PhdThesis Lipka eng - Photo Injector Test Facility at DESY, Location ...

Abstract
In this thesis the measurement of the momentum spread and longitudinal
distribution of electron bunches at the Photo Injector Test facility at DESY
Zeuthen (PITZ) is presented and the design of the experimental setup for
measurement of the complete longitudinal phase space is developed.
For the measurement of the momentum distribution the characteristics of
the used spectrometer dipole were measured and calibrated. The parameters
of the scintillating screen were investigated and no saturation of the light
intensity for the used electron bunch density was observed.
The minimum momentum spread of (65 ± 10) keV/c using the Gaussian
shape of the laser pulse in longitudinal direction and 1 nC bunch charge was
shown to reduce to a value of (33 ± 7) keV/c when using a flat-top laser pulse
distribution. In addition the difference of the radio frequency phase with the
minimum momentum spread and that with the maximum mean momentum
was reduced by applying the flat-top laser pulse distribution from 28 o to 10 o .
Silica aerogel implemented in the vacuum chamber was used as a Cherenkov
radiator for measurement of the longitudinal distribution of the electron
bunches. The aerogel refractive index was shown to be stable under pressure
below 1 mbar and its value of 1.02782 ± 0.00006 was measured. The aerogel
specifications were optimized using Geant-4 simulation in order to reach
good time resolution. The time jitter of the experimental setup and of the
injector was measured to be 0.99 ps, which is negligible in comparison with
the bunch length. The shortest bunch length of FWHM = (6.3 ± 0.1 stat ±
1.2 syst ) mm was measured at the same phase with the minimum momentum
spread. Therefore at this phase the bunch has a high density. This way the
injector was optimized for it’s further application as an electron source for a
Free-Electron Laser.
The experimental setup for measurement of the complete longitudinal
phase space with Cherenkov radiators was designed. In this design only a
fraction of the Cherenkov cone will be used for the measurement. First successful
tests approved the applicability of this approach.
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