1. Laser-wire Measurement Precision Grahame Blair Beijing- BILCW07, 6 th February 2007 Introduction Overview of errors Ongoing technical work in this area Plans for the future.

2. BESSY: T. Kamps DESY : E. Elsen, H. C. Lewin, F. Poirier, S. Schreiber, K. Wittenburg, K. Balewski JAI@Oxford: B. Foster, N. Delerue, L. Corner, D. Howell, M. Newman, A. Reichold, R. Senanayake, R. Walczak JAI@RHUL: G. Blair, S. Boogert, G. Boorman, A. Bosco, L. Deacon, P. Karataev, S. Malton, M. Price I. Agapov (now at CERN) CCLRC: I. Ross KEK: A. Aryshev, H. Hayano, K. Kubo, N. Terunuma, J. Urakawa SLAC: A. Brachmann, J. Frisch, M. Woodley FNAL: M. Ross Laser-wire People

3. Laser-wire Principle PETRAII 2d scanning system DAQ development Crystal calorimeter → PETRA III Ultra-fast scanning Diagnostic tool

4. The Goal: Beam Matrix Reconstruction 50% Reconstruction success  <5% error on σ y NOTE: Rapid improvement with better σ y resolution Reconstructed emittance of one train using 1% error on σ y Conclude: Essential to measure the spot-size at the few % level or better I. Agapov, M. Woodley

5. x y u Skew Correction Error on coupling term: ILC LW Locations E b = 250 GeV x(m)x(m)  y (  m)  opt (° )  u (  m) 39.92.83863.99 17.01.66842.34 17.02.83813.95 39.21.69882.39 7.903.14684.13 44.72.87864.05

6. 2σ scan 2σe2σe 2αJσe2αJσe N train bunches 2σ L =2cτ L 2σ e (1 + s train ) α train σ e Scan of an ILC Train of Bunches Not to scale!

7. Need for Intra-Train Scanning For <0.5% effect, s train <0.12; otherwise, the effect must be subtracted For 1  m bunches, the error after subtracting for any systematic shift (assumed linear ±α train along the train) is: For <0.5% effect, α train <2.6; otherwise, higher precision BPMs required

8. Machine Contributions to the Errors Bunch Jitter Dispersion Assuming  can be measured to 0.1%, then  must be kept < ~ 1mm BPM resolution of 20 nm may be required

9. Alternative Scan Mode R&D currently investigating ultra-fast scanning (~100 kHz) using Electro-optic techniques Alternative: Keep laser beam fixed and use natural beam jitter plus accurate BPM measurements bunch-by-bunch. Needs the assumption that bunches are pure-gaussian For one train, a statistical resolution of order 0.3% may be possible Beam jitter fixed at 0.25 σ BPM resolution fixed at 100 nm Single-bunch fit errors for

10. σ ey σ ex σℓσℓ xRxR laser beam electron bunch √2σℓ√2σℓ For TM 00 laser mode: Laser Conventions

11. Compton Statistics Approximate – should use full overlap integral (as done below…) Where : Laser peak power Detector efficiency (assume Cherenkov system) Compton xsec factor Laser wavelength e-bunch occupancy

12. TM 00 Mode Overlap Integrals Rayleigh Effects obvious Main Errors: Statistical error from fit ~  -1/2 Normalisation error (instantaneous value of  ) – assume ~1% for now. Fluctuations of laser M 2 – assume M 2 known to ~1% Laser pointing jitter 

13. Y. Honda et al E stat E M2 TM 01 TM 00 TM 01 TM 00 TM 01 TM01 gives some advantage for larger spot-sizes

14. Laser Requirements Wavelength  532 nm Mode Quality  1.3 Peak Power  20 MW Average power  0.6 W Pulse length  2 ps Synchronisation  0.3 ps Pointing stability  10  rad ILC-spec laser is being developed at JAI@Oxford based on fiber amplification. L. Corner et al

15. ATF2 LW; aiming initially at f 2 ; eventually f 1 ? TM 00 mode Error resulting from 5% M 2 change Statistical Error From 19-point scan Optimal f-num  1-1.5 for = 532nm Then improve M 2 determination f-2 lens about to be installed at ATF Relative Errors

16. Towards a 1  m LW Wavelength266 nm Mode Quality1.3 Peak Power20 MW FF f-number1.5 Pointing stability 10  rad M 2 resolution1% Normalisation (  ) 2% Beam Jitter 0.25  BPM Resolution20 nm Energy spec. res10 -4 Goals/assumptions EE 2.5 E point 2.2 E jitter 5.0 E stat 4.5 EM2EM2 2.8 Total Error8.0 Resultant errors/10 -3 Could be used for  measurement → E  Final fit, including dispersion preliminary

17. Lens Design + Tests Aspheric doublet N. Delerue et al. Vacuum window f-2 lens has been built and is currently under test. Installation at ATF planned for this year M. Newman, D. Howell et al. Designs for f-1 optics are currently being studied, including:

18. S. Boogert, L. Deacon ATF Ext

19. ATF/ATF2 Laser-wire At ATF2, we will aim to measure micron-scale electron spot- sizes with green (532 nm) light. Two locations identified for first stage (more stages later) 1)0.75m upstream of QD18X magnet 2)1m downstream of QF19X magnet LW-IP (1)LW-IP (2) σ x = 38.92  m σ x = 142.77  m σ y = 7.74  m σ y = 7.94  m Nominal ATF2 optics ATF2 LW-test optics P. Karataev LW-IP (1)LW-IP (2) σ x = 20.43  m σ x = 20  m σ y = 0.9  m σ y = 1.14  m  Ideal testing ground for ILC BDS Laser-wire system

20. ATF LW Plans March 07: Start upgrading ATF LW hardware April 07: aim to install f2 lens system May/Jun 07: aim to take first micron-scale scans Longer term Upgrade laser system to reduce spot-size further Install additional LW systems, building towards emittance measurement system for ATF2. Investigate running with UV light. Implement ultra-fast scanning system (first to be tested at PETRA, funding permitting) Build f-1/1.5 optical system

21. Summary Very active + international programme: - -Hardware - -Optics design - -Advanced lasers - -Emittance extraction techniques - -Data taking + analysis - -Simulation All elements require R&D - -Laser pointing - -M 2 monitoring - -Low-f optics - -Fast scanning - -High precision BPMs Look forward to LW studies at PETRA and ATF ATF2 ideally suited to ILC-relevant LW studies.