Relativistic electromagnetic solitons in a warm quasineutral electron-ion plasma

The one-dimensional model for the interaction of electromagnetic (EM) waves of relativistic amplitude with a multicomponent hot plasma developed in a previous paper [M. Lontano et al., Phys. Plasmas 9, 2562 ~2002] is applied to the case of an electron–ion plasma. It is assumed that the plasma responds to the presence of large amplitude EM fields by retaining its quasineutrality, that is |Ne-ZNi|/Ne<<1, where Ne and Ni are the electron and ion density, respectively, and Z is the ion charge state. Contrary to what happens with drifting solitons, it is found that standing solitons admit relativistic and ultrarelativistic amplitudes, depending on the plasma temperature. Moreover, it is shown that even in ‘‘cold’’ plasmas the finite temperature directly determines the intensity and the shape of the localized solutions. Large amplitude solitons are found also in the case of different electron and ion temperatures. In addition, the ‘‘penetration depth’’ of an EM wave in a relativistic plasma is discussed, and scalings with the temperature and frequency are obtained. The validity limits of the quasineutral approximation is discussed in the light of the results of the available multidimensional numerical simulations and of the first experimental observations of soliton-like EM structures in high density plasmas.