Ionization instability of a relativistic electron beam propagating through a dielectric target

Abstract
Interaction of high intensity laser pulses, (I > 10¹⁸W/cm²) with solid targets is an efficient way of production of high current relativistic electron beams (j_b ~ 10 kA/μm²). Such currents can be transported only under the condition of their charge and current neutralization by the target electrons. This effect is highly dependent on the target conductivity. In a dielectric target, the free electrons are generated due to the field and collisional ionization self-induced by the relativistic electrons. The ionization process is unstable and it can lead to a beam filamentation. We demonstrate here that the electric field ionization is responsible for this instability, and it develops on spatial scales significantly larger than the ionization front thickness.