Physical design of multicell thermionic RF gun with low back bombardment

In order to carry out studies on THz source based on FEL technology and obtain high quality electron beam(heavy current, small energy spread and low emittance), a design scheme of an RF gun with two independent microwave power feed-in ports is proposed. Two microwave feed-in ports will be used to drive the microwave gun. One is used to drive the first cavity and draw electrons from the cathode surface. The other is used to excite the following cavity. There is no electromagnetic coupling between the first cavity and the following cavities. Numerical simulation results show that the electron back bombardment of the thermionic-cathode microwave gun can greatly decrease, the back electron bombardment power within one RF period is no more than 8 kW, and the average back electron bombardment