Post on 16-Dec-2015
LC-ABDP.J. Phillips, W.A. Gillespie (University of Dundee)
S. P. Jamison (ASTeC, Daresbury Laboratory)A.M. Macleod (University of Abertay)
CollaboratorsG. Berden, A.F.G. van der Meer (FELIX)
B. Steffen, E.-A. Knabbe, H. Schlarb, B. Schmidt,P. Schmüser (DESY)
Electro-optic characterisation of bunch longitudinal profile
Why do we need an ultra-fast electron bunch diagnostic?
Machine operation has high influence on beam shape
Wakefields
Synchrotron radiation
Beam – Beam interaction
Electro-optic longitudinal bunch profile measurements
~ ETHz
Propagating electric field
Effective polarisation rotation proportional to Coulomb field
Convert bunch Coulomb field into optical intensity variation.Coulomb field encoded
into optical probeDecoding: temporal intensity variations in single laser pulse
e-bunch
- the chirped laser pulse behind the EO crystal is measured by a short laser pulse with a single shot cross correlation technique
- approx. 1mJ laser pulse energy necessary
Temporal Decoding
Encoding Time Resolution... material response, R()
ZnTe GaP
• velocity mismatch of Coulomb field and probe laser• frequency mixing efficiency(2)()]
Theoretical (but based on some experimental data)
Experimental setup at the VUV-FEL
the laser system is housed outside the accelerator tunnel including 4 nJ, 15 fs Ti:Sa oscillator 1 mJ, 30 fs Ti:Sa amplifier
the laser beam is transported via a 20m vacuum transfer line current setup allows sampling, spectral and temporal decoding currently ZnTe (185µm) and GaP (170µm) crystal mounted
Resulting e-bunches at 450 MeV with 1000 pC in a < 100 fs spike during FEL operation at 32 nm.
Temporal Decoding
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15time [ps]
EO
sig
na
l
)(80 rmsfs
January-February 2007 results...
Electro-optic bunch profile
Transverse Deflecting Cavity bunch profile (LOLA)
)(80 rmsfs
The measured retardationCalculated electric fieldSimulated EO signal / phase retardationMeasured LOLA signal
Data taken with GaP (175 um)Q=0.84 nC, r = 3.8 mm; LOLA Res 3.2 fs /pix
Current data taken at FLASH
Simulation by B. Steffen
Can we get shorter resolution
• Lola measurement Actual bunch profile (10 fs resolution)
• Coulomb angle 1/~ 50 fs for ~ 1000
• Material– GaP
– New material ( Phase matching, 2
considerations)
• Gate pulse width ~ 50 fs– Introduce shorter pulse
– Spectral interferometry
– FROG Measurement
– Try these methods on ERLP
)(80 rmsfs
Research into Fibre lasers
• Clock to be distributed by fibre lasers through stabilised fibres1
• Synchronisation to experiments in future accelerators• Synchronisation of RF to Laser pulses is currently to 30
fs over several hundred meters2
• Inherently low noise
1 FEL 2004 J. Kim et al2 EPAC 2006 A. Winter et al
Our Fibre laser interests
• Fibre system will exist for timing distribution• Exploit for robust / reliability distribution of EO monitors• Dual function of precision arrival time monitor
Requires
Transport of Ti:Sapphire (SHG of Fibre laser ?) knowledge to amplified laser system
Conclusions
• Achieved success at FELIX, DESY
• Measured an Electron Bunch spike at ~ 80 fs (rms)
• Wish to do measurements at SLAC