Emittance-Exchange-Based High Harmonic Generation Scheme for a Short-Wavelength Free Electron Laser

Generation of short-wavelength radiation by a free-electron laser using up-frequency conversion of an electron bunch density modulation is currently an area of active research. We propose a new scheme for producing the longitudinal electron bunch density modulation similar to the recently proposed echo-enabled harmonic generation but based on an emittance exchange beam line and a multislit mask. Beam line analysis and start-to-end simulation are presented.

Figure 1

Illustration of the EEHG-FEL scheme (a) and the EEX-HHG FEL scheme (b).

Figure 2

Simulation results at different locations of the EEX-HHG beam line corresponding to the locations in Fig. 1: (a) bunch transverse phase space after mask at $z1$ in Fig. 1; (b) energy bands created by EEX at $z2$ in Fig. 1; (c) bunch after further acceleration and length compression at $z3$ in Fig. 1; (d) density modulation by modulator 2 at $z4$ in Fig. 1.

Figure 3

CSR effect in EEX with different bending angles: (a) 22°; (b) 12°.

Figure 4

FEL power evolution through the undulator.