The PHIN Photoinjector for CTF3

1
The PHIN Photoinjector for CTF3

• R. LOSITO - ATB/LP
• for the PHIN Team

2
Acknowledgements

• We acknowledge the support of the European
  Community-Research Infrastructure Activity under
  the FP6 Structuring the European Research Area
  programme (CARE, contract number
  RII3-CT-2003-506395).

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OUTLINE

• PHIN overview
• Photocathodes (CERN)
• RF Gun (LAL)
• Laser (RAL)
• Putting all together (CERN)
• Conclusions

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PHIN overview

• PHIN Charge Production with PHotoINjectors is a
  Joint Research Activity in CARE.
• It concerns several projects
• ELBE Superconducting Photoinjector

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PHIN overview

• PHIN Charge Production with PHotoINjectors is a
  Joint Research Activity in CARE.
• It concerns several projects
• Advanced techniques for Laser pulse Shaping

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PHIN overview

• PHIN Charge Production with PHotoINjectors is a
  Joint Research Activity in CARE.
• It concerns several projects
• Generation of monoenergetic beams through
  laser-plasma interaction.

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PHIN overview

• PHIN Charge Production with PHotoINjectors is a
  Joint Research Activity in CARE.
• It concerns several projects
• Research on photocathodes

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PHIN overview

• PHIN Charge Production with PHotoINjectors is a
  Joint Research Activity in CARE.
• It concerns several projects
• CTF3 Photoinjector

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PHIN overview

• The CTF3 photoinjector is being developed in
  collaboration amongst CERN, LAL and RAL
• LAL RF Gun.
• RAL Laser.
• CERN Photocathodes, integration, overall
  coordination, controls, Klystron, commissioning
  and operation.

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PHIN overview
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PHIN overview
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PHIN overview
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Photocathodes (CERN)
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Photocathodes
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Photocathodes

• Rest gas analysis by mass spectrum analyzer

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Photocathodes

• RD on photocathodes
  
  
• Our wish Photocathodes working in the second
  harmonic of Nd doped crystals (green light)
• Visible to UV conversion efficiency 20 25
• Minimum QE _at_ UV 3 during at least 40 working
  hours
• ? Minimum QE _at_ green light 0.6 during at
  least 40 working hours

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Photocathodes

• RD on photocathodes
  
  
• Our wish Photocathodes working in the second
  harmonic of Nd doped crystals (green light)
• Alkali-antimonide photocathodes produced by
  co-evaporation in collaboration inside PHIN CEA
  Bruyère-le-Châtel

• Secondary Emission Enhanced photo-emitter (SEE)
  in collaboration with CEA Bruyère-le-Châtel
• photocathode plug exchange under UHV
• Vacuum separation by transparent window
• Secondary emission enhancement

BNLs proposal
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RF Gun (Courtesy of R. Roux et al.)

• Designed by LAL R. Roux, G. Bienvenu C.
• 8 LAL/CERN videoconferences during the design
  phase. (Guy, Louis, Hans, Gunther, N. Hilleret
  and myself)
• Design started from CTF2 Gun type IV, but ended
  on a completely new gun.
• Optimization for higher charge, lower emittance,
  lowest possible vacuum level (2?10-10 mbar)

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RF Gun
8.3º
CERN GUN type IV
3.4º
PHIN GUN
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RF GUN

• Effect of cathode wall angle

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RF Gun
8.3º
CERN GUN type IV
3.4º
PHIN GUN
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RF GUN

• Effect of Iris Shape

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RF Gun
CERN GUN type IV
PHIN GUN
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RF Gun

• RF Parameters calculated with SUPERFISH
• f3003.052 Q014530 Rs6 MW

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RF Gun

• Coupling determined by Beam Loading

Matching the source in presence of the beam
requires a coupling 2.9
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RF Gun

• With 30 MW, the Beam Loading can be compensated
  by choosing the proper instant to fill the cavity

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RF Gun

• Next step 3D Simulations with HFSS

• Elliptical iris
• Two symmetric couplers to reduce transverse kick
• Overcoupled (b2.9)

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RF Gun

• Another trick to symmetrise the fields Racetrack
  shape for cell iris (Haimson)

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RF Gun
RF gun
coil
5.45 19.6 3.2 1.07 0.36
E (MeV) ex(pmmmrad) sx (mm) sz (mm) sg /g ()
Electric field from 2D design
PARMELA
I 3.51 A
Compensation of space charge forces

• Best Result (Red curve)
• 3 coils close to the cathode , 0.25T max
• RF coupler on last cell after the coil

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RF Gun
Monte-Carlo based simulations of the residual
pressure
P1
P2
P3
P0

• Useless above 40 l/s
• Weak help of a supplementary pumping

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RF Gun

Improvement of static pressure minimize the
out-gassing rate by High temperature bake
Copper in oven 3 days, t 550C Fast cooling
with Ar jet 150C gtNo grain size enhancement

• Thanks to the high T bake-out
• The residual pressure from copper
• outgassing should be reduced by at
• least one order of magnitude
• (down to 10-10 mbar)

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RF Gun

Improvement of static and dynamic pressure Drill
holes in the cells and depose a NEG film in the
volume outside
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RF Gun
42 holes drilled in the gun walls (F4mm) Volume
around the holes coated with NEG
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RF Gun
Aim Bz max ? 0.27 T on the gun, 0 on the
cathode Difficulties few available space, big
inner diameter (180 mm)
Several magnetic arrangements studied with
POISSON 2 coils possible but too close to
the current density limits gt3 coils with
moderate currents -375 A, 170 A and 250 A
coils
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RF Gun summary

• Design based on CERN Gun type IV but
• Overcoupled to match the beam (3.51 A) in the
  long pulse (1.5 ms)
• Beam loading fully compensated
• Emittance growth from space charge compensated
  with coils
• Transverse kicks compensated with geometrical
  tricks
• Vacuum improved with High T bakeout and NEG
  coating close to the cells
• Latest news
• Cold model under construction, delivered in June
• Final Gun to be ordered in July, available at
  CERN December?

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LASER (Courtesy of M. Divall and G. Hirst)

• Designed and being set-up by RAL
• At the edge of technology, several features not
  previously existing on the market (high frequency
  oscillator, fast switching electronics for
  Pockels cells, ultra stable drives for pumping
  diodes etc..).

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LASER

• Proposal reproducing amplification layout of
  PILOT test

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LASER
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LASER

• Amplification scheme modified to allow 50 Hz
  operation

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LASER
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LASER

• Oscillator
• Oscillator frequency increased from 250 MHz
  (CTF2) to 1.5 GHz thanks to availability of new
  technology for passive mode locking of the
  oscillator (SESAM)
• This technology allows well controlled pulse-to
  pulse jitter, and very good amplitude stability
  (lt1), on long term and from pulse to pulse.
• Preliminary tests at the producer premises have
  shown full agreement with specifications
  (HighQLaser, Austria).
• Box just left manufacturer, should arrive this
  week.

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LASER
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LASER

• Mechanical Assembly for the amplifiers heads

• Simple water and electrical connections
• More accurate positioning of the
• focusing optics
• Easy assembly
• Possibility of rotating the rod in situ
• Similar design for the two amplifiers

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LASER
Laser head assembly
Lens
Diodes
water

• NdYLF rod
• 7mm diameter 8 cm long
• 1 doping level
• Deep surface etching for higher fracture limit
• Ordered from Litton Airton
• We will need a spare rod

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LASER
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LASER

• Oscillator (270 kCHF) just arrived at CERN
• Diode Stacks and NdYlf rod for 1st amplifier
  ordered (280 kCHF) (available this summer).
• Price Enquiry for Diode Stacks of 2nd amplifier
  out (Diodes available this fall)
• Mechanical design for amplifier done.
• Pockels cells driver to be found (switch 5 kV in
  333 ps)
• Stable driver (lt1) for pumping diodes built by
  JM Cravero (AB/PO) for 100 Amps. New design needs
  120 Amps.
• Studies on stabilization feedback and phase
  coding started at RAL.

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LASER

• How it will look like

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Putting All Together (CERN)
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Putting All Together

• Klystron Modulator (G. Mc Monagle) to be
  defined
• Waveguide network (G. Mc Monagle) depends on
  above
• Cooling demineralized water 30 C
  thermostated demineralized water already exist
  in CTF2
• RF (J. Sladen) 1.49928 GHz (-25 dBm P -5
  dBm)
• Timing (J. Sladen) 4 low jitter ( 1 ps rms)
  pulses
• Control system standard CTF3 control system
  (ATB-LP CO)

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Conclusions

• PHIN Collaboration going well, good spirit,
  delays due mostly to non technical reasons
• Delays still under control, 3 months with
  respect to original date
• Photocathodes Cs2Te is the baseline, effort to
  improve reproducibility of co-evaporation, RD
  oriented towards PC in the Green
• RF-Gun design completed, now under construction,
  At CERN in November/December
• Laser To be assembled and tested at RAL. Main
  components purchased, delivery probably June 06
• Integration Lasers rooms and Interfaces defined
  (at 80),
• Ya plus ka!!!!