PowerPoint Prsentation des FZ Rossendorf

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Status of the Superconducting RF Photo-injector
Development
Jochen Teichert for the BESSY, DESY, MBI, FZD
collaboration Forschungszentrum
Dresden-Rossendorf Institut für
Strahlenphysik Strahlungsquelle ELBE PF 510119,
01314 Dresden J.Teichert_at_fzd.de
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Outline

• Introduction
• Application Parameters
• Photocathode
• Niobium Cavity
• Cryomodude
• Emittance Compensation
• Laser Diagnostic Beamline

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Introduction Radiation Source ELBE

• 40 MeV, 1 mA CW superconducting linac
• thermionic injector (250 kV DC), pulse frequency
  of 13 MHz (260, 26, MHz)

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Introduction Superconducting RF Photoinjector

• Advantage
• low emittance like NC RF photoinjector high
  average current (CW)
• Use at ELBE
• - high charge (1 nC) high current for neutron
  physics
• - improvement of beam quality for FELs , etc.
• - future laser acceleration, Compton x-ray
  source, ERL
• Prototype test bench for future use at other
  accelerators

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Introduction SRF Gun Parameters
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Introduction
Specific SRF Photoinjector Problems and Open
Questions

• Cavity contamination by particles sputtered from
  cathode (fast Q degradation, low gradient).

• Operation of the photo cathode itself at
• cryogenic temperature.

• Specific geometry of the SC cavity (cathode
• insert).Can we reach the high gradient?

• Its not possible to do the emittance
  compensation
• like in a NC RF gun.

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Photo Cathode NC Cathode in SC Cavity

• Photocathodes ?
• - superconducting
• Nb, Pb
• outside
• Peking Univ.
• DC-SRF gun
• Cs2Te
• highest currents
• diamond
• amplifier

successful Rossendorf ½ - cell gun with NC
cathode D. Janssen et al., NIM-A, Vol.
507(2003)314
- Heat input 5 W
dielectric loss 15 W laser power
1 W - isolated from Nb cavity - liquid N2
cooling - SC Nb choke filter prevents rf flow
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Photo Cathode Cooling System
LN2 reservoir
cathode cooler
cathode
Test bench for thermal conduction measurements,
with electrical heater 20 W - about 40 deg
temperature increase at cathode - delivers 20 mW
radiation power to cavity
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Photo Cathode Cs2Te layer deposition

• New clean room (Class 1000)
• Ultra high vacuum (P lt 10-9 mbar )
• 4 evaporators for Cs Te
• 2 deposition rate sensors
• Measurement of Q.E.
• 262nm laser
• Q.E. during deposition
• life time, Q.E. distribution scan
• Controlled by computer

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Photo Cathode Exchange and Storage
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Cavity - Design
Nb RRR 300 cavity Eacc 25 MV/m in TESLA cells,
Q01x1010 (TESLA 500 specification) 110 mT
maximum magnetic surface field Epeak (TESLA
cells) 50 MV/m Epeak (half-cell) 30
MV/m Ecathode 20 MV/m (retreated cathode)
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Cavity Treatment
Cavity from ACCEL

• RF measurements, mechanical inspection, warm
  tuning
• Chemical etching inside (BCP 100 µm clean
  water rinsing)
• Chemical etching outside (gt20 µm clean water
  rinsing)
• Annealing and H2 outgasing in UHV oven at 800 C
  
• Warm tuning
• Chemical etching inside (final BCP 20 µm
  clean water rinsing)
• Drying in class 10 clean room air 12 h
• Assembly of auxiliaries
• Vacuum leak check
• High pressure rinsing
• Drying in class 10 clean room air 12 h
• Installation of antenna for vertical RF test
• RF Measurement _at_ 1.8 K

Preparation for vertical test
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Cavity Vertical Tests
Tests in the vertical cryostat (1.8 K) at DESY
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Cavity Treatment Vertical Tests
4th vertical test measurement of the 4 modes
electric axis field Ez of the for modes
performance limit comes from half -cell
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Cavity Treatment
He Tank welding final preparation _at_ ACCEL

• Helium tank welding
• Field profile measurments
• Vacuum leak checks
• Chemical etching inside (final BCP 20 µm
  clean water rinsing)
• Drying in class 10 clean room air 12 h
• Assembly of auxiliaries
• Vacuum leak check
• High pressure rinsing
• Drying in class 10 clean room air 12 h
• Vacuum leak check
• To Rossendorf for cryomodule assembly

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Cryomodule test assembly N2 cooldown (Nov. 06)
Cavity alignment test in April 2007
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Emittance Compensation
Studies with - retracted cathode - shaped
cathode - downstream solenoid field later TE
mode in cavity (JanssenVolkov)
details in the talk of Friedrich Staufenbiel
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Laser System

• 500 kHz laser for High-charge mode
• Max. frequency 0.5 MHz
• Lower frequencies for alignment
• Pulse duration 1215 ps
• Laser material NdYLF, pumped by 8 fiber-coupled
  diodes
• Optical layout
• Oscillator (13 MHz)
• Regenerative amplifier
• Short-pulse laser for 13 MHz
• Frequency 13 MHz only
• Mechanical chopper to reduce this frequency
• Expected pulse duration 2 ps (UV)
• Laser material YbKGW or YbYAG
• Layout Power Oscillator, Additive-pulse
  modelocked

Developed by MBI Berlin, see talk of Ingo Will
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Diagnostics Beamline
Developed by BESSY Berlin, Test installation on
the roof of the ELBE cave
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Installation Commissioning

• Just finished
• clean room assembling of main coupler/
• pickups / flanges / both cavity tuners
• adjust choke filter and pre-stressing
• of the tuners by measuring
• passband frequencies
• HOM tuning to suppress out coupling
• of fundamental mode

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Installation Commissioning

• Next
• Assembly of the cryomdule
• Cleaning and white assembly
• of cathode transfer system
• Delivery installation of the
• 500 kHz laser system
• Installation of cryomodule
• transfersystem in the next
• ELBE shutdown in June/July
• -Installation of diagnostics beamline
• in the autumn ELBE shutdown

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Summary

• A SRF photoinjector will be installed at the
  ELBE linac
• in summer 2007 for 1 mA cw operation
• It will improve the beam quality for users
• (higher bunch charge, lower transverse
  emittance)
• It will be a test bench for SRF injector studies
• In the SRF gun cavity design, cleaning and
  clean room handling
• should be better considered

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Thank you for your attention
Collaboration BESSY, Berlin DESY, Hamburg
Zeuthen Max-Born-Institut, Berlin TJNAF, Newport
News University of Peking BINP, Novosibirsk CERN,
Geneva INFN, Frascati CCLRC Daresbury ACCEL GmbH,
Bergisch Gladbach Technische Universität
Dresden IfE-Automatisierung GmbH,
Dresden Ingenieurkontor Stephan, Dresden
The ELBE crew (in the Radebeul vineyards, near
Dresden)
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) and the support of the
German Federal Ministry of Education and
Research grant 05 ES4BR1/8.
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Appendix
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Appendix