning seen for 12-24-24 (factor 2 in four hours) • persistent after refilling • Cleaning with 36 bunches less evident due to losses generated by beam instabilities 12+2x24 12+2x24 12+36 12+36

20. E-cloud measurements • Systematic measurements of pressure rise in the straight sections and heat load in the arcs for different filling patterns to provide input for simulations and guide predictions: • Dependence on bunch intensity • Dependence on bunch train length • Dependence on bunch train spacing • Very preliminary simulation results indicate that SEY~2.5 (assumed 1.7 so far) 12+36 12+24 12+12 1.1x1011 p/bunch 0.8x1011 p/bunch 0.6x1011 p/bunch

21. Scrubbing • Comparison between pressure rise before and after scrubbing run for 12+36 bunches at 450 GeV (reduction by ~1 decade in ~3 days) 31/10: max p @ LSS3 VGPB.5L3.B = 5.5E-7 mbar 04/11: max p @ LSS3 VGPB.2.5L3.B=8E-8 mbar G. Bregliozzi, G. Lanza

22. Heat load on beam screens (33L6) • Not seen during runs with 104 bunches per beam with 150 ns spacing for comparison. L. Tavian

23. Heat load on beam screens (33L6) • After scrubbing: 1x12+4x24 bunches • Reached saturation? • Reduction? e-cloud peak: ~37 mW/m per aperture L. Tavian

24. Beam stability at injection • 12 bunches + 4 trains of 24 bunches spaced by 1.85 ms • Build-up of the electron cloud over more than one train leading to instabilities and emittance blow-up along the trains • Consistent with preliminary results of simulations for SEY~2.5 F. Roncarolo

25. Beam stability at injection • 12 bunches + 1 train of 36 bunches • Build-up occurs already in the first train of 36 bunches with the same effect (instability with approximately 1 s rise-time/blow-up) E. Métral F. Roncarolo

26. Beam stability at injection • Can be stabilized by increasing chromaticity (up to 18 units) and by transverse emittance blow-up  Can be used during a scrubbing period but how far can we go with larger number of bunches? • How does it improve with scrubbing? F. Roncarolo

27. Beam stability at flat-top • Observed instabilities (H faster) with 1x12+4x24 bunches at flat-top when the damper is switched OFF. Not observed for 9x12 bunches for the same machine settings. • Rise-time: few tenth of s (H), 1-2 s (V) • Can be cured by the transverse feedback H. Bartosik, B. Salvant