Chaotic particle heating due to an obliquely propagating wave in a magnetized plasma

Abstract

We study the dynamics of a relativistic charged particle in the presence of a uniform magnetic field and a stationary electrostatic wave that propagates at an arbitrary angle. The wave is considered as a series of periodic pulses which allows us to derive an exact map for the system. In particular, we investigate the heating process of an initially low-energy particle. It is found that abrupt changes in the maximum energy attained by the particle may occur as the angle between the wave propagation and the magnetic field varies. To determine what is the mechanism behind this phenomenon a reduced Hamiltonian that retains the important dynamical features is obtained. Using both Poincaré plots and perturbation theory, we identify that a separatrix reconnection is the key mechanism for the abrupt change in particle response.

Breakdown of the ponderomotive approximation as an acceleration mechanism in wave-particle nonlinear dynamics

“…Following the formal norm of Hamiltonian perturbations, one performs a canonical transformation that removes the high-frequency components of Hamiltonian (3). We consider a generating function F(x, P) ¼ xP þ f(x, P, t) depending on the old coordinate x and on the new momentum P. The relationship between old and new momenta reads p ¼ P þ @f/@x and we look for the function f that renders P a low-frequency variable.…”

“…Here particles can be highly accelerated as they move in phase with the high frequency carriers, as for instance is the case of particle acceleration by self-sustained electromagnetic (EM) waves in plasmas. 2,3 A classic example is the beat-wave accelerator scheme, where a coherent electrostatic plasma wave is nonlinearly generated by the beating of transverse laser modes and particles are resonantly accelerated as they are injected with the proper resonant phase with respect to the electrostatic mode. 4 The beat wave accelerator evolved into a large number of sophisticated variants.…”