Computational study of the three dimensional autoresonance acceleration of electrons cloud in magnetic fields varying on time

Abstract

There are many particle acceleration mechanisms using electromagnetic waves and external magnetic fields where the electron cyclotron resonance condition is preserved. Among these mechanisms, the gyroresonant acceleration proposed by K. Golovanivsky consists of the 2D acceleration of electrons by a circular polarized standing transversal electric wave and a homogeneous magnetic field, which changes on time to compensate the increase of relativistic factor as the electrons are accelerated. By using an analytical model, he obtained a set of differential equations describing both the evolution of the electron energy and the phase shift between the particle velocity and the the electric field component of the microwave field. The 3D simulation of the electrons bunch acceleration by the TE111 cylindrical mode of 2.45 GHz in frequency and the strength of 100 kV/m, said acceleration mechanism is numerically studied. In our numerical scheme, the inhomogeneous magnetic field is produced by a set of 4 current coils, wherein the currents in the central coils change linearly on time. In the transversal mid plane, the initial magnetic field is fitted to the classical resonance value. The concentration of the electron bunch is ne = 2.6 × 108 cm−3, so the simple particle approximation is used. The electron trajectories, its velocities, and energies are obtained from the numerical solution of the relativistic Newton-Lorentz equation. Finally, the number of accelerated electrons was determined, identifying the favorable regions for the acceleration regime. These results can be useful for the design of gyroresonant accelerator devices. It is worth mentioning that said accelerators can be used as X-ray sources when accelerated electrons hit a metallic target.