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abstract:
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The intensity of undulator radiation, not amplified by the
FEL interaction, can be larger than the maximum FEL sig-
nal in the case of an X-ray FEL. In the commissioning of a
SASE FEL it is essential to extract an amplified signal early
to diagnose eventual misalignment of undulator modules or
errors in the undulator field strength.
We developed a numerical code to calculate the radiation
pattern at any position behind a multi-segmented undulator
with arbitrary spacing and field profiles. The output can
be run through numerical spatial and frequency filters to
model the radiation beam transport and diagnostic.
In this presentation we estimate the expected back-
ground signal for the FEL diagnostic and at what point
along the undulator the FEL signal can be separated from
the background. We also discusses how much information
on the undulator field and alignment can be obtained from
the incoherent radiation signal itself.
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