  The UED (ultrafast electron diffraction) beamline of the KAERI's (the Korea
Atomic Energy Research Institute's) WCI (World Class Institute) Center has been
successfully commissioned. We have measured the beam emittance by using the
quadrupole scan technique and the charge by using a novel measurement system we
have developed. In the quadrupole scan, a larger drift distance between the
quadrupole and the screen is preferred because it gives a better thin-lens
approximation. A high bunch-charge beam, however, will undergo emittance growth
in the long drift caused by the space-charge force. We present a method that
mitigates this growth by introducing a quadrupole scan with a short drift and
without using the thin-lens approximation. The quadrupole in this method is
treated as a thick lens, and the emittance is extracted by using the thick-lens
equations. Apart from being precise, our method can be readily applied without
making any change to the beamline and has no need for a big drift space. For
charge measurement, we have developed a system consisting of an in-air Faraday
cup (FC) and a preamplifier. Tests performed utilizing 3.3-MeV electrons show
that the system was able to measure bunches with pulse durations of tens of
femtoseconds at 10 fC sensitivity.

Accelerator Physics;Instrumentation and Detectors