Abstract
Characterizing the rf-to-laser jitter in the photocathode rf gun and its possible origins is important for improving the synchronization and beam quality of the linac based on the photocathode rf gun. A new method based on the rf compression effect in the photocathode rf gun is proposed to measure the rf-to-laser jitter in the gun. By taking advantage of the correlation between the rf compression and the laser injection phase, the error caused by the jitter of the accelerating field in the gun is minimized and thus $10 \mathrm{fs}$ time resolution is expected. Experimental demonstration at the Tsinghua Thomson scattering x-ray source with a time resolution better than 35 fs is reported in this paper. The experimental results are successfully used to obtain information on the possible cause of the jitter and the accompanying drifts.
Highlights
Synchronization between the electron beam and the laser is crucial for the Thomson scattering x-ray source [1,2,3], the seeded x-ray free electron laser [4,5,6], and the MeV ultrafast electron diffractions [7,8,9,10,11]
Further study shows that the bunching ratio is slight sensitivity on the other jitter sources which may cause unwanted error during the measurement, such as the rf amplitude fluctuation in the gun, the rf phase and amplitude in the following acceleration sections. These mean that high time resolution may be achievable for rf-to-laser jitter measurement with this method we proposed in this paper
A high time resolution method based on the laser injection phase related compression in the photocathode rf gun is proposed
Summary
Synchronization between the electron beam and the laser is crucial for the Thomson scattering (or inverse Compton scattering) x-ray source [1,2,3], the seeded x-ray free electron laser [4,5,6], and the MeV ultrafast electron diffractions [7,8,9,10,11]. Further study shows that the bunching ratio is slight sensitivity on the other jitter sources which may cause unwanted error during the measurement, such as the rf amplitude fluctuation in the gun, the rf phase and amplitude in the following acceleration sections These mean that high time resolution may be achievable for rf-to-laser jitter measurement with this method we proposed in this paper. The cathode is simulated and shown, the resolution limited by 5% laser spot size jitter is about 7 fs Another advantage of the bunch train technique is that the result is independent of the longitudinal pulse shaping of each driving laser pulse, which may change during laser transmission
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