Fig. 1. Model structure.

Fig. 2. Opening foil-focused beam in coaxial waveguide.

Fig. 3. Schematic diagram of foils in coordinate system.

Fig. 4. Plot of electric field E_r2versus opening size.

Fig. 5. TTO buncher with two opening foils.

Fig. 6. Plots of electron conductance G_e/G₀versus phase constant for different modes.

Fig. 7. Field distribution associated with 0 mode of TM₀₁ mode.

Fig. 8. Cavity quality factor of buncher.

Fig. 9. Electric field E_zversus time in the cases (a) without and (b) with opening foil.

Fig. 10. Fundamental harmonic current along axial direction.

Fig. 11. Fundamental currents with different opening sizes.

Fig. 12. Fundamental harmonic current along axial direction.

Fig. 13. (a) Plot of electric field E_zversus time and (b) frequency spectrum of output microwave.

Fig. 14. Curves of output power versus time.