When laser-driven fast electron beams transition from a single beam to two or multiple beams, their transport in background plasma no longer follows the conventional parallel convective system but evolves into a multi-component system with three or more distinct velocity populations. In such systems, the breaking of cylindrical symmetry restricts the excitation of wave vectors to specific orientations. Consequently, either filamentation instability is entirely suppressed or a unique filamentation mode emerges, inducing beam stratification rather than fragmentation into filaments. In both scenarios, electromagnetic instabilities are rapidly quenched, leading to significantly enhanced transverse uniformity of both fast electron beams and background plasma compared to single-beam transport. Under collisionless conditions, this uniformity persists for approximately 10 ps, after which magnetic reconnection generates vortices that expel background electrons to form cavities, ultimately creating a background density distribution analogous to filamentation-dominated systems. For typical picosecond laser timescales (~1 ps) in fast ignition, our results suggest a promising pathway to improve transverse beam uniformity during transport, thereby enhancing hot-spot temperature and homogeneity.

laser fusion,instability,fast electrons transport,Simulation