Transformer Ratio at Wakefield Excitation by Train of Electron Bunches with Linear Growth of Current in Dielectric Resonator Electron–Positron Collider

Abstract

The efficiency of electron bunch acceleration by wakefield, excited in two-beam electron-positron dielectric resonator collider by train of electron bunches is determined by transformer ratio (TR). The train of homogeneous bunches, in which current grows linearly along a train, is considered. The length of homogeneous bunch equals to half of excited wavelength 0.5λ. Interval between bunches is ρλ, p = 1, 2,… The conditions have been formulated, when the wakefield pulses from all electron bunches are added. Bunch is injected in dielectric resonator, when the back wavefront of the wakefield pulse is on the bunch-injection boundary of the resonator/cavity. Bunch leaves the resonator, when the first wavefront of wakefield pulse is on the end of the resonator. The conditions for a large TR have been formulated. The wakefield and TR have been derived after N bunch. The computer simulation has been performed taking into account wakefield pulse dispersion spreading and electron bunch transition radiations. The results of analytical investigation are compared with the results of computer simulation. It has been shown that the dependence TR = 2N is performed. Advantage of this mode with large transformer ratio that some injected bunch with decreased current becomes witness. When this bunch is injected it gets in maximum accelerating field.The infinite periodical mode of accelerator operation has been proposed. In this mode, witness-bunches and driver-bunches are injected according to periodic mode. In the infinite periodical mode, short shaped trains of driver-bunches are alternated with witnesses. Large transformer ratio and identical decelerating field for all driver-bunches are provided by this long periodic train.