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 in collaboration with: KEK, KNU, LAL Intra-train Feedback Status

2 Outline Reminder of intra-train FB modes Results of 2013 beam runs (old IP chamber) Results of 2014 beam runs (new IP chamber) Summary + conclusions

FONT5 intra-train FBs ATF2 extraction line 33

FONT5 operation modes 4 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 4

5 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

6 IP kicker Designed by Oxford Fabrication arranged by KEK Installed May 2012

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

8 New kicker A B

Interaction Point FONT System Analogue Front-end BPM processor FPGA-based digital processor Kicker drive amplifier Strip-line kicker Beam Cavity BPM 9 Latency ~ 160ns

2013 beam stabilisation results 1.Upstream FB: beam stabilised at IPB to ~ 300 nm 2. Feed-forward: beam stabilised at IPB to ~ 106 nm 3. IP FB: beam stabilised at IPB to ~ 93 nm 10

IP Feedback Results FB Off Jitter: 170 ± 10 nm FB On Jitter: 93 ± 4 nm FB Off Correlation: 81% 11

IP Feedback Results FB Off Jitter: 170 ± 10 nm FB On Jitter: 93 ± 4 nm FB Off Correlation: 81% FB On Correlation: -16% 12

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

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

15 December 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 IP feedback with beam waist near IPB

16 Nominal optics

17 BPM calibration constant vs. attenuation

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

19 Beam jitter (at waist) vs. attenuation

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

21 High-beta (pencil beam) optics Resolution studies 1) 11/12/14: signal attenuation varied

22 Beam jitter vs. attenuation

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

24 Resolution vs. attenuation

25 Resolution vs. attenuation Resolution appears to be nm! (NB: C >> A, B)

Dependence on sample # (0db) position jitter resolution

Dependence on sample # (0db) position jitter resolution Such a large signal will saturate the electronics: averaging over sample #s is blind to such saturation!

Sigma#uncutPosition /um Jitter /um BPM Cor R value Res (fit) /nm Res (geom) All / / / / / / (1,2) (1,3) 0.06 (2,3) 126+/ / / / / / / / / /-2 77+/-2 86+/ / / / / / / /-2 54+/ / / / / / / /-3 36+/ / / / / / / / / / / / / / / /-7 31+/-7 79 Resolution study (0db, sample 1)

29 High-beta (pencil beam) optics Resolution studies 2) 20/12/14: 714 MHz BPF filters added on inputs to 2 nd stage mixers beam better centred in both x and y

position jitter Dependence on sample # (0db) IPC showing anomalous behaviour

Resolution vs. sample # (0db) FittingGeom 52nm 57nm54nm

0.1 sigma cut on charge (163/2001 pulses remaining) FittingGeom 47nm 51nm Resolution vs. sample # (0db)

Resolution – mean of samples FittingGeom 42nm 47nm55nm FittingGeom 42nm 46nm59nm sigma cut

34 Resolution summary Best direct measurement of resolution with pencil beam 20/12/14: Single sample point: 52-57nm (fitting); 54nm (geometric) : 42-47nm (fitting); 55nm (geometric) No improvement with tight cuts on data! Resolution is plausibly 50nm (possibly as good as 42nm) (Q = 0.4 e10) Evidence that IPC is not behaving well Care must be taken with beam position to avoid saturation; blindly averaging over samples may not reveal saturation!

35 Nominal optics: IPBPM B

36 Best IPFB results Bunch 1: not corrected, jitter ~ 400nm Bunch 2: corrected, jitter ~ 67nm Corrected jitter 67nm  resolution 47nm

37 Best IPFB results

38 Scan of bunch 2 position using IPK Apply constant kicks to bunch 2 to move its vertical position in the IPBPM Then turn on IPFB …

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

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

41 IPFB performance vs. bunch 2 posn. IPFB off IPFB on Kicker drive saturated

IPFB performance vs. QD0FF setting Prediction based on incoming jitters of bunches 1 and 2 and measured bunch 1-2 correlation, assuming perfect FB

43 Jitter vs. QD0FF setting (waist scan) 66nm (single)  49nm (avg.)

Reference cavity diode signal noisy stripline diode

45 Summary + conclusions Started commissioning of new ATF2 IP chamber/IPBPMs Lot of preliminary results; some mysteries to understand IPFB works well: corrects beam jitter to 67nm IPFB prediction matches data We believe this performance is resolution-limited Suspect IPBPM B resolution is currently ~ 50nm We suspect a problem with IPBPM C We are suspicious of reference cavity diode signal