(1/2+1/2+1) cell structure type RF gun

In order to suppress the back bombardment of electrons in RF thermionic guns, a new kind of on axis coupled structure type RF gun was developed. It is composed of two half cells and a full cell. The first half cell is shortened and a half cell is inserted between the first half cell and the main accelerating cell to defocus the particles moving backwards with highest energy, thus the cathode back bombardment power is strongly reduced. For the field stability the π/2 mode is chosen. The electromagnetic field analytical codes SUPERFISH and PAMELA are mainly used to do the calculation and simulation. The average back bombardment power is about 3.6W, assuming the pulse width of 6μs and a repetition rate of 25Hz.