A new mechanism for direct laser energy coupling to heavier ion species in the presence of an external magnetic field has been illustrated. It has been shown that at higher amplitude, the ion disturbances form magnetosonic solitons. A 2D particle-in-cell simulation for an incident laser beam normal to an overdense plasma target in the presence of an external magnetic field has been carried out for this purpose. The external magnetic field is chosen such that the heavier ions remain unmagnetized but the lighter electron species get magnetized at the laser frequency. For conventional lasers of ∼1 μm wavelengths, the magnetic field requirement satisfying the aforementioned condition turns out to be of the order of several hundreds of kilo Tesla. This requirement goes down by one order if pulsed CO2 lasers with wavelengths of ∼10 μm are employed. At present, magnetic fields of several kilo Tesla have already been generated in the laboratory. Keeping this in view, the simulations have been carried out for the pulsed CO2 laser parameters. It is shown that the ion heating is enhanced considerably in the presence of an external magnetic field. Furthermore, it is shown that at a higher intensity of the laser, the ion disturbances acquire higher amplitude to excite Korteweg–de Vries magnetosonic solitons. The solitons, as expected, propagate stably for several thousands of ion plasma periods. However, subsequently, they are seen to develop transverse modulations which grow with time.
Laser plasma in a magnetic field