Time-resolved measurement of electron beam emittance and energy spread with optical transition radiation

In order to analyze the effect of the transient beam quality on the free-electron laser operation, we have measured the time-varying emittance and energy spread with optical transition radiation (OTR) on the basis of submacropulse. The emittance and energy spread were identified by measuring the beam size on the OTR screen with different quadrupole field. The OTR images having the information of beam size were observed by a gated, intensified charge-coupled device (ICCD) camera. The beam sizes were measured with time step of 100–300 ns by controlling gate time of the ICCD camera. We have observed that the emittance was changed from 0.2 to 0.3 π mmmrad and the fractional energy spread was varied from 0.2×10−4 to 7×10−4 during the macropulse of 3 μs.