RAL Template

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Photo-injector laser development CTF3 Design
Marta Divall, Graeme Hirst, Ian Ross, Guy
Suberlucq, Steve Hutchins
M.Divall CLF
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The outline of the talk

• Our role in JRA3
• Milestones and deliverables
• Timescales
• Reminder to the PILOT test results, Pilot to CTF3
• Development programme, system layout
• Oscillator, preamplifier
• High power pumping diodes
• Stability
• Steady-state operation
• Thermal management
• Active feedback stabilisation
• Summary

M.Divall CLF
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Our role in JRA3 PHIN
M.Divall CLF
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CLIC Photo-injector option

• Higher peak current
• Lower emittance

CTF2?PILOT

• Key issues
• Stable pulse train (1.5?s, lt0.1RMS)
• Good quality of the beam(lt30 distortion)
• Optical feedback stabilisation

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PILOT TESTSystem layout
Q 13 nC on 250 pulses
I.N.Ross CLF
M.Divall CLF
June/2002
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Milestones and deliverables

• Milestones
• Increase the power of existing oscillators
  (CCLRC-RAL, CNRS-LOA).
• Optimise the design of the amplifiers for
  required power output at
• minimum cost and complexity (CCLRC-RAL, CERN,
  CNRS-LOA).
• Efficiently convert the laser output wavelength
  to UV using new harmonic generator crystals
  (CCLRC-RAL, CERN, CNRS-LOA).
• Establish ultra-high stability including the use
  of charge and pointing stability feedbacks
  (CCLRC-RAL, CERN, INFN-LNF).
• Deliverables
• High power oscillator.
• Specific amplifiers.
• Specific frequency conversion stages.
• Test of feedback systems.

M.Divall CLF
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Timescales
M.Divall CLF
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PILOT to CTF3Target parameters
M.Divall CLF
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Development programme

• Fourth harmonic generation
• high efficiency
• thermal management

• Photo-cathode performance

• Oscillator
• high cw power 30W
• 1.5GHz mode-locked

• Optics
• good beam quality
• compensation for thermal
• lensing
• high damage thresholds

• Amplifier
• stable output pulse train
• high efficiency (1?m IR laser)
• good beam quality (lensing-effect)

• Diagnostics
• stable operation
• high resolution for stability measurements
• 1-50Hz qcw signal detection

• Feedback-control (?0.1rms)
• laser diode pump current (?s)
• fast optical gate (Pockels-cell)
• accurate monitor (0.1)

M.Divall CLF
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CTF3System layout
Photo cathode
M.Divall CLF
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Oscillator and preamplifier
1.5 GHz NdYLF oscillator was not available on
the market Now it is!!
Mode-locked oscillator in the 200-500mW range 1.5
GHz, synchronized to RF
Higher gain/amplifiers or more amplifiers
Oscillator cw preamplifier
M.Divall CLF
Tender action will be carried out early May of
2004
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CTF3 amplifiersPumping diodes
Survey on high power qcw laser diodes
M.Divall CLF
Tender action will be carried out early May of
2004
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CTF3 amplifiersStability

• Diode pumping
• Steady-state operation
• Feedback-system (Pockels cell, pumping
  current) fast or slow?
• Saturated amplifiers
• Saturated harmonic generation stages

• Temperature of the coolant (wavelength shift of
  diodes)
• Pump current stability
• Oscillator stability
• Ringing in the Pockels cell(s)
• Thermal effect in the harmonic generation stages

M.Divall CLF
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CTF3 amplifiersSteady-state operation
M.Divall CLF
Fast feedback stabilisation is needed!!
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Feedback stabilisation
200V
2V
0V
-2V
-200V
4 ms response time /- 10 change can be
compensated 65 efficient
0.25rms stability over 150?s
Speed needs to be improved (faster
electronics) Built in compensation for
nonlinearity Tests on the real system
M.Divall CLF
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CTF3 amplifiersHigh average power, thermal
management

• Thermal lensing
• Fracture

Compensate with spherical and cylindrical optics
This means 30 Hz maximum repetition rate for safe
operation of the final amplifier!
Could be increased by etched surface finish
M.Divall CLF
Fracture limit measurements for etched
rods Redesign the system with less power in the
final amplifier
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Harmonic generation PILOT laser
LBO type I 2cm for 2? KDP type I 2cm for 4?
5 overall efficiency with 2 ?J, 7.5ps IR pulses
Relay imaging of the end-surface of the amplifier
crystal Same image for both crystals less
space smaller transmission losses Heating
effects can be suppressed by cutting the
pulsetrain before the crystals
M.Divall CLF
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Summary

• Survey of High repetition rate NdYLF oscillators
• Tender action will be carried out early May of
  2004
• for 1.5 GHz mode-locked NdYLF oscillator and
  
• preamplifier with synchronisation to RF

• Same scale as PILOT amplifier
• Studies and test have been done

• Design work
• Survey of high power pumping diodes
• Tender action will be carried out for
• the high power pumping diodes early May of
  2004
• Detailed head design by autumn of 2004
• Fracture limit measurements
• Test results by autumn of 2005

The system to be delivered by 31st of March 2006

• Beam conditioning after the amplifiers
• Comparison of different nonlinear crystals
• Thermal management
• Test results by June of 2005

• Test of existing system
• Purchase faster electronics
• Compensation for nonlinear operation
• Test results by February of 2005

M.Divall CLF