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

1. TIPP ‘ 14International Conference on Technology and Instrumentation in Particle PhysicsMeasurement of nm Electron Beam Sizes using Laser Interference by Shintake Monitor 2-6 June 2014Amsterdam, The Netherlands 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) TIPP14

2. High luminosity requires O(nm) vertical beam size at IP Role of Shintake Monitor at ATF2 ATF2：test prototype of final focus system for ILC ATF：1.3 GeV LINAC , DR  wextremely smallvertical e beam emittance ATF2 Goal 1: verifyLocal Chromaticity Correction scheme by focusing σy to design 37 nm Goal 2: O(nm) beam position stabilization FFS Shintake Monitor is crucial for achieving ATF2 ‘s Goal 1 and demonstrating feasibility of realizing ILC !! Outline of this talk Performance Evaluation Summary & Goals Introduction Recent Beam Time Status Signal Jitters • Systematic errors • Phase jitter study TIPP14

3. Introduction Measurement Scheme Expected Performance Role in Beam Tuning TIPP14

4. Measurement Scheme • use laser interference fringes as target for e- beam • Only device able to measure σy < 100 nm !! • essential for ATF2 beam tuning Nd:YAG pulsed laser (Pro-350) λ = 532 nm (SHG) Split into upper/lower paths phase scan by piezo stage Compton scattered photons detected downstream Piezo e- beam safely dumped Collision of e- beam with laser fringe upper, lower laser paths cross at IP form Interference fringes TIPP14 Y. Yamaguchi , Master Thesis, Univ of Tokyo

5. Focused Beam ： large M N + Small σy N - [rad] N: no. of Compton photons Convolution between e- beam profile and fringe intensity Dilluted Beam ： small M Large σy [rad] 5 Detector measures signal Modulation Depth “M” measurable range determined by fringe pitch depend on crossing angle θ (and λ )　 TIPP14

6. Expected Performance Measures σy* = 25 nm 〜 6 μm with < 10% resolution σy and M for each θ mode select appropriate mode according to beam focusing TIPP14 Y. Yamaguchi , Master Thesis, Univ of Tokyo

7. Laser transported to IP 174 deg. 30 deg. beam pipe optical delay half mirror 2 - 8 deg • Vertical table • 1.7 (H) x 1.6 (V) m • Interferometer • Phase control (piezo stage) • path for each θ mode • （auto-stages + mirror actuators ） Crossing angle continuously adjustable by prism TIPP14

8. Recent Beam Time Status TIPP14

9. 〜 2013 • reduction in signal jitters/ drifts by various hardware improvements laser tuning, detector , collimation 〜 Mar 2014 Mar, 2013 : M 〜 0.3 @174° σy,meas 〜 65 nm （Phys. Rev. Lett. 112, 034802) Apr – May, 2014 • 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) • effective linear / nonlinear knob tuning • reflect improved e- beam stabilization • Consistent measurement of high M @ 174° mid-Apr: Mmeas > 0.4 (σymeas < 57 nm) Focus of this talk For status of even smaller σmeasin 2014 see “K. Kubo et al: IPAC14 Proceedings :TOWARDS INTERNATIONAL LINEAR COLLIDER: EXPERIMENTS AT ATF2 “ M =0.34 +/-0.02 (S/D. ) (σy = 62 +/- 2 nm (S.D) ) Preliminary before error corrections Fringe scans @174° 4/17/2014 TIPP14 9

10. Results before error correction Examples of consistency scans @174 ° in 2014 ～14 hrs later after all linear/nonlinear knobs M =0.34 +/-0.02 (S/D. ) (σy = 62 +/- 2 nm (S.D) ) before knob tuning M = 0.29 +/- 0.04 （S.D.） 　（σy = 66 +/- 4 nm (S.D) Preliminary Preliminary higher M and better stability Beam tuning using sextupoles EFFECTIVE beam tuning : σy > 150 nm  σy < 60 nm within half a day !! M > 0.4 reproduced at beam tuning knobs TIPP14

11. Potential Sources of Signal Jitters Varies with beam condition Also a M reduction factor From PIN-PD signal Further measurements and simulations ongoing to comprehend impact from each source • observe overall sig jitter in fringe scan 〜 20-40% depend on phase • drifts are hard to separate from jitters sometimes TIPP14

12. 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 174 deg 30 deg ATF2 online panel : signal stability trend Hardware improvements to stabilize measurements in 2014 by Shintake Monitor group@ATF2 Regular laser tuning by laser company engineer • (1) reinforcement of detector shielding (Pb and parafine) • Stabilization of e- beam improved tuning multiknobs, orbit feedback • speed up DAQ software : reduced effect from drifts • Adjust laser profile and focusing  Reduce pointing jitter at IP • (5) improved buildup and Q-switch timing stability focal lens scan Relaxed laser focusing After : Rounder profile less intensity bias Before ----- Broad Rayleigh length >〜 4 mm TIPP14 5/29 (174 deg )

13. study of systematic errors (M reduction factors) Focusing on the most dominant “phase Jitter” [[[References: J. Yan, et.al., Nucl.Instrum.Meth. A740 (2014) 131-137 ATF2 collaboration: Phys. Rev. Lett. 112, 034802 Proceedings for this conference TIPP14

14. Systematic errors： M reduction Factor M under-evaluation σy over - evaluation Suppression of signal jitters / drifts helps precise evaluation of M reduction factors dominant Details coming up study of other more complex non-linear, non-Gaussian jitters/ slow drifts are ongoing TIPP14

15. Small σy* especially sensitive to beam jitter !! Phase jitter (Δφ) relative position jitter (Δy) between laser and e- beam Horizontal jitters M reduction factor due to Δφ (ex)　　：ifΔφ = 400 mrad, CΔφ 〜 91 % σy0 = 40 nm  σy,meas = 44 nm • Hard to decouple laser fringe phase jitter from e- beam jitters • conditions change over time Δφ extraction method was developed !! by fitting fringe scan data Mcorr = Mmeas / CΔφ M reduction from Δφ GOAL simulation M0 = 0.636 σy0 = 40 nm simulation Before: fitted M After correction simulation Δφ [rad] Δφ [rad] can correct M almost back to nominal using extracted Δφ TIPP14 15

16. Study of Systematic Modulation Reduction • Focusing on factors hard to suppress • phase jitter Δφ DOMINANT extracted from fringe scan (details coming up) • alignment (position, profile) • 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) Dedicated beam time data for Δφ study was analyzed Recent status : 〜 10 nm systematic over-evaluation of σy(preliminary ) • Important to guarantee reliability of Δφ extraction method • Demonstrated using simulation : Δφ precision better than few % in general • analysis model assumesGaussian 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) TIPP14

17. Simulation study of Δφ extraction precision STEP1: generate fringe scan assume “realistic” ATF2 conditions Signal energy vs phase fringe scan Random Δφ input vertical jitter input simulation BG statistical laser fix {M,φ0, Eavg, Cconst, Cstat} to jitter plot signal jitter vs phase STEP2: extract Δφfrom fitting Model Sig jitter = convolution of phase jitter and vertical jitter Jitter from Δφ simulation input: σy0 = 40 nm, 174°mode Δφ = 0.7 mrad , 24.5 % vertical jitter Δφ , Clinear (2 free parameters) fixed parameters: M, φ0, Eavg , Cconst, Cstat: (estimated) TIPP14

18. Extraction precision for Gaussian distributed phase jitter input Simulation • [1] statistical results of 100 random seeds • X: input ΔΦ • Y: extracted Δφ Nav = 20 vsNav = 50 spread is larger forsmaller Nav large Nav scans are preferred for Δφ study Simulation • [2] Distribution for random 10 samples • X: seed number • Y: extracted Δφ • error <〜 7% for single scan • good to average over multiple scans Assume a “relaistic” ATF2 condition Input: M0 = 0.64, σy0 = 40 nm, 174 deg mode, Nav=50, Clinear = 0.25,Cstat = 0.15, Cconst = 0.05, Δφ = 0. 59 rad TIPP14

19. 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 TIPP14

20. Test using reproduced Δφ measured using phase monitor in 2009 (beam off , old laser system) Mean : 1.77 +/- 0.035 phase monitor no longer installed Δφ_real RMS = 0.448 rad data read out in 3 Hz (0.33 sec) intervals Input “Δφ_real” into fringe scan simulation extract Mmeas and Δφ_out observe effect on Mmeas & M correction using Δφ_out shot-by-shotΔΦ extraction precision better than 5% • 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 TIPP14

21. Effect of phase instability on M Mmeas vs Mcorr = Mmeas / exp(-ΔΦ_out ^2 /2) • Observations • when 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 ) avg and rms of 10 random seeds Need to balance precision issues with time consumption Compare different Nav (# of pulses/phase) =10, 20, 50, 100 • 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 • Why large Nav is better forΔφ extraction ? • higher statistics • effect of drifts resemble faster Gaussian like jitters  suitable for the model used here TIPP14

22. Analysis of phase jitters from real beam time data TIPP14

23. History of phase jitter extracted from fringe scans in 2014 phase jitter Δφ  relative position jitter Δy Convolution of laser and e beam : difficult to separate at present 174 °： σy, meas < 65 nm Mar 2014 Apr-May 2014 Jan – Feb, 2014 RECENT Apr, 2014, 30 deg -- 2-8° , 30 ° : larger σy -- • 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 ) TIPP14

24. Phase Jitter @ 174 °mode derived using dedicated Nav=50 fringe scans example: 4/17 Δφ=0.67 +/- 0.04 rad • 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 M plot 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) RMS jitter plot for Δφ analysis Fai TIPP14

25. Summary < Status > • stable beam tuning and continuous beam size measurements in Apr-May, 2014 • measurement stability 〜 5% • reflects e- beam stabilization and reduction of signal jitters /drifts by KEK members laser interferometer type Shintake Monitor • Only existing device capable of measuring beam sizes < 100 nm • essential for achieving ATF2 goal(s) realizing ILC • 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 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 !!! Goals • identify and suppress sources of jitters / drifts • stable measurement of σy < 40 nm and improve error analysis precision •  achieve ATF2 Goal 1 !!! TIPP14

26. BACKUP SLIDES TIPP14

27. Timing and Power Stability power jitter < ～ 10% Observe signal of PIN-Photodiode @laser hut Timing jitter : 1-3 ns peak to peak Laser Power and Profile Measurements (Apr, 2014) • laser table • round profile • intensity spots evened out • Parallel propagation to final focal lenses • balanced profiles and power (~ 95%) between U and L paths • loss in transport (laser hut  IP) < 7% after transport to IP TIPP14

28. Dedicated study of “fringe Contrast” = total M reduction factor “ Ctot” using data immediately before / after mode switching (174  30°) Total M red, mainly from Δφ  σcorr = 54+/- 1 nm total M reduction for 30°compared to 174 °results M red. derived independently using 30° data only, mainly from Δφ “ Ctot,exp” and “Ctot(30)” consistent , almost no residual M reduction ??!! • this study requires stable beam time conditions (laser & beam) • total M reduction for 30 °is less than 2013 due to hardware upgrades (?) TIPP14

29. signal jitter status : improved since April 2014 stability varies for different periods, efforts for further stabilization still ongoing Relative RMS jitter ΔE/E(φ) Drift of Fitted Initial Phase in 174 deg continuous scans (〜 30 min) this drift is convolution may be from laser and/or beam 174 deg, Apr vs Mar 2014 Δx / (laser spot radius) = 12 +/- 7 % Laser pointing stability : 4/9 from Nav = 50 laserwire scan @174 deg Contribution from σx subtracted ICT: 2E9 TIPP14 Assuming Gaussian laserwire profile (but not always so)

30. Examples of SIMULATION Depending on condition, signal jitters/drifts can cause both under & over evaluation of M difficult to model Bias on M from Static Gaussian like vertical jitters a few % systematic M reduction Fitted M Simulation: Avg of 100 seeds Input : Nav=50, 174 deg , M0 = 0.636, Δφ=0, change 1 C factor at a time, keep others 0 Typical range nonlinear fluctuation: sudden intensity decrease(drift) rel. M error = (Mfit – Mexp) / Mexp ex) 50% reduction simulation In this case, M over-evaluation simulation Nav=20, Clinear = 0.25,Cstat = 0.10, Cconst = 0.05, Δφ = 0. 59 rad TIPP14

31. beforehand …. Construct & confirm laser paths, timing alignment Role of IPBSM in Beam Tuning precise position alignment by remote control Longitudinal：z scan transverse ：laser wire scan laser spot size σt,laser = 15 – 20 μm After all preparations ………. continuously measure σy using fringe scans  Feed back to multi-knob tuning TIPP14

32. #2 IPBSM optics designed for linear S polarization Polarization Measurement Set-up P contamination : Pp/Ps < 1.5 % power ratio Beamtime ： “λ/2 plate scan almost no M reduction due to polarization Also measured “half mirror” reflective properties Rs = 50.3 %, Rp = 20.1 %  match catalogue value half mirror Rotate λ/2 plate angle [deg] S peaks” also yields best power balance between 2 paths !! confirmed “S peaks” maximize M TIPP14

33. actual data (blue) Nav = 20 fringe scan(Mar 11 2014) @ 174 deg mode Sig jitter due to phase jitter (red) is larger at fringe mid point and smaller at fringe peak (compare with bottom plot) RMS signal jitter (green) vs Energy at each phase TIPP14