The filamentation instability of counterpropagating symmetric beams ofelectrons is examined with 1D and 2D particle-in-cell (PIC) simulations, whichare oriented orthogonally to the beam velocity vector. The beams are uniform,warm and their relative speed is mildly relativistic. The dynamics of thefilaments is examined in 2D and it is confirmed that their characteristic sizeincreases linearly in time. Currents orthogonal to the beam velocity vector aredriven through the magnetic and electric fields in the simulation plane. Thefields are tied to the filament boundaries and the scale size of theflow-aligned and the perpendicular currents are thus equal. It is confirmedthat the electrostatic and the magnetic forces are equally important, when thefilamentation instability saturates in 1D. Their balance is apparently thesaturation mechanism of the filamentation instability for our initialconditions. The electric force is relatively weaker but not negligible in the2D simulation, where the electron temperature is set higher to reduce thecomputational cost. The magnetic pressure gradient is the principal source ofthe electrostatic field, when and after the instability saturates in the 1Dsimulation and in the 2D simulation.
展开▼
