Ion Acceleration by Solitary and Shock Waves Driven by Laser- Plasma Interactions

This thesis presents a theoretical study of the interaction of intense, ultrashort laser pulses with overdense plasmas. Main objectives are to understand the basic phenomenon which leads to the formation of non-linear electrostatic coherent wave structures in form of either solitary ion acoustic waves (SAW) or collisionless shock waves (CSW). These different types of waves have been classified according to Sagdeev’s theory and related formulas have been used for comparison with the numerical results. The particular focus is on the effect on ion acceleration, by means of ion refection by the moving electrostatic field associated to the shocks/solitons. An extensive numerical study by 1D PIC simulations has been performed and in particular the differences arising between linearly polarized pulses and circularly polarized pulses have been discussed. In a cold plasma, ion bunches produced by “hole boring” (HB) radiation pressure acceleration at the target surface may propagate in the bulk as solitary waves. The acceleration mechanism of these ion bunches has been discussed pointing out a distinction between shock acceleration (SA) and HB acceleration, also with respect to some recent experimental results. Stability of (SAW) or (CSW) and ion reflection from them has been found to be strongly dependent on the initial velocity distribution of ions. The effect of both the ion and the electron temperature on the generation and evolution of solitary acoustic waves have been discussed

Solitary versus Shock Wave Acceleration in Laser-Plasma Interactions

The excitation of nonlinear electrostatic waves, such as shock and solitons, by ultraintense laser interaction with overdense plasmas and related ion acceleration are investigated by numerical simulations. Stability of solitons and formation of shock waves is strongly dependent on the velocity distribution of ions. Monoenergetic components in ion spectra are produced by "pulsed" reflection from solitary waves. Possible relevance to recent experiments on "shock acceleration" is discussed.Comment: 4 pages, 4 figure