Bunch length measurements in SPEAR3

A series of bunch length measurements were made in SPEAR3 for two different machine optics. In the achromatic optics the bunch length increases from the low-current value of 16.6ps rms to about 30ps at 25ma/bunch yielding an inductive impedance of -0.17Ω. Reducing the momentum compaction factor by a factor of ~60 [1] yields a low-current bunch length of ~4ps rms. In this paper we review the experimental setup and results.