Short pulse generation in dielectric by a sequence of electron bunches

Abstract

Summary form only given. At present the investigations of HF-generation and advanced methods of particle acceleration based on intense plasma wake field excitation are widely and successfully carried out. In particular plasma wake fields have been considered as an efficient method for enhancement of HF-generation in a plasma assistance klystron. Along with this hopeful direction some peculiarities of wake field excitation in dielectric give evidence for pulse shortening and field intensifying that is not peculiar to plasma medium. In previous work (Gai et al., 1988, Onishchenko et al., 1995, Zhang et al., 1997) it was proposed to use wake fields excited in dielectric waveguide by a sequence of electron bunches for intense high-gradient acceleration of charged particles. In the present contribution the theoretical investigations and computer simulation are represented on excitation of very short intense pulses of wake field in circular dielectric waveguide by means of a train of relativistic electron bunches. There are two advantages of such scheme. Firstly, a lot of bunches in a regular sequence are used that leads to coherent summation of wake fields of separate bunches. Secondly, the multimode regime of wake fields excitation provided by dielectric waveguide (and absent for plasma case) allows to interfere of wake fields of many modes resulting in formation of short peaks of high amplitude of electromagnetic field. The calculations are performed for a set of parameters in planned experiments: inner and outer diameters of dielectric waveguide are 1.1 and 3.5 cm, respectively, dielectric permitivity 10, radius of electron bunch is 1 cm, its length 1.7 cm, number of bunches is 3000, number of electrons in each bunch 108 cm-3, energy of electrons is 5 MeV. Simulations of linear and nonlinear stages are carried out.