TIPP ‘ 14International Conference on Technology and

Instrumentation in Particle Physics

Measurement of nm Electron Beam Sizes using Laser Interference by Shintake Monitor

2-6 June 2014 Amsterdam, The Netherlands

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Jacqueline Yan, S. Komamiya, （ Univ. of Tokyo, Graduate School of Science ）Y. Kamiya （ Univ. of Tokyo, ICEPP ）

T.Okugi, T.Terunuma, T.Tauchi, K.Kubo (KEK)

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ATF2 ： test prototype of final focus system for ILC

Role of Shintake Monitor at ATF2Role of Shintake Monitor at ATF2

ATF2 Goal 1: verify Local Chromaticity Correction scheme by focusing σy to design 37 nm Goal 2: O(nm) beam position stabilization

FFS

High luminosity requires O(nm) vertical beam size at IP

ATF ： 1.3 GeV LINAC , DR wextremely small vertical e beam emittance

Outline of this talkOutline of this talk

Recent Beam Recent Beam Time Status Time Status

Performance Performance EvaluationEvaluation Summary Summary

& Goals& GoalsIntroductionIntroduction

Signal Signal JittersJitters

• Systematic errors Systematic errors • Phase jitter studyPhase jitter study

Shintake Monitor is crucial for achieving ATF2 ‘s Goal 1 and demonstrating feasibility of realizing ILC !!

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Introduction

Measurement SchemeMeasurement SchemeExpected PerformanceExpected PerformanceRole in Beam TuningRole in Beam Tuning

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Compton scattered photons detected downstream

Collision of e- beamwith laser fringe

upper, lower laser paths cross at IP

form Interference fringes

Piezo

• use laser interference fringes as target for e- beamOnly device able to measure σy < 100 nm !!• essential for ATF2 beam tuning

Measurement SchemeMeasurement Scheme

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e- beam safely

dumped

Split into upper/lower paths phase scan by piezo stage

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Nd:YAG pulsed laser (Pro-350) λ = 532 nm (SHG)

Y. Yamaguchi , Master Thesis, Univ of Tokyo

N +

N -

[rad]

[rad]

N: no. of Compton photonsConvolution between e- beam profile and fringe intensity

Focused Beam ： large M

Dilluted Beam ： small M

Small σy

Large σy

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Detector measures signal Modulation Depth “M” 　 measurable range

determined by fringe pitch

depend on crossing angle θ (and λ )

)2/sin(2

ykd

M

d

kNN

NN

y

yy

)cos(ln2

2

)(2exp)cos( 2

M

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Crossing angle θ

174° 30° 8° 2°

Fringe pitch 266 nm 1.03 μm 3.81 μm 15.2 μm

Lower limit 25 nm 80 nm 350 nm 1.2 μm

Upper limit 110 nm 400 nm 1.4 μm 6 μm

)2/sin(2

ykd

M

dy

)cos(ln2

2

Measures σy* = 25 nm 〜 6 μm with < 10% resolution

Expected PerformanceExpected Performance

select appropriate mode according to beam focusing

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σσyy and M and M for each θ modefor each θ mode

6Y. Yamaguchi , Master Thesis, Univ of Tokyo

174 deg. 30 deg.

2 - 8 deg

Crossing angle continuously adjustable by prism TIPP14 7

Vertical table Vertical table 1.7 (H) x 1.6 (V) m

• InterferometerInterferometer• Phase control (piezo stage) Phase control (piezo stage)

path for each θ mode 　（ auto-stages + mirror actuators

）

beam pipe

Laser transported to IP

optical delay

half mirror

Recent Beam Time Status Recent Beam Time Status

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Mar, 2013 : M 〜 0.3 @174° σy,meas 〜 65 nm

〜 〜 20132013

Apr – May, 2014Apr – May, 2014

reduction in signal jitters/ drifts by various hardware improvements laser tuning, detector , collimation

〜 〜 Mar 2014Mar 2014

• effective linear / nonlinear knob tuning • reflect improved e- beam stabilizationConsistent measurement of high M @ 174°

mid-Apr: Mmeas > 0.4 (σymeas < 57 nm)

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HIGHLIGHTS of PERFORMANCE• stable contribution to e- beam tuning• Best measurement stability 〜 5%• small σy requires very low beam intensity due to wake-field effects (investigating)

• Actual σy may be smaller after correcting for systematic errors (dedicated studies ongoing)

4/17/2014 9

Fringe scans @174°

For status of even smaller σmeas in 2014 see “K. Kubo et al: IPAC14 Proceedings :TOWARDS INTERNATIONAL LINEAR COLLIDER: EXPERIMENTS AT ATF2 “

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（ Phys. Rev. Lett. 112, 034802)

Focus of this talk

Preliminary before error corrections

M =0.34 +/-0.02 (S/D. ) 　 　 (σy = 62 +/- 2 nm (S.D) )

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Examples of consistency scans @174 ° in 2014 before knob tuning M = 0.29 +/- 0.04 （ S.D. ） 　（ σy = 66 +/- 4 nm (S.D)

～ 14 hrs later 　 after all linear/nonlinear knobs M =0.34 +/-0.02 (S/D. ) 　 　 (σy = 62 +/- 2 nm (S.D) )

higher M and better stability

Results before error correction

M > 0.4 reproduced at beam tuning knobs

EFFECTIVE beam tuning :

σy > 150 nm σy < 60 nm within half a day !!

PreliminaryPreliminary

Beam tuning using sextupoles

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Status

Laser pointing jitters(H relative position jitter “ Δx”)

• observed by profile monitor & laser wire mode : 〜 5-10% of laser profile radius

Phase jitter Δφ Vertical laser-beam relative position jitter “Δy”

Estimated by fitting of jitters in fringe scansStill need independent measurement of either laser or beam jitter

Laser power jitter < 10%

Timing jitter 1 – 3 ns peak to peak, 　　　 add < few % to signal jitters

statistical fluctuations Depend on photon statistics : detector properties, collimation, beam intensity, etc….

Other minor factors

• BG fluctuation, • e- beam current monitor resolution

< 5 % each, BG is not a issue recently with high S/N

Varies with beam condition

Potential Sources of Signal Jitters

• observe overall sig jitter in fringe scan 〜 20-40% depend on phase• drifts are hard to separate from jitters sometimes

Also a M reduction factor

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From PIN-PD signal

Further measurements and simulations ongoing to comprehend impact from each source

issue of “oscillating” Compton signal jitters (period 〜 few min) pointing jitters related to complex internal structure of laser profile@ IP eg. non-Gaussian multi- components

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30 deg174 deg

ATF2 online panel : signal stability trend

(1) reinforcement of detector shielding (Pb and parafine)

(2)Stabilization of e- beam improved tuning multiknobs, orbit feedback(3) speed up DAQ software : reduced effect from drifts (4) Adjust laser profile and focusing Reduce pointing jitter at IP(5) improved buildup and Q-switch timing stability

5/29 (174 deg )

focal lens scan

-----Broad Rayleigh length > 〜 4 mm

by Shintake Monitor group@ATF2

Relaxed laser focusing

Hardware improvements to stabilize measurements in 2014

Before After : Rounder profile less intensity bias

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Regular laser tuning by laser company engineer

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Focusing on the most dominant “phase Jitter”

study of systematic errors

(M reduction factors)

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[[[References: 1. J. Yan, et.al., Nucl.Instrum.Meth. A740 (2014) 131-1372. ATF2 collaboration: Phys. Rev. Lett. 112, 0348023. Proceedings for this conference

Error source M reduction factor

phase jitter(V relative position jitter )

study using simulation and analyze actual data

Fringe tilt (z, t) Optimization by “tilt scan”

Laser polarization polarization measured optimize by “ λ / 2 plate scan ”

MisalignmentLaser profile

shot-by-shot fluctuation and non-Gaussian components of laser profile may lead to 10-20% in M reduction

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Details coming up

Systematic errors ： M reduction Factor

σy over - evaluation

　 　　　

M under-evaluation

Suppression of signal jitters / drifts helps precise evaluation of M reduction factors

dominant

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study of other more complex non-linear, non-Gaussian jitters/ slow drifts are ongoing

Before: fitted M After correction

Phase jitter (Δφ)Phase jitter (Δφ)relative position jitter (Δy) between laser relative position jitter (Δy) between laser and e- beamand e- beam

• Hard to decouple laser fringe phase jitter from e- beam jitters

• conditions change over time

(ex)(ex) 　　：　　： ifif Δφ = 400 mrad, Δφ = 400 mrad, CΔφ CΔφ 〜 〜 91 % 91 % σσy0y0 = 40 nm = 40 nm σ σy,meas y,meas = 44 nm= 44 nm

M reduction factor due to Δφ M reduction factor due to Δφ

M reduction from Δφ

Δφ [rad]

Horizontal jitters

Small σy* especially sensitive to beam jitter !!

Δφ extraction method was developed !!by fitting fringe scan data

TIPP14 can correct M almost back to nominal using extracted Δφ　　

simulation

Δφ [rad]

simulationM0 = 0.636σy0 = 40 nm

Mcorr = Mmeas / CΔφ

simulation

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GOAL

Focusing on factors hard to suppress

• phase jitter Δφ DOMINANT extracted from fringe scan (details coming up)• alignment (position, profile)

Important to guarantee reliability of Δφ extraction method

Demonstrated using simulation : Δφ precision better than few % in general

analysis model assumes Gaussian jitter distribution however reality may be more complex …..• confirmed by testing variety of non-Gaussian (non-linear) jitters / drifts what effects do they have on “Mmeas “ and “Δφ_out “ ? ( details coming up)

Dedicated beam time data for Δφ study was analyzed

Recent status : 〜 10 nm systematic over-evaluation of σy (preliminary )

Potential Causes for phase jitter Laser pointing instability combined with mirror misalignment / vibrations electron beam jitter (ΔΦ is a convolution of laser and e beam)

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Study of Systematic Modulation ReductionStudy of Systematic Modulation Reduction

Simulation study of Δφ extraction precision

fix {M,φ0, Eavg, Cconst, Cstat} to jitter plot

signal jitter vs phase

STEP1: generate fringe scan assume “realistic” ATF2 conditions

fringe scan

Jitter from Δφ

Model

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Signal energy vs phase

vertical jitter input

input: σy0 = 40 nm, 174°mode Δφ = 0.7 mrad , 24.5 % vertical jitter

simulation

simulation

Random Δφ input

Δφ , Clinear (2 free parameters) fixed parameters: M, φ0, Eavg , Cconst, Cstat: (estimated)

STEP2: extract Δφ from fitting

Sig jitter = convolution of phase jitter and vertical jitter

BG statistical laser

spread is larger for smaller Nav

Nav = 20 vs Nav = 50

Simulation

[2] Distribution for random 10 samples•X: seed number • Y: extracted Δφ

• error < 〜 7% for single scan good to average over multiple scans

large Nav scans are preferred for Δφ study

Assume a “relaistic” ATF2 conditionInput: M0 = 0.64, σy0 = 40 nm, 174 deg mode, Nav=50, Clinear = 0.25,Cstat = 0.15, Cconst = 0.05, Δφ = 0. 59 rad

Simulation

[1] statistical results of 100 random seeds • X: input ΔΦ• Y: extracted Δφ

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Extraction precision for Gaussian distributed phase jitter input

Simulation for effect of

non-linear jitters/ drifts on measured Modulation and phase jitter analysis

Using imitation of actually measured laser fringe phase jitters

Input: M0 = 0.64, σy0 = 40 nm, 174 deg Clinear = 0.25, Cconst = 0.05, Cstat = 0.15

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Mean : 1.77 +/- 0.035

Δφ_real RMS = 0.448 rad

data read out in 3 Hz (0.33 sec) intervals

Test using reproduced Δφ measured using phase monitor in 2009 (beam off , old laser system)

1. Input “Δφ_real” into fringe scan simulation 2. extract Mmeas and Δφ_out 3. observe effect on Mmeas & M correction using

Δφ_out

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phase monitor no longer installed

Extracted results: •Δφ_out = 0.43 +/- 0.04 (rms) 10 random seeds close to Δφ_real RMS

also added “slow linear drift “• OK if drift < 150 mrad/ min (similar to real drift)

Nav=50

shot-by-shotΔΦ extraction precision better than 5%

Effect of phase instability on MMmeas vs Mcorr = Mmeas / exp(-ΔΦ_out ^2 /2)

Observationswhen averaged over multiple scans, Mmeas is not far off from nominal (few % error)

• poor Δφ_out precision for small Nav

For large Nav (> 50) :• relatively good ΔΦ_out precision• correct almost back to nominal M0 (< 〜 1% error )

Compare different Nav (# of pulses/phase) =10, 20, 50, 100

avg and rms of 10 random seeds

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Why large Nav is better for Δφ extraction ?• higher statistics• effect of drifts resemble faster Gaussian like jitters suitable for the model used here

impact from nonlinear fluctuations depends on ….. rate of jitters/ drifts location, statistics (Nav) of fringe scan very difficult to model ; detailed study of all different scenarios is ongoing

Need to balance precision issues with time consumption

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Analysis of phase jitters from real beam time data

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History of phase jitter extracted from fringe scans in 2014

Mar 2014

Jan – Feb, 2014

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Apr, 2014, 30 deg

Apr-May 2014

Large difference in Δφ between 30 deg (300-600 mrad) and 174 deg (600-850 mrad)

　　 maybe due to :•effect of laser pointing jitter : longer path length after 50% beamsplitter for 174 °•impact from e- beam jitter (ΔΦ = 2*π*Δy /d d (174)= 266 nm vs d(30) = 1028 nm )

174 ° ： σy, meas < 65 nm

-- 2-8° , 30 ° : larger σy --

RECENT

phase jitter Δφ relative position jitter Δy Convolution of laser and e beam : difficult to separate at present

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Phase Jitter @ 174 °mode derived using dedicated Nav=50 fringe scans

Recent Phase Jitters @ 174°mode are similar •4/9: Δφ=0.82 +/- 0.10 rad•4/10 : Δφ=0.85 +/- 0.06 rad•4/17 : Δφ=0.67 +/- 0.04 rad•5/22 : Δφ=0.74 +/- 0.04 rad

example: 4/17 Δφ=0.67 +/- 0.04 rad

M plot

RMS jitter plot for Δφ analysis Fai

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ΔΦ (=2*π*Δy/d) very different between 30° and 174 ° however Δy / σymeas is similar (50-60%)

Indicate significance of e beam jitter (?)

Difficult to separate laser and beam factors

anticipating independent measurement of e- beam jitter @ IP by O(nm) resolution cavity BPMs (commissioning)

laser interferometer type Shintake Monitor Only existing device capable of measuring beam sizes < 100 nm essential for achieving ATF2 goal(s) realizing ILC

SummarySummary

< Status > stable beam tuning and continuous beam size measurements in Apr-May, 2014

measurement stability 〜 5% 5% reflects e- beam stabilization and reduction of signal jitters /drifts by KEK membersreduction of signal jitters /drifts by KEK members

GoalsGoals identify and suppress sources of jitters / drifts

stable measurement of σy < 40 nm and improve error analysis precision

achieve ATF2 Goal 1 !!!

For status of small σmeas , see“K. Kubo et al: IPAC14 Proceedings : TOWARDS INTERNATIONAL LINEAR COLLIDER: EXPERIMENTS AT ATF2 “

dedicated study of systematic errors of Shintake Monitor dedicated study of systematic errors of Shintake Monitor data analysis & data analysis & simulation

after correction for the dominant M reduction factor phase jitter : maybe REAL σy is 〜 10 nm smaller Close to achieving ATF Goal 1 !!!

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BACKUP SLIDES

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power jitter < ～ 10%

Timing jitter : 1-3 ns peak to peak

Timing and Power Stability

Observe signal of PIN-Photodiode @laser hut

Laser Power and Profile Measurements (Apr, 2014)

Parallel propagation to final focal lenses

balanced profiles and power (~ 95%) between U and L paths

loss in transport (laser hut IP) < 7%

laser table• round profile•intensity spots evened out

after transport to IPTIPP14 27

174 deg Mmeas(174)0.29 +/-0.01 σmeas = 66+/- 1 nm

　 Ctot(174) > 0.66

　 Mcorr 0.44 +/-0.02

30 deg Mmeas(30) 0.77+/-0.01 σmeas = 81+/- 2 nm

　 Mexp 0.82+/-0.01

　 Ctot,exp 0.93+/-0.01

　 ---------------- ----------------

　 Ctot(30) >0.94

using data immediately before / after mode switching (174 30°)

• this study requires stable beam time conditions (laser & beam)

• total M reduction for 30 °is less than 2013 due to hardware upgrades (?)

total M reduction for 30°compared to 174 °results

“ Ctot,exp” and “Ctot(30)” consistent , almost no residual M reduction ??!!

Total M red, mainly from Δφ

M red. derived independently using 30° data only, mainly from Δφ

Dedicated study of “fringe Contrast” = total M reduction factor “ Ctot”

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σcorr = 54+/- 1 nm

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Laser pointing stability : 4/9 from Nav = 50 laserwire scan @174 deg

Δx / (laser spot radius) = 12 +/- 7 %

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Contribution from σx subtracted

Assuming Gaussian laserwire profile (but not always so)

ICT: 2E9

signal jitter status : improved since April 2014 stability varies for different periods, efforts for further stabilization still ongoing

174 deg, Apr vs Mar 2014

Drift of Fitted Initial Phase in 174 deg continuous scans ( 〜 30 min)

this drift is convolution may be from laser and/or beam

Relative RMS jitter ΔE/E(φ)

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Examples of SIMULATIONDepending on condition, signal jitters/drifts can cause both under & over evaluation of M

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Fitted M

Typical range

Bias on M from Static Gaussian like vertical jitters

a few % systematic M reduction

Input : Nav=50, 174 deg , M0 = 0.636, Δφ=0, change 1 C factor at a time, keep others 0

Simulation: Avg of 100 seeds

difficult to model

nonlinear fluctuation:sudden intensity decrease(drift)

In this case, M over-evaluation

ex) 50% reduction

Nav=20, Clinear = 0.25,Cstat = 0.10, Cconst = 0.05, Δφ = 0. 59 rad

simulation

simulation

rel. M error = (Mfit – Mexp) / Mexp

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transverse ： laser wire scan 　　　　　　　

precise position alignment by remote control

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Role of IPBSM in Beam TuningRole of IPBSM in Beam Tuning 　　

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beforehand …. Construct & confirm laser paths, timing alignment

Longitudinal ： z scan 　

After all preparations ……….

continuously measure σy using fringe scans Feed back to multi-knob tuning

laser spot size σt,laser = 15 – 20 μm

almost no M reduction due to polarization

Polarization MeasurementPolarization Measurement

P contamination : Pp/Ps < 1.5 %

Set-up

IPBSM optics designed for linear S polarization

Also measured “half mirror” reflective properties

Rs = 50.3 %, Rp = 20.1 % match catalogue value

half mirror

power ratio

confirmed “S peaks” maximize M

Beamtime ： “ λ/2 plate scan

S peaks” also yields best power balance between 2 paths !!

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#2

Rotate λ/2 plate angle [deg]

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actual data (blue)Nav = 20 fringe scan(Mar 11 2014) @ 174 deg mode

RMS signal jitter (green)

vsEnergy at each phase

Sig jitter due to phase jitter (red) is larger at fringe mid point and smaller at fringe peak(compare with bottom plot)

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