(talk)
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16th December 2003 G. Blair, RHUL 1
The Laser System at PETRA WireThe Laser System at PETRA WireG. A. Blair, Royal Holloway Univ. LondonG. A. Blair, Royal Holloway Univ. London
ACFA Workshop, MumbaiACFA Workshop, Mumbai
1616thth December 2003 December 2003
Accelerator-Related Session Accelerator-Related Session
• Motivation for the projectMotivation for the project• Laserwire at PETRALaserwire at PETRA
- Environment at PETRAEnvironment at PETRA- Installation of HardwareInstallation of Hardware- First measurementsFirst measurements
• Conclusions and Outlook Conclusions and Outlook
16th December 2003 G. Blair, RHUL 2
MotivationMotivation
• Maximise Luminosity performance of Linear ColliderMaximise Luminosity performance of Linear Collider• Control of transverse beam size and emittance in the Beam Control of transverse beam size and emittance in the Beam
Delivery System (BDS) and at the Interaction Point (IP)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 Development of standard diagnostic tool for LC and LC Test
Facility operation based on optical scattering structures Facility operation based on optical scattering structures Laserwire, Laser-InterferometerLaserwire, Laser-Interferometer
• FeaturesFeatures- Resolution error smaller than 10%Resolution error smaller than 10%- Fast (intra-train) scanningFast (intra-train) scanning- Non-destructive for electron beamNon-destructive for electron beam- Resistant to high power electron beamResistant to high power electron beam
Dyx
repeb HfNn
L **
2
4
16th December 2003 G. Blair, RHUL 3
Trans.+Long. ProfilesTrans.+Long. Profiles
Trans: 10-100 mLong: ~200 m
Trans: 10-100 nm
16th December 2003 G. Blair, RHUL 4
LC Layout and ParametersLC Layout and Parameters
CLICCLIC NLC/GLCNLC/GLC TESLATESLA
BDSBDSxx/ / mm
yy/ / mm3.4 to 153.4 to 15
0.35 to 2.60.35 to 2.67 to 507 to 50
1 to 51 to 520 to 15020 to 150
1 to 251 to 25
IPIPxx/ n/ nmm
yy/ n/ nmm196196
4.54.5335335
4.54.5535535
55
16th December 2003 G. Blair, RHUL 5
Optical Scattering StructuresOptical Scattering Structures
• Scanning of finely focused laser beam through electron beamScanning of finely focused laser beam through electron beam• Detection of Compton photons (or degraded electrons) as function Detection of Compton photons (or degraded electrons) as function
of relative laser beam positionof relative laser beam position• ChallengesChallenges
- Produce scattering structure smaller than beam sizeProduce scattering structure smaller than beam size- Provide fast scanning mechanismProvide fast scanning mechanism- Achieve efficient signal detection / background suppressionAchieve efficient signal detection / background suppression
16th December 2003 G. Blair, RHUL 6
Laserwire for PETRALaserwire for PETRA
EnergyEnergy
Bunch LengthBunch Length
Charge/bunchCharge/bunch
Hor. beam sizeHor. beam size
Ver. beam sizeVer. beam size
E/GeVE/GeV
zz/ps/ps
nCnC
xx//mm
yy//mm
4.5 to 124.5 to 12
~100~100
1 to 31 to 3
500 to 100500 to 100
~100~100
• Positron Electron Tandem Positron Electron Tandem Ring AcceleratorRing Accelerator
• Injector for HERA, upgrade to Injector for HERA, upgrade to synchrotron light sourcesynchrotron light source
Long free straight sectionLong free straight section Easy installation of hardware Easy installation of hardware
due to existing access pipe due to existing access pipe and hut outside tunnel areaand hut outside tunnel area
• Q-switch Nd:YAG with SHGQ-switch Nd:YAG with SHG• From CERN LEP polarimeterFrom CERN LEP polarimeter Trans Mode: large MTrans Mode: large M22 ~9 ~9 Long Mode: stability Long Mode: stability ± 20%, ± 20%,
beating beating ps substructure ps substructure Homegrown timing unit for Homegrown timing unit for
external triggering external triggering
WavelengthWavelength
EnergyEnergy
PulselengthPulselength
ReprateReprate
Beam sizeBeam size
DivergenceDivergence
l/nml/nm
E/mJE/mJ
dt/nsdt/ns
ffreprep/Hz/Hz
x,yx,y/mm/mm
/mrad/mrad
1064/5321064/532
250/90250/90
1010
3030
~7~7
0.70.7
Laser parameter
PETRA parameter
16th December 2003 G. Blair, RHUL 7
Laserwire for PETRALaserwire for PETRA
16th December 2003 G. Blair, RHUL 8
Signal and BackgroundsSignal and Backgrounds
• Signal: Compton scattering Signal: Compton scattering • Background sources:Background sources:
- Synchrotron radiationSynchrotron radiation- Cosmic raysCosmic rays- BremsstrahlungBremsstrahlung
• Simulation with Geant4 plusSimulation with Geant4 plus
tool kits with realistic setuptool kits with realistic setup
16th December 2003 G. Blair, RHUL 9
Setup at PETRASetup at PETRA
HALL EAST
Q-SWITCH
TUNNEL AREA
EMBL HUT
OUTIN
OUT IN
INOUT
LASER
PD TRIGGER BOX
SCOPE
PIT.Y
PIT.E
CAL
BPM
IP
PD@IP
PETRATIMING
e+
COMPTONPHOTONS
16th December 2003 G. Blair, RHUL 10
Installation at PETRAInstallation at PETRA
16th December 2003 G. Blair, RHUL 11
Installation at PETRAInstallation at PETRA
16th December 2003 G. Blair, RHUL 12
Lab Measurements at RHULLab Measurements at RHUL
16th December 2003 G. Blair, RHUL 13
Installation at PETRAInstallation at PETRA
16th December 2003 G. Blair, RHUL 14
DetectorDetector• Requirements for detector materialRequirements for detector material
- short decay time (avoid pile up)short decay time (avoid pile up)- short radiation lengthshort radiation length- small Moliere radiussmall 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 Energy resolution
better than 5% better than 5%
16th December 2003 G. Blair, RHUL 15
Detector CalibrationDetector Calibration
• Detector studies with DESY II testbeamDetector studies with DESY II testbeam• Beamline with electrons with energy Beamline with electrons with energy
from 450 MeV to 6 GeVfrom 450 MeV to 6 GeV• Ten detector crystals were calibrated Ten detector crystals were calibrated
using a single PMTusing a single PMT• Combination of nine crystals in matrixCombination of nine crystals in matrix• ResolutionResolution
- High intrinsic resolutionHigh intrinsic resolution- Full matrix less good Full matrix less good
16th December 2003 G. Blair, RHUL 16
First Photons 31.07.03First Photons 31.07.03
Laser on Laser off
Photodiode at IP
Q-switch
Calorimeter
16th December 2003 G. Blair, RHUL 17
First Beam Profile ScansFirst 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 nCBunch charge = avg. current / (reprate * Nbunches) = 6.5 nC
• Laser energy measured: 40 mJ (specs 90 mJ), PLaser energy measured: 40 mJ (specs 90 mJ), PLL= 4 MW= 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 steerersClosed symmetric bumps using four steerers- Bump length: 50 m, max offset: 10 mmBump length: 50 m, max offset: 10 mm
• Operation of fast piezo scannerOperation of fast piezo scanner
16th December 2003 G. Blair, RHUL 18
The LaserThe Laser
• The laser has been given to us by B. Dehning from CERN. It The laser has been given to us by B. Dehning from CERN. It has been used at LEP to measure beam polarizationhas 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 synchronization to PETRA beam by triggering the Q-switch
Pockels-cellPockels-cell• transverse beam quality is modest (multimode)transverse beam quality is modest (multimode)
• measured spot size at IP: measured spot size at IP: σσLL = (80 = (80 ± 10)± 10) μμmm
16th December 2003 G. Blair, RHUL 19
Measurement of the Measurement of the longitudinal Profilelongitudinal Profile
• The longitudinal profile has been measured with a streak The longitudinal profile has been measured with a streak camera: FESCA 200 from Hamamatsucamera: FESCA 200 from Hamamatsu
• largest window of the camera: 500 ps with a resolution of 5 largest window of the camera: 500 ps with a resolution of 5 ps (fwhh)ps (fwhh)
• The camera was triggered with the laser via a fast photo The camera was triggered with the laser via a fast photo diodediode
• Problem: Problem: stability of the trigger probably not better than 0.5 nsstability of the trigger probably not better than 0.5 ns
16th December 2003 G. Blair, RHUL 20
Averaged ProfileAveraged Profile• Measured averaged profile: Measured averaged profile:
fits to gaussian with a width of 12.5 ns (as expected) fits to gaussian with a width of 12.5 ns (as expected)
16th December 2003 G. Blair, RHUL 21
Structure in the Longitudinal Structure in the Longitudinal ProfileProfile
• Example of a single shot measurement of the profileExample of a single shot measurement of the profile500 ps window, resolution 5 ps 500 ps window, resolution 5 ps
60 ps
66 ps
16th December 2003 G. Blair, RHUL 22
Unfortunately, the structure is Unfortunately, the structure is not stablenot stable
• The longitudinal structure is due to longitudinal mode The longitudinal structure is due to longitudinal mode beating – this was expectedbeating – 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, RHUL 23
Laser Laser Transverse Transverse
ProfileProfile
Units – number of CCD pixels
16th December 2003 G. Blair, RHUL 24
Laser SummaryLaser Summary• As expected for a this type of laser, the longitudinal As expected for a this type of laser, the longitudinal
profile shows substructure due to mode beatingprofile shows substructure due to mode beating• The spikes have a width of 30 to 60 ps and a distance of The spikes have a width of 30 to 60 ps and a distance of
60 to 80 ps60 to 80 ps• Unfortunately, the structure is not stable and changes Unfortunately, the structure is not stable and changes
from shot to shotfrom shot to shot• To overcome this, the laser has to be equipped with a To overcome this, the laser has to be equipped with a
frequency stabilized seed laser or eventually with an frequency stabilized seed laser or eventually with an EtalonEtalon
• Hot spots a problemHot spots a problem
16th December 2003 G. Blair, RHUL 25
Orbit ScanOrbit 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 Moving beam orbit up and down
with vertical orbit bumpwith 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 Mainly synchrotron radiation and bremsstrahlungand bremsstrahlung
- Rate changed by factor 10Rate changed by factor 10• Signal rate expected at peakSignal rate expected at peak
- 200 200 γγs x 380 MeV avg Energys x 380 MeV avg Energy
16th December 2003 G. Blair, RHUL 26
Result Orbit ScanResult Orbit Scan
• Gaussian approximation of beam shape Gaussian approximation of beam shape
σσm m = (0.175 = (0.175 ± 0.020± 0.020statstat ± 0.038 ± 0.038syssys) mm) mm
• Vertical beam sizeVertical beam size
σσee = sqrt( = sqrt(σσmm - - σσLL ) )
laser laser σσLL = (40 = (40 ± ± 10)10) μμmm
σσee = (170 = (170 ± 23 ± 37) ± 23 ± 37) μμmm• Result of fit sensitive to Result of fit sensitive to
background modellingbackground modelling• Systematic error dominated Systematic error dominated
by vertical orbit jitterby vertical orbit jitter• More measurements and More measurements and
understaning of bkg sources understaning of bkg sources necessarynecessary
16th December 2003 G. Blair, RHUL 27
Fast Scanner OperationFast Scanner Operation
• Next scan with remote Next scan with remote controlled fast scannercontrolled fast scanner
• Orbit position stableOrbit position stable• Scan range: Scan range: ± 2.5 mrad± 2.5 mrad
- Scan line = range * fScan line = range * flenslens==
0.625 mm (± 20%)0.625 mm (± 20%)• Change amplitude of scanner Change amplitude of scanner
power supply (1-100V)power supply (1-100V)• Take 5k countsTake 5k counts• Record laser IP image with Record laser IP image with
CCDCCD• Move laser beamMove laser beam• Take 5k counts ...Take 5k counts ...
SCANNER
125 mm
IMAGINGLENS
TODUMP
VIEWPORTMIRROR SPLITTER
CCD
BEAM
LENS
16th December 2003 G. Blair, RHUL 28
Data and AnalysisData 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 Positron beam position stable
within within ± 40 ± 40 μμmm• Moving low energy pedestalMoving low energy pedestal• No background modelNo background model• Orbit stable Orbit stable bkg const. bkg const.• Simple pedestal cut insteadSimple pedestal cut instead• Sufficient background Sufficient background
rejectionrejection
16th December 2003 G. Blair, RHUL 29
New Setting 5.12.03New Setting 5.12.03
• 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 0.458 mALow current: 7.1 mA, first bunch 0.458 mA
- Bunch charge = avg. current / (reprate * Nbunches) = 3.9 nCBunch charge = avg. current / (reprate * Nbunches) = 3.9 nC
• High current: 40.5 mA, first bunch 2.686 mAHigh current: 40.5 mA, first bunch 2.686 mA- Bunch charge = 22.3 nCBunch charge = 22.3 nC
• Vertical and horizontal orbit bumps to steer positron beam Vertical and horizontal orbit bumps to steer positron beam into laser beaminto laser beam- Closed symmetric bumps using four steerersClosed 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, RHUL 30
Results 04.12.03 DataResults 04.12.03 Data
• Slopy Gaussian approximation of beam shapeSlopy Gaussian approximation of beam shape
σσm m =(68 =(68 ± ± 3 3 ± ± 20) 20) μμm at low currentm at low current
σσm m =(80 =(80 ± ± 6 6 ± ± 20) 20) μμm at high currentm at high current
16th December 2003 G. Blair, RHUL 31
Conclusions and OutlookConclusions and Outlook
• Laserwire at PETRA produced first compton photons and Laserwire at PETRA produced first compton photons and measure vertical beam size Next steps:measure vertical beam size Next steps:
• Full characterisation of laser: beam size, divergence, and Full characterisation of laser: beam size, divergence, and power (stability) with slot scans and imaging techniquespower (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 Start designing a complete laser-wire emittance measurement system for the LC BDS. measurement system for the LC BDS.
16th December 2003 G. Blair, RHUL 32
CollaboratorsCollaborators
• 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:Close contact with:• SLACSLAC• KEK KEK
16th December 2003 G. Blair, RHUL 33
People People
Thanks to PETRA and BKR shift crews !Thanks to PETRA and BKR shift crews !
K Balewski, G Blair, S Boogert, G Boorman, J K Balewski, G Blair, S Boogert, G Boorman, J Bosser, J Carter, J Frisch, Y Honda, S Bosser, J Carter, J Frisch, Y Honda, S Hutchins, T Kamps, T Lefevre, H C Lewin, F Hutchins, T Kamps, T Lefevre, H C Lewin, F Poirier, I N Ross, M Ross, H Sakai, N Poirier, I N Ross, M Ross, H Sakai, N Sasao, P Schmüser, S Schreiber, J Sasao, P Schmüser, S Schreiber, J Urukawa, M Wendt, K Wittenburg,Urukawa, M Wendt, K Wittenburg,