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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
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CLIC Final Doublet Region
6
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CLIC IP FB performance
Single random seed of GM C
Resta Lopez
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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
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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
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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
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IP kicker
Designed by Oxford
Fabricationarrangedby KEK
Installed May 2012
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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
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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%
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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
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IP kicker IPBPMs
FONT digital
FB
IPBPMelectronics
FONTamplifier
e-
Tests started November 2013
New IP chamber installed Summer 2013
Honda electronics
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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
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Nominal optics
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BPM calibration constant vs. attenuation
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BPM calibration constant vs. attenuation
Indicative ofsaturation ofelectronics
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Beam jitter (at waist) vs. attenuation
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Beam jitter (at waist) vs. attenuation
Consistent with true beam jitter ~ 300nm (beam not tuned after DR extr. kicker issue)
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High-beta (pencil beam) optics
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Beam jitter vs. attenuation
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Beam jitter vs. attenuation
Consistent with true beam jitter ~ 500nm (pencil beam large)
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Resolution vs. attenuation
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Resolution vs. attenuation
Resolution appearsto be 200-300nm!(NB: C >> A, B)
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Nominal optics: IPFB @ IPBPM B
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Best IPFB results
Bunch 1: not corrected,jitter ~ 400nm
Bunch 2: corrected,jitter ~ 67nm Corrected jitter 67nm
<< apparent resolution!
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Best IPFB results
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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 …
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IPFB performance vs. bunch 2 posn.
IPFB off
IPFB on
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IPFB performance vs. bunch 2 posn.
IPFB off
IPFB on
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Best standard jitter measurement
66nm(single) 49nm(avg.)
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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