Nonlinear saturation of the two-plasmon decay instability in magnetized plasmas.

Abstract

It is shown that the Landau damping of electron plasma waves (EPWs) is significantly enhanced in a transverse magnetic field with tens of teslas due to a strong modification of the electron velocity distribution function formed in the two-plasmon-decay (TPD) process. The Landau damping even in the range of 0.1<kλ_{D}<0.25 (k is the wave number of EPW; λ_{D} is the Debye length) is important. As a result, the TPD instability saturates at a lower level in the transverse magnetic field; in particular, the convective TPD is significantly suppressed. Meanwhile the laser transmission increases, and the risk of target preheating from hot electrons is also effectively diminished. In addition, the influences of magnetic fields with different strengths and directions on the evolution of TPD are investigated. The results show that as long as the magnetic field can effectively confine the hot electrons and change the electron velocity distribution function, the development of TPD can be mitigated. Finally, we directly investigate the TPD evolution in plasmas with the bi-Maxwellian distribution in order to construct the environment with an external transverse magnetic field. Due to the direct enhancement of EPW Landau damping, the development of TPD remains at a relatively low level in both its linear and nonlinear stages. This further demonstrates the importance of this nonlinear saturation mechanism of TPD in magnetized plasmas.