ACCELERATING OF THE ELECTRONS OF ELECTRON BUNCHES IN A WAVEGUIDE LOADED DIELECTRIC STRUCTURE

The paper presents some results of experimental studies of the excitation of wake fields and the acceleration of electrons in waveguide-dielectric structures (DS) upon injection of a sequence of electron bunches into them. Exper-iments have shown an increase in the amplitude of the wake wave and the acceleration of a small fraction of elec-trons when the wavelength of the excited field is equal to the doubled bunch length. A simple physical model of the observed phenomenon is given. Also, the paper proposes a method for accelerating a part of each electron bunch in the steady-state mode of the resonator dielectric structure. Some of the electrons are “cut out” by the collimator and enter the accelerating phase of the previously excited wake wave. The wave is displaced due to the difference in the distances traveled by the wave and the accelerated part of the electrons.

DYNAMICS OF PLASMA EXCITED BY THE PERIODIC SEQUENCE OF RELATIVISTIC ELECTRON BUNCHES

Wake wave excited by the resonant sequence of electron bunches grows to high amplitude after passage of several bunches. As electron bunches are injected into plasma at the same point, it results to high-amplitude plasma oscillations at the limited area in the plasma volume. Relaxation of the wake wave causes plasma heating via Landau damping. It moves to background plasma pressing-out from this area. So plasma density spatial distribution is disturbed. Such density profile deformation causes plasma frequency deviation, so that initial Cherenkov resonance is broken. Local plasma density decreases almost linearly with time. Front of the density perturbation has the shape similar to collision less shock wave.

EVOLUTION OF THE WAKE WAVE EXCIDED BY THE SEQUENCE OF THE RELATIVISTIC ELECTRON BUNCHES

The amplitude of plasma waves, excited by the resonant sequence of electron bunches, saturates after passage of some number of bunches. This behavior was observed and simulated, using particle-in-cell code, but was not completely explained yet. Our study of this behavior was carried out via computer simulation, using modified PDP3 code − 2D3V PIC code for axially symmetric geometry and relativistic collisionless plasma. Simulation demonstrated that amplitude saturation was caused by the plasma pressing-out from the area of the most intensive wake field. This hypothesis has been verified by the obtained electrical and magnetic field spectra, temperature and density maps and density profile for various simulation times.