Formation and expansion of current filaments during the decay of a cylindrical plasma region with hot electrons heated at the interface of cold plasma and vacuum

Based on two- and three-dimensional numerical simulations, a new physical phenomenon is predicted during the decay of an elongated plasma region with hot electrons formed as a result of target ablation in vacuum by a femtosecond laser pulse focused on its surface by a cylindrical lens into a stripe with a width of several to hundreds of microns. It is established that both in the absence and in the presence of external magnetic field (up to $\sim 10^3$ T), oriented along the target surface in the direction of the axis of the semicylinder with electrons heated to keV energies, the multiple formation of thin filaments of the electron current and their further expansion together with the cold plasma cloud's expansion can occur. It is shown that an inhomogeneous system of such filaments with the transverse dimensions ranging from a few to tens of microns develops due to the Weibel-type instability resulting from the anisotropic cooling of an expanding electron cloud and exists at times ranging from picoseconds to nanoseconds, creating localized magnetic fields ranging in strength from a few to several hundreds of T.