1. 1 Feedback On Nanosecond Timescales (FONT): Philip Burrows Neven Blaskovic, Douglas Bett*, Talitha Bromwich, Glenn Christian, Michael Davis, Colin Perry John Adams Institute, Oxford University * Now at CERN IP Feedback

2. 2 Outline Reminder of CLIC IP FB prototype ATF2 IP FB concept Results of recent beam runs Summary + conclusions

3. 3 IP beam feedback concept Last line of defence against relative beam misalignment Measure vertical position of outgoing beam and hence beam-beam kick angle Use fast amplifier and kicker to correct vertical position of beam incoming to IR FONT – Feedback On Nanosecond Timescales

4. CLIC Final Doublet Region 4

5. 5

6. 6

7. 7 CLIC IP FB performance Single random seed of GM C Resta Lopez

8. 8 For noisy sites: CLIC IP FB performance  factor 2 - 3 improvement

9. FONT5 intra-train FBs at ATF2 ATF2 extraction line 99

10. FONT5 operation modes at ATF2 10 Aim to stabilise beam in IP region using 2-bunch spill: 1. Upstream FB: monitor beam at IP 2. Feed-forward from upstream BPMs  IP kicker 3. Local IP FB using IPBPM signal and IP kicker 10

11. 11 IP kickerIPBPMs FONT digital FB IPBPM electronics FONT amplifier e- ATF2 IP FB loop scheme Eventual goal is to stabilise the small ATF2 beam (design 37nm) at the nanometer level

12. 12 IP kicker Designed by Oxford Fabrication arranged by KEK Installed May 2012

13. 13 Nanometer beam FB at ATF2 IP Much harder than IPFB at ILC or CLIC! Only 1 beam  must measure beam position directly nm-level stabilisation requires nm-level position meas.  Cavity BPMs (rather than striplines) Cavities slower, signal processing more involved Cavities required to resolve 2 bunches within << 300ns with high spatial resolution  Low-Q cavities  Low-latency, high-resolution signal processor

14. 14 IP kickerIPBPMs FONT digital FB IPBPM electronics FONT amplifier e- Preparatory tests June 2013 Existing IPBPMs Honda low-latency electronics

15. 15 New kicker A B

16. Interaction Point FONT System Analogue Front-end BPM processor FPGA-based digital processor Kicker drive amplifier Strip-line kicker Beam Cavity BPM 16 Latency ~ 160ns

17. 2013 beam stabilisation results 1.Upstream FB: beam stabilised at IP to ~ 300 nm 2. Feed-forward: beam stabilised at IP to ~ 106 nm 3. IP FB: beam stabilised at IP to ~ 93 nm 17

18. IP Feedback Results FB Off Jitter: 170 ± 10 nm FB On Jitter: 93 ± 4 nm FB Off Correlation: 81% 18

19. IP Feedback Results FB Off Jitter: 170 ± 10 nm FB On Jitter: 93 ± 4 nm FB Off Correlation: 81% FB On Correlation: -16% 19

20. In vacuum IP-BPMs and piezo movers BPM A&B BPM C Piezo Movers (PI) Piezo Movers (Cedrat) BPMs – Bolted aluminum plates, no brazing because of In- vacuum. – BPM A&B bolted together. – BPM C is independent. Piezo mover – BPM units are mounted on the base with three piezo movers. – Dynamic range of each mover is +/- 150 um. IP Slide from Terunuma Initial alignment need to be better than this. Installed summer 2013

21. 21 IP kickerIPBPMs FONT digital FB IPBPM electronics FONT amplifier e- Tests started November 2013 New IP chamber installed Summer 2013 Honda electronics

22. 22 2014 beam tests IP chamber was removed, re-worked and re-installed New IPBPMs were fabricated Commissioning began in October 2014 Some preliminary results to show today: Longitudinal IP position set at each IPBPM in turn: position calibration + beam jitter studies High-beta (‘pencil-beam’) optics: BPM resolution Beam waist IP feedback

23. 23 Nominal optics

24. 24 BPM calibration constant vs. attenuation

25. 25 BPM calibration constant vs. attenuation Indicative of saturation of electronics

26. 26 Beam jitter (at waist) vs. attenuation

27. 27 Beam jitter (at waist) vs. attenuation Consistent with true beam jitter ~ 300nm (beam not tuned after DR extr. kicker issue)

28. 28 High-beta (pencil beam) optics

29. 29 Beam jitter vs. attenuation

30. 30 Beam jitter vs. attenuation Consistent with true beam jitter ~ 500nm (pencil beam large)

31. 31 Resolution vs. attenuation

32. 32 Resolution vs. attenuation Resolution appears to be 200-300nm! (NB: C >> A, B)

33. 33 Nominal optics: IPFB @ IPBPM B

34. 34 Best IPFB results Bunch 1: not corrected, jitter ~ 400nm Bunch 2: corrected, jitter ~ 67nm Corrected jitter 67nm << apparent resolution!

35. 35 Best IPFB results

36. 36 Scan of bunch 2 position using IPK Apply constant kicks to bunch 2 to move its vertical position in the IPBPM  measurement closer to ‘zero’ should have better resolution Then turn on IPFB …

37. 37 IPFB performance vs. bunch 2 posn. IPFB off IPFB on

38. 38 IPFB performance vs. bunch 2 posn. IPFB off IPFB on

39. 39 Best standard jitter measurement 66nm (single)  49nm (avg.)

40. 40 Summary + conclusions Started commissioning of new ATF2 IP chamber/IPBPMs Lot of preliminary results; many mysteries to understand IPFB works well: corrects beam jitter to 67nm We believe this performance is resolution-limited Suspect IPBPM B resolution is currently < 50nm Contradiction between direct resolution measurements (200-300nm) and IPFB performance (67nm) We suspect a problem with IPBPM C, which degrades the 3-BPM resolution measurement BPM performance depends strongly on beam position ~ 0