LBBD-collaboration Laserwire update

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LBBD-collaboration Laserwire update

• Adams Institute (Oxford/Royal Holloway)
• G Blair, G Boorman, J Carter
• N Delerue, C Driouichi, F Poirier, B Foster, D
  Howell
• DESY
• K Balewsk, H C Lewin, S Schreiber, M Wendt, K
  Wittenburg,
• BESSY
• T Kamps
• University College London
• S Boogert, S Malton
• Rutherford Laboratory
• I. Ross
• SLAC
• J. Frisch, M. Ross

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Introduction

• Outline of the PETRA laserwire system and recent
  results
• PETRA
• Laserwire setup
• Scan results
• Compton signal
• Laser measurements
• Plans for ATF extraction line laserwire
• Chamber design
• Scanning
• Compton calorimeter
• Readout and control

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PETRA laserwire

• Compton scattering of laser beam with electron
  beam
• Detect Comton photons colinear with electron beam
  by bending the electron beam out of the way
• Compton signal modulated by the spatial overlap
  of the beam distributions
• For the exisiting system at 7 GeV beam energy
  expect Compton rate 103 photons

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Laser light transport
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Scanning and focusing optics setup

• Scanner
• PI piezoelectric stack
• ? 2.5 mrad tilt range and kHz scanning
  frequency
• Focusing lens
• 125 mm, air spaced doublet from CVI

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Post interaction diagnostics optics

• Need to measure laser beam size at collision
• Re-image laser spot using 4f relay

• Transverse profile of laser measured using CCD
  camera
• Basler A300/A600 series cameras
• Firewire readout
• 10?m pixel size

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Compton calorimeter

• Requirements for detector material
• short decay time (avoid pile up)
• short radiation length
• small Moliere radius
• Cuboid detector crystals made of PbWO4
• 3x3 matrix of 18x18x150 mm crystals
• Energy resolution better than 5

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Fast scanner operation (December 2003)

• Positron beam in PETRA
• 7 GeV
• Low current setup 7.1 mA, first bunch 0.458 mA
  (3.9 nC)
• High current 40.5 mA, first bunch 2.686 mA (22.3
  nC)
• Find compton signal via beam bump in x and y
• Varied the voltage to the piezo scanner from 0 to
  100 V
• corresponding to ?2.5 mrad tilt
• taking 5000 calorimeter readings at each point
• Complete scan took 40 mins
• Background signal 20k events without laser pulse
• Large variations in the signal due to the laser
  mode beating

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Profile measurements at PETRA

• Exponential background and Gaussian
  approximation of beam shape, fit results in
• sm (68 3 14) mm at low current
• sm (80 6 16) mm at high current

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Laser beam profile measurements (S. Malton)

• Laser beam size significant systematic error in
  size determination
• Create IP focus before and after laser transport
  down to tunnel
• Measure laser beam size as function of distance
  along beam using CCD cameras
• Beam waist 35-40 microns
• M2 and sigma improve after beam transport to
  tunnel
• Errors large in tunnel due to ambient light

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DAQ and software upgrade (S. Boogert G. Boorman)

• Previous running
• Totally manual system, calorimeter/scanner/bpm
  readout
• 1 hour to take a scan
• Incomplete data format and unsyncronised
• Upgrades since December 2003
• Scanner motion triggered from PETRA trigger
• General trigger fanout card with programmable
  delays, 0.5ns resolution
• National instruments (NI) DAQ slow trigger system
  for triggering components
• Fast photodiodes and power meter digitisation
• PETRA data server, beam currents, BPM positions,
  vacuum status
• Integrated Labview DAQ program

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PETRA conclusions and outlook

• Last scans performed December 2002
• No new scanning data since then, only runs to
  understand the Compton spectrum success
• Problems with laser/access to PETRA
• Low Compton rate
• Total flux now consistent with expectations
• DESY has designed a new beam pipe with window
• Should increase Compton rate by two orders of
  magnitude
• Laser beam transverse size
• Measured using CCD cameras, consistent with
  measured electron beam size
• Next PETRA laserwire shift next week at DESY
• New laser (Modern NdYAG, Mode locked system?)
• Vertical optical system for x and y size
  measurement (being designed now)

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ATF extraction line laserwire
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ATF extraction line laserwire

• Test laserwire optics concept in the extraction
  line
• Install chamber before summer 2005
• Standard system with laser spot size 5mm
• Or during shutdown fall 2005
• Advanced system 1mm spot size
• Pulse structure and ILC timing
• Must wait until extraction kicker issue is
  resolved

• ATF parameters
• Energy 1.28 GeV
• Bunch length 26 ps
• Charge gt 0.5 1010
• Beam size at IP down to 1x70mm
• Laser parameters
• 300 mJ per pulse
• 200 ps pulse length
• Wavelength 532 nm
• Rep. rate 10 Hz

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Chamber design (D. Howell N. Delerue)

• Design underway at Oxford
• Knife edge scanner
• OTR screen
• Optics probably inside vacuum vessel
• First design ready in the next few weeks,
  according to Nicolas
• Scanning
• Initially no active scanning, allow position
  jitter to scan electron beam across laser beam
• Electo-optic scanning
• Acoustic-optic scanning

• Custom lens design (1 mm spot design)
• fgt25mm
• D/f gt 0.933
• Pure silica, due to radiation damage
• Compound lens, have to worry about glues in UHV
• Local diagnostics
• Traditional wire scanner
• ATF BPMs

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Read out and control

• ILC bunch timing
• Transfer experience from PETRA
• Similar concepts for
• Compton detector
• Tiggering
• Readout and DAQ
• We are currently discussing how much of the
  existing PETRA system can be transferred directly
  to ATF extraction line

• Interface to existing diagnostics
• Nicolas has already done the ATF_CONTROL for
  FEATHER project
• BPM measurements
• Corrector control
• Wire scanner control
• good to use same detector for laser and wire
  scanners

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Issues related to ATF beam

• Position jitter in the extraction line
• Could use stripline BPMs to reconstruct electron
  beam position at laserwire IP
• 1 mm resolution possible?
• Laser performance
• Operational stability
• Must obtain characteristics, such as
• longitudinal profile
• transverse profile
• Does this data exist?

• Laser light delivery optics
• Assume mostly in place for the polarised e
  measurements
• Compton detector
• Lead glass calorimeter, a la PETRA
• Air Cerenkov detector with APD for visible photon
  detection

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ATF laserwire conclusions

• Recent discussions favour production of an
  optical system capable of producing 1mm spot
  sizes
• Chamber design well underway at Oxford
• Lens design will start soon
• but later installation
• Compton calorimeter and DAQ
• Cold technology choice, short bunch spacing not
  an issue
• Developments at PETRA more applicable to the ATF
• UK laserwire collaborators are looking forward to
  a successful collaboration and many visits to
  Japan