Generation and optimization of electron bunch trains from nonlinear longitudinal space charge oscillation

We report the generation and optimization of electron bunch trains consisting of femtosecond microbunches with picosecond spacing using nonlinear longitudinal space charge oscillations at the Tsinghua Thomson scattering X-ray source platform. The electron source parameters were optimized to enhance the final bunching of the electron bunch trains with different numbers of microbunches and modulation periods. Seven or 15 microbunches with a total beam charge of up to similar to 1 nC were produced in the experiment, and the spacing was tuned from 0.5 to 1.4 ps by changing the launching phase of the radiofrequency gun. After the formation of microbunches, the beam was accelerated to similar to 45 MeV with an S-band linac to freeze the longitudinal phase space. Narrow-band coherent transition radiation from the bunch trains that passed through a thin Al film was measured.