16th December 2003 G. Blair, RHUL1 The Laser System at PETRA Wire G. A. Blair, Royal Holloway Univ. London ACFA Workshop, Mumbai 16 th December 2003 Accelerator-Related Session Motivation for the projectMotivation for the project Laserwire at PETRALaserwire at PETRA -Environment at PETRA -Installation of Hardware -First measurements Conclusions and OutlookConclusions and Outlook

16th December 2003 G. Blair, RHUL2 Motivation Maximise Luminosity performance of Linear ColliderMaximise Luminosity performance of Linear Collider Control of transverse beam size and emittance in the Beam Delivery System (BDS) and at the Interaction Point (IP)Control of transverse beam size and emittance in the Beam Delivery System (BDS) and at the Interaction Point (IP) Conventional techniques (wirescanner) at their operational limitConventional techniques (wirescanner) at their operational limit Development of standard diagnostic tool for LC and LC Test Facility operation based on optical scattering structures  Laserwire, Laser-InterferometerDevelopment of standard diagnostic tool for LC and LC Test Facility operation based on optical scattering structures  Laserwire, Laser-Interferometer FeaturesFeatures -Resolution error smaller than 10% -Fast (intra-train) scanning -Non-destructive for electron beam -Resistant to high power electron beam

16th December 2003 G. Blair, RHUL3 Trans.+Long. Profiles Trans:  m Long: ~200  m Trans: nm

16th December 2003 G. Blair, RHUL4 LC Layout and Parameters CLICNLC/GLCTESLABDS  x / m  y / m 3.4 to to to 50 1 to 5 20 to to 25 IP  x / n m  y / n m

16th December 2003 G. Blair, RHUL5 Optical Scattering Structures Scanning of 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

16th December 2003 G. Blair, RHUL6 Laserwire for PETRA Energy Bunch Length Charge/bunch Hor. beam size Ver. beam size E/GeV  z /ps nC  x /m  y /m 4.5 to 12 ~100 1 to to 100 ~100 Positron Electron Tandem Ring Accelerator Injector for HERA, upgrade to synchrotron light source  Long free straight section  Easy installation of hardware due to existing access pipe and hut outside tunnel area Q-switch Nd:YAG with SHG From CERN LEP polarimeter  Trans Mode: large M 2 ~9  Long Mode: stability ± 20%, beating  ps substructure  Homegrown timing unit for external triggeringWavelengthEnergyPulselengthReprate Beam size Divergencel/nmE/mJdt/ns f rep /Hz  x,y /mm /mrad 1064/532250/901030~70.7 Laser parameter PETRA parameter

16th December 2003 G. Blair, RHUL7 Laserwire for PETRA

16th December 2003 G. Blair, RHUL8 Signal and Backgrounds Signal: Compton scatteringSignal: Compton scattering Background sources:Background sources: -Synchrotron radiation -Cosmic rays -Bremsstrahlung Simulation with Geant4 plusSimulation with Geant4 plus tool kits with realistic setup tool kits with realistic setup

16th December 2003 G. Blair, RHUL9 Setup at PETRA

16th December 2003 G. Blair, RHUL10 Installation at PETRA

16th December 2003 G. Blair, RHUL11 Installation at PETRA

16th December 2003 G. Blair, RHUL12 Lab Measurements at RHUL

16th December 2003 G. Blair, RHUL13 Installation at PETRA

16th December 2003 G. Blair, RHUL14 Detector Requirements for detector materialRequirements for detector material -short decay time (avoid pile up) -short radiation length -small Moliere radius Cuboid detector crystals made of PbWO4Cuboid detector crystals made of PbWO4 3x3 matrix of 18x18x150 mm crystals3x3 matrix of 18x18x150 mm crystals Energy resolution better than 5%Energy resolution better than 5%

16th December 2003 G. Blair, RHUL15 Detector Calibration Detector studies with DESY II testbeamDetector studies with DESY II testbeam Beamline with electrons with energy from 450 MeV to 6 GeVBeamline with electrons with energy from 450 MeV to 6 GeV Ten detector crystals were calibrated using a single PMTTen detector crystals were calibrated using a single PMT Combination of nine crystals in matrixCombination of nine crystals in matrix ResolutionResolution -High intrinsic resolution -Full matrix less good

16th December 2003 G. Blair, RHUL16 First Photons Laser onLaser off Photodiode at IP Q-switch Calorimeter

16th December 2003 G. Blair, RHUL17 First Beam Profile Scans Positron beam in PETRAPositron beam in PETRA Beam energy: 7 GeVBeam energy: 7 GeV Bunch pattern: 14 x 1 bunch evenly filledBunch pattern: 14 x 1 bunch evenly filled Average current: 12 mAAverage current: 12 mA -Bunch charge = avg. current / (reprate * Nbunches) = 6.5 nC Laser energy measured: 40 mJ (specs 90 mJ), P L = 4 MWLaser energy measured: 40 mJ (specs 90 mJ), P L = 4 MW Optimization: qswitch delay, timing of ADC sample pointOptimization: qswitch delay, timing of ADC sample point Vertical and horizontal orbit bumps to steer positron beamVertical and horizontal orbit bumps to steer positron beam -Closed symmetric bumps using four steerers -Bump length: 50 m, max offset: 10 mm Operation of fast piezo scannerOperation of fast piezo scanner

16th December 2003 G. Blair, RHUL18 The Laser The laser has been given to us by B. Dehning from CERN. It has been used at LEP to measure beam polarizationThe laser has been given to us by B. Dehning from CERN. It has been used at LEP to measure beam polarization It’s a Nd:YAG Q-switched system, running with 30 HzIt’s a Nd:YAG Q-switched system, running with 30 Hz pulse energy measured: 40 mJ, power: 4 MWpulse energy measured: 40 mJ, power: 4 MW synchronization to PETRA beam by triggering the Q-switch Pockels-cellsynchronization to PETRA beam by triggering the Q-switch Pockels-cell transverse beam quality is modest (multimode)transverse beam quality is modest (multimode) measured spot size at IP: σ L = (80 ± 10) μmmeasured spot size at IP: σ L = (80 ± 10) μm

16th December 2003 G. Blair, RHUL19 Measurement of the longitudinal Profile The longitudinal profile has been measured with a streak camera: FESCA 200 from HamamatsuThe longitudinal profile has been measured with a streak camera: FESCA 200 from Hamamatsu largest window of the camera: 500 ps with a resolution of 5 ps (fwhh)largest window of the camera: 500 ps with a resolution of 5 ps (fwhh) The camera was triggered with the laser via a fast photo diodeThe camera was triggered with the laser via a fast photo diode Problem: stability of the trigger probably not better than 0.5 nsProblem: stability of the trigger probably not better than 0.5 ns

16th December 2003 G. Blair, RHUL20 Averaged Profile Measured averaged profile: fits to gaussian with a width of 12.5 ns (as expected)Measured averaged profile: fits to gaussian with a width of 12.5 ns (as expected)

16th December 2003 G. Blair, RHUL21 Structure in the Longitudinal Profile Example of a single shot measurement of the profile 500 ps window, resolution 5 psExample of a single shot measurement of the profile 500 ps window, resolution 5 ps 60 ps 66 ps

16th December 2003 G. Blair, RHUL22 Unfortunately, the structure is not stable The longitudinal structure is due to longitudinal mode beating – this was expectedThe longitudinal structure is due to longitudinal mode beating – this was expected The beating changes from shot to shotThe beating changes from shot to shot 30 ps 79 ps

16th December 2003 G. Blair, RHUL23 Laser Transverse Profile Units – number of CCD pixels

16th December 2003 G. Blair, RHUL24 Laser Summary As expected for a this type of laser, the longitudinal profile shows substructure due to mode beating As expected for a this type of laser, the longitudinal profile shows substructure due to mode beating The spikes have a width of 30 to 60 ps and a distance of 60 to 80 ps The spikes have a width of 30 to 60 ps and a distance of 60 to 80 ps Unfortunately, the structure is not stable and changes from shot to shotUnfortunately, the structure is not stable and changes from shot to shot To overcome this, the laser has to be equipped with a frequency stabilized seed laser or eventually with an Etalon To overcome this, the laser has to be equipped with a frequency stabilized seed laser or eventually with an Etalon Hot spots a problemHot spots a problem

16th December 2003 G. Blair, RHUL25 Orbit Scan First scan with signal on scopeFirst scan with signal on scope Then sampling of peak using ADCThen sampling of peak using ADC Moving beam orbit up and down with vertical orbit bumpMoving beam orbit up and down with vertical orbit bump 5k counts at each orbit position5k counts at each orbit position 3 min for each spectrum3 min for each spectrum 40 min for complete scan40 min for complete scan Background with 20k countsBackground with 20k counts -Mainly synchrotron radiation and bremsstrahlung -Rate changed by factor 10 Signal rate expected at peakSignal rate expected at peak -200 γs x 380 MeV avg Energy

16th December 2003 G. Blair, RHUL26 Result Orbit Scan Gaussian approximation of beam shapeGaussian approximation of beam shape σ m = (0.175 ± stat ± sys ) mm σ m = (0.175 ± stat ± sys ) mm Vertical beam size σ e = sqrt(σ m - σ L ) laser σ L = (40 ± 10) μm σ e = (170 ± 23 ± 37) μm Result of fit sensitive to background modelling Systematic error dominated by vertical orbit jitter More measurements and understaning of bkg sources necessary

16th December 2003 G. Blair, RHUL27 Fast Scanner Operation Next scan with remote controlled fast scannerNext scan with remote controlled fast scanner Orbit position stableOrbit position stable Scan range: ± 2.5 mradScan range: ± 2.5 mrad -Scan line = range * f lens = mm (± 20%) mm (± 20%) Change amplitude of scanner power supply (1-100V)Change amplitude of scanner power supply (1-100V) Take 5k countsTake 5k counts Record laser IP image with CCDRecord laser IP image with CCD Move laser beamMove laser beam Take 5k counts...Take 5k counts...

16th December 2003 G. Blair, RHUL28 Data and Analysis Seven scan points recordedSeven scan points recorded 5 min / point5 min / point 40 min for full scan40 min for full scan Positron beam position stable within ± 40 μmPositron beam position stable within ± 40 μm Moving low energy pedestalMoving low energy pedestal No background modelNo background model Orbit stable  bkg const.Orbit stable  bkg const. Simple pedestal cut insteadSimple pedestal cut instead Sufficient background rejectionSufficient background rejection

16th December 2003 G. Blair, RHUL29 New Setting Positron beam in PETRAPositron beam in PETRA Beam energy: 7 GeVBeam energy: 7 GeV Posittron beam optics not as in October scans!Posittron beam optics not as in October scans! Bunch pattern: 14 x 1 bunch evenly filledBunch pattern: 14 x 1 bunch evenly filled Low current: 7.1 mA, first bunch mALow current: 7.1 mA, first bunch mA -Bunch charge = avg. current / (reprate * Nbunches) = 3.9 nC High current: 40.5 mA, first bunch mAHigh current: 40.5 mA, first bunch mA -Bunch charge = 22.3 nC Vertical and horizontal orbit bumps to steer positron beam into laser beamVertical and horizontal orbit bumps to steer positron beam into laser beam -Closed symmetric bumps using four steerers Scanning of laser beam using the fast piezo scannerScanning of laser beam using the fast piezo scanner

16th December 2003 G. Blair, RHUL30 Results Data Slopy Gaussian approximation of beam shapeSlopy Gaussian approximation of beam shape σ m =(68 ± 3 ± 20) μm at low current σ m =(68 ± 3 ± 20) μm at low current σ m =(80 ± 6 ± 20) μm at high current σ m =(80 ± 6 ± 20) μm at high current

16th December 2003 G. Blair, RHUL31 Conclusions and Outlook Laserwire at PETRA produced first compton photons and measure vertical beam size Next steps:Laserwire at PETRA produced first compton photons and measure vertical beam size Next steps: Full characterisation of laser: beam size, divergence, and power (stability) with slot scans and imaging techniquesFull characterisation of laser: beam size, divergence, and power (stability) with slot scans and imaging techniques Update all readout software, merge BPM and PMT softwareUpdate all readout software, merge BPM and PMT software Do more systematic scans with the fast scannerDo more systematic scans with the fast scanner Go to smaller spot sizes and reduce error barsGo to smaller spot sizes and reduce error bars Build second dimension scanner.Build second dimension scanner. Start designing a complete laser-wire emittance measurement system for the LC BDS.Start designing a complete laser-wire emittance measurement system for the LC BDS.

16th December 2003 G. Blair, RHUL32 Collaborators DESYDESY BESSY (Thanks to T. Kamps for many of these slides)BESSY (Thanks to T. Kamps for many of these slides) UK: RHUL, UCL, RAL, (Oxford).UK: RHUL, UCL, RAL, (Oxford). CERN: (Laser, plus collaboration)CERN: (Laser, plus collaboration) Close contact with: SLACSLAC KEKKEK

16th December 2003 G. Blair, RHUL33 People Thanks to PETRA and BKR shift crews ! Thanks to PETRA and BKR shift crews ! K Balewski, G Blair, S Boogert, G Boorman, J Bosser, J Carter, J Frisch, Y Honda, S Hutchins, T Kamps, T Lefevre, H C Lewin, F Poirier, I N Ross, M Ross, H Sakai, N Sasao, P Schmüser, S Schreiber, J Urukawa, M Wendt, K Wittenburg,