Coherent Synchrotron Radiation studies at the A0 photoinjector
The New Superconducting RF Photoinjector a High-Average...
Transcript of The New Superconducting RF Photoinjector a High-Average...
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE
Jochen Teichert for the BESSY-DESY-FZD-MBI collaboration and the ELBE crew
The New Superconducting RF Photoinjector a High-Average Current & High-Brightness Gun
High-Power Workshop, UCLA, Los Angeles 14 – 17 January 2009
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE
Generation of high-brightness electron beams
LASER
PHOTO CATHODE
1. direct production of short pulses:
laser & photo cathode
2. high acceleration field at cathode:
radio frequency field
3. CW operation for high average current:
superconducting cavity
SRF PHOTO INJECTOR
RF FIELD
SC NIOBIUM CAVITY
e-
INTRODUCTION
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE
DESIGN & PARAMETERS
e-beam
Cathode
Choke Filter Half Cell
3 TESLA Cell
design value: Epeak = 50 MV/m (TESLA cavities at DESY) obtained: Epeak ≈ 20 MV/m
MAIN COMPONENTS
The heart – superconducting niobium cavity In liquid He tank Top = 2.0 K (31 mbar)
SC Nb: Tc = 9.3 K superfluid He: TSF = 2.17 K
Maximum RF acceleration field is limited by particle pollution: quenches & field emission
Field value sufficient for gun operation, but to meet the design values fabrication of new cavities with advanced design is under way
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE
cathode
cathode cooler
LN2 reservoir
Ø10 mm Cs2Te cone for positioning & thermal contact
pressure spring bayonet fixing
Requires special support and cooling system • no mechanical contact with Nb cavity • cooling with liquid nitrogen (77 K)
MAIN COMPONENTS
The photo cathode • normal conducting • semiconductor (NEA) Cs2Te advantages: high quantum effic. > 5 % @ λ= 262 nm long life time robust (UHV 10-9 mbar)
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE ELBE USER FACILITY
• New Injector for the ELBE SC Linac • Test Bench for SRF Gun R&D
150 TW Laser
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE COMMISSIONING - FIRST ELECTRON BEAM
Cu cathode
First beam of the 3½ cell superconducting rf photo gun on November 12th, 2007
Beam spot on the first YAG screen in the BESSY diagnostics beamline
RF: Eacc = 5 MV/m f = 1300. 38327 MHz, 150 Hz bandwidth Pdiss = 6 W Laser: 263 nm, 100 kHz reprate 0.4 W power (4 µJ) temporal profile: 15 ps FWHM Gaussian lateral profile: 4 mm x 6mm spot, Gaussian Cathode: Cu, Q.E. ≈ 10-6
Electron beam: 2.0 MV energy 50 nA average current,0.5 pC bunch charge
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE Cs2Te PHOTO CATHODES
Photo cathode preparation lab at FZD
preparation process storage & recovery
May 08: First set of Cs2Te cathodes in the SRF gun
Quantum efficiency scan in SRF gun
Q.E. = 10-3
insufficient vacuum in transfer chamber during manipulation
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE BEAM PARAMETER MEASUREMENT
Schottky scan – energy & energy spread screen DV04 (YAG) 4.4 m from cathode
screen DV05 same optical path as DV04
-160°, σx = 600 µm
energy energy spread
15 pC
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE BEAM PARAMETER MEASUREMENT
Transverse Emittance – Solenoid scan
screen DV02 screen DV01
solenoid for emittance compensation, field precisely measured
Measurement: 2 MeV energy
laser: temporal:15 ps FWHM Gaussian lateral: 2.7 mm diam. sharp edge
-160° 20 pC
σx = 320 µm
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE
parameter present cavity new “high gradient cavity” measured ´08 ELBE high charge ELBE high charge
final electron energy 2.1 MeV 3 MeV ≤9.5 MeV peak field 13.5 MV/m 18 MV/m 50 MV/m laser rep. rate 1 – 125 kHz 13 MHz 2 – 250 kHz 13 MHz ≤500 kHz laser pulse length (FWHM)
15 ps 4 ps 15 ps 4 ps 15 ps
laser spot size 2.7 mm 5.2 mm 5.2 mm 2 mm 5 mm bunch charge ≤ 200 pC 77 pC 400 pC 77 pC 1 nC max. aver. Current 1 µA 1 mA 100 µA 1 mA 0.5 mA peak current 13 A 20 A 26 A 20 A 67 A transverse. norm. emittance (rms)
3±1 mm mrad @ 80 pC
2 mm mrad 7.5 mm mrad 1 mm mrad 2.5 mm mrad
SRF Gun Parameter
BEAM PARAMETERS
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Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf
Radiation Source ELBE SUMMARY
First Run of SRF Gun operation: about 100 h with Cu cathode, 400 h with Cs2Te Iav = 1 µA, total 15 C (diagnostic mode & radiation safety permission)
Problems during commissioning: • Cavity cleaning and low gradient • wrong cavity π-mode frequency at 2 K (corrected in winter shut-down) • insufficient vacuum in cathode transfer system (improved in winter shut-down)
Answers to the „big“ questions: • basic principle (NC photo cathode) works well, no limits found • high current operation: answer will be given in the first run in 2009 • high gradient and higher brightness: needs an improved cavity Future: • Oct.- Jan. 09: correction of π-mode frequency for operation at ELBE • 2009: connection to ELBE for tests and user operation run with high current • test bench for SRF gun R&D (FP7, EuCARD) emittance compensation methods, alternative photo cathodes (GaAs) • fabrication of two improved cavities, funded by BMBF, replacement in 2010