Relativistic laser-plasma interaction by multi-dimensional particle-in-cell simulations

Interaction of relativistically strong laser pulses with plasmas is investigated by a multi-dimensional particle-in-cell (PIC) code VLPL (Virtual Laser Plasma Laboratory) [Bull. Am. Phys. Soc. 41, 1502 (1996)]. Acceleration of background electrons to multi-MeV energies, generation of 100 MG magnetic fields, and dynamics of ion channel boring are studied. It is shown that direct ${v\times B}$ push by the laser pulse in the presence of an azimuthal dc magnetic field effectively accelerates background plasma electrons to energies significantly higher than the ponderomotive potential. The authors call this novel effect “$\mathrm{B-}$ loop” acceleration mechanism. It is dominant in near-critical plasma, or when plasma waves disappear due to wavebreaking. Laser channeling in under- and overdense plasmas is also studied. Energy spectra of the accelerated electrons and ions and the laser energy conversion efficiency at the critical surface are presented. It is shown that the accelerated electrons propagate in the form of magnetized jets. This physics is crucial for the fast ignitor concept in inertial confinement fusion.