Fig. 1. Scheme of EEHG

Fig. 2. The vortex generation scheme based on EEHG

Fig. 3. The evolution of the electron beam phase space

Fig. 4. Helical bunching distribution along the electron beam at the exit of the second dispersion section

Fig. 5. The evolution of the FEL radiation in radiator

Fig. 6. The evolution of the bunching factor along the radiator

Fig. 7. The transverse phase distribution of the microbunching