Research On The Interaction Of Electron-Bunch In Dielectric Filled Cavity

The wake field acceleration can break through the limitation of traditional acceleration mechanism,and can provide a higher acceleration gradient,so it has a wider application prospect.When the motion of the electron-bunch in the dielectric-filled cavity satisfies the condition of Cherenkov radiation,a wake field with a high acceleration gradient will be excited.The dielectric wake field acceleration mechanism can reduce the cost of the accelerator significantly.Therefore,it is crucial to research the acceleration of the tail field.The main work of this paper is as follows:1.The expressions of the wake field,the wake field energy and the induced charge on the inner wall of the cavity are obtained when the infinite thin single electron bunch moves along the axis of the dielectric-filled cylindrical cavity at any time.If the speed of the light in the dielectric is c_ε and the velocity of the electron-bunch is v_ε,the Cherenkov radiation will be excited at v_ε＞c_ε.When the electron bunch is located in the cavity,the field in the cavity has two contributions:the reflection from the wall and the direct from source(electron bunch).When the electron bunch leaves the cavity,the field in the cavity only the former contribution remains.2.The analytical solutions of the wake field and wake field energy excited by infinitely thin multiple electron-bunches moving along the axis of the dielectric-filled cylindrical cavity at any time are obtained.When there are multiple infinitely thin electron bunches in the cavity,the electron-bunches will interact with each other,and the electric field will do positive and negative work to the electron-bunches.When the electric field does negative work to the electrons,and the electron energy will decrease,resulting in wake field energy in the cavity increases;When the electric field does positive work on the electron-bunches,the electron energy increases,and the wake field energy in the cavity decreases.The fields excited by multiple electron-bunches partially cancel each other out,and the electric field cannot be directly enhanced by multiple electron-bunches in the cavity.3.Considering the actual situation,the electron bunch has a longitudinal dimension.We assumed that the electron bunch are uniformly distributed in the longitudinal direction.On the basis of the infinitely thin single electron bunch model,the analytical solution of the wake field and wake field energy excited by finite length single electron bunch moving along the axis of the dielectric-filled cylindrical cavity at any time are obtained.The acceleration gradient and wake field energy excited by the finite-length electron-bunch are lower than the acceleration gradient and the wake field energy of the infinite thin one.From the energy spectrum,low-frequency energy is main contribution of the entire wake field energy,and as the increase of the bunch length,wake field of the high frequency band vanish rapidly.According to the electron-bunch resonance conditions,the electric field is successfully enhanced by using multiple electron-bunches,which solves the problem in Chapter 2 that the electric field cannot be enhanced well due to the interaction of multiple bunches in the cavity at the same time.Further,we research the mechanism of radiation of an electron bunch moving in a dielectric with a velocity exceeding the speed of light.The numerical results show that the average power is proportional to the square of the number of electrons,which is super radiation.