Trainee (index-no 8122-T1)

Undulator Wakefield Measurement in the Aramis Beamline

In SwissFEL at PSI we are injecting relativistic electrons into the periodic magnetic field of an
undulator to generate coherent emission of photons in the X-ray regime. For best performance
the field strength of the undulator has to be maximize with results in a very narrow gap for the
electrons to pass through.
This narrow aperture of the SwissFEL vacuum chamber leads to a self-interaction of the
electron bunch, passing through the vacuum chamber, called wakefields. They cause a change
in the electrons energy, dependent on their position within the bunch. This «temporal»
information can be measured by tilting the beam with dispersion, where the transverse
position correlates with the particle energy. If the beam is tilted in one plane before the
undulator and then in the other plane after it, any deviation from a linear correlation can be
attributed to the wakefield potential. If the beam has a well-defined energy chirp it allows then
for a temporal reconstruction of this wake potential.
The project consists of setting up SwissFEL for the large bandwidth mode, leaking out
dispersion and record the electron distribution for various gaps of the undulator. The results
are then benchmarked with the theoretical wakefield model.