1D3V PIC simulation of propagation of relativistic electron beam in an inhomogeneous plasma

A recent experimental observation has shown efficient transport of Mega Ampere of electron currents through aligned carbon nanotube arrays [Phys. Rev Letts. 108, 235005 (2012)]. The result was subsequently interpreted on the basis of suppression of the filamentation instability in an inhomogeneous plasma [Phys. Plasmas 21, 012108 (2014)]. This inhomogeneity forms as a result of the ionization of the carbon nanotubes. In the present work a full 1D3V Particle-in-Cell (PIC) simulations have been carried out for the propagation of relativistic electron beams (REB) through an inhomogeneous background plasma. The suppression of the filamentation instability, responsible for beam divergence, is shown. The simulation also confirms that in the nonlinear regime too the REB propagation is better when it propagates through a plasma whose density is inhomogeneous transverse to the beam. The role of inhomogeneity scale length, its amplitude and the transverse beam temperature etc., in the suppression of the instability is studied in detail.