Stochastic Heating in Ultra High Intensity Laser-Plasma Interaction

A large number of issues remain open in the study of laser-matter interaction at very high intensities. Recently, particle-in-cell (PIC) code simulations results published by Tajima, Kishimoto, and Masaki and also experimental results obtained by Mulser, Kanapathipillai and Hoffmann have shown that the irradiation of very high intensity lasers on clustered matter leads to a very efficient heating of electrons. Tajima, Kishimoto, Masaki, and Kanapathipillai have shown that chaos seems to be the origin of the strong laser coupling with clusters. It was confirmed in PIC code simulations, in the case of two counterpropagating laser pulses, that stochastic heating can lead to their acceleration . Therefore, the issue that we will address is the stability of electron motion in the fields of one electromagnetic wave alone or in those of an electromagnetic wave and a constant homogeneous magnetic field or in those of several waves. In the case of a nonmagnetized plasma interacting with several electromagnetic waves, the use of Chirikov criterion to predict the conditions when this heating takes place will be emphasized. The solution of Hamilton-Jacobi equation, in the case of one wave, will be used to identify resonances. The effect of the different parameters will be described by using the Chirikov criterion. Above the Chirikov threshold, and for electron trajectories with their initial conditions in the overlapping region of two or more resonances, stochastic heating will be evidenced by computing single particle energies. PIC code simulations results obtained with the code CALDER will be presented.