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For many years a streak camera has been used for
observing the longitudinal distribution of the particles in
any LEP e+ or e- bunch (5-50 ps r.m.s. length) on a turn
by turn basis, using synchrotron light. In 1996, a
comparison made with the longitudinal vertex
distributions of 3 LEP experiments allowed the
identification and elimination of certain systematic errors
in the streak camera measurements. In 1997, a new bunch
length measurement technique was commissioned that
uses the high frequency slope of the bunch power
spectrum from a button pickup. In 1998, this new method
was confronted with measurements from the streak
camera and the LEP experiments. The measurements
made in 1996 and 1998 are presented, with emphasis on
the calibration of the two instrumental methods and their
respective precision and limitations.
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