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Title: PowerPoint Prsentation des FZ Rossendorf


1
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
2
Outline
  • Introduction
  • Application Parameters
  • Photocathode
  • Niobium Cavity
  • Cryomodude
  • Emittance Compensation
  • Laser Diagnostic Beamline

3
Introduction Radiation Source ELBE
  • 40 MeV, 1 mA CW superconducting linac
  • thermionic injector (250 kV DC), pulse frequency
    of 13 MHz (260, 26, MHz)

4
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

5
Introduction SRF Gun Parameters
6
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.

7
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
8
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
9
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

10
Photo Cathode Exchange and Storage
11
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)
12
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
13
Cavity Vertical Tests
Tests in the vertical cryostat (1.8 K) at DESY
14
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
15
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

16
Cryomodule test assembly N2 cooldown (Nov. 06)
Cavity alignment test in April 2007
17
Emittance Compensation
Studies with - retracted cathode - shaped
cathode - downstream solenoid field later TE
mode in cavity (JanssenVolkov)
details in the talk of Friedrich Staufenbiel
18
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
19
Diagnostics Beamline
Developed by BESSY Berlin, Test installation on
the roof of the ELBE cave
20
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

21
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

22
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

23
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.
24
Appendix
25
Appendix
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