Three-Dimensional Effects Induced by Charged Particle Beams and Radiation Pulses in Plasmas

Abstract

This PhD thesis concerns the 3D effects that are generated by the self-consistent interaction of very intense relativistic charged-particle beams or ultra-short and ultra-intense laser pulses with a plasma. These effects are usually encountered in the new plasma-based accelerator techniques, in the inertial fusion and in a number of astrophysical problems. This thesis work is a theoretical investigation within the context of the general beam physics, but oriented to the applications for the new plasma-based acceleration schemes. When very intense relativistic charged-particle beams or ultra-short and ultra-intense electromagnetic radiation beams are traveling in a plasma, due to both their longitudinal and transverse profiles, a modification of the local properties of the are introduced. The general mechanism is called ake field interaction. In the case of charged particles, the violation of the local neutrality caused by the traveling beam excites large amplitude fields, leading to the so-called Plasma Wake Field (PWF) excitation. These fields have a 3D character in terms of components and profiles. They are driven by the particle but on longer time scales the wake fields act on the beam itself. Sufficiently long beams experience the transverse PWF effects, such as self-focusing, filamentation and collapse. However, in a controlled way, they can be used to manipulate the beam in a lens, usable to enhance the luminosity in the final stage of very compact linear colliders for nano-sized beams. In the case of ultra-short and ultra intense laser pulses, the ultra-strong ponderomotive effects introduced by both the ultrashort longitudinal and transverse profiles modifies the local density associated with large amplitude electric fields, leading to the so-called Laser Wake Field (LWF) excitation. Similarly to the case of particle beams, the laser pulse drives this mechanism, but on the longer time scales it experiences the reaction of the that affects the beam propagation. Starting from a fluid model of the system plasma + beam, the self consistent PWF and LWF excitations have been described obtaining in both cases a Zakharov-like system of equations, coupling a sort of nonlinear Schrodinger equation (describing the spatio-temporal evolution of a complex function whose squared modulus is proportional to the beam density/intensity profile). Within both quantum-like (Thermal Wave Model) and quantum context, novel linear and nonlinear collective vortex states of a charged-particle beam (as a collective manifestation of the orbital angular momentum) have been obtained, nonlocal effects investigated, and conditions for the self-focusing and collapse discussed. In addition a scheme of lens for nanobeams has been put forward. Taking into account the weak and moderate nonlocal regimes, the dynamics of the ultra-short and ultra-intense laser pulses have been investigated in the case of self-injection acceleration; additionally, solitary solutions have been found and the evolution of the beam collapse has been observed. All the above investigations have been carried out both analytically and/or numerically. They have been carried out within the INFN national collaboration NTA SL COMB and NTA SL SITE (former PLASMON-X project) devoted to the PWF- and LWF- based acceleration, respectively, also in collaboration with the following distinguished scholars: the late Professor Padma Kant Shukla (Ruhr-Universitat Bochum, Bochum, Germany; Professor Dusan Jovanovic (Institute of Physics, University of Belgrade, Belgrade, Serbia); Dr. Sergio De Nicola (INO-C.N.R., Pozzuoli, Italy).