1. SPS scrubbing experience: electron cloud observables L. Mether on behalf of the LIU-SPS e-cloud team LIU SPS scrubbing review, September 8, 2015

2. Outline Electron cloud Electron cloud monitors Electron cloud evolution during cycle Electron cloud evolution over scrubbing Arc pressures Pressure gauges Pressure evolution during cycle Pressure evolution over scrubbing Summary

3. Electron cloud monitors Large aperture dipole magnets installed in a straight section Vertical magnetic fields, set to B = 0.12 T, field in SPS bends at injection Each magnet is equipped with a liner… Stainless steel MBA/MBB type vacuum chamber, with holes drilled along the side …with a strip detector on the outside 48 channels Signal integrated over multiple turns (20 – 200 ms) Provide transverse profile of electron distribution Help to understand the e-cloud evolution and scrubbing process in SPS bends

4. Electron cloud during SPS cycle Nominal SPS 25 ns cycle 4 batches of 72 bunches, 1.2x10 11 p + /bunch

5. Electron cloud during SPS cycle Electron cloud signal along nominal 25 ns cycle E-cloud signal low, but still visible Large enhancement during ramp to flat top, mainly due to bunch shortening Ramp Nominal intensity MBB MBA

6. Electron cloud during SPS cycle Horizontal profile of electron cloud signal MBA MBB

7. Electron cloud with high-intensity beam During the four scrubbing runs this year, the machine was run mainly with a high-intensity beam, with around 2x10 11 p + /bunch For this purpose a scrubbing cycle with up to 4 batches of 72 bunches, at flat bottom was used

8. E-cloud signal in MBA and MBB monitors along scrubbing cycle Ramp Electron cloud twice as strong as for nominal intensity beam Significantly more electron cloud in MBB chamber than in MBA High intensity Nominal intensity Electron cloud with high-intensity beam MBB MBA MBB MBA

9. Electron cloud with high-intensity beam Horizontal profile of electron cloud signal Electron cloud extends beyond region scrubbed with nominal intensity beam High intensity Nominal intensity MBA MBB

10. Electron cloud with high-intensity beam Horizontal profile of electron cloud signal This region has been effectively scrubbed! High intensity W50 Nominal intensity MBA MBB High intensity W25

11. Electron cloud evolution during scrubbing Study the evolution of signal in electron cloud monitors over scrubbing period MBA and MBB chambers Two observation points: − Signal after first injection − Maximum signal along cycle MBB MBA

12. Electron cloud evolution during scrubbing E-cloud signal in MBA monitor after injection of first batch W16 W17 W23W25

13. Electron cloud evolution during scrubbing Maximum e-cloud signal in MBA monitor First batch Maximum signal W16 W17 W23W25

14. Electron cloud evolution during scrubbing E-cloud signal in MBB monitor after injection of first batch W16 W17 W23W25

15. Electron cloud evolution during scrubbing Maximum e-cloud signal in MBB monitor First batch Maximum signal W16 W17 W23W25

16. Outline Electron cloud Electron cloud monitors Evolution during cycle Evolution during scrubbing Arc pressures Pressure gauges Evolution during cycle Evolution during scrubbing Summary

17. Arc pressures Pressure gauges located between dipole magnets in each arc We follow two families of gauges: X2940 MBAMBB X0660 MB B Located between an MBA and an MBB dipole Located between 2 MBB dipoles

18. Arc pressures along cycle Pressures during nominal intensity cycle with ramp and high-intensity flat-bottom scrubbing cycle Gauges X0660 (MBB-MBB) High intensityNominal intensity Ramp

19. Arc pressure evolution during scrubbing Pressure rise over scrubbing cycle at gauge 40660 Located between two MBB dipoles W16 W17 W23W25

20. Arc pressure evolution during scrubbing Pressure rise over scrubbing cycle at gauge 42940 Located between an MBA and an MBB dipole W16 W17 W23W25

21. Summary & conclusion Electron cloud with high-intensity beam Electron cloud is more than doubled with high intensity vs nominal intensity at flat bottom − MBB type chamber more prone to e-cloud than MBA type chamber Scrubbing efficiency Based on data from electron cloud monitors and pressures: − Conditioning seen mainly in the first week of high-intensity beam − Full suppression not seen over four batches E-cloud monitors provide information also along the cycle: − Significant improvement seen after the injection of one batch: full suppression in MBA, significant reduction in MBB Conclusion SEY lowered during scrubbing, but not sufficiently to fully suppress e-cloud Effect of scrubbing seems to level off − If further scrubbing can be done, required timescales much longer than days/a few weeks

22. Thank you for your attention!