Model for the generation of toroidal and poloidal magnetic fields in a laser-produced plasma

A mechanism of simultaneous generation of toroidal and poloidal magnetic fields in an underdense region of a laser-produced plasma is discussed. The mechanism relies on the fact that at least a part of the incident transverse mode of the laser field undergoes a linear conversion into a longitudinal mode in the thermal plasma. It involves the conversion of ordered kinetic motion of the charged particles in the presence of the field into the energy of the induced magnetic fields both in poloidal and toroidal directions. The analysis is based on obtaining perturbative solutions of the two-fluid model of a hot nondissipative plasma. Our numerical results show that both the toroidal and poloidal fields increase with the laser intensity, and that the former dominates over the latter. Further, the toroidal fields decrease with increasing pulse lengths and increase rather slowly with an increase in laser wavelengths. However, the poloidal fields seem to be insensitive to the laser pulse lengths but they increase exponentially with the laser wavelengths. Finally, toroidal fields have a tendency to decrease as the critical surface is approached. The poloidal fields show a contrary behavior.