Novel concepts for laser-plasma-based acceleration of electrons using ultrahigh power laser pulses.

Abstract

Analytical and numerical studies of plasma physics in ultra-intense plasma wave generation, electron injection, and wavebreaking are performed, which are relevant to the subject of plasma wake-field accelerators. A method for generating large-amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in one dimension both theoretically and numerically (using both Maxwell-fluid and particle-in-cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite-rise-time sine shapes. A resonant region of the plasma-wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. Resonant excitation is found to be superior for electron acceleration to either beatwave or single-pulse excitation because comparable plasma wave amplitudes may be generated at lower plasma densities, reducing electron-phase detuning, or at lower laser intensities, reducing laser-plasma instabilities. The idea of all-optical acceleration of electrons in the wakefield is also discussed. It is shown that the injection of background plasma electrons can be accomplished using the large ponderomotive force of an injection laser pulse in either collinear or transverse geometry with respect to the direction of pump propagation, thus removing the necessity of an expensive first-stage linac system for injection of electrons. Detailed nonlinear analysis of the trapping and acceleration of electrons inside the separatrix of the wakefield is formulated and compared with PIC (Particle-In-Cell) and fluid simulations. The three-dimensional wave-breaking of relativistic plasma waves driven by a ultrashort high-power lasers, is described within a framework of cold 2-D fluid theory. It is shown that the transverse nonlinearity of the plasma wave results in temporally increasing transverse plasma oscillation in the wake of the laser pulse, inevitably inducing wave-breaking below the 1-D threshold. A condition for wave-breaking is obtained and evaluated.