3rd September 2004 G. Blair, RHUL1 Laser Wire Update G. A. Blair Royal Holloway Univ. London ECFA LC Workshop Durham 2 nd September 2004 Laser-wire at PETRA -Environment at PETRA -Installation of Hardware -First measurements -Calorimeter studies Intermational R&D Plans Conclusions and Outlook

3rd September 2004 G. Blair, RHUL2 Laser-wire Principle Scan finely focused laser beam through electron beam Detection of Compton photons (or degraded electrons) as function of relative laser beam position Challenges -Produce scattering structure smaller than beam size -Provide fast scanning mechanism -Achieve efficient signal detection / background suppression

3rd September 2004 G. Blair, RHUL3 Laserwire for PETRA Energy Bunch Length Charge/bunch Hor. beam size Ver. beam size E/GeV s z /ps nC s x /mm s y /mm 4.5 to 12 ~100 1 to 3.5 to.1 ~.1 Wavelength Energy Pulselength Reprate Beam size Divergence l/nm E/mJ dt/ns f rep /Hz s x,y /mm q/mrad 1064/ / ~7 0.7 Laser parameters PETRA parameters

3rd September 2004 G. Blair, RHUL4 Signal and Environment

3rd September 2004 G. Blair, RHUL5 Setup at PETRA

3rd September 2004 G. Blair, RHUL6 viewport BPM PETRA interaction chamber

3rd September 2004 G. Blair, RHUL7 The Laser The laser was donated by CERN (it was used at LEP to measure beam polarization) INd:YAG Q-switched system, running at 30 Hz pulse energy measured: 40 mJ, power: 4 MW synchronization to PETRA beam by triggering the Q-switch transverse beam quality is modest (multimode) measured spot size at IP: σ L = (80 ± 10) μm Average profile Width=12 ns

3rd September 2004 G. Blair, RHUL8 Longitudinal mode quality The longitudinal structure is due to longitudinal mode beating – this was expected The beating changes from shot to shot 30 ps 79 ps 1 P eff 0.39 RMS →Effective laser power T. Byatt, RHUL MSc

3rd September 2004 G. Blair, RHUL9

3rd September 2004 G. Blair, RHUL10

3rd September 2004 G. Blair, RHUL11

3rd September 2004 G. Blair, RHUL12

3rd September 2004 G. Blair, RHUL13

3rd September 2004 G. Blair, RHUL14

3rd September 2004 G. Blair, RHUL15 CCD Resolution CCD Photodiode Focusing lens Removable mirror Knife edge Measure voltage of photodiode as knife edge steps through beam - -Fit plot to Error function to deduce width of beam Fit image on CCD for width of beam Minimise both spots to fix positions of CCD and knife edge Move focusing lens to change beam width at both points S. Malton

3rd September 2004 G. Blair, RHUL16 CCD Resolution (cont.) CCD 9.9  m pixel width Gaus + Gaus + Pol1 fit Pixel Value Pixel Number Number of Pixels AOI Knife Edge scan Error function fit s1s1 s2s2 S. Malton

3rd September 2004 G. Blair, RHUL17 CCD Resolution (cont.) Linear fit - -Linearity lost at large spot size - -Gaussian background indistinguishable from signal Single gaussian fit more accurate above 150  m S. Malton

3rd September 2004 G. Blair, RHUL18 Light transport

3rd September 2004 G. Blair, RHUL19 Lab Measurements at RHUL

3rd September 2004 G. Blair, RHUL20 Installation at PETRA CCD camera

3rd September 2004 G. Blair, RHUL21 Detector Requirements for detector material - -short decay time (avoid pile up) - -Small radiation length/Moliere radius Cuboid detector crystals made of PbWO4 3x3 matrix of 18x18x150 mm crystals Energy resolution better than 5%

3rd September 2004 G. Blair, RHUL22 Energy Calibration

3rd September 2004 G. Blair, RHUL23 Detector Calibration Detector studies with DESY II testbeam Beamline with electrons with energy from 450 MeV to 6 GeV Combination of nine crystals in matrix PMT has since suffered radiation damage and has been replaced

3rd September 2004 G. Blair, RHUL24 Results Data Gaussian approximation of beam shape σ m =(68 ± 3 ± 20) μm at low current σ m =(80 ± 6 ± 20) μm at high current

3rd September 2004 G. Blair, RHUL25 Cosmics in Calorimeter – new PMT (2004) Before Run After Run K. Wittenburg

3rd September 2004 G. Blair, RHUL26 July 04 Data J. Carter

3rd September 2004 G. Blair, RHUL27 July 04 Data J. Carter

3rd September 2004 G. Blair, RHUL28 July 04 Data J. Carter

3rd September 2004 G. Blair, RHUL29 July 04 Data + BDSIM Simulation J. Carter Exit angle: 24 mrad Num. photons:3.90 Cut E >= 0.12 GeV

3rd September 2004 G. Blair, RHUL30 July 04 Data + BDSIM Simulation J. Carter Exit angle: 14 mrad Num. photons: Cut E >= 0.16 GeV

31 Stewart Boogert Laserwire DAQ and software ● Complex problem – Essentially many single channels of a “normal” high energy experiment ● CCDs : monitor laser beam size ● BPM : electron beam position ● Scanner : optics control and fast scanning ● Calorimeter – Control and DAQ proving to be challenging ● Lots of effort on technical level

32 Stewart Boogert DAQ structure ● Examples of individual component readout – Each component responds to simple messages over TCP/IP – Data stored locally and merged later for analysis – Wide range of rates and data volumes are problematic ● Future – Valuable experience for future laserwire experiments – Dedicated VME readout for experiments at ATF BPM CAL CCD Local control Control room TCP/IP

3rd September 2004 G. Blair, RHUL33 Vertical Breadboard To be installed this shutdown Improve beam-finding capability Allow 2-d scans Increased diagnostics Increased flexibility laser electrons R. Senanayake

3rd September 2004 G. Blair, RHUL34 New Laser Will aim for a Q-switched > ~ 10 MW per pulse Good mode quality (M2 ~ 1.3?) 1kHz rep rate Diode pumped We are currently exploring options and contacting suppliers Hope to install early 2005

3rd September 2004 G. Blair, RHUL35 Next steps Full characterisation of laser: beam size, divergence, and power (stability) with slot scans and imaging techniques Update all readout software, merge BPM and PMT software Do more systematic scans with the fast scanner Go to smaller spot sizes and reduce errors Build second dimension (x) scanner. New laser (Early 05?) New vacuum vessel (Dec 04?) New DAQ (Ongoing) Start designing a complete laser-wire emittance measurement system for the LC BDS. Look to ATF for micron-scale laserwire system

3rd September 2004 G. Blair, RHUL36 International ATF Laser-wire Project Extraction line: sigma_y ~ 5  m, intra-train fast scanning Clear additional technical challenges to PETRA experiment SLAC expertise will bolster the project Very constructive discussions are ongoing We have started to explore the technical details and preliminary designs Exciting opportunity to establish a nucleus within the GDI. Location found in ATF extraction line:

3rd September 2004 G. Blair, RHUL37

3rd September 2004 G. Blair, RHUL38

3rd September 2004 G. Blair, RHUL39 ATF LASER-WIRE DESIGN SPECIFICATIONS E-beam parametersdimensions 50μm x 5μm bunch length30ps bunch separation2.8ns train length60-300ns Laser requirementswavelength530nm pulse power100MW pulse duration50ps pulse energy5mJ pulse train energy mJ spot size2μm (F/4 optic) depth of focus35μm Scanning requirementsangular scan range0.5mrad (for 10 x 5μm spot and 50mm lens) scan rate at e-beam0.1 – 0.5mrad/μs I. Ross

3rd September 2004 G. Blair, RHUL40 ACTIVE SCANNING TECHNIQUES Scan Range in mrad Acceptable?Scan Rate in mrad/μs Acceptable? 1)Mirror8.5 Yes0.2 No 2)Acousto-optic2.2 Yes0.2 No 3)Electro-optic1.5 Yes150 Yes EO DEFLECTOR TELESCOPEBEAM TRANSPORT F/4 FOCUSING e-BEAM 0.5μm 20 – 100 PULSES I. Ross

3rd September 2004 G. Blair, RHUL41 PASSIVE SCAN TECHNIQUE Use a Misaligned Multipass Cavity HR MIRROR λ/4 POCKELS CELL GATE F/4 FOCUSING POLARISING BEAMSPLITTER LASER 0.5μm SINGLE PULSE 420mm (1.4ns) e-BEAM Mirror spacing determines the inter-pulse interval to match to 2.8ns Slight mirror tilt from perfect auto-collimation or slight shear of one lens gives scanning with equally spaced foci and a controllable spacing PC gate switches pulse into cavity Need to keep round-trip losses very low to ensure sufficient passes at sufficient power Other designs possible I. Ross

3rd September 2004 G. Blair, RHUL42 Collaborators DESY: S.Schreiber, K. Wittenburg, H-C Lewin, K. Balewski BESSY: T. Kamps RHUL: G.Blair, G. Boorman, RA: C. Driouichi, I. Agapov PhD: J. Carter, M. Price UCL: RA: S. Boogert PhD: S. Malton RAL: I. Ross Oxford: B. Foster, A Reichold, D. Howell RA: N. Delerue + Mech+Elec tech. CERN: (Laser, plus collaboration) KEK: J. Urakawa, H. Hayano, K. Pavel, K. Kubo et al. Close contact with: SLAC: (M. Ross, J. Frisch et al.)

3rd September 2004 G. Blair, RHUL43 Summary Laser-wire project is very active RA, Students working across detector R&D, accelerator physics, DAQ, optics, lasers, analysis, design – in a truly global environment. PETRA laser-wire is being better understood – look forward to “routine” fast data taking… need more dedicated PETRA runs. PETRA laser will be replaced, new vacuum vessel, DAQ … ATF laser-wire is being planned and first designs are being studied. Global collaboration will form, both at ATF and at PETRA – discussions currently underway. New people joining the collaboration, starting in Autumn Additional major effort in beam diagnostics simulation and incorporation into BDS (and other regions) design. Room for wider collaboration and synergy – polarimetry, longitudinal profile, energy spectrometry.