Fig. 1. Simple classification of charged particle accelerators（modified from Ref.[10]）

Fig. 2. Principle of the high-voltage DC accelerators

Fig. 3. Difficulties in accelerating repeatedly by electrostatic fields

Fig. 4. Repeated acceleration with time-varying electromagnetic fields

Fig. 5. Principle of the betatron and a schematic of the annular vacuum chamber

Fig. 6. Diagram of the principle of multiple acceleration from professor G. Ising’s pioneer publication（1924）

Fig. 7. Principle of the linear induction accelerator

Fig. 8. Alternating voltage and principle of phase stability

Fig. 9. A schematic of the Wideröe linac structure^[28]

Fig. 10. A pillbox cavity and the TM₀₁₀ mode electric and magnetic fields in it^[29]

Fig. 11. A schematic of the Alvarez drift-tube linac structure^[9]

Fig. 12. A schematic of the interdigital H-mode DTL^[31]

Fig. 13. Standing wave coupled cavity structures

Fig. 14. A schematic of a four-vane RFQ structure

Fig. 15. Intuitive model of traveling wave acceleration

Fig. 16. Disk-loaded waveguide structures

Fig. 17. Principle of laser wake field acceleration (LWFA) and the capillary discharge waveguide of Berleeley Lab Laser Accelerator (BELLA)^[44]

Fig. 18. Schematic drawing of a classical cyclotron

Fig. 19. Pole faces of the isochronous cyclotrons

Fig. 20. A spiral and a radial fixed-field alternating-gradient (FFAG) accelerator^[54]

Fig. 21. Sketch of a microtron

Fig. 22. Sketch of the synchrotrons

Fig. 23. Sketch of a combinative optical system

Fig. 24. Rhodotron acceleration scheme

Fig. 25. Evolution of acceleration mechanism（modified from Ref.[3]）