From filamentation to stratification: Instability dynamics in scissors-shaped relativistic beam-plasma system

Counter-streaming systems are a canonical model for beam-plasma instabilities, such as the filamentation instability, which is critical in high-energy density physics. However, scenarios involving intersecting fast electron beams break the cylindrical symmetry inherent to such systems. Here, we introduce the scissors-shaped configuration, a fundamental multivelocity-component system that captures this broken symmetry. Through theoretical analysis and particle-in-cell simulations, we reveal a dramatic shift in the instability dynamics: the system undergoes a stratification mode instead of filamentation. This mode is rapidly quenched by magnetic reconnection, leading to a quasistable state with magnetic energy two orders of magnitude lower than in the counter-streaming case. This discovery establishes a principle of passive instability control via geometric configuration, offering a perspective on beam-plasma interactions in astrophysics and inertial confinement fusion. The underlying physics is verifiable in upcoming multilaser experiments.