1 FONT IP Feedback System Implications of increase of L* Philip Burrows John Adams Institute Oxford University

2 Outline Reminder of system concept General considerations TDR design Implications of changing L* Technical issues + summary

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

4 Beam parameters ILC 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 6 3 1nm Longitudinal IP beam size um Luminosity **34

5 Beam parameters ILC 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 6 3 1nm Longitudinal IP beam size um Luminosity **34

6 General considerations Time structure of bunch train: ILC (500 GeV): c bunches w. c. 500 ns separation CLIC (3 TeV): c. 300 bunches w. c. 0.5 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

7 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

8 ILC IR: SiD for illustration Door SiD Cavern wall

9 ILC IR: SiD for illustration Door SiD Cavern wall

10 Final Doublet Region (SiD)

11 Final Doublet Region (SiD)

12 QD0 – QF1 Region (SiD)

13 QD0 – QF1 Region (SiD)

14 Final Doublet Region (SiD)

IP Region (SiD)

Beamcal – QD0 Region (SiD)

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

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

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

21 KickerBPM 1 Digital feedback Analogue BPM processor Drive amplifier BPM 2 BPM 3 e- ILC prototype: FONT4 at KEK/ATF BPM resolution ~ 0.3um Latency ~ 130ns Drive power > ILC

22 FONT4 latency

23 ILC IP FB performance

24 Implications of increased L* Latency = electronics + beam flight time Electronics = 87ns (today’s technology) Simple model: BPM + kicker at L from IP beam flight time = 2 L/0.3 ns For bunch-by-bunch FB want: 500GeV: L*/0.3 < 554ns  L < 70m

25 Implications of increased L* Latency = electronics + beam flight time Electronics = 87ns (today’s technology) Simple model: BPM + kicker at L from IP beam flight time = 2 L/0.3 ns For bunch-by-bunch FB want: 500GeV: L*/0.3 < 554ns  L < 70m 1 TeV: L*/0.3 < 366ns  L < 42m

26 Implications of increased L* Latency = electronics + beam flight time Electronics = 87ns (today’s technology) Simple model: BPM + kicker at L from IP beam flight time = 2 L/0.3 ns For bunch-by-bunch FB want: 500GeV: L*/0.3 < 554ns  L < 70m 1 TeV: L*/0.3 < 366ns  L < 42m ??: L*/0.3 < 150ns  L < 9m

27 Increasing L* from 3.5m to 4m

SiD Schematic (Door Closed) SiD MDI U. Tokyo T. Markiewicz/SLAC HCALDoor YokePACMAN QD0 Cryostat QF1 Cryostat QD0 L*=3.5m QF1 L*=9.5m QD0 Service Pipe FB Kicker FB BPM BeamCal PolyCarbonate LumiCal W Mask Beampipe ECALECAL Movers Beampipe Spider Support Bellows & Flange 28 of 51

Increasing L* from 3.5m to 4m No impact if BPM + kicker stay (roughly) in same places If push QD0 back by 0.5m could move kicker in front of QD0 (Glen says this has some attractive aspects) Reduces lever arm x2 (no problem) Would need shorter kicker than TDR (no problem) ATF2: 30cm kicker, 1inch diameter aperture  100 urad kick on 1 GeV beam  400 nrad kick on 250 GeV beam  1600 nm correction of beam at 4m lever arm

30 Increasing L* from 3.5m to 4m If push QD0 back by 0.5m and leave kicker behind QD0 Could add a BPM on incoming beamline in front of QD0

SiD Schematic (Door Closed) SiD MDI U. Tokyo T. Markiewicz/SLAC HCALDoor YokePACMAN QD0 Cryostat QF1 Cryostat QD0 L*=3.5m QF1 L*=9.5m QD0 Service Pipe FB Kicker FB BPM BeamCal PolyCarbonate LumiCal W Mask Beampipe ECALECAL Movers Beampipe Spider Support Bellows & Flange 31 of 51

32 Practical considerations Wherever they go, need to design: Mechanical integration of BPM + kicker into beamline Routing of cables Location, support + shielding of electronics If downstream of QD0, check backgrounds Larger distance from IP puts potential sources of broadcast RF further from detector

33 Example: ATF2 IP kicker

CLIC Final Doublet Region 34

CLIC Final Doublet Region 35

36 Conclusions IP FB system can be adjusted to suit a slightly larger L* without performance compromise Better to have kicker downstream of QD0? Would be simpler to keep all hardware on same side of push-pull beamline split (presumably downstream side: need to locate electronics on detector)

37 Extra material

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

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

40 IP kickerCavity IPBPM FONT digital FB KEK IPBPM electronics FONT amplifier e- ATF2 ‘IPFB’ tests 2014

41 Layout with new IP kicker

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

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

44 Incoming jitter ~ 200nm June 2014 IPFB results

45 Incoming jitter ~ 200nm June 2014 IPFB results Corrected jitter ~ 87nm

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) 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 …