Direct Ion Heating in Overdense Plasmas by a Standing Whistler Wave

Interaction of overdense plasmas with counter-irradiating relativistic intensity lasers under a strong magnetic field is investigated by one-dimensional Particle-in-Cell simulations. It is found that a large-amplitude ion acoustic wave is excited promptly due to a standing wave formed by the counter propagating Whistler waves. This ion wave appears only when the magnetic field strength is further stronger than the cyclotron resonance condition, which is given by the balance between the laser and electron cyclotron frequencies. Through this process, ions obtain a large amount of energy predominantly and directly from the electromagnetic waves. The ion temperature could be much higher than the electron temperature in this regime. The propagation of a large-amplitude whistler wave under a strong magnetic field could be an interesting mechanism for an efficient heating of ions or electrons in overdense plasmas.