1. Fast Beam Collision Feedbacks for luminosity optimisation at next-generation lepton colliders
Philip Burrows
John Adams Institute
Oxford University

2. Outline Introduction and system concept ILC design status
CLIC design status
FONT prototype systems performance
Outstanding technical issues
Summary

3. Compact Linear Collider (CLIC)
Drive Beam Generation Complex
1.5 TeV / beam
Main Beam Generation Complex

4. International Linear Collider
c. 250 GeV / beam
31 km

5. Beam parameters
ILC CLIC 3 TeV

6. Beam parameters
ILC CLIC 3 TeV
Electrons/bunch **10

7. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train

8. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train
Bunch separation ns

9. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train
Bunch separation ns
Train length us

10. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz

11. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz
Horizontal IP beam size nm
Vertical IP beam size nm

12. Beam parameters ILC 500 CLIC 3 TeV Electrons/bunch 2 0.37 10**10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz
Horizontal IP beam size nm
Vertical IP beam size nm
Longitudinal IP beam size um
Luminosity **34

13. Beam parameters ILC 500 1000 CLIC 3 TeV
Electrons/bunch **10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz
Horizontal IP beam size nm
Vertical IP beam size nm
Longitudinal IP beam size um
Luminosity **34

14. Beam parameters ILC 500 1000 CLIC 3 TeV
Electrons/bunch **10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz
Horizontal IP beam size nm
Vertical IP beam size nm
Longitudinal IP beam size um
Luminosity **34

15. Beam parameters ILC 500 1000 CLIC 3 TeV
Electrons/bunch **10
Bunches/train
Bunch separation ns
Train length us
Train repetition rate Hz
Horizontal IP beam size nm
Vertical IP beam size nm
Longitudinal IP beam size um
Luminosity **34

16. 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:
Robert Apsimon, Neven Blaskovic Kraljevic, Douglas Bett, Philip Burrows, Glenn Christian, Christine Clarke, Ben Constance, Michael Davis, Tony Hartin, Young Im Kim, Simon Jolly, Steve Molloy, Gavin Neson, Colin Perry, Javier Resta Lopez, Christina Swinson

17. General considerations
Time structure of bunch train:
ILC (500 GeV): c bunches w. c. 500 ns separation
CLIC (3 TeV): c bunches w. c ns separation
Feedback latency:
ILC: O(100ns) latency budget allows digital approach
CLIC: O(10ns) latency requires analogue approach
Recall speed of light: c = 30 cm / ns:
FB hardware should be close to IP (especially for CLIC!)
Two systems, one on each side of IP, allow for redundancy

18. IP FB Design Status: ILC
Engineering design documented in ILC TDR (2013):
1. IP beam position feedback:
beam position correction up to nm vertical at IP
2. IP beam angle feedback: hardware located few 100 metres upstream
conceptually very similar to position FB, less critical
3. Bunch-by-bunch luminosity signal (from ‘BEAMCAL’)
‘special’ systems requiring dedicated hardware + data links

19. ILC IR: SiD for illustration
Door
SiD
Cavern wall

20. ILC IR: SiD for illustration
Door
SiD
Cavern wall

21. Final Doublet Region (SiD)

22. Final Doublet Region (SiD)

23. QD0 – QF1 Region (SiD)

24. QD0 – QF1 Region (SiD)

25. Final Doublet Region (SiD)

26. IP Region (SiD)

27. IP Region (SiD)

28. Beamcal – QD0 Region (SiD)

29. Tom Markiewicz, Marco Oriunno, Steve Smith
IP FB BPM Detail (SiD)
Tom Markiewicz, Marco Oriunno, Steve Smith

30. ILC FB prototype: FONT at KEK/ATF
Kicker
BPM 1
BPM 2
BPM 3 e-
Drive
amplifier
Analogue BPM
processor
Digital feedback

31. ILC prototype: FONT4 at KEK/ATF
Kicker
BPM 1
BPM 2
BPM 3 e-
Drive
amplifier
Analogue BPM
processor
Digital feedback

32. ILC prototype: FONT4 at KEK/ATF
Kicker
BPM 1
BPM 2
BPM 3 e-
Drive
amplifier
Analogue BPM
processor
Digital feedback
BPM resolution ~ 0.3um
Latency ~ 130ns
Drive power > 300nm
@ ILC

33. Stripline BPM resolution
ATF2 stripline BPMs: single-pass beam, bunch Q ~ 1 nC
330 nm rms

34. Latency

35. ILC IP FB performance

36. IP FB Design Status: CLIC
Conceptual design developed and documented in CLIC CDR (2012)
NB primary method for control of beam collision overlap is via vibration isolation of the FF magnets, and dynamic correction of residual component motions
IP position feedback:
beam position correction up to nm vertical at IP
More realistic engineering design being developed now

37. CLIC Final Doublet Region

38. CLIC Final Doublet Region

39. CLIC Final Doublet Region

40. CLIC prototype: FONT3 at KEK/ATF
Kicker
BPM 1
BPM 2
BPM 3 e-
Analogue BPM
processor

41. CLIC prototype: FONT3 at KEK/ATF
Kicker
BPM 1
BPM 2
BPM 3 e-
Analogue BPM
processor
Electronics latency ~ 13ns
Drive power > 50nm
@ CLIC

42. CLIC IP FB performance
Single random seed of GM C

43. CLIC IP FB performance
For noisy sites:
 factor improvement

44. Outstanding Technical Issues
Component designs need to be optimised for tight spatial environments
Routing of cables
Operation of (ferrite) devices in large, spatially-varying B-field
Further studies of radiation environment
Electronics location, rad hardness, shielding
RF interference: beam  FB electronics
kicker  detector

45. Summary
Well developed IP collision FB system designs for both ILC and CLIC
Simulations demonstrate luminosity recovery capability
Demonstrated prototypes with required performance parameters
Progress on designing customised beamline components + optimising layout
Ideas applicable at XFELs + rings

46. Latest beam results from ATF2
Beam size ~ 44 nm achieved (Kuroda)
First attempts at stabilisation of small beam at nm level (ATF2 goal 2)

47. FONT5 installation at ATF2
ATF2 extraction line 47

48. Upstream FB performance
2 bunches
separated
by 274ns:
measure #1
correct #2
Bunch 1

49. Upstream FB performance
2 bunches
separated
by 274ns:
measure #1
correct #2
Bunch 1
Bunch 2 corrected
to c. 0.5um
(resolution limit)
Bunch 2

50. Upstream FB performance
Witness BPM c. 30m downstream
Beam correction preserved

51. New IP chamber installed summer 2013
JAI, KEK, KNU, LAL
3 cavity BPMs
Commissioning
started November:
alignment,
BPM signals,
beam jitter …

52. ATF2 ‘IPFB’ tests 2014 e- IP kicker Cavity IPBPM FONT amplifier
KEK IPBPM
electronics
FONT digital FB

53. Layout with new IP kicker

54. June 2014 beam test results
Centre beam in BPM using mover  optimise resolution

55. June 2014 beam jitter
Centre beam in BPM using mover  optimise resolution
resolution ~ 60 nm

56. June 2014 IPFB results
Incoming jitter ~ 200nm

57. June 2014 IPFB results
Incoming jitter ~ 200nm
Corrected jitter ~ 87nm

58. Latest beam results from ATF2
Beam size ~ 44 nm achieved (Kuroda)
First attempts at stabilisation of small beam at nm level (ATF2 goal 2)
Cavity BPMs with resolution ~ 60nm
Working IPFB system stabilising beam to
~ 87nm (at BPM resolution limit)
October: improved BPM electronics
(design 2nm?) coming from KNU
FB studies ongoing …