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

Outline

• Reminder of CLIC IP FB prototype

• ATF2 IP FB concept

• Results of recent beam runs

• Summary + conclusions

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

CLIC Final Doublet Region

4

CLIC Final Doublet Region

5

CLIC Final Doublet Region

6

7

CLIC IP FB performance

Single random seed of GM C

Resta Lopez

8

For noisy sites:

CLIC IP FB performance

factor 2 - 3 improvement

FONT5 intra-train FBs at ATF2

ATF2 extraction line

99

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 kicker10

11

IP kicker IPBPMs

FONT digital

FB

IPBPMelectronics

FONTamplifier

e-

ATF2 IP FB loop scheme

Eventual goal is to stabilise the small ATF2 beam (design 37nm)at the nanometer level

12

IP kicker

Designed by Oxford

Fabricationarrangedby KEK

Installed May 2012

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

IP kicker IPBPMs

FONT digital

FB

IPBPMelectronics

FONTamplifier

e-

Preparatory tests June 2013

Existing IPBPMs

Honda low-latency electronics

15

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

16

Latency ~ 160ns

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

IP Feedback Results

FB Off Jitter: 170 ± 10 nmFB On Jitter: 93 ± 4 nm

FB Off Correlation: 81%

18

IP Feedback Results

FB Off Jitter: 170 ± 10 nmFB On Jitter: 93 ± 4 nm

FB Off Correlation: 81%

FB On Correlation: -16%19

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

IP kicker IPBPMs

FONT digital

FB

IPBPMelectronics

FONTamplifier

e-

Tests started November 2013

New IP chamber installed Summer 2013

Honda electronics

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

Nominal optics

24

BPM calibration constant vs. attenuation

25

BPM calibration constant vs. attenuation

Indicative ofsaturation ofelectronics

26

Beam jitter (at waist) vs. attenuation

27

Beam jitter (at waist) vs. attenuation

Consistent with true beam jitter ~ 300nm (beam not tuned after DR extr. kicker issue)

28

High-beta (pencil beam) optics

29

Beam jitter vs. attenuation

30

Beam jitter vs. attenuation

Consistent with true beam jitter ~ 500nm (pencil beam large)

31

Resolution vs. attenuation

32

Resolution vs. attenuation

Resolution appearsto be 200-300nm!(NB: C >> A, B)

33

Nominal optics: IPFB @ IPBPM B

34

Best IPFB results

Bunch 1: not corrected,jitter ~ 400nm

Bunch 2: corrected,jitter ~ 67nm Corrected jitter 67nm

<< apparent resolution!

35

Best IPFB results

36

Scan of bunch 2 position using IPK

Apply constant kicksto bunch 2 to move itsvertical position in theIPBPM

measurement closer to ‘zero’ should havebetter resolution

Then turn on IPFB …

37

IPFB performance vs. bunch 2 posn.

IPFB off

IPFB on

38

IPFB performance vs. bunch 2 posn.

IPFB off

IPFB on

39

Best standard jitter measurement

66nm(single) 49nm(avg.)

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