Observation of Dark-current Signals from the S-band Structures of the Slac Linac

It is well known that the electromagnetic fields in highgradient RF structures can cause electron emission from the metallic structure walls. If the emitted electrons are captured and accelerated by the accelerating fields socalled “dark-current” is induced. Dark-currents have been measured and studied for various RF structures. In this paper we present measurements of RF induced signals for the SLC S-band structures. For nominal gradients of 17 MV/m it is shown that the dark-current can be strong enough to significantly reduce the signal-to-noise ratio of the SLC beam wire scanners. We also show results from RF measurements in the dipole band. The measurements are compared to more direct observations of dark-current and it is tried to connect the results to possible effects on the accelerated particle beam.