European Linear Collider Workshop ECFA LC2013BDS+MDI

IPBSMBeam Size Measurement & Performance Evaluation

May 29 , 2013DESY

ECFA LC 2013

Jacqueline Yan, S. Komamiya, M. Oroku, Y. Yamaguchi

（ The University of Tokyo, Graduate School of Science ）T. Yamanaka, Y. Kamiya, T. Suehara （ The University of Tokyo, ICEPP ）

T.Okugi, T.Terunuma, T.Tauchi, T.Naito, K.Kubo, S.Kuroda, S.Araki, J.Urakawa (KEK)

113/05/29

Introduction

Measurement SchemeMeasurement SchemeExpected PerformanceExpected PerformanceRole in Beam TuningRole in Beam Tuning

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ATF2 ： Linear Collider FFS test facility@KEK

Role of IPBSM (Shintake Monitor) at ATF2Role of IPBSM (Shintake Monitor) at ATF2

IPBSM is crucial for achieving ATF2 ‘s Goal 1 !!focus σy to design 37 nm verify Local Chromaticity Correction

FFS

Ultra-focused vertical beam size at IP !!　 Crucial for high luminosity

IPBSM

OutlineOutline Beam Time Status Beam Time Status Dec 2012 Dec 2012 Spring 2013Spring 2013

• IPBSM PerformanceIPBSM Performance• Error studiesError studies• Hardware UpgradesHardware Upgrades

Summary Summary & Goals & Goals and Plansand Plans

IntroductionIntroduction

13/04/04ATFII Review

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ATF ： 1.28 GeV LINAC , DR high quality e- beam with extremely small normalized vertical emittance γεy

ATF2 Goal 2: O(nm) beam trajectory stabilization

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 !!

• 　　 Crucial for ATF2 beam tuning and realization of ILC

Measurement SchemeMeasurement Scheme

ECFA LC 2013

e- beam safely

dumped

Split into upper/lower paths phase scan　by　piezo　stage

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　 Detector measures signal Modulation Depth “M” 　

N +

N -

[rad]

[rad]

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　 measurable range determined by fringe pitch　

　 depend on crossing angle θ (and λ ) 　

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

)2/sin(2

ykd

M

d

kNN

NN

y

yy

)cos(ln2

2

)(2exp)cos( 2

M

Focused Beam ： large M

Dilluted Beam ： small M

Small σy

Large σy

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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 20 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* = 20 nm 〜 few 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

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174 deg. 30 deg.

2 - 8 deg

Crossing angle continuously adjustable by prism 13/05/29

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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

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

Beam Time Status Beam Time Status

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12/20 : 　1st success in M detection

at 174 deg mode

Beam time status in 2012 　

stable measurements of M 〜 0.55

Feb ； 30 deg mode commissioned ( 1st M detection on 2/17)

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　　 M = 0.52 ± 0.02 (stat) σy = 166.2 ± 6.7 (stat) [nm]

• 2 - 8 ° mode: clear contrast （ Mmeas ～ 0.9)• Prepared 174 deg mode commissioning

Suppress systematic errors Higher laser path stability / reliability

High M measured at 　 30 ° mode 　Contribute with stable operation to ATF2 beam focusing / tuning study 　　

(10 x x*, 3 x y* optics)

Spring runSpring run

Major optics reform of 2012 summer

Winter runWinter run

Last 2 days in Dec runMeasured many times M = 0.15 – 0.25 　　（ correspond to σy 〜 70 – 82 nm ）　　

　Large step towards achieving ATF2 ‘s goal !!　 error studies ongoing aimed at deriving “true beamsize”　

　 preliminary

　 preliminary

*　　IPBSM　systematic　errors　uncorrected** under low e beam intensity ( 　〜 1E9 e / bunch)

10 x βx* , 1 x βy*

By IPBSM group@KEK

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measured M over continuous reiteration of linear /nonlinear@ tuning knobs @ 174 ° mode

Beam time status in 2013 Spring 　

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dedicated data for error studies under analysis

ex ）　 consecutive 10 fringe scans

　 preliminary

Time passed

measure M vs time after all conditions optimized

preliminary

Stable IPBSM performance major role in beam tuning

10 x x*, 1 x y*

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　 174 ° mode ”consistency scan”

moving towards goal of σy = 37 nm :higher IPBSM precision and stability & looser current limits of normal / skew sextupoles current

　　 M 〜 0.306 ± 0.043 (RMS) correspond to σy 　〜 65 nmBest record

from Okugi-san’s Fri operation meeting slides

Other studies using IPBSMOther studies using IPBSM

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Beam intensity scan

others: •Test various linear / nonlinear tuning knobs• IPBSM systematic error studies

“Reference Cavity scan” in high β region

(ex: 30 deg mode)

wakefield studies

Check linearity of BG levels in IPBSM detector Observe “steepness” of intensity dependence compare with other periods to test effects of orbit tuning and / or hardware improvement for wake suppression 　

(ex: 30 deg mode)beam intensity 5E9 / bunch

BG level

ex: spring 2012 : Adjust curvature of laser cavity mirrors

Aim:Suppress systematic error sourcesHigher alignment precision & reproducibility 　

Proved greatly effective in 2012 winter run

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Optics reform of 2012 summer By IPBSM group@KEK

improvements details

alignment precision match focal point to IPInjection position / angle into lensRe-optimize expander / reducer

consistency , reproducibilitybefore / after mode switching

• focal point scan for all modes• CW laser + reference lines on new base plates• new IP target (screen monitor)

• θ mode switching technique {small linear stage + mirror actuators } 　 　 now: independent for each mode (before: shared rotating stages)

balanced profiles suppress difference in path length & focal point 　

Tuning of main laser

Aim for a more Gaussian profile

by Spectra Physics

Reform laser profile and spatial coherence (adjust YAG rod & cavity mirrors)

Exchange flash lamp seeding laser tuning ( oscillation stability)

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ECFA LC 2013

Small linear stage+ mirror actuator

Firm lens holders

just after injection onto vertical table

Confirm fine alignment using CW laser and transparent IP target

check positioning of lens, mirror, prism

prism CW laser spot

inside IP chamber

laser waist &

crossing point

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Performance Evaluation #1: Performance Evaluation #1: StabilityStability

Signal jitter sourcesSignal jitter sourcesphase drift / jitterphase drift / jitter

Laser timing & powerLaser timing & power

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Demonstration of stability in IPBSM operation Demonstration of stability in IPBSM operation : : signal Jittersignal Jitter

long term stable performance is maintained under various scan conditions “standard” Long range scans dedicated to error studies : just as stable (jitter is not increased) compared to usual scans

(beam & IPBSM conditions, analysis method kept consistent)

data range Comp sig jitter (@peak of fringe scans)

130314_155758 20 radNav = 10

21.1 %

130314_165737 20 radNav = 10

25.2 %

130314_163420 20 radNav = 20

24.3%

130314_163952 60 radNav = 10

25.4 %

130314_164840 60 radNav = 10

26.3 %

Usual scans immediately before & after

Comp Sig. jitter is quite consistent at generally 20 – 25 % (@peak of fringe scans)

Fine scanNav = 20 events at each phase step

Long range scans 60 rad(usually 20 rad)

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16Long scans from other periods show similar stability

preliminary

Signal jitter: 24.3 %(at peaks)

1st of 2 consecutive long range scans

Signal jitter: 25 %(at peaks)

2nd of 2 consecutive long range scans

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60 rad rangepreliminary S/N ~ 5.8

60 rad scans dedicated to 60 rad scans dedicated to error studyerror study

Stability is maintained for long range scans (fluctuation / drift e.g. BG, phase, timing, power, ect…)

consecutive fringe scans : consecutive fringe scans : drift < 70 mrad / min (drift < 70 mrad / min ( negligible) negligible)

Phase Drift

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final set of scans on 3/8 : very stable final set of scans on 3/8 : very stable

(initial phase) (initial phase) vs (time)vs (time)

(initial phase) (initial phase) vs (time)vs (time)

Comp SignalComp Signal Jitter Jitter

BGBG jitterjitter

signal jitter derived directly signal jitter derived directly from actual fringe scans from actual fringe scans (peaks)(peaks) ：： 20 – 25% 20 – 25% 　　

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*scaled by S/N

iCT monitor fluctuation

Relative beam –laser positionRelative beam –laser position

* Intrinsic CsI detector energy resolution (GEANT4 sim.)　

detector energy resolution

Signal Jitter Sources

< 10%

under investigation

< 1 %

~ 3 %

6 - 7 % (monitored by PIN-PD signal)

< 5 % ICT monitor accuracy measured Comp sig energy normalized by beam intensity

varies with beam condition

Spring, 2013: 174 deg modecontribution to Sig Jitter ΔEsig / Esig, avg

Study of Signal FluctuationStudy of Signal Fluctuation

~ 1 % (from photo-diode)

Prepared offline veto for large timing, power jittered events

•hard to separate from other fluctuation sources hard to separate from other fluctuation sources (laser (laser pointing jitters, drifts, ect….)pointing jitters, drifts, ect….)• jitters can vary greatly over timejitters can vary greatly over time

Phase Jitter / Relative Position JitterPhase Jitter / Relative Position Jitter

Can’t push all fluctuation to phase jittersCan’t push all fluctuation to phase jitters

fitted energy jitters with contributions from statistics, timing, BG , and Δx

preliminary

take high statistics scans (Nav ~ 100) under optimized conditions for dedicated analysistake high statistics scans (Nav ~ 100) under optimized conditions for dedicated analysis

derive horizontal rel position jitter Δx using high statistic laserwire scan

if if Δy < 0.3 * σy Δy < 0.3 * σy (ATF2 beamline design)(ATF2 beamline design) CΔy > 90 % for σy* = 65 nmCΔy > 90 % for σy* = 65 nm

Issue 1: Δy Issue 1: Δy M reduction M reduction

Important to grasp residual M reduction factors in order to derive the true beamsize

Issue 2 : fluctuation source during fringe scanIssue 2 : fluctuation source during fringe scanIf Δx 〜 2.5 μm cause 　〜 4 % signal jitters (assume Gaussian profile σlaser = 10 μm)

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possibly veto jittered points under clearly identified causesGoal: 　 achieve precise Mmeas (σy,meas )

λ/ 2 plate setting

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IP area:QD0, QF1

MFB2FF : "vertical IP-phase BPM"

ATF2 beamline & BPMsATF2 beamline & BPMs

Check for correlation of signal jitters with e beam orbit in BPMs e.g. MREF3FF (high β location for “ref cavity scan” )

synchronize fringe scan data with all ATF2 monitors e.g. BPMs, ICT monitors

ex): check y position jitter@IP using MFB2FF : "vertical IP-phase BPM”

e beam orbit

jitterjitter （（ RMSRMS ）） 〜 〜 1.3 ns1.3 ns

Relative timing cutRelative timing cut (beam – laser)(beam – laser)e.g. 1-sigma

Observe ΔEsig dependence on Esig :

Investigate Signal FluctuationInvestigate Signal Fluctuation

Anticipate O(nm) res. measurement of Anticipate O(nm) res. measurement of beam position jitter at IP by beam position jitter at IP by IPBPMsIPBPMs (under commissioning)(under commissioning)

[1] improve hardware [2] data selection

Performance Evaluation #2:Performance Evaluation #2:Modulation Reduction FactorsModulation Reduction Factors

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（１）　“ Direct Method” consecutive mode switching , under same beam condition consecutive mode switching , under same beam condition (e.g. : 2 ° (e.g. : 2 ° 7 ° 7 ° 30 ° ) 30 ° ) use a σy that yields very high M at low θ mode use a σy that yields very high M at low θ mode observe upper limit on M observe upper limit on Mmeasmeas

Note) apply to a particular dedicated data sample

（２）　“ Indirect Method” 　　Evaluate each individual factor offline and “sum up”

Note) 　 represents the typical conditions of a particular period however …… hard to derive overall M reduction (e.g. some factors lack quantitative evaluation, vary over time, only can get “worst limit”)

Study of M reduction

Modulation Reduction Factor

Under-evaluate M, over-evaluate σy 　 　　　

How to evaluate M reduction?

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Plan for assessment of M reduction factorsPlan for assessment of M reduction factors

how to find out bias due to “uncertain” individual factors: (e.g. relative position jitter, spatial coherence)

At a low θ mode : measure a large M (near resolution limit) using a sufficiently small σy compare results with higher θ modes

example: if we measure M corresponding to σy = 350 nm at 7 deg mode expect M = 0.98 at 2.75 deg mode (try to keep within 2-8 deg) what if we get only 0.95 ??? Ctotal 〜 0.97 no individual bias factor worse than 0.97

Note:• conditions may vary over time confirm with repeated measurements• need prove that these factors are really independent of θ

priorities1st : suppress M reduction aim for Ctotal 〜 12nd: precisely evaluate any residual errors derive the “true beam size”

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test using “direct method”

Error source M reduction factor

Fringe tilt (z, t)

profile imbalance Cpro > 98.5%

power imbalance Cpow > 99 %

Laser polarization Optimized to “S state” using λ / 2 plate

Phase drift not major issue

Laser path alignment Ct,pos : ~ 99 %, Cz,pos : > 98 %

Major bias if unattended to

relative position jitter (phase jitter) Spatial coherence

Limited by alignment precision

Could be major bias

Measured polarization and half mirror reflective properties

Resolution of mirror actuators aligning laser to beam

ECFA LC 2013

Spring 2013, 174 deg

power measured directly for each path

drift : < 70 mrad / min during consecutive fringe scans

Still quantitatively uncertain

under evaluation:

Beamtime final optimization by “tilt scan”

assume Gaussian laser profile (spot size)

Individual M Reduction Factors 　　

Represent typical condition of a particular period

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laser polarization related measurements

polarization measured just after injection onto vertical table•very close to linearly S polarization • should be very little polarization related M reduction

resultsresults

λ/ 2 plate setting

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ECFA LC 2013

90 deg cycle

“P contamination”: Pp/Ps = (1.46± 0.06) %

Set-up

IPBSM laser optics is designed for pure linear S polarization

to precisely confirm there is no residual M reduction ……. next plan individual measurements for upper and lower paths near IP

Hardware prepared carry out in June

also measured reflective properties of “half mirror”

Rs = 50.3 %, Rp = 20.1 % Match catalog specifications !!

half mirror

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power ratio

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lower

“S peaks” (maximum M) also yield best power balance Minimize M reduction

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S peak

P peak

45 deg between S and P

During Beamtime “λ/2 plate scan “ to maximize M

laser polarization and power balanceand power balance

Rotate λ/2 plate angle

lens

upper

power meter

investigate power balance: U vs L path

90 deg 180 deg

Rotate λ/2 plate and measure high power Immediately in front of final focus lenses

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M reduction factor due to power imbalance

Mismatch in axis between fringe and beam

transverse longitudinal

laser path observed on lens: precision ~ 0.5 mm (few mrad)

Fringe TiltFringe Tilt

issues: • Position drifted by the time we scan• e beam may also be rotated in transverse

Current method ：　“ tilt scan”fringe pitch / roll adjustment: observe M reduction “ Ctilt “

(70 - 80% if uncorrected) directly use e beam as reference for tilt adjustment

27(study of fringe tilt by Okugi-san)

important adjustment to eliminate M reduction

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ex fringe pitchM 0.07 0.32 　　　

Mirrors for adjusting tilt M174L Y 　

(8.9 mm 9.01 mm )

beamsize monitor using laser interference Only existing device capable of measuring σy < 100 nm Indispensible for achieving ATF2 goals and realizing ILC

< Status > contribute with stable operation to continuous beam size tuning Consistent measurement of M 〜 0.3 （ 174 ° mode) at low beam intensity

correspond to σy ~ 65 nm (assuming no M reduction) Application of various linear / non-linear multi- knobs dedicated studies of e beam and IPBSM errors

<towards performance improvement> 　Performance significantly improved by laser optics reformssuppressed error sources, improved laser path reliability & reproducibility

SummarySummary

ECFA LC 2013

Maintain / improve beamtime performance : e.g. stability, precisionAssess residual systematic errors derive the “true beam size” stable measurements of σy < 50 nm within this run　　　

GoalsGoals

Shintake Monitor (IPBSM)

Towards confirming σy = 37 nm

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ECFA LC 2013

Backup

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•hard to separate from other fluctuation sources hard to separate from other fluctuation sources (laser (laser pointing jitters, drifts, ect….)pointing jitters, drifts, ect….)• jitters can vary greatly over timejitters can vary greatly over time

Phase Jitter / Relative Position JitterPhase Jitter / Relative Position Jitter

Can’t push all fluctuation to phase jittersCan’t push all fluctuation to phase jitters

fitted energy jitters with contributions from statistics, timing, BG , and Δx

preliminary

take high statistics scans (Nav ~ 100) under optimized conditions for dedicated analysistake high statistics scans (Nav ~ 100) under optimized conditions for dedicated analysis

derive horizontal rel position jitter Δx using high statistic laserwire scan

if if Δy < 0.3 * σy Δy < 0.3 * σy (ATF2 beamline design)(ATF2 beamline design) CΔy > 90 % for σy* = 65 nmCΔy > 90 % for σy* = 65 nm

Issue 1: Δy Issue 1: Δy M reduction M reduction

Important to grasp residual M reduction factors in order to derive the true beamsize

Issue 2 : fluctuation source during fringe scanIssue 2 : fluctuation source during fringe scanIf Δx 〜 2.5 μm cause 　〜 4 % signal jitters (assume Gaussian profile σlaser = 10 μm)

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Ex #2: check y position jitter@IP using MFB2FF : "vertical IP-phase BPM”

EX#1: MQD10BFF (high β location near ref cavity MREF3FF)

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simulation

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

Expected PerformanceExpected Performance must select appropriate mode

according to beam focusing

ECFA LC 2013

Resolution for each θ modefor each θ mode

nm (syst.) (stat.) 237 -04

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Laser interference scheme

k_1

B_1

k_2

B_2

phase　scan　by　optical　delay

x

y

Θ

Φ

Time averages magnetic field causes inverse Compton scattering

・ phase shift at IP α・ wave number component along y-axis 2ky = 2k sin φ・ modulation depends on cosθ

S-polarized laser

Wave number vector of two laser paths

Fringe pitch

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Calculation of beam size

phase　[rad]

Signal　energy　[a.u.]

0 2π

Save

Small　beamLarge　beam

Small　beam　size

S+

Large　beam　size

S-

Total signal energy measured by γ-detector

Convolution of ・ Laser magnetic field ： Sine curve・ Electron beam profile ： Gaussian

M : Modulation depth

Laser magnetic field Electron Beam profile with beam size σy along y-direction

S± : Max / Min of Signal energy

phase　[rad]

Signal　energy　[a.u.]

0 2π

Save

Small　beamLarge　beam

Small　beam　size

S+

Large　beam　size

S-

phase　[rad]

Signal　energy　[a.u.]

0 2π

Save

Small　beamLarge　beam

Small　beam　size

S+

Large　beam　size

S-

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Gamma detector

Gamma

Gamma

Beam longitudinal direction: 33cm (17.7radiation length)

Calorimeter like gamma detector•Multi layered CsI(Tl) scintillator•PMT R7400U (Hamamatsu Photonics)

Width : 10 cmHeight : 5 cm

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Phase control by optical delay line

piezo　stage

Optical delay line (~10 cm) Controlled by piezo stage

piezostage

laser beam

Δ stage

Movement by piezo stage : Δstage

Phase shift

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measurement scheme

electron beam

Total energy of gamma ray

wire position

gamma

wire scanner, laser wire

Phase of laser fringe

measurablebeamsize ~ 1μm

measurablebeamsize < 100nm

Shintake monitor

Total energy of gamma ray

Calculate beam size from Gaussian sigma

Calculate beam size from contrast

of sine curve

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laser path misalignmentlaser path misalignment

transverse

　longitudinal

　 precision of alignmnet by mirror actuator • Δz, 　 about 15-20% of σz,laser (from zscan)• Δt 　　　 about 5-10% of σt, laser * (from laserwire scan)

　 　 σz,laser about half of σt,laser

longitudinal Cz- pos > 98.9 % transverse Ct-pos ~ 99.9 %

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If Δy ~ 0.3 σy 　 C 　〜 88.4% for 70 nm @ 174 degC 　〜 96.2% for 150 nm@30 deg modeC 〜 97.7% for 500 nm@7 deg mode

phase jitter observed from fringe scan: about 200 mrad ?? C 〜　 98 % (????)

Phase (relative position) jitterPhase (relative position) jitter

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