Longitudinal Diagnostics of Electron Bunches Using Coherent Transition Radiation. Daniel Mihalcea. Northern Illinois University Department of Physics. Outline:. Fermilab/NICADD overview Michelson interferometer Bunch shape determination Experimental results Conclusions.
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Longitudinal Diagnostics of Electron Bunches Using Coherent Transition Radiation
Northern Illinois University
Department of Physics
Fermilab, Jan. 16, 2007
Fermilab NICADD Photo-injector Laboratory
U. of Chicago, U. of Rochester, UCLA, U. of Indiana, U. of Michigan, LBNL, NIU, U. of Georgia, Jlab, Cornell University
DESY, INFN-Milano, IPN-Orsay, CEA-Saclay
Michelson interferometer for longitudinal diagnostics
(University of Georgia & NIU)
Autocorrelation = I1/I2
- Molectron pyro-electric
- Golay cell (opto-acoustic)
Get I1 and I2
Basic Principle (1)
Backward transition radiation
Detector aperture 1 cm
related to longitudinal charge distribution:
Basic Principle (2)
Intensity of Optical Transition Radiation:
Coherent part N2
To determine (z) need to know I() and the phase of f()
Due to detector sensitivity:
Need bunch compression !
RF field in booster cavity
Electron bunch before compression
Molectron pyro-electric detectors
Path difference (mm)
Experimental results (1)
Experimental results (2)
Still need to account for:
Golay detectors: no problem with interference !
Experimental results (3)
Apparatus response function:
Low detector sensitivity
Experimental results (4)
Molectron pyroelectric detectors
Experimental results (5)
Experimental results (6)
Complicated bunch shapes
Stack 4 laser pulses
Select 1st and 4th pulses (t 15ps)
Experimental results (7)
Double-peaked bunch shapes
K-K method may not be accurate for complicate bunch shapes !
K-K method accuracy
R. Lai and A. J. Sievers, Physical Review E, 52, 4576, (1995)
K-K method accurate if:
Calculated widths are still correct !
Major problem: the response function is not flat.
1. Complete I() based on some assumptions at low and high frequencies.
R. Lai, et al. Physical Review E, 50, R4294, (1994).
S. Zhang, et al. JLAB-TN-04-024, (2004).
2. Avoid K-K method by assuming that bunches have a predefined shape and make some assumptions about I() at low frequencies.
A. Murokh, et al. NIM A410, 452-460, (1998).
M. Geitz, et al. Proceedings PAC99, p2172, (1999).
D. Mihalcea, C. L. Bohn, U. Happek and P. Piot, Phys. Rev. ST Accel. Beams 9, 082801 (2006).